http://nanowiki.no/api.php?action=feedcontributions&feedformat=atom&user=KenrogerNanoWiki - Brukerbidrag [nb]2026-06-11T19:58:22ZBrukerbidragMediaWiki 1.44.2http://nanowiki.no/index.php?title=TOKS3001_-_Medisinsk_toksikologi&diff=4000TOKS3001 - Medisinsk toksikologi2009-05-17T11:00:58Z<p>Kenroger: /* Definitions */</p>
<hr />
<div>{{Infobox<br />
|Fakta vår 2009<br />
|*Foreleser: Diverse<br />
*Vurderingsform: Skriftlig eksamen (100 %)<br />
*Eksamensdato: 18.05.2009<br />
*Fagbok: Casarett & Doull´s Toxicology: The Basic Science of Poisons, 6th edition. ISBN: 0071470514<br />
}}<br />
<br />
{{Infobox<br />
|Semesteroppgave<br />
|* Det er en obligatorisk semesteroppgave i faget.<br />
}}<br />
<br />
Forelesninger er to ganger i uka fra første uka i februar til siste uka i mars. I tillegg kommer en semesteroppgave (gruppearbeid). Eksamen baserer seg på forelesninger og utdelt materiale. <br />
<br />
= Core Curriculum =<br />
== Toxicokinetics ==<br />
<br />
===Definitions===<br />
''Xenobiotic'' (X.): A chemical that is not native in the body, or is present in much higher concentration than normal.<br />
<br />
''Toxic effect'': A change in physiological conditions caused by an effect of xenobiotics on the cellular level creating a decrease in health or behavior.<br />
<br />
''Toxicodynamics'': Mechanism of the toxic effect, reactivity, receptors and organ types.<br />
<br />
''Toxicokinetics'': Uptake, transport and lingering time/concentration of X.<br />
<br />
''Absorption'': Transport from the place of disposition to blood with a rate constant <math>k_a</math>.<br />
<br />
''Bolus'': A dosage of X. administered directly into the plasma.<br />
<br />
''Elimination'': Biotransformation, exhalation or excretion of X. X. does not need to be removed from the body, only made unavailable in its original form.<br />
<br />
''First pass metabolism'': The metabolism of a X that occurs in liver during the first passage.<br />
<br />
''Bioavailability (F)'': The fraction of a given dose D (X-parent compound) that reaches circulation in an unchanged form.<br />
<br />
''Enteroheptic circulation'': Absorption from small intestine to blood --> liver --> conjugate --> bile --> small intestine --> hydrolyzed --> parent compound --> reasorbed into blood<br />
<br />
''Distribution Equilibrium'': A state where consenstrations of a substanse in different organs are in equilibrium with each other.<br />
<br />
===Introduction===<br />
There are two main ways to model toxicokinetics: Compartmental models and physiological models. The compartmental models are described more in detail below, and involve modeling organ systems by simple relations without involving physiology, i.e. the rate constants used are acquired from measurements alone. The physiological model looks at theoretical, or physiological, models to predict rate constants of the organs in the body. This involves factors such as:<br />
*Blood flow through organs<br />
*Absorption of the small intestine<br />
**Villi and microvilli in the intestine: These greatly increase the intestinal area, so absorption into the blood for selected X. is greatly enhanced here.<br />
**Active and passive diffusion: Some substances can diffuse directly across tissues, but most require some form of transport proteins. The mechanisms of these proteins determine how effectively and selectively xenobiotics are absorbed.<br />
**There is also metabolism in the intestine, by e.g. the cytochrome P450 3A4 (CYP3A4) enzyme which can activate many prodrugs.<br />
**Drug export from cells via P-glycoprotein is a very important mechanism which greatly reduces the amount of many xenobiotics that are absorbed.<br />
*The portal vein collects blood from the intestine and goes directly to the liver, where many substances are metabolized and their bioavailability is reduced. This is called first-pass metabolism, where the drugs are metabolized before reaching general systemic circulation. <br />
*After being metabolized in the liver many xenobiotics are conjugated and marked for excretion into the bile. The bile is excreted in the small intestine, where the drugs can be un-conjugated and reabsorbed, passing into the liver again. This is called the entero-hepatic circulation, and keeps plasma concentration of xenobiotics low in general.<br />
*Other special barriers, such as the blood-brain barrier and the placenta also greatly effect the distribution of xenobiotics.<br />
<br />
===Compartmental models===<br />
A model often used to model toxicokinetics is the compartmental model. In the compartmental model there is a central compartment representing the blood plasma and rapidly equilibrating tissues (e.g. liver and kidney), and side-compartments of more slowly equilibrating tissues. The simplest such model is the one-compartment model. Here there is only one compartment, which means all the modeled tissues are rapidly equilibrating. In this model a bolus will decay exponentially, i.e. measuring the logarithm of the plasma concentration over time gives a linear plot. Conversely, if experimental data holds with this description, it can be modeled by the one-compartment model. The decay is elimination, and elimination happens from the central compartment. <br />
<br />
=== Rate constants and elimination ===<br />
There are several rate constants involved in toxicokinetics. There are elimination and absorption rate constant, <math>k_e</math> and <math>k_a</math>, which describes elimination from and absorption into the central compartment (see below) if the dose is administered e.g. orally. In multi-compartment models there are also distribution and redistribution constants, e.g. <math>k_{12}</math> and <math>k_{21}</math>, which describes rates between the compartments.<br />
<br />
An example of a rate constant is the excretion rate constant through the kidney, <math>k_r</math>. In the kidney, glomerular filtration has a certain rate, tubular excretion another, and and reabsorption into the tubules a third. Thus, the excretion from the kidneys is given by <math>k_r=k_{f}+k_{ts}-k_{tr}</math>, where <math>f</math> - feces, <math>ts </math>- tubular secretion and <math>tr</math>- tubular reabsorption. Similar models can be made for other organs, both absorbative and eliminative. <br />
<br />
The elimination rates can follow different rate laws. Generally, in a one-compartment model, there is a first-order rate law, e.g. <math>-\frac{d C(t)}{dt}=k_e * C(t)</math>. Other rate laws hold if e.g. the elimination system is saturated, then <math>-\frac{d C(t)}{dt}=const.</math>.<br />
<br />
Integrating the formula above gives<br />
<br />
<math>C(t)=C_0 e^{-k_{el} t}</math>,<br />
<br />
and further manipulation gives e.g. the half-life of X. in the blood to be <math>t_{1/2}=\frac{ln 2}{k_e}</math>.<br />
<br />
Often the concentration is plotted on a semilogarithmic plot versus time. If this yields a straight line, we have a one-compartment model. <math>k_e</math> can be predicted from the slope, and <math>C_0</math> by extrapolation. <br />
<br />
If the semilogarithmic plot of plasma concentration of X. versus time does not yield a straight line, higher compartmental models must be used. In the higher-compartment model the tissues connected to the plasma equilibrate more slowly with the plasma, so the plasma concentration falls off more rapidly in the beginning, in what is called the ''distribution phases'', before the concentration profile again is as for the one-compartment model above. If there are two phases, one distribution phase and one linear phase (the eliminiation phase), we have a two-compartment model, which usually can be modeled by:<br />
<br />
<math>C(t)=A e^{-\alpha t}+B e^{-\beta t}</math>,<br />
<br />
where <math>\beta</math> corresponds to <math>k_{e}</math> above, and can be treated the same way.<br />
<br />
If C is measured for e.g. an orally distributed drug there is also an absorption phase where the concentration increases over a certain time.<br />
<br />
=== Toxicokinetic Parameters ===<br />
There are several parameters that can be used to describe the models in more experiment-friendly terms. At the heart is C(t), the plasma concentration of X. at a given time. X is the total amount of X. in the body. The parameter V, called the volume of distribution, which relates X and C. V tells how large a volume is needed to distribute the total amount of the xenobiotic (X), so the concentration of X. in V is the same as in the blood (C). Mathematically, this gives <math>V=\frac{X}{C}</math>.<br />
<br />
D is the administered dosage. AUC is the area under the concentration/time curve from 0 to infinity. The bioavailability of X. is given as <math>F=\frac{AUC_{a}}{AUC_{i.v.}}</math>, which gives the fraction in plasma when administered e.g. orally compared to intra venously. This gives another relation: <math>V=\frac{D \times F}{k_{el} \times AUC}</math> for a non-i.v. delivered drug. The denominator term is the plasma concentration. For a one-compartment model this can often be approxomated as <math>V=\frac{D \times F}{C_0}</math>, or <math>V=\frac{X}{C}</math> as above for an i.v. delivered dosage (D=X).<br />
<br />
Clearance (Cl) is a term the that describes the volume of plasma that is cleared of X. per unit time, and can be given as the sum of clearances from each of the eliminating organs (<math>Cl_{total}=Cl_{renal}+Cl_{hepatic}+...</math>). The total body clearance is given by <math>Cl=\frac{D_{i.v.}}{AUC}</math>, which gives units of volume/time. Using the relations from above this can be seen to be equivalent to <math>Cl_t=V \times k_{el}</math> for a one-compartment model.<br />
<br />
If more than one dose is given, the dosage interval is given by <math>\tau</math>. Giving a dose either continuously, or with a certain interval, allows one to reach a steady state concentration, where there is a balance between absorption and elimination. By definition, this is equal to <math>5 \times C(t_{1/2})</math>. Equivalent equations for this is:<br />
*<math>C_{ss}=\frac{F\times D}{Cl_t \times \tau}=\frac{F\times D}{k_e\times V \times \tau}</math><br />
<br />
If the steady state is reached by a dosage D every <math>\tau</math>, there is naturally an oscillation of steady state values, given by <math>\frac{C_{ss}^{max}}{C_{ss}^{min}}=e^{k_e \tau}</math>. By replacing the bioavailable dosage per time (<math>\frac{F \times D}{\tau}</math>) with an constant infusion rate <math>k_0</math> on obtains <math> C_{ss}=\frac{k_0}{Cl_t}</math>. Often it is desirable to reach steady state concentration as quickly as possible. In this case a bolus dose that immediately gives <math>C_{ss}</math> in the plasma. This dose is then given by <math>D_{bolus}=C_{ss}\times V</math>.<br />
<br />
==Metabolism of xenobiotics==<br />
The biotransformation and metabolism of xenobiotics is of great importance in maintaining homeostasis. Some enzymes are very important for these metabolic reactions. There are several types of enzymes, responsible for oxidation, reduction, hydrolysis and conjugation of xenobiotics. These reaction are divided into two phases: Phase I and phase II.<br />
<br />
===Phase I reactions===<br />
<br />
Phase I reactions are the primary biotransformation of xenobiotics. This includes oxidation, hydrolysis or reduction, and generally introduces or reveals a functional group that increases the hydrophilicity of the xenobiotic a small amount. One very important oxidase is the cytochrome P-450 (CYP) family which are found in most lifeforms. CYP is a heme-containing enzyme family involved in electron transport. The most common reaction is oxidation of an organic substrate by using molecular oxygen as an electron acceptor, i.e. <math>RH + O_2 + 2H^+ + 2e^- \rightarrow ROH + H_2 O</math>. During the oxidation of certain compounds such as aliphatic alkenes and aromatic hydrocarbonds by CYP highly reactive species called epoxides can be formed. This is called activation of the xenobiotic, in which the metabolite form of the xenobiotic is more reactive than the original form. Epoxides can bind to DNA and are possibly mutagenic or carcinogenic. Therefore, in virtually all cells there are CYP-dependent oxidations there is enzyme called ''epoxide hydrolase'' which reacts the epoxide group with water to produce diols. CYP enzymes are especially prevalent in the liver, and play a vital role in regulating the toxicity of a number of compounds that pass trough the liver. Important members of the CYP family are CYP3A4, which metabolises a great variety of compounds, and is present at high concentrations in the liver, CYP1A2 and CYP2D6, which metabolise a many different drugs, among them caffeine. CYP2E1 is less prevalent enzyme, but important since it metabolises small polar molecules such as ethanol.<br />
<br />
=== Phase II reactions ===<br />
Conjugation with various groups, such as acetylation, methylation, sulfonation, conjugation with glutathion and glucuronidation are the phase II reactions. In general (with the exception of acetylation and methylation) these cause a large increase in hydrophilicity of the conjugate, which allows the xenobiotic to be easily eliminated. These reactions generally proceed much quicker than the phase I reactions, and can either follow a phase I reaction or proceed directly. <br />
<br />
Glucuronidation is a major pathway of biotransformation of xenobiotics in humans. In glucoronidation the xenobiotic is conjugated with the cofactor uride diphosphate-glucuronic acid, creating a highly water soluble molecule, which can be excreted in urine or bile, depending on the total size of the molecule. This reaction is catalyzed by UDP-glucuronosyltransferase, and requires a hydroxyl, carboxyl or thiol group (roughly), so this will often follow a phase I reaction that provides such groups. Other important pathways are glutathione conjugation (catalyzed by glutathione -S-transferase) and GSH (glycine-cysteine-glutamic acid) conjugation. <br />
<br />
''GAH, kan noen som faktisk var på denne forelesningen skrive noe her, notatene hans er forferdelige!''<br />
<br />
== Risk assessment ==<br />
In addition to the knowledge about toxicokinetics and toxicodynamics, there is a whole greater field of risk assessment to see if a given xenobiotic represents a threat in certain situation. There are two main ways to determine toxicity in general, the epidemiological and toxilogical methods. Epidemology is the study of toxicity of substances in man. The disadvantage of this method is that it only can be performed post-exposure. Toxicology is the study of substances working in cells and animals. This can be done pre-exposure, but requires extrapolations to be applicable to humans. <br />
<br />
The general system for risk assessment is as follows:<br />
*Hazard identification<br />
*Expose assessment to determine total daily exposure (TDE)<br />
*Effect assessment of the TDE<br />
*Risk characterization and action<br />
<br />
===Hazard identification===<br />
Questions asked: 1. Can people be exposed? This is answered by checking individual habitats, work places, etc to see if there is any exposure risk at all. If yes, the next question is: Can toxic effects occur? This is answered by knowledge of toxicity, structure, like compounds, etc. If the answer is yes, one proceeds to exposure assessment.<br />
<br />
===Exposure assessment===<br />
There are standardized rules for TDE depending on form of exposure. Formulas for this can be:<br />
*<math>\text{TDE}_{environment}=\text{inhale} + \text{eat}=\frac{C_{air}[mg/m^3]\times V_{inhale} [20m^3/day]}{W_{body} [70 kg]} + \sum_{i=1}^n \frac{intake/day [kg] \times C_i [mg/kg]}{W}</math><br />
*<math>\text{TDE}_{work}=\text{inhale} + \text{skin}=\frac{C_{air}[mg/m^3]\times V_{inhale} [0.8m^3/hour]\times WT[8h]}{W_{body} [70 kg]} + \frac{A_{skin}[2000cm^2]\times Th_{matrix}[0.01cm]\times C_{subst. in matrix}[mg/cm^3]\times n}{W}, n=1...10</math><br />
<br />
===Effect assessment===<br />
Firstly, more detailed toxicology data is acquired. For substances that are produced more than one ton per year this data is required, for lesser substances it might not be available. Many tests can be done to acquire this type of data:<br />
*Acute toxicity -> dose vs. percentage of test animals dead.<br />
**Dead animals get a full pathology, with target organ and type of toxicity present.<br />
**The dosage is a single dosage, then wait 14 days and monitor behavior, GI trouble, cramps, etc.<br />
**<math>\text{LD}_{50}</math>is the dose at which 50% of the animals die within 14 days, this is an important number.<br />
*Irritation/sensitization, often done one guinea pigs or rabbits.<br />
*No observed adverse effect limits (NOAELs) are calculated from 28 days repeated administration.<br />
*In vitro testing of cell, genetic testing (Ames test), chromosomal tests and toxicokinetics.<br />
*If the substance has a distribution of more than 1000 tons per year, the studies are larger, including fertility and long term effects.<br />
<br />
===Risk characterization===<br />
After the exposure and effects have been characterized, the total risk is assessed. This includes:<br />
*Relevance and quality of previous testing<br />
**Choice of animal, are the results applicable to humans?<br />
**Is the toxicokinetic data of sufficient quality?<br />
*Extrapolation of the acquired data<br />
**Total daily exposure (TDE) compared to acceptable daily input (ADI) over a lifetime<br />
**Calculated by <math>\text{ADI}=\frac{\text{NOAEL}}{\text{Uncertainty factors (UF)}}</math>, where UF is 10 for animal to man and man to man (!). If lowest adverse effect limit (LOAEL) is used instead, another factor of ten is added.<br />
**Certain factor can modify the equation, e.g. if the metabolism of the specific xenobiotic is identical in the animal and human.<br />
<br />
If the results give that <math>\text{TDE}\geq \text{ADI}</math>, action is taken to reduce the TDE.<br />
<br />
An example of the importance of the quality of data is well known in the case of thalomide, which was tested, but tested on the wrong animals so the extrapolations where not valid. Another example is for <math>\beta</math>-naphthylamine, a drug that caused many cases of urinary bladder infection. In the liver this substance is not particularly harmful, and is oxidised by a CYP enzyme, producing and active and carcinogen form of the drug. But in the liver it is immediately conjugated with glucuronic acid, which makes it soluble and allows it to be secreted into the urine, and does not bind to DNA. In rats and mice this is the end result, and the substance is excreted and no adverse effects are observed. Dogs, on the other hand, contain <math>\beta</math>-glucuronidase, an enzyme in the bladder that hydrolyses the bond to glucuronic acid, redeeming the active and carcinogenic form of the drug. Since there are no UDP glucuronosyltransferase enzymes in the bladder, the drug stays in this activated form and binds to DNA, causing urinary bladder cancer. Initially, this drug was only tested on rats and mice and other animals that do not have <math>\beta</math>-glucuronidase in the bladder, this was not discovered. Humans do have this enzyme, which lead to many cases of urinary bladder cancer due to the use of the "wrong" test animals.<br />
<br />
== Eksterne linker ==<br />
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*[http://www.ntnu.no/studier/emner?emnekode=TOKS3001 NTNUs fagbeskrivelse]<br />
*[http://www.ntnu.no/studieinformasjon/timeplan/v09/?emnekode=TOKS3001-1 Timeplan Vår09]<br />
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[[Kategori:Fag]]</div>Kenrogerhttp://nanowiki.no/index.php?title=TOKS3001_-_Medisinsk_toksikologi&diff=3970TOKS3001 - Medisinsk toksikologi2009-05-09T08:32:10Z<p>Kenroger: /* Rate constants and elimination */</p>
<hr />
<div>{{Infobox<br />
|Fakta vår 2009<br />
|*Foreleser: Diverse<br />
*Vurderingsform: Skriftlig eksamen (100 %)<br />
*Eksamensdato: 18.05.2009<br />
*Fagbok: Casarett & Doull´s Toxicology: The Basic Science of Poisons, 6th edition. ISBN: 0071470514<br />
}}<br />
<br />
{{Infobox<br />
|Semesteroppgave<br />
|* Det er en obligatorisk semesteroppgave i faget.<br />
}}<br />
<br />
Forelesninger er to ganger i uka fra første uka i februar til siste uka i mars. I tillegg kommer en semesteroppgave (gruppearbeid). Eksamen baserer seg på forelesninger og utdelt materiale. <br />
<br />
= Core Curriculum =<br />
== Toxicokinetics ==<br />
<br />
===Definitions===<br />
''Xenobiotic'' (X.): A chemical that is not native in the body, or is present in much higher concentration than normal.<br />
<br />
''Toxic effect'': A change in physiological conditions caused by an effect of xenobiotics on the cellular level creating a decrease in health or behavior.<br />
<br />
''Toxicodynamics'': Mechanism of the toxic effect, reactivity, receptors and organ types.<br />
<br />
''Toxicokinetics'': Uptake, transport and lingering time/concentration of X.<br />
<br />
''Absorption'': Transport from the place of disposition to blood with a rate constant <math>k_a</math>.<br />
<br />
''Bolus'': A dosage of X. administered directly into the plasma.<br />
<br />
''Elimination'': Biotransformation, exhalation or excretion of X. X. does not need to be removed from the body, only made unavailable in its original form.<br />
<br />
''First pass metabolism'': The metabolism of a X that occurs in liver during the first passage.<br />
<br />
''Bioavailability (F)'': The fraction of a given dose D (X-parent compound) that reaches circulation in an unchanged form.<br />
<br />
''Enteroheptic circulation'': Absorption from small intestine to blood --> liver --> conjugate --> bile --> small intestine --> hydrolyzed --> parent compound --> reasorbed into blood<br />
<br />
===Introduction===<br />
There are two main ways to model toxicokinetics: Compartmental models and physiological models. The compartmental models are described more in detail below, and involve modeling organ systems by simple relations without involving physiology, i.e. the rate constants used are acquired from measurements alone. The physiological model looks at theoretical, or physiological, models to predict rate constants of the organs in the body. This involves factors such as:<br />
*Blood flow through organs<br />
*Absorption of the small intestine<br />
**Villi and microvilli in the intestine: These greatly increase the intestinal area, so absorption into the blood for selected X. is greatly enhanced here.<br />
**Active and passive diffusion: Some substances can diffuse directly across tissues, but most require some form of transport proteins. The mechanisms of these proteins determine how effectively and selectively xenobiotics are absorbed.<br />
**There is also metabolism in the intestine, by e.g. the cytochrome P450 3A4 (CYP3A4) enzyme which can activate many prodrugs.<br />
**Drug export from cells via P-glycoprotein is a very important mechanism which greatly reduces the amount of many xenobiotics that are absorbed.<br />
*The portal vein collects blood from the intestine and goes directly to the liver, where many substances are metabolized and their bioavailability is reduced. This is called first-pass metabolism, where the drugs are metabolized before reaching general systemic circulation. <br />
*After being metabolized in the liver many xenobiotics are conjugated and marked for excretion into the bile. The bile is excreted in the small intestine, where the drugs can be un-conjugated and reabsorbed, passing into the liver again. This is called the entero-hepatic circulation, and keeps plasma concentration of xenobiotics low in general.<br />
*Other special barriers, such as the blood-brain barrier and the placenta also greatly effect the distribution of xenobiotics.<br />
<br />
===Compartmental models===<br />
A model often used to model toxicokinetics is the compartmental model. In the compartmental model there is a central compartment representing the blood plasma and rapidly equilibrating tissues (e.g. liver and kidney), and side-compartments of more slowly equilibrating tissues. The simplest such model is the one-compartment model. Here there is only one compartment, which means all the modeled tissues are rapidly equilibrating. In this model a bolus will decay exponentially, i.e. measuring the logarithm of the plasma concentration over time gives a linear plot. Conversely, if experimental data holds with this description, it can be modeled by the one-compartment model. The decay is elimination, and elimination happens from the central compartment. <br />
<br />
=== Rate constants and elimination ===<br />
There are several rate constants involved in toxicokinetics. There are elimination and absorption rate constant, <math>k_e</math> and <math>k_a</math>, which describes elimination from and absorption into the central compartment (see below) if the dose is administered e.g. orally. In multi-compartment models there are also distribution and redistribution constants, e.g. <math>k_{12}</math> and <math>k_{21}</math>, which describes rates between the compartments.<br />
<br />
An example of a rate constant is the excretion rate constant through the kidney, <math>k_r</math>. In the kidney, glomerular filtration has a certain rate, tubular excretion another, and and reabsorption into the tubules a third. Thus, the excretion from the kidneys is given by <math>k_r=k_{f}+k_{ts}-k_{tr}</math>, where <math>f</math> - feces, <math>ts </math>- tubular secretion and <math>tr</math>- tubular reabsorption. Similar models can be made for other organs, both absorbative and eliminative. <br />
<br />
The elimination rates can follow different rate laws. Generally, in a one-compartment model, there is a first-order rate law, e.g. <math>-\frac{d C(t)}{dt}=k_e * C(t)</math>. Other rate laws hold if e.g. the elimination system is saturated, then <math>-\frac{d C(t)}{dt}=const.</math>.<br />
<br />
Integrating the formula above gives<br />
<br />
<math>C(t)=C_0 e^{-k_{el} t}</math>,<br />
<br />
and further manipulation gives e.g. the half-life of X. in the blood to be <math>t_{1/2}=\frac{ln 2}{k_e}</math>.<br />
<br />
Often the concentration is plotted on a semilogarithmic plot versus time. If this yields a straight line, we have a one-compartment model. <math>k_e</math> can be predicted from the slope, and <math>C_0</math> by extrapolation. <br />
<br />
If the semilogarithmic plot of plasma concentration of X. versus time does not yield a straight line, higher compartmental models must be used. In the higher-compartment model the tissues connected to the plasma equilibrate more slowly with the plasma, so the plasma concentration falls off more rapidly in the beginning, in what is called the ''distribution phases'', before the concentration profile again is as for the one-compartment model above. If there are two phases, one distribution phase and one linear phase (the eliminiation phase), we have a two-compartment model, which usually can be modeled by:<br />
<br />
<math>C(t)=A e^{-\alpha t}+B e^{-\beta t}</math>,<br />
<br />
where <math>\beta</math> corresponds to <math>k_{e}</math> above, and can be treated the same way.<br />
<br />
If C is measured for e.g. an orally distributed drug there is also an absorption phase where the concentration increases over a certain time.<br />
<br />
=== Toxicokinetic Parameters ===<br />
There are several parameters that can be used to describe the models in more experiment-friendly terms. At the heart is C(t), the plasma concentration of X. at a given time. X is the total amount of X. in the body. The parameter V, called the volume of distribution, which relates X and C. V tells how large a volume is needed to distribute the total amount of the xenobiotic (X), so the concentration of X. in V is the same as in the blood (C). Mathematically, this gives <math>V=\frac{X}{C}</math>.<br />
<br />
D is the administered dosage. AUC is the area under the concentration/time curve from 0 to infinity. The bioavailability of X. is given as <math>F=\frac{AUC_{a}}{AUC_{i.v.}}</math>, which gives the fraction in plasma when administered e.g. orally compared to intra venously. This gives another relation: <math>V=\frac{D \times F}{k_{el} \times AUC}</math> for a non-i.v. delivered drug. The denominator term is the plasma concentration. For a one-compartment model this can often be approxomated as <math>V=\frac{D \times F}{C_0}</math>, or <math>V=\frac{X}{C}</math> as above for an i.v. delivered dosage (D=X).<br />
<br />
Clearance (Cl) is a term the that describes the volume of plasma that is cleared of X. per unit time, and can be given as the sum of clearances from each of the eliminating organs (<math>Cl_{total}=Cl_{renal}+Cl_{hepatic}+...</math>). The total body clearance is given by <math>Cl=\frac{D_{i.v.}}{AUC}</math>, which gives units of volume/time. Using the relations from above this can be seen to be equivalent to <math>Cl_t=V \times k_{el}</math> for a one-compartment model.<br />
<br />
If more than one dose is given, the dosage interval is given by <math>\tau</math>. Giving a dose either continuously, or with a certain interval, allows one to reach a steady state concentration, where there is a balance between absorption and elimination. By definition, this is equal to <math>5 \times C(t_{1/2})</math>. Equivalent equations for this is:<br />
*<math>C_{ss}=\frac{F\times D}{Cl_t \times \tau}=\frac{F\times D}{k_e\times V \times \tau}</math><br />
<br />
If the steady state is reached by a dosage D every <math>\tau</math>, there is naturally an oscillation of steady state values, given by <math>\frac{C_{ss}^{max}}{C_{ss}^{min}}=e^{k_e \tau}</math>. By replacing the bioavailable dosage per time (<math>\frac{F \times D}{\tau}</math>) with an constant infusion rate <math>k_0</math> on obtains <math> C_{ss}=\frac{k_0}{Cl_t}</math>. Often it is desirable to reach steady state concentration as quickly as possible. In this case a bolus dose that immediately gives <math>C_{ss}</math> in the plasma. This dose is then given by <math>D_{bolus}=C_{ss}\times V</math>.<br />
<br />
==Metabolism of xenobiotics==<br />
The biotransformation and metabolism of xenobiotics is of great importance in maintaining homeostasis. Some enzymes are very important for these metabolic reactions. There are several types of enzymes, responsible for oxidation, reduction, hydrolysis and conjugation of xenobiotics. These reaction are divided into two phases: Phase I and phase II.<br />
<br />
===Phase I reactions===<br />
<br />
Phase I reactions are the primary biotransformation of xenobiotics. This includes oxidation, hydrolysis or reduction, and generally introduces or reveals a functional group that increases the hydrophilicity of the xenobiotic a small amount. One very important oxidase is the cytochrome P-450 (CYP) family which are found in most lifeforms. CYP is a heme-containing enzyme family involved in electron transport. The most common reaction is oxidation of an organic substrate by using molecular oxygen as an electron acceptor, i.e. <math>RH + O_2 + 2H^+ + 2e^- \rightarrow ROH + H_2 O</math>. During the oxidation of certain compounds such as aliphatic alkenes and aromatic hydrocarbonds by CYP highly reactive species called epoxides can be formed. This is called activation of the xenobiotic, in which the metabolite form of the xenobiotic is more reactive than the original form. Epoxides can bind to DNA and are possibly mutagenic or carcinogenic. Therefore, in virtually all cells there are CYP-dependent oxidations there is enzyme called ''epoxide hydrolase'' which reacts the epoxide group with water to produce diols. CYP enzymes are especially prevalent in the liver, and play a vital role in regulating the toxicity of a number of compounds that pass trough the liver. Important members of the CYP family are CYP3A4, which metabolises a great variety of compounds, and is present at high concentrations in the liver, CYP1A2 and CYP2D6, which metabolise a many different drugs, among them caffeine. CYP2E1 is less prevalent enzyme, but important since it metabolises small polar molecules such as ethanol.<br />
<br />
=== Phase II reactions ===<br />
Conjugation with various groups, such as acetylation, methylation, sulfonation, conjugation with glutathion and glucuronidation are the phase II reactions. In general (with the exception of acetylation and methylation) these cause a large increase in hydrophilicity of the conjugate, which allows the xenobiotic to be easily eliminated. These reactions generally proceed much quicker than the phase I reactions, and can either follow a phase I reaction or proceed directly. <br />
<br />
Glucuronidation is a major pathway of biotransformation of xenobiotics in humans. In glucoronidation the xenobiotic is conjugated with the cofactor uride diphosphate-glucuronic acid, creating a highly water soluble molecule, which can be excreted in urine or bile, depending on the total size of the molecule. This reaction is catalyzed by UDP-glucuronosyltransferase, and requires a hydroxyl, carboxyl or thiol group (roughly), so this will often follow a phase I reaction that provides such groups. Other important pathways are glutathione conjugation (catalyzed by glutathione -S-transferase) and GSH (glycine-cysteine-glutamic acid) conjugation. <br />
<br />
''GAH, kan noen som faktisk var på denne forelesningen skrive noe her, notatene hans er forferdelige!''<br />
<br />
== Risk assessment ==<br />
In addition to the knowledge about toxicokinetics and toxicodynamics, there is a whole greater field of risk assessment to see if a given xenobiotic represents a threat in certain situation. There are two main ways to determine toxicity in general, the epidemiological and toxilogical methods. Epidemology is the study of toxicity of substances in man. The disadvantage of this method is that it only can be performed post-exposure. Toxicology is the study of substances working in cells and animals. This can be done pre-exposure, but requires extrapolations to be applicable to humans. <br />
<br />
The general system for risk assessment is as follows:<br />
*Hazard identification<br />
*Expose assessment to determine total daily exposure (TDE)<br />
*Effect assessment of the TDE<br />
*Risk characterization and action<br />
<br />
===Hazard identification===<br />
Questions asked: 1. Can people be exposed? This is answered by checking individual habitats, work places, etc to see if there is any exposure risk at all. If yes, the next question is: Can toxic effects occur? This is answered by knowledge of toxicity, structure, like compounds, etc. If the answer is yes, one proceeds to exposure assessment.<br />
<br />
===Exposure assessment===<br />
There are standardized rules for TDE depending on form of exposure. Formulas for this can be:<br />
*<math>\text{TDE}_{environment}=\text{inhale} + \text{eat}=\frac{C_{air}[mg/m^3]\times V_{inhale} [20m^3/day]}{W_{body} [70 kg]} + \sum_{i=1}^n \frac{intake/day [kg] \times C_i [mg/kg]}{W}</math><br />
*<math>\text{TDE}_{work}=\text{inhale} + \text{skin}=\frac{C_{air}[mg/m^3]\times V_{inhale} [0.8m^3/hour]\times WT[8h]}{W_{body} [70 kg]} + \frac{A_{skin}[2000cm^2]\times Th_{matrix}[0.01cm]\times C_{subst. in matrix}[mg/cm^3]\times n}{W}, n=1...10</math><br />
<br />
===Effect assessment===<br />
Firstly, more detailed toxicology data is acquired. For substances that are produced more than one ton per year this data is required, for lesser substances it might not be available. Many tests can be done to acquire this type of data:<br />
*Acute toxicity -> dose vs. percentage of test animals dead.<br />
**Dead animals get a full pathology, with target organ and type of toxicity present.<br />
**The dosage is a single dosage, then wait 14 days and monitor behavior, GI trouble, cramps, etc.<br />
**<math>\text{LD}_{50}</math>is the dose at which 50% of the animals die within 14 days, this is an important number.<br />
*Irritation/sensitization, often done one guinea pigs or rabbits.<br />
*No observed adverse effect limits (NOAELs) are calculated from 28 days repeated administration.<br />
*In vitro testing of cell, genetic testing (Ames test), chromosomal tests and toxicokinetics.<br />
*If the substance has a distribution of more than 1000 tons per year, the studies are larger, including fertility and long term effects.<br />
<br />
===Risk characterization===<br />
After the exposure and effects have been characterized, the total risk is assessed. This includes:<br />
*Relevance and quality of previous testing<br />
**Choice of animal, are the results applicable to humans?<br />
**Is the toxicokinetic data of sufficient quality?<br />
*Extrapolation of the acquired data<br />
**Total daily exposure (TDE) compared to acceptable daily input (ADI) over a lifetime<br />
**Calculated by <math>\text{ADI}=\frac{\text{NOAEL}}{\text{Uncertainty factors (UF)}}</math>, where UF is 10 for animal to man and man to man (!). If lowest adverse effect limit (LOAEL) is used instead, another factor of ten is added.<br />
**Certain factor can modify the equation, e.g. if the metabolism of the specific xenobiotic is identical in the animal and human.<br />
<br />
If the results give that <math>\text{TDE}\geq \text{ADI}</math>, action is taken to reduce the TDE.<br />
<br />
An example of the importance of the quality of data is well known in the case of thalomide, which was tested, but tested on the wrong animals so the extrapolations where not valid. Another example is for <math>\beta</math>-naphthylamine, a drug that caused many cases of urinary bladder infection. In the liver this substance is not particularly harmful, and is oxidised by a CYP enzyme, producing and active and carcinogen form of the drug. But in the liver it is immediately conjugated with glucuronic acid, which makes it soluble and allows it to be secreted into the urine, and does not bind to DNA. In rats and mice this is the end result, and the substance is excreted and no adverse effects are observed. Dogs, on the other hand, contain <math>\beta</math>-glucuronidase, an enzyme in the bladder that hydrolyses the bond to glucuronic acid, redeeming the active and carcinogenic form of the drug. Since there are no UDP glucuronosyltransferase enzymes in the bladder, the drug stays in this activated form and binds to DNA, causing urinary bladder cancer. Initially, this drug was only tested on rats and mice and other animals that do not have <math>\beta</math>-glucuronidase in the bladder, this was not discovered. Humans do have this enzyme, which lead to many cases of urinary bladder cancer due to the use of the "wrong" test animals.<br />
<br />
== Eksterne linker ==<br />
<br />
*[http://www.ntnu.no/studier/emner?emnekode=TOKS3001 NTNUs fagbeskrivelse]<br />
*[http://www.ntnu.no/studieinformasjon/timeplan/v09/?emnekode=TOKS3001-1 Timeplan Vår09]<br />
<br />
[[Kategori:Valgbare emner]]<br />
[[Kategori:Fag 8. semester]]<br />
[[Kategori:Fag]]</div>Kenrogerhttp://nanowiki.no/index.php?title=TOKS3001_-_Medisinsk_toksikologi&diff=3969TOKS3001 - Medisinsk toksikologi2009-05-09T08:06:15Z<p>Kenroger: /* Definitions */</p>
<hr />
<div>{{Infobox<br />
|Fakta vår 2009<br />
|*Foreleser: Diverse<br />
*Vurderingsform: Skriftlig eksamen (100 %)<br />
*Eksamensdato: 18.05.2009<br />
*Fagbok: Casarett & Doull´s Toxicology: The Basic Science of Poisons, 6th edition. ISBN: 0071470514<br />
}}<br />
<br />
{{Infobox<br />
|Semesteroppgave<br />
|* Det er en obligatorisk semesteroppgave i faget.<br />
}}<br />
<br />
Forelesninger er to ganger i uka fra første uka i februar til siste uka i mars. I tillegg kommer en semesteroppgave (gruppearbeid). Eksamen baserer seg på forelesninger og utdelt materiale. <br />
<br />
= Core Curriculum =<br />
== Toxicokinetics ==<br />
<br />
===Definitions===<br />
''Xenobiotic'' (X.): A chemical that is not native in the body, or is present in much higher concentration than normal.<br />
<br />
''Toxic effect'': A change in physiological conditions caused by an effect of xenobiotics on the cellular level creating a decrease in health or behavior.<br />
<br />
''Toxicodynamics'': Mechanism of the toxic effect, reactivity, receptors and organ types.<br />
<br />
''Toxicokinetics'': Uptake, transport and lingering time/concentration of X.<br />
<br />
''Absorption'': Transport from the place of disposition to blood with a rate constant <math>k_a</math>.<br />
<br />
''Bolus'': A dosage of X. administered directly into the plasma.<br />
<br />
''Elimination'': Biotransformation, exhalation or excretion of X. X. does not need to be removed from the body, only made unavailable in its original form.<br />
<br />
''First pass metabolism'': The metabolism of a X that occurs in liver during the first passage.<br />
<br />
''Bioavailability (F)'': The fraction of a given dose D (X-parent compound) that reaches circulation in an unchanged form.<br />
<br />
''Enteroheptic circulation'': Absorption from small intestine to blood --> liver --> conjugate --> bile --> small intestine --> hydrolyzed --> parent compound --> reasorbed into blood<br />
<br />
===Introduction===<br />
There are two main ways to model toxicokinetics: Compartmental models and physiological models. The compartmental models are described more in detail below, and involve modeling organ systems by simple relations without involving physiology, i.e. the rate constants used are acquired from measurements alone. The physiological model looks at theoretical, or physiological, models to predict rate constants of the organs in the body. This involves factors such as:<br />
*Blood flow through organs<br />
*Absorption of the small intestine<br />
**Villi and microvilli in the intestine: These greatly increase the intestinal area, so absorption into the blood for selected X. is greatly enhanced here.<br />
**Active and passive diffusion: Some substances can diffuse directly across tissues, but most require some form of transport proteins. The mechanisms of these proteins determine how effectively and selectively xenobiotics are absorbed.<br />
**There is also metabolism in the intestine, by e.g. the cytochrome P450 3A4 (CYP3A4) enzyme which can activate many prodrugs.<br />
**Drug export from cells via P-glycoprotein is a very important mechanism which greatly reduces the amount of many xenobiotics that are absorbed.<br />
*The portal vein collects blood from the intestine and goes directly to the liver, where many substances are metabolized and their bioavailability is reduced. This is called first-pass metabolism, where the drugs are metabolized before reaching general systemic circulation. <br />
*After being metabolized in the liver many xenobiotics are conjugated and marked for excretion into the bile. The bile is excreted in the small intestine, where the drugs can be un-conjugated and reabsorbed, passing into the liver again. This is called the entero-hepatic circulation, and keeps plasma concentration of xenobiotics low in general.<br />
*Other special barriers, such as the blood-brain barrier and the placenta also greatly effect the distribution of xenobiotics.<br />
<br />
===Compartmental models===<br />
A model often used to model toxicokinetics is the compartmental model. In the compartmental model there is a central compartment representing the blood plasma and rapidly equilibrating tissues (e.g. liver and kidney), and side-compartments of more slowly equilibrating tissues. The simplest such model is the one-compartment model. Here there is only one compartment, which means all the modeled tissues are rapidly equilibrating. In this model a bolus will decay exponentially, i.e. measuring the logarithm of the plasma concentration over time gives a linear plot. Conversely, if experimental data holds with this description, it can be modeled by the one-compartment model. The decay is elimination, and elimination happens from the central compartment. <br />
<br />
=== Rate constants and elimination ===<br />
There are several rate constants involved in toxicokinetics. There are elimination and absorption rate constant, <math>k_e</math> and <math>k_a</math>, which describes elimination from and absorption into the central compartment (see below) if the dose is administered e.g. orally. In multi-compartment models there are also distribution and redistribution constants, e.g. <math>k_{12}</math> and <math>k_{21}</math>, which describes rates between the compartments.<br />
<br />
An example of a rate constant is the excretion rate constant through the kidney, <math>k_r</math>. In the kidney, glomerular filtration has a certain rate, tubular excretion another, and and reabsorption into the tubules a third. Thus, the excretion from the kidneys is given by <math>k_r=k_{gf}+k_{te}-k_{tr}</math>. Similar models can be made for other organs, both absorbative and eliminative. <br />
<br />
The elimination rates can follow different rate laws. Generally, in a one-compartment model, there is a first-order rate law, e.g. <math>-\frac{d C(t)}{dt}=k_e * C(t)</math>. Other rate laws hold if e.g. the elimination system is saturated, then <math>-\frac{d C(t)}{dt}=const.</math>.<br />
<br />
Integrating the formula above gives<br />
<br />
<math>C(t)=C_0 e^{-k_{el} t}</math>,<br />
<br />
and further manipulation gives e.g. the half-life of X. in the blood to be <math>t_{1/2}=\frac{ln 2}{k_e}</math>.<br />
<br />
Often the concentration is plotted on a semilogarithmic plot versus time. If this yields a straight line, we have a one-compartment model. <math>k_e</math> can be predicted from the slope, and <math>C_0</math> by extrapolation. <br />
<br />
If the semilogarithmic plot of plasma concentration of X. versus time does not yield a straight line, higher compartmental models must be used. In the higher-compartment model the tissues connected to the plasma equilibrate more slowly with the plasma, so the plasma concentration falls off more rapidly in the beginning, in what is called the ''distribution phases'', before the concentration profile again is as for the one-compartment model above. If there are two phases, one distribution phase and one linear phase (the eliminiation phase), we have a two-compartment model, which usually can be modeled by:<br />
<br />
<math>C(t)=A e^{-\alpha t}+B e^{-\beta t}</math>,<br />
<br />
where <math>\beta</math> corresponds to <math>k_{e}</math> above, and can be treated the same way.<br />
<br />
If C is measured for e.g. an orally distributed drug there is also an absorption phase where the concentration increases over a certain time. <br />
<br />
=== Toxicokinetic Parameters ===<br />
There are several parameters that can be used to describe the models in more experiment-friendly terms. At the heart is C(t), the plasma concentration of X. at a given time. X is the total amount of X. in the body. The parameter V, called the volume of distribution, which relates X and C. V tells how large a volume is needed to distribute the total amount of the xenobiotic (X), so the concentration of X. in V is the same as in the blood (C). Mathematically, this gives <math>V=\frac{X}{C}</math>.<br />
<br />
D is the administered dosage. AUC is the area under the concentration/time curve from 0 to infinity. The bioavailability of X. is given as <math>F=\frac{AUC_{a}}{AUC_{i.v.}}</math>, which gives the fraction in plasma when administered e.g. orally compared to intra venously. This gives another relation: <math>V=\frac{D \times F}{k_{el} \times AUC}</math> for a non-i.v. delivered drug. The denominator term is the plasma concentration. For a one-compartment model this can often be approxomated as <math>V=\frac{D \times F}{C_0}</math>, or <math>V=\frac{X}{C}</math> as above for an i.v. delivered dosage (D=X).<br />
<br />
Clearance (Cl) is a term the that describes the volume of plasma that is cleared of X. per unit time, and can be given as the sum of clearances from each of the eliminating organs (<math>Cl_{total}=Cl_{renal}+Cl_{hepatic}+...</math>). The total body clearance is given by <math>Cl=\frac{D_{i.v.}}{AUC}</math>, which gives units of volume/time. Using the relations from above this can be seen to be equivalent to <math>Cl_t=V \times k_{el}</math> for a one-compartment model.<br />
<br />
If more than one dose is given, the dosage interval is given by <math>\tau</math>. Giving a dose either continuously, or with a certain interval, allows one to reach a steady state concentration, where there is a balance between absorption and elimination. By definition, this is equal to <math>5 \times C(t_{1/2})</math>. Equivalent equations for this is:<br />
*<math>C_{ss}=\frac{F\times D}{Cl_t \times \tau}=\frac{F\times D}{k_e\times V \times \tau}</math><br />
<br />
If the steady state is reached by a dosage D every <math>\tau</math>, there is naturally an oscillation of steady state values, given by <math>\frac{C_{ss}^{max}}{C_{ss}^{min}}=e^{k_e \tau}</math>. By replacing the bioavailable dosage per time (<math>\frac{F \times D}{\tau}</math>) with an constant infusion rate <math>k_0</math> on obtains <math> C_{ss}=\frac{k_0}{Cl_t}</math>. Often it is desirable to reach steady state concentration as quickly as possible. In this case a bolus dose that immediately gives <math>C_{ss}</math> in the plasma. This dose is then given by <math>D_{bolus}=C_{ss}\times V</math>.<br />
<br />
==Metabolism of xenobiotics==<br />
The biotransformation and metabolism of xenobiotics is of great importance in maintaining homeostasis. Some enzymes are very important for these metabolic reactions. There are several types of enzymes, responsible for oxidation, reduction, hydrolysis and conjugation of xenobiotics. These reaction are divided into two phases: Phase I and phase II.<br />
<br />
===Phase I reactions===<br />
<br />
Phase I reactions are the primary biotransformation of xenobiotics. This includes oxidation, hydrolysis or reduction, and generally introduces or reveals a functional group that increases the hydrophilicity of the xenobiotic a small amount. One very important oxidase is the cytochrome P-450 (CYP) family which are found in most lifeforms. CYP is a heme-containing enzyme family involved in electron transport. The most common reaction is oxidation of an organic substrate by using molecular oxygen as an electron acceptor, i.e. <math>RH + O_2 + 2H^+ + 2e^- \rightarrow ROH + H_2 O</math>. During the oxidation of certain compounds such as aliphatic alkenes and aromatic hydrocarbonds by CYP highly reactive species called epoxides can be formed. This is called activation of the xenobiotic, in which the metabolite form of the xenobiotic is more reactive than the original form. Epoxides can bind to DNA and are possibly mutagenic or carcinogenic. Therefore, in virtually all cells there are CYP-dependent oxidations there is enzyme called ''epoxide hydrolase'' which reacts the epoxide group with water to produce diols. CYP enzymes are especially prevalent in the liver, and play a vital role in regulating the toxicity of a number of compounds that pass trough the liver. Important members of the CYP family are CYP3A4, which metabolises a great variety of compounds, and is present at high concentrations in the liver, CYP1A2 and CYP2D6, which metabolise a many different drugs, among them caffeine. CYP2E1 is less prevalent enzyme, but important since it metabolises small polar molecules such as ethanol.<br />
<br />
=== Phase II reactions ===<br />
Conjugation with various groups, such as acetylation, methylation, sulfonation, conjugation with glutathion and glucuronidation are the phase II reactions. In general (with the exception of acetylation and methylation) these cause a large increase in hydrophilicity of the conjugate, which allows the xenobiotic to be easily eliminated. These reactions generally proceed much quicker than the phase I reactions, and can either follow a phase I reaction or proceed directly. <br />
<br />
Glucuronidation is a major pathway of biotransformation of xenobiotics in humans. In glucoronidation the xenobiotic is conjugated with the cofactor uride diphosphate-glucuronic acid, creating a highly water soluble molecule, which can be excreted in urine or bile, depending on the total size of the molecule. This reaction is catalyzed by UDP-glucuronosyltransferase, and requires a hydroxyl, carboxyl or thiol group (roughly), so this will often follow a phase I reaction that provides such groups. Other important pathways are glutathione conjugation (catalyzed by glutathione -S-transferase) and GSH (glycine-cysteine-glutamic acid) conjugation. <br />
<br />
''GAH, kan noen som faktisk var på denne forelesningen skrive noe her, notatene hans er forferdelige!''<br />
<br />
== Risk assessment ==<br />
In addition to the knowledge about toxicokinetics and toxicodynamics, there is a whole greater field of risk assessment to see if a given xenobiotic represents a threat in certain situation. There are two main ways to determine toxicity in general, the epidemiological and toxilogical methods. Epidemology is the study of toxicity of substances in man. The disadvantage of this method is that it only can be performed post-exposure. Toxicology is the study of substances working in cells and animals. This can be done pre-exposure, but requires extrapolations to be applicable to humans. <br />
<br />
The general system for risk assessment is as follows:<br />
*Hazard identification<br />
*Expose assessment to determine total daily exposure (TDE)<br />
*Effect assessment of the TDE<br />
*Risk characterization and action<br />
<br />
===Hazard identification===<br />
Questions asked: 1. Can people be exposed? This is answered by checking individual habitats, work places, etc to see if there is any exposure risk at all. If yes, the next question is: Can toxic effects occur? This is answered by knowledge of toxicity, structure, like compounds, etc. If the answer is yes, one proceeds to exposure assessment.<br />
<br />
===Exposure assessment===<br />
There are standardized rules for TDE depending on form of exposure. Formulas for this can be:<br />
*<math>\text{TDE}_{environment}=\text{inhale} + \text{eat}=\frac{C_{air}[mg/m^3]\times V_{inhale} [20m^3/day]}{W_{body} [70 kg]} + \sum_{i=1}^n \frac{intake/day [kg] \times C_i [mg/kg]}{W}</math><br />
*<math>\text{TDE}_{work}=\text{inhale} + \text{skin}=\frac{C_{air}[mg/m^3]\times V_{inhale} [0.8m^3/hour]\times WT[8h]}{W_{body} [70 kg]} + \frac{A_{skin}[2000cm^2]\times Th_{matrix}[0.01cm]\times C_{subst. in matrix}[mg/cm^3]\times n}{W}, n=1...10</math><br />
<br />
===Effect assessment===<br />
Firstly, more detailed toxicology data is acquired. For substances that are produced more than one ton per year this data is required, for lesser substances it might not be available. Many tests can be done to acquire this type of data:<br />
*Acute toxicity -> dose vs. percentage of test animals dead.<br />
**Dead animals get a full pathology, with target organ and type of toxicity present.<br />
**The dosage is a single dosage, then wait 14 days and monitor behavior, GI trouble, cramps, etc.<br />
**<math>\text{LD}_{50}</math>is the dose at which 50% of the animals die within 14 days, this is an important number.<br />
*Irritation/sensitization, often done one guinea pigs or rabbits.<br />
*No observed adverse effect limits (NOAELs) are calculated from 28 days repeated administration.<br />
*In vitro testing of cell, genetic testing (Ames test), chromosomal tests and toxicokinetics.<br />
*If the substance has a distribution of more than 1000 tons per year, the studies are larger, including fertility and long term effects.<br />
<br />
===Risk characterization===<br />
After the exposure and effects have been characterized, the total risk is assessed. This includes:<br />
*Relevance and quality of previous testing<br />
**Choice of animal, are the results applicable to humans?<br />
**Is the toxicokinetic data of sufficient quality?<br />
*Extrapolation of the acquired data<br />
**Total daily exposure (TDE) compared to acceptable daily input (ADI) over a lifetime<br />
**Calculated by <math>\text{ADI}=\frac{\text{NOAEL}}{\text{Uncertainty factors (UF)}}</math>, where UF is 10 for animal to man and man to man (!). If lowest adverse effect limit (LOAEL) is used instead, another factor of ten is added.<br />
**Certain factor can modify the equation, e.g. if the metabolism of the specific xenobiotic is identical in the animal and human.<br />
<br />
If the results give that <math>\text{TDE}\geq \text{ADI}</math>, action is taken to reduce the TDE.<br />
<br />
An example of the importance of the quality of data is well known in the case of thalomide, which was tested, but tested on the wrong animals so the extrapolations where not valid. Another example is for <math>\beta</math>-naphthylamine, a drug that caused many cases of urinary bladder infection. In the liver this substance is not particularly harmful, and is oxidised by a CYP enzyme, producing and active and carcinogen form of the drug. But in the liver it is immediately conjugated with glucuronic acid, which makes it soluble and allows it to be secreted into the urine, and does not bind to DNA. In rats and mice this is the end result, and the substance is excreted and no adverse effects are observed. Dogs, on the other hand, contain <math>\beta</math>-glucuronidase, an enzyme in the bladder that hydrolyses the bond to glucuronic acid, redeeming the active and carcinogenic form of the drug. Since there are no UDP glucuronosyltransferase enzymes in the bladder, the drug stays in this activated form and binds to DNA, causing urinary bladder cancer. Initially, this drug was only tested on rats and mice and other animals that do not have <math>\beta</math>-glucuronidase in the bladder, this was not discovered. Humans do have this enzyme, which lead to many cases of urinary bladder cancer due to the use of the "wrong" test animals.<br />
<br />
== Eksterne linker ==<br />
<br />
*[http://www.ntnu.no/studier/emner?emnekode=TOKS3001 NTNUs fagbeskrivelse]<br />
*[http://www.ntnu.no/studieinformasjon/timeplan/v09/?emnekode=TOKS3001-1 Timeplan Vår09]<br />
<br />
[[Kategori:Valgbare emner]]<br />
[[Kategori:Fag 8. semester]]<br />
[[Kategori:Fag]]</div>Kenrogerhttp://nanowiki.no/index.php?title=TOKS3001_-_Medisinsk_toksikologi&diff=3968TOKS3001 - Medisinsk toksikologi2009-05-09T08:01:24Z<p>Kenroger: /* Introduction */</p>
<hr />
<div>{{Infobox<br />
|Fakta vår 2009<br />
|*Foreleser: Diverse<br />
*Vurderingsform: Skriftlig eksamen (100 %)<br />
*Eksamensdato: 18.05.2009<br />
*Fagbok: Casarett & Doull´s Toxicology: The Basic Science of Poisons, 6th edition. ISBN: 0071470514<br />
}}<br />
<br />
{{Infobox<br />
|Semesteroppgave<br />
|* Det er en obligatorisk semesteroppgave i faget.<br />
}}<br />
<br />
Forelesninger er to ganger i uka fra første uka i februar til siste uka i mars. I tillegg kommer en semesteroppgave (gruppearbeid). Eksamen baserer seg på forelesninger og utdelt materiale. <br />
<br />
= Core Curriculum =<br />
== Toxicokinetics ==<br />
<br />
===Definitions===<br />
''Xenobiotic'' (X.): A chemical that is not native in the body, or is present in much higher concentration than normal.<br />
<br />
''Toxic effect'': A change in physiological conditions caused by an effect of xenobiotics on the cellular level creating a decrease in health or behavior.<br />
<br />
''Toxicodynamics'': Mechanism of the toxic effect, reactivity, receptors and organ types.<br />
<br />
''Toxicokinetics'': Uptake, transport and lingering time/concentration of X.<br />
<br />
''Absorption'': Transport from the place of disposition to blood with a rate constant <math>k_a</math>.<br />
<br />
''Bolus'': A dosage of X. administered directly into the plasma.<br />
<br />
''Elimination'': Biotransformation, exhalation or excretion of X. X. does not need to be removed from the body, only made unavailable in its original form.<br />
<br />
''First pass metabolism'': The metabolism of a X that occurs in liver during the first passage.<br />
<br />
''Bioavailability (F)'': The fraction of a given dose D (X-parent compound) that reaches circulation in an unchanged form.<br />
<br />
===Introduction===<br />
There are two main ways to model toxicokinetics: Compartmental models and physiological models. The compartmental models are described more in detail below, and involve modeling organ systems by simple relations without involving physiology, i.e. the rate constants used are acquired from measurements alone. The physiological model looks at theoretical, or physiological, models to predict rate constants of the organs in the body. This involves factors such as:<br />
*Blood flow through organs<br />
*Absorption of the small intestine<br />
**Villi and microvilli in the intestine: These greatly increase the intestinal area, so absorption into the blood for selected X. is greatly enhanced here.<br />
**Active and passive diffusion: Some substances can diffuse directly across tissues, but most require some form of transport proteins. The mechanisms of these proteins determine how effectively and selectively xenobiotics are absorbed.<br />
**There is also metabolism in the intestine, by e.g. the cytochrome P450 3A4 (CYP3A4) enzyme which can activate many prodrugs.<br />
**Drug export from cells via P-glycoprotein is a very important mechanism which greatly reduces the amount of many xenobiotics that are absorbed.<br />
*The portal vein collects blood from the intestine and goes directly to the liver, where many substances are metabolized and their bioavailability is reduced. This is called first-pass metabolism, where the drugs are metabolized before reaching general systemic circulation. <br />
*After being metabolized in the liver many xenobiotics are conjugated and marked for excretion into the bile. The bile is excreted in the small intestine, where the drugs can be un-conjugated and reabsorbed, passing into the liver again. This is called the entero-hepatic circulation, and keeps plasma concentration of xenobiotics low in general.<br />
*Other special barriers, such as the blood-brain barrier and the placenta also greatly effect the distribution of xenobiotics.<br />
<br />
===Compartmental models===<br />
A model often used to model toxicokinetics is the compartmental model. In the compartmental model there is a central compartment representing the blood plasma and rapidly equilibrating tissues (e.g. liver and kidney), and side-compartments of more slowly equilibrating tissues. The simplest such model is the one-compartment model. Here there is only one compartment, which means all the modeled tissues are rapidly equilibrating. In this model a bolus will decay exponentially, i.e. measuring the logarithm of the plasma concentration over time gives a linear plot. Conversely, if experimental data holds with this description, it can be modeled by the one-compartment model. The decay is elimination, and elimination happens from the central compartment. <br />
<br />
=== Rate constants and elimination ===<br />
There are several rate constants involved in toxicokinetics. There are elimination and absorption rate constant, <math>k_e</math> and <math>k_a</math>, which describes elimination from and absorption into the central compartment (see below) if the dose is administered e.g. orally. In multi-compartment models there are also distribution and redistribution constants, e.g. <math>k_{12}</math> and <math>k_{21}</math>, which describes rates between the compartments.<br />
<br />
An example of a rate constant is the excretion rate constant through the kidney, <math>k_r</math>. In the kidney, glomerular filtration has a certain rate, tubular excretion another, and and reabsorption into the tubules a third. Thus, the excretion from the kidneys is given by <math>k_r=k_{gf}+k_{te}-k_{tr}</math>. Similar models can be made for other organs, both absorbative and eliminative. <br />
<br />
The elimination rates can follow different rate laws. Generally, in a one-compartment model, there is a first-order rate law, e.g. <math>-\frac{d C(t)}{dt}=k_e * C(t)</math>. Other rate laws hold if e.g. the elimination system is saturated, then <math>-\frac{d C(t)}{dt}=const.</math>.<br />
<br />
Integrating the formula above gives<br />
<br />
<math>C(t)=C_0 e^{-k_{el} t}</math>,<br />
<br />
and further manipulation gives e.g. the half-life of X. in the blood to be <math>t_{1/2}=\frac{ln 2}{k_e}</math>.<br />
<br />
Often the concentration is plotted on a semilogarithmic plot versus time. If this yields a straight line, we have a one-compartment model. <math>k_e</math> can be predicted from the slope, and <math>C_0</math> by extrapolation. <br />
<br />
If the semilogarithmic plot of plasma concentration of X. versus time does not yield a straight line, higher compartmental models must be used. In the higher-compartment model the tissues connected to the plasma equilibrate more slowly with the plasma, so the plasma concentration falls off more rapidly in the beginning, in what is called the ''distribution phases'', before the concentration profile again is as for the one-compartment model above. If there are two phases, one distribution phase and one linear phase (the eliminiation phase), we have a two-compartment model, which usually can be modeled by:<br />
<br />
<math>C(t)=A e^{-\alpha t}+B e^{-\beta t}</math>,<br />
<br />
where <math>\beta</math> corresponds to <math>k_{e}</math> above, and can be treated the same way.<br />
<br />
If C is measured for e.g. an orally distributed drug there is also an absorption phase where the concentration increases over a certain time. <br />
<br />
=== Toxicokinetic Parameters ===<br />
There are several parameters that can be used to describe the models in more experiment-friendly terms. At the heart is C(t), the plasma concentration of X. at a given time. X is the total amount of X. in the body. The parameter V, called the volume of distribution, which relates X and C. V tells how large a volume is needed to distribute the total amount of the xenobiotic (X), so the concentration of X. in V is the same as in the blood (C). Mathematically, this gives <math>V=\frac{X}{C}</math>.<br />
<br />
D is the administered dosage. AUC is the area under the concentration/time curve from 0 to infinity. The bioavailability of X. is given as <math>F=\frac{AUC_{a}}{AUC_{i.v.}}</math>, which gives the fraction in plasma when administered e.g. orally compared to intra venously. This gives another relation: <math>V=\frac{D \times F}{k_{el} \times AUC}</math> for a non-i.v. delivered drug. The denominator term is the plasma concentration. For a one-compartment model this can often be approxomated as <math>V=\frac{D \times F}{C_0}</math>, or <math>V=\frac{X}{C}</math> as above for an i.v. delivered dosage (D=X).<br />
<br />
Clearance (Cl) is a term the that describes the volume of plasma that is cleared of X. per unit time, and can be given as the sum of clearances from each of the eliminating organs (<math>Cl_{total}=Cl_{renal}+Cl_{hepatic}+...</math>). The total body clearance is given by <math>Cl=\frac{D_{i.v.}}{AUC}</math>, which gives units of volume/time. Using the relations from above this can be seen to be equivalent to <math>Cl_t=V \times k_{el}</math> for a one-compartment model.<br />
<br />
If more than one dose is given, the dosage interval is given by <math>\tau</math>. Giving a dose either continuously, or with a certain interval, allows one to reach a steady state concentration, where there is a balance between absorption and elimination. By definition, this is equal to <math>5 \times C(t_{1/2})</math>. Equivalent equations for this is:<br />
*<math>C_{ss}=\frac{F\times D}{Cl_t \times \tau}=\frac{F\times D}{k_e\times V \times \tau}</math><br />
<br />
If the steady state is reached by a dosage D every <math>\tau</math>, there is naturally an oscillation of steady state values, given by <math>\frac{C_{ss}^{max}}{C_{ss}^{min}}=e^{k_e \tau}</math>. By replacing the bioavailable dosage per time (<math>\frac{F \times D}{\tau}</math>) with an constant infusion rate <math>k_0</math> on obtains <math> C_{ss}=\frac{k_0}{Cl_t}</math>. Often it is desirable to reach steady state concentration as quickly as possible. In this case a bolus dose that immediately gives <math>C_{ss}</math> in the plasma. This dose is then given by <math>D_{bolus}=C_{ss}\times V</math>.<br />
<br />
==Metabolism of xenobiotics==<br />
The biotransformation and metabolism of xenobiotics is of great importance in maintaining homeostasis. Some enzymes are very important for these metabolic reactions. There are several types of enzymes, responsible for oxidation, reduction, hydrolysis and conjugation of xenobiotics. These reaction are divided into two phases: Phase I and phase II.<br />
<br />
===Phase I reactions===<br />
<br />
Phase I reactions are the primary biotransformation of xenobiotics. This includes oxidation, hydrolysis or reduction, and generally introduces or reveals a functional group that increases the hydrophilicity of the xenobiotic a small amount. One very important oxidase is the cytochrome P-450 (CYP) family which are found in most lifeforms. CYP is a heme-containing enzyme family involved in electron transport. The most common reaction is oxidation of an organic substrate by using molecular oxygen as an electron acceptor, i.e. <math>RH + O_2 + 2H^+ + 2e^- \rightarrow ROH + H_2 O</math>. During the oxidation of certain compounds such as aliphatic alkenes and aromatic hydrocarbonds by CYP highly reactive species called epoxides can be formed. This is called activation of the xenobiotic, in which the metabolite form of the xenobiotic is more reactive than the original form. Epoxides can bind to DNA and are possibly mutagenic or carcinogenic. Therefore, in virtually all cells there are CYP-dependent oxidations there is enzyme called ''epoxide hydrolase'' which reacts the epoxide group with water to produce diols. CYP enzymes are especially prevalent in the liver, and play a vital role in regulating the toxicity of a number of compounds that pass trough the liver. Important members of the CYP family are CYP3A4, which metabolises a great variety of compounds, and is present at high concentrations in the liver, CYP1A2 and CYP2D6, which metabolise a many different drugs, among them caffeine. CYP2E1 is less prevalent enzyme, but important since it metabolises small polar molecules such as ethanol.<br />
<br />
=== Phase II reactions ===<br />
Conjugation with various groups, such as acetylation, methylation, sulfonation, conjugation with glutathion and glucuronidation are the phase II reactions. In general (with the exception of acetylation and methylation) these cause a large increase in hydrophilicity of the conjugate, which allows the xenobiotic to be easily eliminated. These reactions generally proceed much quicker than the phase I reactions, and can either follow a phase I reaction or proceed directly. <br />
<br />
Glucuronidation is a major pathway of biotransformation of xenobiotics in humans. In glucoronidation the xenobiotic is conjugated with the cofactor uride diphosphate-glucuronic acid, creating a highly water soluble molecule, which can be excreted in urine or bile, depending on the total size of the molecule. This reaction is catalyzed by UDP-glucuronosyltransferase, and requires a hydroxyl, carboxyl or thiol group (roughly), so this will often follow a phase I reaction that provides such groups. Other important pathways are glutathione conjugation (catalyzed by glutathione -S-transferase) and GSH (glycine-cysteine-glutamic acid) conjugation. <br />
<br />
''GAH, kan noen som faktisk var på denne forelesningen skrive noe her, notatene hans er forferdelige!''<br />
<br />
== Risk assessment ==<br />
In addition to the knowledge about toxicokinetics and toxicodynamics, there is a whole greater field of risk assessment to see if a given xenobiotic represents a threat in certain situation. There are two main ways to determine toxicity in general, the epidemiological and toxilogical methods. Epidemology is the study of toxicity of substances in man. The disadvantage of this method is that it only can be performed post-exposure. Toxicology is the study of substances working in cells and animals. This can be done pre-exposure, but requires extrapolations to be applicable to humans. <br />
<br />
The general system for risk assessment is as follows:<br />
*Hazard identification<br />
*Expose assessment to determine total daily exposure (TDE)<br />
*Effect assessment of the TDE<br />
*Risk characterization and action<br />
<br />
===Hazard identification===<br />
Questions asked: 1. Can people be exposed? This is answered by checking individual habitats, work places, etc to see if there is any exposure risk at all. If yes, the next question is: Can toxic effects occur? This is answered by knowledge of toxicity, structure, like compounds, etc. If the answer is yes, one proceeds to exposure assessment.<br />
<br />
===Exposure assessment===<br />
There are standardized rules for TDE depending on form of exposure. Formulas for this can be:<br />
*<math>\text{TDE}_{environment}=\text{inhale} + \text{eat}=\frac{C_{air}[mg/m^3]\times V_{inhale} [20m^3/day]}{W_{body} [70 kg]} + \sum_{i=1}^n \frac{intake/day [kg] \times C_i [mg/kg]}{W}</math><br />
*<math>\text{TDE}_{work}=\text{inhale} + \text{skin}=\frac{C_{air}[mg/m^3]\times V_{inhale} [0.8m^3/hour]\times WT[8h]}{W_{body} [70 kg]} + \frac{A_{skin}[2000cm^2]\times Th_{matrix}[0.01cm]\times C_{subst. in matrix}[mg/cm^3]\times n}{W}, n=1...10</math><br />
<br />
===Effect assessment===<br />
Firstly, more detailed toxicology data is acquired. For substances that are produced more than one ton per year this data is required, for lesser substances it might not be available. Many tests can be done to acquire this type of data:<br />
*Acute toxicity -> dose vs. percentage of test animals dead.<br />
**Dead animals get a full pathology, with target organ and type of toxicity present.<br />
**The dosage is a single dosage, then wait 14 days and monitor behavior, GI trouble, cramps, etc.<br />
**<math>\text{LD}_{50}</math>is the dose at which 50% of the animals die within 14 days, this is an important number.<br />
*Irritation/sensitization, often done one guinea pigs or rabbits.<br />
*No observed adverse effect limits (NOAELs) are calculated from 28 days repeated administration.<br />
*In vitro testing of cell, genetic testing (Ames test), chromosomal tests and toxicokinetics.<br />
*If the substance has a distribution of more than 1000 tons per year, the studies are larger, including fertility and long term effects.<br />
<br />
===Risk characterization===<br />
After the exposure and effects have been characterized, the total risk is assessed. This includes:<br />
*Relevance and quality of previous testing<br />
**Choice of animal, are the results applicable to humans?<br />
**Is the toxicokinetic data of sufficient quality?<br />
*Extrapolation of the acquired data<br />
**Total daily exposure (TDE) compared to acceptable daily input (ADI) over a lifetime<br />
**Calculated by <math>\text{ADI}=\frac{\text{NOAEL}}{\text{Uncertainty factors (UF)}}</math>, where UF is 10 for animal to man and man to man (!). If lowest adverse effect limit (LOAEL) is used instead, another factor of ten is added.<br />
**Certain factor can modify the equation, e.g. if the metabolism of the specific xenobiotic is identical in the animal and human.<br />
<br />
If the results give that <math>\text{TDE}\geq \text{ADI}</math>, action is taken to reduce the TDE.<br />
<br />
An example of the importance of the quality of data is well known in the case of thalomide, which was tested, but tested on the wrong animals so the extrapolations where not valid. Another example is for <math>\beta</math>-naphthylamine, a drug that caused many cases of urinary bladder infection. In the liver this substance is not particularly harmful, and is oxidised by a CYP enzyme, producing and active and carcinogen form of the drug. But in the liver it is immediately conjugated with glucuronic acid, which makes it soluble and allows it to be secreted into the urine, and does not bind to DNA. In rats and mice this is the end result, and the substance is excreted and no adverse effects are observed. Dogs, on the other hand, contain <math>\beta</math>-glucuronidase, an enzyme in the bladder that hydrolyses the bond to glucuronic acid, redeeming the active and carcinogenic form of the drug. Since there are no UDP glucuronosyltransferase enzymes in the bladder, the drug stays in this activated form and binds to DNA, causing urinary bladder cancer. Initially, this drug was only tested on rats and mice and other animals that do not have <math>\beta</math>-glucuronidase in the bladder, this was not discovered. Humans do have this enzyme, which lead to many cases of urinary bladder cancer due to the use of the "wrong" test animals.<br />
<br />
== Eksterne linker ==<br />
<br />
*[http://www.ntnu.no/studier/emner?emnekode=TOKS3001 NTNUs fagbeskrivelse]<br />
*[http://www.ntnu.no/studieinformasjon/timeplan/v09/?emnekode=TOKS3001-1 Timeplan Vår09]<br />
<br />
[[Kategori:Valgbare emner]]<br />
[[Kategori:Fag 8. semester]]<br />
[[Kategori:Fag]]</div>Kenrogerhttp://nanowiki.no/index.php?title=TOKS3001_-_Medisinsk_toksikologi&diff=3967TOKS3001 - Medisinsk toksikologi2009-05-09T07:55:21Z<p>Kenroger: /* Definitions */</p>
<hr />
<div>{{Infobox<br />
|Fakta vår 2009<br />
|*Foreleser: Diverse<br />
*Vurderingsform: Skriftlig eksamen (100 %)<br />
*Eksamensdato: 18.05.2009<br />
*Fagbok: Casarett & Doull´s Toxicology: The Basic Science of Poisons, 6th edition. ISBN: 0071470514<br />
}}<br />
<br />
{{Infobox<br />
|Semesteroppgave<br />
|* Det er en obligatorisk semesteroppgave i faget.<br />
}}<br />
<br />
Forelesninger er to ganger i uka fra første uka i februar til siste uka i mars. I tillegg kommer en semesteroppgave (gruppearbeid). Eksamen baserer seg på forelesninger og utdelt materiale. <br />
<br />
= Core Curriculum =<br />
== Toxicokinetics ==<br />
<br />
===Definitions===<br />
''Xenobiotic'' (X.): A chemical that is not native in the body, or is present in much higher concentration than normal.<br />
<br />
''Toxic effect'': A change in physiological conditions caused by an effect of xenobiotics on the cellular level creating a decrease in health or behavior.<br />
<br />
''Toxicodynamics'': Mechanism of the toxic effect, reactivity, receptors and organ types.<br />
<br />
''Toxicokinetics'': Uptake, transport and lingering time/concentration of X.<br />
<br />
''Absorption'': Transport from the place of disposition to blood with a rate constant <math>k_a</math>.<br />
<br />
''Bolus'': A dosage of X. administered directly into the plasma.<br />
<br />
''Elimination'': Biotransformation, exhalation or excretion of X. X. does not need to be removed from the body, only made unavailable in its original form.<br />
<br />
''First pass metabolism'': The metabolism of a X that occurs in liver during the first passage.<br />
<br />
''Bioavailability (F)'': The fraction of a given dose D (X-parent compound) that reaches circulation in an unchanged form.<br />
<br />
===Introduction===<br />
There are two main ways to model toxicokinetics: Compartmental models and physiological models. The compartmental models are described more in detail below, and involve modeling organ systems by simple relations without involving physiology, i.e. the rate constants used are acquired from measurements alone. The physiological model looks at theoretical, or physiological, models to predict rate constants of the organs in the body. This involves factors such as:<br />
*Blood flow through organs<br />
*Absorption of the small intestine<br />
**Villi and microvilli in the intestine: These greatly increase the intestinal area, so absorption for selected X. is greatly enhanced here.<br />
**Active and passive diffusion: Some substances can diffuse directly across tissues, but most require some form of transport proteins. The mechanisms of these proteins determine how effectively and selectively xenobiotics are absorbed.<br />
**There is also metabolism in the intestine, by e.g. the cytochrome P450 3A4 (CYP3A4) enzyme which can activate many prodrugs.<br />
**Drug export from cells via P-glycoprotein is a very important mechanism which greatly reduces the amount of many xenobiotics that are absorbed.<br />
*The portal vein collects blood from the intestine and goes directly to the liver, where many substances are metabolized and their bioavailability is reduced. This is called first-pass metabolism, where the drugs are metabolized before reaching general systemic circulation. <br />
*After being metabolized in the liver many xenobiotics are conjugated and marked for excretion into the bile. The bile is excreted in the small intestine, where the drugs can be un-conjugated and reabsorbed, passing into the liver again. This is called the entero-hepatic circulation, and keeps plasma concentration of xenobiotics low in general.<br />
*Other special barriers, such as the blood-brain barrier and the placenta also greatly effect the distribution of xenobiotics.<br />
<br />
<br />
===Compartmental models===<br />
A model often used to model toxicokinetics is the compartmental model. In the compartmental model there is a central compartment representing the blood plasma and rapidly equilibrating tissues (e.g. liver and kidney), and side-compartments of more slowly equilibrating tissues. The simplest such model is the one-compartment model. Here there is only one compartment, which means all the modeled tissues are rapidly equilibrating. In this model a bolus will decay exponentially, i.e. measuring the logarithm of the plasma concentration over time gives a linear plot. Conversely, if experimental data holds with this description, it can be modeled by the one-compartment model. The decay is elimination, and elimination happens from the central compartment. <br />
<br />
=== Rate constants and elimination ===<br />
There are several rate constants involved in toxicokinetics. There are elimination and absorption rate constant, <math>k_e</math> and <math>k_a</math>, which describes elimination from and absorption into the central compartment (see below) if the dose is administered e.g. orally. In multi-compartment models there are also distribution and redistribution constants, e.g. <math>k_{12}</math> and <math>k_{21}</math>, which describes rates between the compartments.<br />
<br />
An example of a rate constant is the excretion rate constant through the kidney, <math>k_r</math>. In the kidney, glomerular filtration has a certain rate, tubular excretion another, and and reabsorption into the tubules a third. Thus, the excretion from the kidneys is given by <math>k_r=k_{gf}+k_{te}-k_{tr}</math>. Similar models can be made for other organs, both absorbative and eliminative. <br />
<br />
The elimination rates can follow different rate laws. Generally, in a one-compartment model, there is a first-order rate law, e.g. <math>-\frac{d C(t)}{dt}=k_e * C(t)</math>. Other rate laws hold if e.g. the elimination system is saturated, then <math>-\frac{d C(t)}{dt}=const.</math>.<br />
<br />
Integrating the formula above gives<br />
<br />
<math>C(t)=C_0 e^{-k_{el} t}</math>,<br />
<br />
and further manipulation gives e.g. the half-life of X. in the blood to be <math>t_{1/2}=\frac{ln 2}{k_e}</math>.<br />
<br />
Often the concentration is plotted on a semilogarithmic plot versus time. If this yields a straight line, we have a one-compartment model. <math>k_e</math> can be predicted from the slope, and <math>C_0</math> by extrapolation. <br />
<br />
If the semilogarithmic plot of plasma concentration of X. versus time does not yield a straight line, higher compartmental models must be used. In the higher-compartment model the tissues connected to the plasma equilibrate more slowly with the plasma, so the plasma concentration falls off more rapidly in the beginning, in what is called the ''distribution phases'', before the concentration profile again is as for the one-compartment model above. If there are two phases, one distribution phase and one linear phase (the eliminiation phase), we have a two-compartment model, which usually can be modeled by:<br />
<br />
<math>C(t)=A e^{-\alpha t}+B e^{-\beta t}</math>,<br />
<br />
where <math>\beta</math> corresponds to <math>k_{e}</math> above, and can be treated the same way.<br />
<br />
If C is measured for e.g. an orally distributed drug there is also an absorption phase where the concentration increases over a certain time. <br />
<br />
=== Toxicokinetic Parameters ===<br />
There are several parameters that can be used to describe the models in more experiment-friendly terms. At the heart is C(t), the plasma concentration of X. at a given time. X is the total amount of X. in the body. The parameter V, called the volume of distribution, which relates X and C. V tells how large a volume is needed to distribute the total amount of the xenobiotic (X), so the concentration of X. in V is the same as in the blood (C). Mathematically, this gives <math>V=\frac{X}{C}</math>.<br />
<br />
D is the administered dosage. AUC is the area under the concentration/time curve from 0 to infinity. The bioavailability of X. is given as <math>F=\frac{AUC_{a}}{AUC_{i.v.}}</math>, which gives the fraction in plasma when administered e.g. orally compared to intra venously. This gives another relation: <math>V=\frac{D \times F}{k_{el} \times AUC}</math> for a non-i.v. delivered drug. The denominator term is the plasma concentration. For a one-compartment model this can often be approxomated as <math>V=\frac{D \times F}{C_0}</math>, or <math>V=\frac{X}{C}</math> as above for an i.v. delivered dosage (D=X).<br />
<br />
Clearance (Cl) is a term the that describes the volume of plasma that is cleared of X. per unit time, and can be given as the sum of clearances from each of the eliminating organs (<math>Cl_{total}=Cl_{renal}+Cl_{hepatic}+...</math>). The total body clearance is given by <math>Cl=\frac{D_{i.v.}}{AUC}</math>, which gives units of volume/time. Using the relations from above this can be seen to be equivalent to <math>Cl_t=V \times k_{el}</math> for a one-compartment model.<br />
<br />
If more than one dose is given, the dosage interval is given by <math>\tau</math>. Giving a dose either continuously, or with a certain interval, allows one to reach a steady state concentration, where there is a balance between absorption and elimination. By definition, this is equal to <math>5 \times C(t_{1/2})</math>. Equivalent equations for this is:<br />
*<math>C_{ss}=\frac{F\times D}{Cl_t \times \tau}=\frac{F\times D}{k_e\times V \times \tau}</math><br />
<br />
If the steady state is reached by a dosage D every <math>\tau</math>, there is naturally an oscillation of steady state values, given by <math>\frac{C_{ss}^{max}}{C_{ss}^{min}}=e^{k_e \tau}</math>. By replacing the bioavailable dosage per time (<math>\frac{F \times D}{\tau}</math>) with an constant infusion rate <math>k_0</math> on obtains <math> C_{ss}=\frac{k_0}{Cl_t}</math>. Often it is desirable to reach steady state concentration as quickly as possible. In this case a bolus dose that immediately gives <math>C_{ss}</math> in the plasma. This dose is then given by <math>D_{bolus}=C_{ss}\times V</math>.<br />
<br />
==Metabolism of xenobiotics==<br />
The biotransformation and metabolism of xenobiotics is of great importance in maintaining homeostasis. Some enzymes are very important for these metabolic reactions. There are several types of enzymes, responsible for oxidation, reduction, hydrolysis and conjugation of xenobiotics. These reaction are divided into two phases: Phase I and phase II.<br />
<br />
===Phase I reactions===<br />
<br />
Phase I reactions are the primary biotransformation of xenobiotics. This includes oxidation, hydrolysis or reduction, and generally introduces or reveals a functional group that increases the hydrophilicity of the xenobiotic a small amount. One very important oxidase is the cytochrome P-450 (CYP) family which are found in most lifeforms. CYP is a heme-containing enzyme family involved in electron transport. The most common reaction is oxidation of an organic substrate by using molecular oxygen as an electron acceptor, i.e. <math>RH + O_2 + 2H^+ + 2e^- \rightarrow ROH + H_2 O</math>. During the oxidation of certain compounds such as aliphatic alkenes and aromatic hydrocarbonds by CYP highly reactive species called epoxides can be formed. This is called activation of the xenobiotic, in which the metabolite form of the xenobiotic is more reactive than the original form. Epoxides can bind to DNA and are possibly mutagenic or carcinogenic. Therefore, in virtually all cells there are CYP-dependent oxidations there is enzyme called ''epoxide hydrolase'' which reacts the epoxide group with water to produce diols. CYP enzymes are especially prevalent in the liver, and play a vital role in regulating the toxicity of a number of compounds that pass trough the liver. Important members of the CYP family are CYP3A4, which metabolises a great variety of compounds, and is present at high concentrations in the liver, CYP1A2 and CYP2D6, which metabolise a many different drugs, among them caffeine. CYP2E1 is less prevalent enzyme, but important since it metabolises small polar molecules such as ethanol.<br />
<br />
=== Phase II reactions ===<br />
Conjugation with various groups, such as acetylation, methylation, sulfonation, conjugation with glutathion and glucuronidation are the phase II reactions. In general (with the exception of acetylation and methylation) these cause a large increase in hydrophilicity of the conjugate, which allows the xenobiotic to be easily eliminated. These reactions generally proceed much quicker than the phase I reactions, and can either follow a phase I reaction or proceed directly. <br />
<br />
Glucuronidation is a major pathway of biotransformation of xenobiotics in humans. In glucoronidation the xenobiotic is conjugated with the cofactor uride diphosphate-glucuronic acid, creating a highly water soluble molecule, which can be excreted in urine or bile, depending on the total size of the molecule. This reaction is catalyzed by UDP-glucuronosyltransferase, and requires a hydroxyl, carboxyl or thiol group (roughly), so this will often follow a phase I reaction that provides such groups. Other important pathways are glutathione conjugation (catalyzed by glutathione -S-transferase) and GSH (glycine-cysteine-glutamic acid) conjugation. <br />
<br />
''GAH, kan noen som faktisk var på denne forelesningen skrive noe her, notatene hans er forferdelige!''<br />
<br />
== Risk assessment ==<br />
In addition to the knowledge about toxicokinetics and toxicodynamics, there is a whole greater field of risk assessment to see if a given xenobiotic represents a threat in certain situation. There are two main ways to determine toxicity in general, the epidemiological and toxilogical methods. Epidemology is the study of toxicity of substances in man. The disadvantage of this method is that it only can be performed post-exposure. Toxicology is the study of substances working in cells and animals. This can be done pre-exposure, but requires extrapolations to be applicable to humans. <br />
<br />
The general system for risk assessment is as follows:<br />
*Hazard identification<br />
*Expose assessment to determine total daily exposure (TDE)<br />
*Effect assessment of the TDE<br />
*Risk characterization and action<br />
<br />
===Hazard identification===<br />
Questions asked: 1. Can people be exposed? This is answered by checking individual habitats, work places, etc to see if there is any exposure risk at all. If yes, the next question is: Can toxic effects occur? This is answered by knowledge of toxicity, structure, like compounds, etc. If the answer is yes, one proceeds to exposure assessment.<br />
<br />
===Exposure assessment===<br />
There are standardized rules for TDE depending on form of exposure. Formulas for this can be:<br />
*<math>\text{TDE}_{environment}=\text{inhale} + \text{eat}=\frac{C_{air}[mg/m^3]\times V_{inhale} [20m^3/day]}{W_{body} [70 kg]} + \sum_{i=1}^n \frac{intake/day [kg] \times C_i [mg/kg]}{W}</math><br />
*<math>\text{TDE}_{work}=\text{inhale} + \text{skin}=\frac{C_{air}[mg/m^3]\times V_{inhale} [0.8m^3/hour]\times WT[8h]}{W_{body} [70 kg]} + \frac{A_{skin}[2000cm^2]\times Th_{matrix}[0.01cm]\times C_{subst. in matrix}[mg/cm^3]\times n}{W}, n=1...10</math><br />
<br />
===Effect assessment===<br />
Firstly, more detailed toxicology data is acquired. For substances that are produced more than one ton per year this data is required, for lesser substances it might not be available. Many tests can be done to acquire this type of data:<br />
*Acute toxicity -> dose vs. percentage of test animals dead.<br />
**Dead animals get a full pathology, with target organ and type of toxicity present.<br />
**The dosage is a single dosage, then wait 14 days and monitor behavior, GI trouble, cramps, etc.<br />
**<math>\text{LD}_{50}</math>is the dose at which 50% of the animals die within 14 days, this is an important number.<br />
*Irritation/sensitization, often done one guinea pigs or rabbits.<br />
*No observed adverse effect limits (NOAELs) are calculated from 28 days repeated administration.<br />
*In vitro testing of cell, genetic testing (Ames test), chromosomal tests and toxicokinetics.<br />
*If the substance has a distribution of more than 1000 tons per year, the studies are larger, including fertility and long term effects.<br />
<br />
===Risk characterization===<br />
After the exposure and effects have been characterized, the total risk is assessed. This includes:<br />
*Relevance and quality of previous testing<br />
**Choice of animal, are the results applicable to humans?<br />
**Is the toxicokinetic data of sufficient quality?<br />
*Extrapolation of the acquired data<br />
**Total daily exposure (TDE) compared to acceptable daily input (ADI) over a lifetime<br />
**Calculated by <math>\text{ADI}=\frac{\text{NOAEL}}{\text{Uncertainty factors (UF)}}</math>, where UF is 10 for animal to man and man to man (!). If lowest adverse effect limit (LOAEL) is used instead, another factor of ten is added.<br />
**Certain factor can modify the equation, e.g. if the metabolism of the specific xenobiotic is identical in the animal and human.<br />
<br />
If the results give that <math>\text{TDE}\geq \text{ADI}</math>, action is taken to reduce the TDE.<br />
<br />
An example of the importance of the quality of data is well known in the case of thalomide, which was tested, but tested on the wrong animals so the extrapolations where not valid. Another example is for <math>\beta</math>-naphthylamine, a drug that caused many cases of urinary bladder infection. In the liver this substance is not particularly harmful, and is oxidised by a CYP enzyme, producing and active and carcinogen form of the drug. But in the liver it is immediately conjugated with glucuronic acid, which makes it soluble and allows it to be secreted into the urine, and does not bind to DNA. In rats and mice this is the end result, and the substance is excreted and no adverse effects are observed. Dogs, on the other hand, contain <math>\beta</math>-glucuronidase, an enzyme in the bladder that hydrolyses the bond to glucuronic acid, redeeming the active and carcinogenic form of the drug. Since there are no UDP glucuronosyltransferase enzymes in the bladder, the drug stays in this activated form and binds to DNA, causing urinary bladder cancer. Initially, this drug was only tested on rats and mice and other animals that do not have <math>\beta</math>-glucuronidase in the bladder, this was not discovered. Humans do have this enzyme, which lead to many cases of urinary bladder cancer due to the use of the "wrong" test animals.<br />
<br />
== Eksterne linker ==<br />
<br />
*[http://www.ntnu.no/studier/emner?emnekode=TOKS3001 NTNUs fagbeskrivelse]<br />
*[http://www.ntnu.no/studieinformasjon/timeplan/v09/?emnekode=TOKS3001-1 Timeplan Vår09]<br />
<br />
[[Kategori:Valgbare emner]]<br />
[[Kategori:Fag 8. semester]]<br />
[[Kategori:Fag]]</div>Kenrogerhttp://nanowiki.no/index.php?title=TMT4320_-_Nanomaterialer&diff=975TMT4320 - Nanomaterialer2008-12-16T19:26:20Z<p>Kenroger: /* Hollow nanofibers by electrospinning */</p>
<hr />
<div>{{Infobox<br />
|Fakta høst 2008<br />
|*Foreleser: Fride Vullum<br />
*Stud-ass: Katja Ekroll Jahren og Ørjan Fossmark Lohne<br />
*Vurderingsform: Skriftlig eksamen<br />
*Eksamensdato: 18. desember<br />
}}<br />
<br />
{{Infobox<br />
|Øvingsopplegg høst 2008<br />
|* Antall godkjente: 6/12<br />
* Innleveringssted: Utenfor R7<br />
* Frist: Tirsdager 16:00 (?)<br />
}}<br />
<br />
<br />
Emnet skal gi en innføring i grunnleggende kjemisk prinsipper for å lage nanomaterialer. Stikkord: "Self-assembled" monolag ([[SAM]]) og hvordan disse kan formes ved myk litografi og "dip pen" nanolitografi, syntese av tredimensjonale multilag strukturer. Tynne filmer ved kjemisk gassfase deponering. Syntese av nanopartikler, nanostaver, nanorør og nanoledninger. Våtkjemiske syntese av oksidbaserte nanomaterialer. "Self-asembly" av kolloidale mikrokuler til fotoniske krystaller, porøse nanomaterialer, blokk-kopolymere som nanomaterialer. "Self assembly" av store byggeblokker til funksjonelle anordninger. Under vil det etterhvert vokse fram et lite kompendium i faget. Dette følger i utgangspunktet pensumlista som gjelder for høsten 2008.<br />
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<br />
==Chapter 1: Nanochemistry Basics ==<br />
Not terribly important.<br />
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==Chapter 2: Soft Lithography==<br />
===Self-assembled monolayers (SAMs)===<br />
*The typical example of a SAM is a layer of alkanethiols on a gold substrate. <br />
*The S-H bond is cleaved by oxidation on the gold surface and a covalent Au-S covalent bond is formed. <br />
*The alkanethiols are tilted off-axis from the normal. The angle depends on the surface. (30 ° for a {111} gold surface, 10 ° for a silver surface). <br />
*The end group on the alkanethiols can be tailored to achieve different monolayer properties, thus modifying the surface properties of the structure.<br />
<br />
===PDMS stamp===<br />
* PDMS (PolyDiMethylSiloxane) is a soft elastic polymer.<br />
* A master (casting) of the stamp, with the desired pattern, is made with electron or UV-lithography. The master is silanized and made hydrophobic so removing of the stamp becomes easier.<br />
* Liquid PDMS is then poured into the master, after which it is cured and a finished PDMS stamp is removed from the master.<br />
* The critical dimensions of the stamp are limited by the lithography techniques used, and for [[photolithography]] the wavelengths of the light used to expose the [[photoresist]] limits the dimensions. Typical CDs given are, for lateral dimensions within the range of 500nm-200µm, and for the height of patterns 200nm-20µm. <br />
* The PDMS stamp can be dipped in alkanethiol solutions (or solutions of other molecules, collectively known as "chemical ink") and be stamped onto surfaces.<br />
* PDMS stamps work on both planar and curved surfaces.<br />
* For the stamp to properly print a pattern onto a surface, the molecules need to adhere to the stamp from the solution, but the affinity for binding to the surface has to be stronger.<br />
<br />
===Hydrophilic / Hydrophobic stamps===<br />
* The endgroup/terminal group on the alkanethiols (or other molecules used) determine the properties of the monolayer, f. ex. a OH-terminal group makes the monolayer hydrophilic, while a <math>CH_3</math>-group makes it hydrophobic.<br />
* Wetability is determined by the polarity of the endgroups.<br />
* By introducing a wetability gradient or abrupt changes in wetability, different effects can be obtained:<br />
** Square drops, by having checkerboard square patterns of hydrophilic monolayers with hydrophobic lines inbetween, and condensating water onto the surface. This is called condensation figures and results from the condensation on the hydrophilic areas, when the substrate is cooled below the dew point. The diffraction pattern of the structure can be studied for obtaining information on the kinetics and structure of the water droplets. This can be used in biological sensing.<br />
** Droplets "running uphill" by having wetability gradients. The droplets are moving towards the more hydrophilic areas, against the force of gravity.<br />
** Nanoring arrays can be synthesized using the condensation figures as templates for molding. A solvent precursor which wets the regions between the microdroplets is added and then evaporated. Deposition of precursor occurs around the perimeter of the droplets. Finally, the water droplets is evaporated, and the precursor remains on the substrate as nanorings. <br />
** Solid state patterning by dipping a SAM-patterned substrate in a precursor solution. This creates microdroplets with a predetermined precursor concentration, which on evaporation and vertical drying leaves behind an array of size-tunable solid precursor dots.<br />
<br />
===Printing thin films===<br />
* As long as the adhesion between the chemical ink and the substrate is stronger than the adhesion between the ink and the stamp, printing thin films is no problem<br />
* Metal thin films can be evaporated onto a PDMS stamp (f. ex. gold). Evaporation gives homogenous and directional coatings, and no covering of the side walls on the stamp. This pattern is printed onto a SAM-primed substrate with exposed thiol groups (gold adheres strongly to the metal layer).<br />
* This is a very gentle technique for metal film depositing, good for making contacts on fragile layers. Also good for making 3D stuctures by printing multiple layers. Also, there is no need for photoresist because the pattern is printed directly.<br />
<br />
===Electrically contacting SAMs===<br />
* Molecular electronic devices need to make good electrical contact with SAMs.<br />
* Making electrical contacts by vapor deposition on the SAMs may sometimes be more convenient than thin-film printing with a PDMS stamp.<br />
* Other, less gentle methods of metal deposition than printing with PDMS stamps (sputtering, CVD, etc) can cause the metal layer to penetrate the SAM and deposit on the substrate, or even diffuse into the substrate, introducing defects to the structure.<br />
* Morale: Use stamps to deposit metals on SAMs!<br />
<br />
===Patterning by photocatalysis===<br />
* Photocatalysis is used to remove parts of a SAM (making patterns)<br />
* Titania (<math>TiO_2</math>) can photocatalytically decompose organic molecules.<br />
* A quartz slide patterned with titanium dioxide in the required pattern using ALD is pressed against a wafer with the SAM on it. <br />
* The assembly is exposed to UV radiation, triggering the degradation of the (organic) SAM. When titania is exposed to UV, radiation free radicals are created, which react with the organic molecues, removing the parts of the SAM that is in contact with the titania. Thus, the substrate in these areas is revealed.<br />
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<br />
==Kapittel 3: Building layer-by-layer==<br />
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<br />
===Electrostatic superlattices===<br />
* LbL multilayer films formed by alternate immersion in suspensions of opposite charges. Electrostatic interactions are responsible for the LbL growth.<br />
* A primer layer with a charge adheres to the substrate. The substrate is then dipped in a solution of polyelectrolytes of opposite charge from the primer layer. This process can be repeated numerous times in order to get the desired thickness or functionality of the film.<br />
* Any species bearing multiple ionic charges can be layered, f. ex. an amphiphile.<br />
* The anionic layered materials can be exfoliated with bulky cations to create electrostatic superlattices.<br />
* As the amount and identity of constituents of each layer can be controlled, a composition gradient can easily be constructed throughout the structure. <br />
** Quantum dots (QD) with different size can be introduced in the layer structure, creating a gradient in fluorescent colours.<br />
*<br />
* The layer separation can be modified by varying the pH, salt concentration (screening of electrostatic interactions) or polyelectrolyte charge density.<br />
* Can be applied to curved surfaces, as coating of microspheres or rods.<br />
<br />
===Some applications===<br />
* Electrochromic layers, used in "smart windows" for instance.<br />
** Electrochromism is a optical change (absorption of light in this case) in the material upon oxidation or reduction.<br />
** The absorption of light can therefore be modified by applying a voltage to a film of alternating polyelectrolytes.<br />
** Smart windows are made by adsorbing polyelectrolytes on a conductive glass (indium tin oxide) by the LbL technique. Applying a voltage over the polyelectrolyte layer can change the glass from colored to transparent. Also the color depend on the layer thickness, thicker layer gives a darker color (more absorption of light).<br />
* Construction of cantilevers for chemical sensing, using photolithography and LbL.<br />
* Hollow spheres can be made by LbL growth on a templating microsphere.<br />
** The template can be dissolved by HF.<br />
** Chemicals can be encapsulated inside the hollow spheres (f. ex. medicine).<br />
** Layer separation can be modified by adding electrolyte solution, making it possible to tune diffusion in and out of the hollow sphere, thereby controlling release of encapsulated chemicals.<br />
<br />
===Analysis, measuring film thickness===<br />
* Indirect techniques:<br />
** Optical spectroscopy: If the substrate is transparent, and the film absorbs light at a certain wavelength, the film thickness can be found by monitoring the optical absorption as a function of number of layers. A dye can be introduced to ensure absorption. Easy to perform but hard to interpret - must know the observation area and extinction coefficient of the absorbing group.<br />
** Ellipsometry: Film is probed by polarized light, and change in polarization in the reflected light is measured. This can be used to find the refractive index, thickness, roughness and orientation of a thin film. Ellipsometry works with films much thinner than the wavelength of light - down to atomic layers. A theoretical fitting must be done to extract the required parameters from the experimental data.<br />
** Quartz crystal microbalance (QCM): Quartz (piezoelectric material) in an alternating electric field contracts/expands with a characteristic oscillation frequency. When mass is added to a QCM the frequency decreases, which correlates directly with the amount of mass added. This allows real-time thickness measurements when the density of the material is known. Works well for hard materials like metals and ceramics, but not for viscoelastic materials.<br />
* Direct techniques: <br />
** Label each layer with heavy metal atoms and image by TEM. <br />
** Alternately, deposit a thin gold layer on top of the surface and image cross section by TEM.<br />
<br />
===Non-electrostatic lbl assembly===<br />
* LbL doesn't need electrostatic bridges - can use hydrogen bonding, ligand-receptor interactions or even covalent bonds.<br />
* Example: DNA-multilayers by hydrogen bonding (adenine-thymine and guanine-cytosine bridges).<br />
* Hydrogen bonds can be broken again by changing the pH, or can be strengthened by UV irradiation.<br />
<br />
===Low-pressure layers===<br />
* '''Molecular beam epitaxy (MBE)'''<br />
** Performed in ultrahigh vacuum, sources of constituents (elemental) are heated, and a thin film alloyed from the constituents is deposited. The result is a single crystal film with homogeneous thickness grown epitaxially on the substrate. <br />
** The substrate should have a similar lattice constant to that of the layer deposited. If the lattice constant of the substrate is substantially different from that of the deposited material, there will be a dewetting effect where the material can form quantum dots.<br />
** Because of the low pressure, there is no reaction between different precursors. <br />
** The advantages over CVD and ALD is that no impurities or contaminants exists, also there is a minimum of crystal defects. The grow-rate is very low (about 1 monolayer per second), thus this technique gives exact control of layer thickness and composition.<br />
* '''Chemical vapor deposition (CVD)'''<br />
** Volatile precursors are introduced in gas phase in a low-pressure reactor chamber. <br />
** Argon or nitrogen gas are usually used as carrier gas to dilute the precursor and achieve optimal pressure and concentration. <br />
** The substrate is heated, and the precursor reacts or decomposes at the surface to create a film, where the film thickness depends on amount of precursor and time allowed for reaction to occur.<br />
** There are several different types of CVD reactors, such as cold wall and hot wall reactors. There are also plasma enhanced reactors (PECVD) where the electric field in the plasma can force growth of nanowires in the direction of the electric field. <br />
** CVD can be used to make monocrystalline, polycrystalline, amorph and epitactic films. The disadvantage over MBE is greater risk of introducing contaminants and defects into the film.<br />
<br />
===Lbl self-limiting reactions===<br />
* Atomic layer deposition: Similar to CVD, but usually carried out in solution (can use gas as precursors).<br />
* Iterative saturating reactions. ALD is a self-limiting process where only one layer at a time is deposited. When the first layer is deposited it needs to be reactivated in order to grow a second layer. It is therefore easy to control thickness down to the atomic scale.<br />
* Material can be deposited uniformly into deep trenches, porous structures and around particles.<br />
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<br />
== Kapittel 4: Nanocontact printing and writing ==<br />
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===Soft lithography and microcontact printing ===<br />
* Sub 100 nm Soft Lithography: Previous chapters has covered printing on 10.000-100 nm scale. Need for further miniaturization because of demand for more power, efficiency, and density. This can be done by manipulating PDMS stamp, Dip Pen Nanolithography (DPN), Whittling Nanostructures or by Nanoplotters<br />
<br />
===Manipulating PDMS stamp===<br />
* Manipulating PDMS stamp can be done in various ways, and seven of the basic ideas will now be explained. Illustrating pictures are in the book and in the slides.<br />
# Compress the stamp, mold to get a new stamp with inverse pattern, peel off and repeat. The new stamp has lower dimensions than the master.<br />
# Apply force perpendicular onto stamp when on substrate. The areas in contact with substrate will then increase, and spaces in between gets smaller.<br />
# Size reduction by reactive spreading of ink when in contact with substrate. The contact time + properties of the ink decide to which degree the ink spreads. The printed area is increased and the spacing between is reduced.<br />
# Size reduction by extraction of inert filler (just like removing water from a sponge).<br />
# Size reduction by swelling the stamp in toluene. The areas in contact with the surface are increased in size while the spacing between is reduced. <br />
# Size reduction by stretching stamp so that dimensions get smaller in one direction and larger in another.<br />
# Size reduction by double-printing.<br />
* Overpressure printing<br />
** Defect-free contact printing is restricted to a certain range of height-to-width ratios. If ratio is outside 0.2-2, the roof of the grooves on stamp will touch the substrate. Too high perpendicular force on stamp has the same effect, but overpressure can also be used to form new patterns such as micron scale discs and rings of ferromagnetic core-shell nanoparticles. Nanoparticles are then transferred to PDMS stamp by Langmuir-Blodgett technique (chapter 6) and then into contact with Au-coated silicon substrate. <br />
*** Low pressure => discs, high pressure => rings.<br />
*Limitations<br />
** Deformation can be a shortcoming if care is not taken with the dimensions of surface relief pattern in the stamp, as this can give unwanted deformations. Quality of printed pattern will not be good.<br />
<br />
===Dip pen nanolithography===<br />
* Alkanethiols can be written on gold substrate with AFM tip. The alkanethiols are delivered to the tip via a water meniscus, and this can be adapted to suit other surface chemistries. The result is 10 nm fine patterns of molecules (biomolecules, polymers etc.) on metals, semiconductors and dielectrics. <br />
* Sol-gel DPN: patterning of solid-state materials. Nanoscale patterns are written using a metal oxide sol-gel precursor in a solvent carrier. The sol-gel precursors are hydrolyzed to metal oxide by use of atmospheric moisture and water meniscus at the tip-substrate interface. pH, substrate temperature and post treatment can be varied. Temperature treatment is necessary.<br />
*Enzyme DPN: A scanning microscope tip can be used to deliver an enzyme via a water meniscus to a specific site on a biomolecule with nanometer presicion. This can be used to control biochemical reactions locally. After patterning, the enzyme is activated by metal ions to start the reaction. Deactivation is achieved by washing with de-ionized water. This method leads to the possibility of bionanodegradable electronic and optical devices.<br />
*Electrostatic DPN: Like thin films can be made of charged polyelectrolytes, an AFM tip can "draw" lines or structures of charged polymers on a oppositely charged substrate, with for example specific electrical properties to build nanoscale electronic devices.<br />
*Electrochemical DPN: The meniscus that forms between surface and tip is used as a nanochemical reactor. Electrochemical deposition or etching (oxidation) can be done by applying voltage between tip and substrate. Ex: making platinum lines can be done by reducing Pt salt at -4 V, and silica lines can be made by oxidation of a silicon surface at +10 V.<br />
<br />
===Whittling of nanostructures (section 4.19)===<br />
* Only be able to explain basic principle<br />
**The spatial extent of SAMs can be reduced by so-called "whittling". Whittling is an electrochemical desorption process where a voltage applied will cause ligands at the peripheries of a structure to desorb. The spatial extent of desorption is directly proportional with time. It has been found that the larger the accessibility of a molecule, the lower the desorbation voltage is (fig. 4.22).<br />
<br />
===Nanoplotters and nanoblotters===<br />
* The principle is to increase the low throughput DPN methodology, by using parallell DPN.<br />
*Nanoplotter: An array of parallel cantilevers can write SAM nanopatterns simultaneously.<br />
** The cantilevers are electrically driven by differential thermal expansion.<br />
*Nanoblotters: An PDMS inkwell has been created to deliver ink to the nanoplotter cantilever tips (fig. 4.26)<br />
** Inkwells are capped with a semipermeable PDMS membrane. By contacting the DPN tips to the membrane, ink diffuses to wet the tip.<br />
<br />
===Combinatorial libraries===<br />
*DPN can be used to put different materials together in the research of new material composition. With DPN, many different combinations can be made with small material amounts used (in theory only single molecules).<br />
*Parallel DPN can accelerate the analyzing of reactions, and increase the rate of discovery of new materials.<br />
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<br />
== Kapittel 5: Nano-rod, nanotube, nanowire self-assembly ==<br />
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===Templating nanowires and nanorods===<br />
Templates can be used for making solid nanorods and nanotubes of controlled size. Examples of templates are alumina, silicon, zeolites and lipid bilayers. If the holes are completely filled nanorods and nanowires result, while a partial filling with continuous coating gives rise to nanotubes.<br />
<br />
===Making modulated diameter silicon templates===<br />
A p-doped silicon wafer is put in aqueous HF and an oxidizing potential is applied. The result from this is nanoporous silicon with a random network of pores. The diameter of the pores can be tuned by controlling the voltage or current. The higher the current is, the wider the channels get. If the current is modulated during oxidation, the resulting structure is an array of modulated diameter nanochannels. If perfectly ordered pores are desired, the wafer can be lithographically patterned with regular array of nanowells in advance. The electric field will then be focused at the tip of these wells.<br />
<br />
===Making porous alumina membranes===<br />
Porous alumina membranes can be made by anodic oxidation of lithograpically embossed aluminum sheet in phosphoric or oxalic acid electrolyte (the almunium sheet functions as the anode).<br />
<br />
<math> 2Al + 3PO_4^{3-} \rightarrow Al_2O_3 + 3PO_3^{3-}</math><br />
<br />
The residual Al and <math>Al_2O_3</math> is removed by mercuric chloride and phosphoric acid. The diameter is controlled and can be 20-500nm. Mechanisms that give ordered channels are the fact that electric fields created by applied voltage (which is concentrated at the tips of the growing tubes) repell each other, and that we have volume expansion when aluminum becomes alumina. Temperature is also a factor that affects the reaction.<br />
In this process oxygen diffuses through the alumina layer from the electrolyte and alumina grows at the alumina/aluminum interface, while alumina is slowly dissolved at the alumina/electrolyte interface. This growth/dissolution comes to an equilibrium at the bottom of the pore, giving a specific thickness for a certain current/voltage. The growth of alumina is still allowed to continue upwards (along the pore walls) where the electric field is weaker, giving longer pores. Growth continues until the electric field is quenced or there is no more aluminum left.<br />
<br />
===Modulated diameter gold nanorods===<br />
With use of silicon template. The back surface of the silicon membrane is subjected to a local thermal oxidation which formes silica. The silica is then removed by HF. By proceeding with a KOH anisotropic etch on the same area, and a dip in HF, the pores in the template are opened. A gold sputter deposition can then be done on the backside. This gold layer acts as a catalyst for continued electroless deposition of gold. Finally, the silicon membrane is etched away, and the gold nanorod dispersion can be collected.<br />
<br />
===Modulated composition nanorods/nanobarcodes===<br />
Modulated composition nanorods can be made by electrochemical deposition of different metal segments within the channels of an alumina template (electrodeposition will be better explained in the following section). Any type of material that can be electrodeposited can be used in the nanobarcodes. One synthesis route is to evaporate thin metal film to one side of an alumina membrane. This metal film function as the cathode, and metal deposition begins at the bottom. Bath can be switched between different metal salts to grow several segments. The lenght of the metal segments scales directly with the current. The alumina membrane is dissolved using sodium hydroxide, and the metal backing is dissolved using acid. <br />
<br />
Nanobarcodes can be used to tag molecules in analytical chemistry and biology. Characteristic of metals are optical reflectivity, which means that different segments of the barcode nanorod can be distinguished in optical microscopy. Probe molecules must be anchored to different segments, and the rods must be dispersed in analyte containing target molecules which bear a luminescent label. By molecular recognition, the target molecules bind to the probe molecules (ex: ligand-receptor binding for biological applications). By looking at the segments that light up, it can be decided which molecules exist in the solution.<br />
<br />
===Electroplating/electrodeposition===<br />
The part to be plated is the cathode, while the anode is made of the material to be plated. Both components are immersed in electrolyte solution. The dissolved metal ions (cations) are reduced at the interface between the solution and the cathode when current is applied.<br />
<br />
===Electroless deposition===<br />
This is an auto-catalytic plating method that involves several simultaneous reactions in an aqueous solution. The reaction involves plating of a metal onto a conductive surface and occurs without the use of external electrical power. This is accomplished when hydrogen is released by a reducing agent and thus producing a negative charge on the surface of the metal. There is no direct control over length or thickness of the deposited layer. This needs to be calibrated with regards to concentration of precursor and amount of time that reaction is allowed to run.<br />
<br />
===Nanotubes===<br />
Nanotubes can be made by partial filling of the membranes radially. This means that a uniform coating must be deposited on the pore walls. One way to do this is by letting fluid spontaneously wet inside the template pores. Fluids that can be used are molten polymers, polymer solution or sol-gel preparation. These are coated onto template using capillary forces resulting from small diameter channels with a large available surface. Solidification of these fluids can be done by heating, cooling, waiting or using a catalyst. With this method it is difficult to control the wall thickness. <br />
Another way to make nanotubes is by using LbL growth procedure inside the pores. This can be done by CVD of gas phase species, solution phase ALD or LbL electrostatic assembly. Wall thickness is easier to control with these methods. <br />
Finally, the membrane is dissolved. It can also be deposited other material inside the remaining void to get coaxially coated rod or wire. <br />
<br />
Nanotubes can also be made from LbL electrostatic coating of nanorods. The rods can be dissolved afterwards, and will leave a closed-ended tube. This method is applicable to any material that can be coated onto a nanorod and not be affected by the etching step. <br />
<br />
===Magnetic Nanorods===<br />
Magnetic metals such as iron, cobalt or nickel can easily be deposited into membranes. Magnetic properties are direction and size dependent. By applying a magnetic field, the segments become permanently magnetized and there will be attractions between the rods. If the thickness of the magnetic segments on a nanorod is smaller than the diameter, magnetization is perpendicular to the rod axis, and they will self assemble into 3D bundles. If the thickness is bigger than the diameter, magnetization is parallel to the rod axis, and they will align in chains of rods. If the thickness is the same as the diameter they will be in random aggregates. <br />
<br />
Magnetic nanorods can be used for separation of molecules. A tri-segmented Au-Ni-Au nanorods can be used as affinity template for histidine- tagged proteins. Nickel selectively captures the labeled protein, and a magnetic field can be used to separate the rod with the captured protein from the rest of the solution of biomolecules. After this, the proteins can be chemically released from the magnetic nanorod. The gold segments must be in the rod to protect nickel from the etching during dissolution of alumina template after electrodeposition, and also to prevent aggregation.<br />
<br />
===Making Single Crystal Nanowires===<br />
Single crystal nanowires can be made by Vapor-Liquid-Solid (VLS) synthesis, Supercritical Fluid-Liquid-Solid (SFLS) synthesis or by Pulsed laser deposition. <br />
<br />
*VLS Synthesis<br />
A catalyst droplet first melts on a substrate, then becomes saturated with precursors. Elements extrude out of the catalyst droplet as a single crystal nanowire in a furnace where the temperature is controlled to maintain liquid state of the catalyst droplet. Micrometer length with diameter less than 10 nm can be done. The diameter is controlled by the diameter of the catalyst droplet, and growth stops when the nanowire pass out of the hot zone, if the precursor is depleted or the catalyst droplet no longer is in liquid state. One example is to use laser ablation of Fe-Si target to evaporate the precursors and to create a Fe-Si nanocluster catalyst droplet. The Si nanowire grow with the (111) lattice planes perpendicular to the growth axis due to epitaxy at the nanocluster-nanowire interface. Doping can be done by controlling stoichiometry of the target, or by introducing dopant into gas phase during growth.<br />
<br />
*SFLS Synthesis<br />
Similar to VLS, but used for materials with a higher eutectic temperature. This technique increases the variety of available source materials. The solvent is pressurized above its critical point to reach higher temperatures. Can be applied to semiconductor/metal combinations (Ga/GaAs, In/InN) with eutectic temperature below 600 degrees. Au is used as catalytic seed, and diameter depends on this. <br />
<br />
*Pulsed laser deposition<br />
A high-power pulsed laser is used to ablate a target (pulsed laser ablation) in a vacuum chamber, meaning that the pulsed laser vaporizes small parts of the target for each pulse. This creates a plume of vaporized precursor material which is allowed to deposit as a thin film onto a substrate that is placed in the reaction chamber. When small catalyst particles are placed on the substrate, small single crystal nanowires can be grown. The diameter of the nanowires are determined by the diameter of the catalyst particles. <br />
<br />
===Nanowires branch out===<br />
Can create branched nanowires by VLS growth. The catalytic nanoclusters from solution placed on specific point on the body of a parent nanowire before growth. The process can be repeated for a hyper-branched construction. This could be the future development of nanowire electronics in 3D. <br />
<br />
===Quantum Size Effects (QSE)=== <br />
QSE appear when the particle size becomes smaller than the exciton size for the material (about 5 nm for silicon). Exciton is a bound state of an electron and an electron hole in an insulator or semiconductor, which is defined by the energy gap between the valence band and the conduction band. Color of the emitted light is determined by the size of gap energy. Gap energy increases with decreasing nanowire diameter. This can be used for LEDs and lasers. Both quantum confined nanoclusters and nanowires show QSE, but anisotropy make them different. Luminescent nanoclusters emits plane-polarized light, while nanorods exhibits linearly polarized light. <br />
<br />
===Alignment methods===<br />
Alignment methods include electric field based alignment, microfluidic alignment and Langmuir-Blodgett technique. <br />
<br />
*Electric Field Based Alignment<br />
Apply voltage between two micropatterned electrodes to produce electric field. Charges within a nanowire in solution become polarized, creating an attraction between the electrodes and the nanowire. The electric field is quenched when the gap between the electrodes are bridged by a nanowire. This eliminates absorption of a second nanowire at the same electrodes. Metal spots can be evaporated onto insulator surface to focus the electric field.<br />
<br />
*Microfluidic Alignment <br />
A PDMS stamp with a series of parallel rectangular grooves is used for this purpose. The channels are aligned under a microscope with electrodes that have been previously patterned on a substrate (these will function as metal contacts for the conducting or semiconducting lines made by this method). A drop of nanowire suspension is flowed into the microchannels by capillary forces, and solvent evaporation aligns the wires at the edges of the channels. <br />
<br />
*Langmuir-Blodgett Technique<br />
A Langmuir film is created when hydrophobic molecules float on a water-air surface, and an aligned monolayer is formed at the interface when external film pressure is applied. The balance of surface tension forces determines the profile of the meniscus formed when a substrate is pushed into this liquid. If the substrate is hydrophobic it will experience deposition of the amphiphiles during immersion. If it is hydrophilic it will experience deposition during retraction. A nanowire array can be made by firstly compressing the interface to increase the surface density of nanowires (so they align parallel to each other), and then do a double dip. The second dip must be done so that the wires align normal to the previous once. It is important that the film pressure is mantained at a constant magnitude during the immersion.<br />
<br />
===Applications===<br />
Application areas for these methods are in LED’s, transistors and in nanowire UV photodetectors. <br />
<br />
====LED====<br />
A LED can be made by assembling an n-doped and a p-doped semiconductor nanowire perpendicular to each other. This is done by [[TMT4320_-_Nanomaterialer#Alignment_methods|electric field based alignment]] with two electrode pairs aligned perpendicular to each other where voltage is applied to one pair at a time. They can also be assembled by using the microfluidic approach. When a potential is applied across the junction, light is emitted when electrons recombine with holes at the junction between the differently doped wires. Color of the emitted light depends on composition and condition of semiconducting material used. The LED can only conduct current in one direction. With positive voltage current flows. With negative voltage current is inhibited. The key for success is to achieve abrupt and uncontaminated junction between n- and p-doped wire. Efficiency can be improved by using core-shell-shell nanowire axial heterostructure. The greatest challenge is to make arrays of closely spaced junctions because the nanowires are so thin. This leads to the pitch problem, how to pack light sources into smallest possible area.<br />
<br />
====Transistors====<br />
A transistor can switch or amplify signals, and has three terminals (n-p-n). The n-type region attached to the negative end of the battery sends electrons into p-region, and the n-type region attached to the positive end slows the electrons down. The p-type region in the middle does both. Because of this, a depletion layer develops between the base and the emitter, and the base and the collector. The thickness of the layer is varied by the potential in each region. Active bipolar n-p-n transistor can be built from heavy and lightly n-doped nanowires crossing a common p-type wire base. <br />
<br />
Nanowire transistors can be used as sensors. Si nanowires are naturally coated with silica through VLS synthesis. This makes it easy for surface silanol groups to attach to the wire. If probe molecules are anchored to the surface silanols, highly sensitive real time electrically based sensors can be made. Low levels of chemical and biological species can be detected. Boron doped silicon nanowire is used as a FET. The wire is self assembled across electrodes (source and drain), and aminoethylsilane anchored to SiOH surface groups. The conductance of the wire changes with pH linearly due to protonation or deprotonation of the amine. An increase of the surface negative charge (deprotonation) attracts additional holes into the p-channel and the conductance is enhanced. The reverse action at low pH, an increase of surface positive charge causes protonation which repell holes from the channel. The conductance is decreased. Almost any type of molecule can be anchored to silica, so sensors can be designed to detect almost anything. For example, a biotin could be strapped to the surface amine groups to detect streptavidin. <br />
<br />
====Nanowire UV photodetector====<br />
The conductivity of ZnO nanowires is extremely sensitive to ultraviolet light exposure, which means that UV light can switch the nanowires between ON and OFF states. ZnO nanowires are highly insulating in the dark, but UV light with wavelength less than 380 nm decreases resistivity by 4 to 6 orders of magnitude. These nanowire photoconductors exhibit excellent wavelength selectivity. Green light (532nm) gives no response, while less intense UV light increases conductivity 4 orders. The response cut-off wavelength is at about 370 nm. <br />
<br />
===Simplifying complex nanowires===<br />
Complex oxides with superconducting, ferroelectric and ferromagnetic properties can not easily be made as nanowires by conventional methods. MgO nanowires must be used as templates. Firstly, single crystal orthogonal MgO nanowires are grown on single crystal MgO substrate. Oxygen is flowed over <math>Mg_3N_2</math> at 900 degrees as precursor for VLS, using Au catalyst. After the MgO nanowires have been made, the complex metal oxide is deposited by pulsed laser deposition to create a shell on the surface of MgO wires. Another approach to simplify complex nanowires is to use hydrothermal synthesis. This can be used to make <math>PbTiO_3</math> nanorods which is a ferroelectric material and potentially useful as building blocks in nanoelectrochemical systems. (Amorphous <math>PbTiO_{(3-X)}OH_{2X}</math> (mulig jeg rettet feil/misforstod?) precursor is mixed with sodium dodecyl benzene sulfonate surfactant and reacted at 48 h at 180 degrees at alkaline conditions in the presence of a substrate.) The nanorods obtained have a squared cross section 35-400 nm, and up to 5 um long. The rods grow in the (001) direction by self-assembly of nanocubes to anisotropic mesocrystals, which is ripened into nanorods.<br />
<br />
===Electrospinning===<br />
Electrospinning is nanofiber extrusion in a capillary jet. A polymer solution or polymer sol-gel pass through a high voltage metal capillary to create a thin charged stream. The stream undergoes stretching, bending and solvent evaporation. The charged nanofibers are driven to ground electrodes. The dimensions of the fibers depend on solvent viscosity, conductivity, surface tension and precursor concentration. The collector electrodes can be patterned to make organized arrays between them by electrostatic self assembly. The electrodes can be grounded simultaneously or sequentially. This can be used to make single layer or multilayer nanowire architectures. <br />
<br />
====Hollow nanofibers by electrospinning==== <br />
Hollow nanofibers can be made by co-axial double capillary electrospinning that creates heavy mineral oil core with inorganic polymer around (Ti and PVP). The core-shell nanofibers are collected on an aluminum or silicon substrate and hydrolyzed. The oily core can be extracted with octane, which creates nanotubes with amorphous <math>TiO_2</math> + PVP. To crystallize <math>TiO_2</math> and oxidate PVP, the tubes can be calcined (varmebehandlet) in air at 500 degrees.<br />
<br />
====Dual electrospinning====<br />
A side by side spinneret can be used to make bicomponent fibers. Ex: two solutions containing <math>TiO_2</math>/<math>SnO_2</math> are simultaneously jetted. This is calcined. A heterojunction of <math>SnO_2</math>/<math>TiO_2</math> can create devices with extremely high quantum efficiency and photocatalytic activity for treatment of organic pollutants in water and air. <br />
<br />
===Carbon nanotubes===<br />
<br />
Carbon nanotubes (CNT) was discovered in 1991 by Iijima, and have had a great impact on nanotechnology. The CNTs are made of rolled up graphite sheets to create a hollow tube. Both single-walled (SWNT) and layered multi-walled (MWNT) nanotubes exist.<br />
<br />
====Structure====<br />
Carbon nanotubes exist in three different structures, depending on the angle at which the graphite sheet is rolled up. These are characterized by their different properties in electron transport. The achiral tubes, which are the "zig-zag" and "armchair" tubes, are metallic. The metallic tubes have two mini-bands between the valence and conduction band. Quantum mechanical tunneling leads to electrical conductivity. For these, ballistic electron transport have been observed, which means that there is electrical conductivity with no phonon or surface scattering. The chiral tubes are semiconducting, and is the most common found of the CNTs.<br />
<br />
====Synthesis methods====<br />
*'''Arc discharge'''<br />
**A very high DC voltage is applied between two sets of hollow graphite electrodes with transition metals (Fe, Ni, Co) and graphite powder.<br />
**The high voltage cause an [http://http://en.wikipedia.org/wiki/Electrical_breakdown electrical breakdown] (creation of a conductive plasma) of the inert gas filling the gap between the electrodes. This cause temperatures to reach 2000-3000 degrees, which cause evaporation the electrode graphite.<br />
** The gas pressure, gas flow rate and transition metal concentration determine the yield of nanotubes.<br />
**This technique creates high quality MWNTs and SWNTs, but it has a low yield (about 30 wt%).<br />
*'''Laser ablation'''<br />
** The evaporation method of target material used in [[pulsed laser deposition]].<br />
** The target material consist of graphite mixed with transition metals as catalysts, and is placed at the end of a quartz tube enclosed in a furnace.<br />
** The target is exposed to an argon ion laser beam that vaporizes graphite and nucleates CNTs.<br />
** Argon at 1200 degrees flow through the reactor and carries the graphite vapor and the nucleated CNTs. <br />
** Nucleated CNTs are deposited on the colder chamber walls where they grow as the vaporized carbon condences.<br />
** The technique has a high yield (70 wt%) of primarly SWNTs, but is more expensive than arc discharge and CVD.<br />
*'''CVD'''<br />
** <math>CO</math> and <math>CH_4</math> is used as precursors in a quartz tube reactor at 700-900 degrees. The pressure is at an atmospheric level or slightly lower.<br />
** Transition metal deposited on a substrate (Si, mica, quartz or alumina) cause the precursor to dissociate at the surface of the substrate. <br />
** SWNTs are produced at high temperatures and a low supply of carbon precursor.<br />
** MWNTs are produced at lower temperatures (600-750 degrees)<br />
** The most common industrial production method, but it can be problematic to separate the catalyst particles which exist at the end of the tubes. This is usually done by acid treatment, which can destroy the nanotube structure.<br />
<br />
====Separation of nanotubes====<br />
Carbonaceous impurities an metal catalysts can be removed by a high temperature treatment in oxygen, followed by boiling in a diluted mineral acid. The carbon nanotubes can then be sorted by length by precipitation from non-solvent followed by centrifugation. Also, the metallic tubes can be separated from the semiconducting by electrophoresis or precipitation by evaporation of an octadecylamine solution.<br />
<br />
====Properties====<br />
<br />
=====Mechanical=====<br />
CNTs are a extremely strong material compared to other known high-strength materials (high-carbon steel, kevlar). It has the highest specific strength value (strength-to-mass-ratio) of the currently discovered materials in the world. It also has a very high Young's modulus (E-modulus) and tensile strength. When the tubes is bended they deform reversibly. It's excellent mechanical properties makes it useful for lightweight fibers for strengthening of plastic, ceramic and metals. The properties were demonstrated creating a rotational actuator.<br />
<br />
=====Electrical=====<br />
As mentioned earlier, the achiral tubes, which are the "zig-zag" and "armchair" tubes, are metallic, meaning that they have two mini-bands between the valence and conduction band. Quantum mechanical tunneling leads to electrical conductivity. For these, ballistic electron transport have been observed, which means that there is electrical conductivity with no phonon or surface scattering. The chiral tubes are semiconducting, and is the most common found of the CNTs.<br />
<br />
=====Chemical=====<br />
Carbon nanotubes are made of Carbon (C) and are by default chemically inert. They can be made chemically active by opening their ends by oxidation with a strong acid such as nitric acids, which also introduces carboxylate functionalities.<br />
<br />
====Carbon nanotube chemistry====<br />
Carbon nanotubes have strong van der Waals interactions between the walls, which cause them to precipitate when dispersed in a solution. Chemical modification of the nanotubes has been used to make them soluble. Oxidation with nitric acid opens the ends of the CNTs and introduces polar carboxylate groups, which makes them water soluble. Another method is to expose the CNTs to a starch solution, the big starch molecules wraps around the nanotubes by van der Waals interactions. Re-precipitation is possible by adding amylase (breaks down the starch). This method is disrupts the properties of the CNTs to a lesser degree than the former method.<br />
<br />
The nanotubes is reactive with many species due to dangling <math>pi</math>-bonds on the inside and outside of the tube. The versatility in chemical species than can be anchored to the tubes, makes it possible to create a chemical force microscopy by using carbon nanotubes at the end of an AFM tip.<br />
<br />
CNTs have also been used as a sensor. A FET CNT device is made by placing a tube between two electrodes (source and drain) on a Si-substrate (gate). Because CNTs have a conjugated pi-electron system, they can bind to benzene-derivatives. The electron donating ability of the benzene-derivatives depend on the substituents on the benzene rings, and affect the electron density of the tubes. This change in electron density is detected as a change in conductivity.<br />
<br />
====Aligning of carbon nanotubes====<br />
*'''Evaporation induced self-assembly (EISA):''' CNTs are dispersed in evaporating water, and a substrate is dipped perpendicular into the solution. At the meniscus, there is a an accelerated evaporation because of the increased surface area. This cause a net flux of the tubes towards the meniscus, where they align parallel to the water interface and deposits on the substrate. The tubes aggregate to reduce area of the liquid-air interface.<br />
*'''SAM patterning:''' A substrate is hydrophilic patterned by a SAM, an the rest of the substrate is made hydrophobic. When the substrate is exposed to an aqueous suspension of CNTs by f. ex. DPN, the nanotubes is confined to the hydrophilic areas. If the hydrophilic areas are small enough, they could trap single tubes.<br />
*'''Pre-existing patterns:''' Aligned growth of CNTs perpendicular to the surface is achieved by perpendicular CVD growth of carbon nanotubes on a pre-existing pattern of Fe-catalyst particles on a Si-substrate. This method can be used to create a [[photonic crystal]] of CNTs.<br />
*'''AC/DC electric fields:''' A combination of AC and DC electric fields can align CNTs between micropatterned electrons. The AC field attracts the tubes, and the DC field trap a single nanotube between the electrode by electrostatic attraction. The aasembly mechanism is a combination of polarization-induced movement, potential gradient flow and electrostatic-induced attraction forces. When the DC field is dominant, unwanted particles deposit between electrodes, when the AC field dominates, several tubes are attracted but most of them is shorter than the electrode gap. Choosing the right ratio of the electric fields is therefore essential to achieve a high yield of aligned CNTs.<br />
<br />
====Applications====<br />
As mentioned earlier in this section, CNTs can be used as sensors, fiber-strengthening of composite materials and added to materials to improve conductivity.<br />
<br />
<br />
<br />
<br />
== Kapittel 6: Nanocluster Self-Assembly ==<br />
<br />
<br />
<br />
<br />
===Capped nanoclusters===<br />
<br />
A capped nanocluster is a nanometer scale particle with well-defined positions of the constituent atoms. They nucleate from atoms and enter a size range where they behave electronically as molecular nanoclusters. As the number of atoms increases further, they cross over into the nanoscale size domain where quantum size effects dominate, they become quantum dots. A capped nanocluster has a monolayer of a capping ligand on the surface, which can be a polymer or an alkane thiol (if the surface is silver or gold) or some other molecule with an end group that will bind to the surface of the nanocluster. The capping molecules will prevent further growth of the nanocluster. Capping groups serve multiple purposes:<br />
*Change solubility properties<br />
*Enable size-selective crystallization<br />
*Surface functionalization<br />
*Protect nanoclusters from luminescence or charge-carrier quenching<br />
<br />
===General principles for synthesis of capped nanoclusters (arrested nucleation and growth)===<br />
<br />
One general synthesis method is the arrested nucleation and growth synthesis. The basic idea is to rapidly create a large number of nucleated seeds (of desired materials) and then allow these to grow at the same rate below supersaturation conditions. This method can be described by the following steps: <br />
* Desired precursors are added to a solution, which is held at an intermediate temperature (200-400 °C depending on the materials. Temperature needs to be high enough to overcome the activation energy for the reaction). <br />
* Precursors need to be added at an amount that is over the saturation point for the materials in that specific solution. <br />
* Materials will rapidly nucleate (precipitate) and start growing.[[Bilde:Cappedcluster.jpg|900px|thumb|right|An illustration of growing of clusters, quenching and stabilizing with capping agents]] Once the first molecules have reacted and created a small seed, the energy required for further growth is smaller than the initial activation energy. The nucleated seed can therefore continue to grow below the saturation concentration for the precursor materials. <br />
* Once the nanoclusters reach a certain size range, which may vary from one material to the other, capping agents are added to the solution. These molecules will adsorb on the surface of the nanoclusters and prevent further growth (passivation). Surfactants are also added to the solution to stabilize the cluster, by preventing aggregation. The nanoclusters that are formed will not all have the same diameter, but a range of different diameter clusters will be formed. This can be due to for example concentration gradients in the reactor or reaction medium.<br />
<br />
===Minimize size dispersity by confining the reaction space===<br />
<br />
[[Bilde:Nanocrystals_in_nanobeakers.JPG|900px|thumb|left|An illustration of how to make a confined reaction space]]<br />
<br />
The size of the capped nanoclusters can be controlled by growing them in nanowells made by the methode in figure below. The nanowells are obtained by patterning a silicon wafer with a layer of well-ordered microspheres. By pressing the microspheres against the wafer and at the same time melt the surface of the wafer with a pulsed laser, molten silicon will flow into the voids between the spheres. The size of the nanowells depend on the size of the spheres, the energy density of the laser pulse and applied mechanical pressure, while the size of the crystals depend on the well volume and concentration of the reactants. The crystals can be removed by ultrasound. The downside of the approach is that the amount of nanocrystals obtained will be quiet small.<br />
<br />
===Tuning properties through physical dimensions rather than chemical composition (QSE)===<br />
<br />
When electrons are confined in space, the size invariant continuum of electronic states of bulk matter transforms into size-dependent discrete electronic states in a quantum dot. At the 1-5 nm length scale, which is the CdSe nanocluster size range, the parent continuous electron bands of the bulk semiconductor becomes discrete. The nanoclusters then belong to the quantum size regime, and the properties begin to scale in a predictable fashion with size. By looking at the Schrödinger wave equation it can be seen that there is a wavelength shift towards the blue spectrum in the energy of the first exciton band. Band gap scales with the reciprocal of the square of the radius of the nanocluster. The wavelengths absorbed change, and the colors of the nanoclusters can be altered from yellow to red, by changing the physical size of the clusters.<br />
<br />
===How can different phases occur for smaller size particles?===<br />
<br />
Similar to temperature and pressure, phase transformations in bulk materials are dependent on size. Phase transitions that are prohibited or slowed down by activation energies in the bulk, can occur much more readily in nanocrystals of the same material. Because of the small size of the crystal, the influence of bulk and surface-free energies are different from in a bulk matter. Phase transformations show a distinct dependence on nanocrystal size. It can be shown that phase transformation for nanoclusters can occur just by exposing them to a different chemical environment at room temperature.<br />
<br />
===Making nanoclusters water soluble===<br />
<br />
Why? Water is cheap, widely available and use of it avoids the disposal of organic solvents, which can be quite harmful for the environment (green chemistry). You can use the same principles as for the SAM surface chemistry. A hydrophilic SAM is made by choosing a hydrophilic group such as a carboxylate, ammonium or oligo ethylene glycol. In the case of a gold nanocluster, a thiol with a terminal carboxyl group gives an ionized, water loving carboxylate when in aqueous solution. Hydrophobic nanoclusters can be wrapped by amphiphilic polymers. The polymer coating is stabilized by partially cross linking the anhydride groups with bis(6-aminohexyl)amine. The key physical properties of the nanocluster is mantained. Can also coat with silica. Often, the resulting crystals bear a surface charge, which allows their use in electrostatic layer-by-layer deposition.<br />
<br />
===Separation of nanoclusters by size using using a non-solvent and centrifugation===<br />
<br />
Nanoclusters can be dissolved in toluene and by gradually adding a non-solvent (e.g. acetone) the nanoclusters will precipitate. The largest clusters precipitate first. Every time a bit of acetone is added the solution is centrifuged and the precipitate collected. The result is highly monodisperse nanoclusters collected in each fraction.<br />
<br />
===Superlattice===<br />
<br />
A superlattice is a material with periodically alternating layers of several substances. Such structures possess periodicity both on the scale of each layer's crystal lattice and on the scale of the alternating layers.<br />
<br />
===Assembling of superlattices===<br />
<br />
A superlattice can be assembled by means of these techniques: <br />
*Tri-layer solvent diffusion crystallization - Three immiscible solvents are arranged to form separate layers in a test tube. Bottom layer →capped CdSe nanoclusters dissolved in toluene. Middle layer →buffer layer of 2-propanol selected for poor solvent properties with respect to the nanoclusters. Top layer →non-solvent for the nanoclusters such as methanol. The process involves slow diffusion of the nanoclusters from the toluene bottom layer and the methanol from the top layer into the buffer layer. The change in solvent properties causes a slow and controlled nucleation and growth of capped CdSe nanocluster crystals.<br />
*Sedimentation – <br />
*Evaporation induced self-assembly – Strong capillary forces in an evaporating water meniscus drives the nanocomponents into close-packing.<br />
*Langmuir-Blodgett – A dilute monolayer of capped silver nanoclusters is spread on an air-water interface. Using Langmuir – Blodgett “equipment”, this monolayer can gradually be compressed until a compact monolayer is formed. A patterned PDMS stamp can then be dipped into the solution, causing adsorption of the nanoclusters on the stamp. <br />
<br />
===Why do we want to make superlattices?===<br />
<br />
Making superlattices can give you a material with unique properties. Heterocrystals is ordered assemblies of more than one component. The properties of the superlattice does not necessarily equal the sum of the properties of the individual constituents. “The ability to assemble different nanoclusters with size-tunable optical, electronic and magnetic properties into well-defined structures gives us the opportunity to examine new effects due to electronic and magnetic coupling between constituent units” – nanochemistry, a chemical approach to nanomaterials. <br />
<br />
===How capping agents(different type and length) affect the properties of the structure===<br />
<br />
The length and size of the capping agents determine the separation between nanoclusters and the packing in a superstructure. The superlattice period is thus altered by varying capping agents.<br />
<br />
=== Alloying core-shell nanoclusters===<br />
<br />
Thermally driven inter-diffusion of core and shell elements to form solid-solution nanocrystals:<br />
*Redox transmetallation reaction<br />
*Co core diminish in diameter with the accompanying growth of a uniform thickness platinum shell capped by a ligand. <br />
*Annealing at high temperatures cause Co and Pt inter-diffusion to form a solid-solution alloy<br />
Can be used to tune optical absorbtion and luminescence properties. It this process is utilised for core-shell metal nanocrystals, a precise command over their magnetic properties may be possible.<br />
<br />
=== Nanocluster-polymer composites ===<br />
<br />
A nanocluster-polymer composite is a nanocluster stabilized in a polymer. A polymer which prevents nanocluster phase separation and agglomeration, and which does not cause quenching of luminescence, can be used to tune the colors of capped nanoclusters.<br />
<br />
How can it be used for down-conversion of light? <br />
<br />
One example is down conversion of light made by encapsulating a GaN LED in a sheath of capped semiconductor nanoclusters in a polymer. A 425 nm wavelenght emitted from the encapsulated GaN LED evokes a 590 nm light emission from the nanocluster-polymer sheath. This process is responsible for the down conversion of light energy.<br />
<br />
=== Different size nanoclusters labeled with different fluorescent molecules used in biology ===<br />
<br />
*Label cells to allow observation of biological interactions in real-time<br />
*Coat nanoclusters with active biological agents for interaction with biological systems<br />
*Requirements for biological labelling: water-solubility and a coating which must provide biocompatibility<br />
Example:<br />
* CdSe quantum dots with a ZnSshell is encapsulated in the hydrophobic core of a micelle. This tags are highly luminescent and extremely biocompatible. Can be used to cellular events and organism development ''in vivo''.<br />
<br />
=== Tetrapods and principles of the synthesis ===<br />
<br />
*A nanocrystal with four tetrahedrally disposed arms. <br />
*The syntesis is achived through manipulation of the temperature and capping agent. CdTe has two common crystal polymorphs (wurtzite-hxagonal and zinc blende – cubic) where growth of one over the other can be controlled by synthesis temperature. Nucleation sites on the zinc blende structure serve as templates for the growth of wurtzite “arms”. A long chain acid (ODAP)which selectively binds to the lateral facets of hexagonal CdTe serves to confine wurtizite CdTe growth along only on spatial dimension. Length and width of the wurtzite arms could be independently tuned by changing the Cd:Te and Cd:ODAP ratios respectively.<br />
<br />
=== Photochromic metal nanoclusters (section 6.31) ===<br />
<br />
* After embedding silver nanoclusters in a titania matrix, one can use UV-light to photo reduce the the metal salt. This makes the the silver nanoclusters absorb most light. Later, one can use light with different wavelength to induce local oxidation of silver nanoclusters of specific size. For example will red light cause cause oxidation of nanoclusters in the red light band which will cause them to reflect red light and therefore appear red, and white light (all wavelengths) will cause oxidation of all nanoclusters which makes the substrate will appear white.<br />
<br />
=== What is a buckyball and what can it be used for? What special properties does it exhibit? ===<br />
<br />
Molecules that are composed of 60 carbon atoms, in the form of a hollow sphere. 20 hexagons and 12 pentagons. <br />
Buckyballss are stable, but not totally unreactive. In a buckyballall the carbons are conjugated through a huge circular pi-cloud, which can be easily reduced and loaded with up to 4 electrons. The anionic buckyballcan function as a good reducing agent and reduce nitrogen to ammonia with high yield. Other atoms can be trapped inside buckyballs to form inclusion compounds. Buckyballs are potentially the smallest building blocks that can be used to improve computing power in the near future.<br />
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== Kapittel 7: Microspheres – Colors from the Beaker ==<br />
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Nå ferdig med så mye som forfatteren greide, men finn gjerne ut resten og del det med alle! TC holder også på med denne<br />
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===What is a photonic crystal (PC)? ===<br />
*It is a structure of regularly repeating regions of high and low dielectric constant with a periodicity at the scale of wavelength of optical light. It can be a ordered crystal with alternating layers of the crystal material and air gaps.<br />
*The propagation of light is affected by the structure, which defines allowed and forbidden electronic energy band gaps. Photons therefore propagate through the medium - or not - depending on their wavelength.<br />
*Wavelengths of light that are allowed to travel are known as modes, and groups of allowed modes form bands. Disallowed bands of wavelengths are called photonic band gaps (PBG) (the range of wavelength don't propagate).<br />
*For a photonic crystal with a full photonic band gap, all incident light is reflected and all light created inside the crystal is trapped. The crystal must have a high dielectric crystal to achieve this.<br />
*A stopgap is a incomplete photonic band gap.<br />
*1D PC (planes) is a crystal which only inhibit light to travel in one direction.<br />
*2D PC (rods) inhibits light to travel in two directions.<br />
*3D PC (spheres) inhibits litght to travel in any direction and has a full photonic band gap, whilst 1D and 2D only have so called stopgaps.<br />
*A naturally occuring photonic crystal is the gemstone opal.<br />
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===Photonic Crystal defects===<br />
*Point defects: Holes, missing spheres, in a 3D PC can trap light inside the crystal <br />
*Line defects: Many holes which make a line can guide light through a crystal. The light reflects of the walls inside the defect, and can be guided along and around edges and turns.<br />
*Plane defects: A missing plane or a defect in a plane can make photons slip through to the other side. Planes consisting of another type of material can cause the perfect reflection curve of a PBG-crystal to drop at certain wavelengths depending on the size of the defect. A planar defect exists at the interface between two layers of differently sized microspheres. The planar defect introduce a transition in refractive index between the two layers.<br />
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===Making defects=== <br />
*Writing defects: A organic monomer is absorbed into a photonic crystal and multiphoton laser writing using a confocal optical microscope induced polymerization of the monomer creates small line inside the photonic lattice. Then you treat the crystal and remove the polymer. In reversed opal structures you can use laser microwriting where you attach a laser to a scanning optical microscope which again changes the phase (which again changes the refractive index) of the inverse opal by annealing.<br />
*Synthesizing planar defects: Introducing a dense layer or a layer with spheres of a different size than the surrounding colloidal crystal. Dense layers can be introduced by either CVD, electrolyte LbL, PDMS-stamps or maybe another deposition technique. The process consists of growing a photonic crystal, then using electrolyte LbL-deposition or PDMS-stamp make a thin film before making another photonic crystal. It's like a sandwich.<br />
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===Manipulating photonic crystals usage=== <br />
*Color of the structure is partially determined by the size of its spheres according to Bragg's law, because this determines the lattice plane spacings. Small spheres give blue/purple colors and larger spheres goes towards red (from yellow to green and then red).<br />
*Non-close-packed polymerized colloidal crystalline arrays can be made to swell or shrink by external influence. As the diffraction colors of the crystal depend on the spacing between microspheres you can place a hydrogel between the spheres and this gel will swell or shrink depending on external environments. This will make the color change when the gel shrinks or swells as the pH, temperature, water concentration or ionic strength changes. The dimensions of the crystal is altered.<br />
*The dielectric constant can be changed by changing the material, the structure of the crystal ''or something else that others edit in here''<br />
*An example: Removal of cation causes a hydrogel to shrink, which can be detected at even very small concentrations. The order of cation complexation determines how sensitive the sensor is. Cation selectively binds covalently to the polymer network, sol-gel or hydrogel.<br />
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===Core-corona, core-shell-corona and multi-shell microspheres===<br />
Corona is the term always used for the outermost layer of multi-shell microspheres. A corona usually consist of a monolayer with functional end groups, that can either passivate or impart different surface functionalities to the structure. Core-corona and core-shell-corona can be made by both re-growth and one stage growth as multishell microspheres probably is better off being made by the re-growth process. The purpose of making these spheres is to put a lot more functionalities into just one sphere. The shells can be fluorescent, magnetic, photoactive, semiconductive, sacrificial or something else pulled out of a hat.<br />
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===Growth synthesis=== <br />
*One stage: Reagents are mixed and the microspheres are obtained in solution by a nucleation and growth. This method is usually faster than re-growth.<br />
*Re-growth: First a sees is produced. The seed is then allowed to grow in several steps. Surface tension controls the shape, where low surface tension gives spherical particles. Re-growth is usually slower, but gives a higher yield compared to one-stage.<br />
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===Self assembly of photonic crystals=== <br />
*Sedimentation (be able to explain in more detail): The self-assembly of microspheres dispersed in an aqueos solution in a container under gravity. The microspheres settle at the bottom at a velocity determined by Stokes equation. This depends on the radius of the spheres, the density of solvent and spheres and the viscosity of the liquid. Usually, a slow settling is necessary to control the growth of the crystal. This is achieved by increasing the density and viscosity of the solvent.<br />
*Electrophoresis: The motion of dispersed microspheres relative to a liquid in the presence of a space uniform electric field.<br />
*Hydrodynamic shear: Same as the parallel plate confinement, only that shear forces are responsible for the sphere assembly.<br />
*Spin coating '''– noen som veit?'''<br />
*Langmuir-Blodgett layer-by-layer (be able to explain in more detail): Hydrophobic microspheres float at a compressed water-air interface. Because of the compression, the spheres align in a ordered phase, which can be collected by dipping a PDMS stamp into the solution.<br />
*Parallel plate confinement: Force spheres to assemble by placing them between two parallel plates and slowly moving one plate closer to the other. Important with slow movement to prevent defects. This can be done both dry and in fluid. It is necessary to increase density and viscosity of solvent so that settling occurs slowly in order to control structure and shape, and to avoid defects.<br />
*Evaporation induced self-assembly, EISA (be able to explain in more detail) Capillary forces drive the assembly of spheres in a solution as you remove a wetting plate out of the solution. These the need to be dried and this can cause cracking. Vertical substrate is placed in a dispersion of microspheres. As solvent evaporates, the microspheres are driven by convective forces (forces from movement in solvent towards wall, surface, water meniscus) to the solvent-air meniscus. The layer thickness is determined by the diameter of the microspheres, their volume, concentration and the wetting properties of the solvent on the substrate.<br />
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===Colloidal aggregates=== <br />
*Colloidal aggregates (CA) are made either by templated pattern in a surface or by aggregation in a homogeneous emulsion. By template confinement, a pit in a substrate is made by photolitographically patterning followed by etching, where the colloidal spheres can aggregate.<br />
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'''Emulsion-way:'''<br />
*They are disperse microspheres in a solvent such as toulene.<br />
*Add dispersion to solution of surfactant and water<br />
*Stir or shake to get emulsion<br />
*Toulene evapourates and as toulene droplets shrink, microspheres are pulled together in a stable cluster through capillary forces.<br />
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'''Photonic crystal marbles by electrospraying:'''<br />
*Photonic crystal marbles can be created by using a technique called electrospraying. Aqueous dispersion of microspheres is forced under pressure, through a small aperture in a syringe in the presence of an AC electric field. Surface charge on the liquid jet make it break into homogeneously sized spherical particles. Each droplet contains a preset quantity of microspheres. As the water evaporates from the microsphere suspension droplet, the capillary forces in conjunction with colloidal forces cause the microspheres to self-assemble within the droplets to create a closed packed spherical colloidal crystal.<br />
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===Bragg-Snell law===<br />
*The reflected light has a wavelength depending on Bragg's and Snell's law. This then tells us that the wavelength of the first stop band is proportional to distance between the lattice plains. This gives that the longer the distance between the plains (bigger microspheres) gives longer diffracted wavelength.<br />
<math>\lambda_{c(hkl)} = 2d_{hkl}\sqrt{\langle \epsilon \rangle - sin^2{\theta}} </math><br />
der <math>\langle \epsilon \rangle</math> is the effective dielectric constant of the colloidal crystal.<br />
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===Cracking===<br />
Colloidal crystals are found to crack after crystallization, thermal and chemical anneling. This happens when the thin hydration layers around the crystal spheres dry out, which cause lattice contraction. This creates capillary stress and thermal expansion. To prevent cracking you can dry the crystal slowly or use hydrophobic spheres to eliminate the hydration layer. Confining spheres in templates can also reduce cracking by localizing the cracks at the crystal edges. Methods for preventing this is:<br />
*Necking at room temperature using vapor phase alternating chemical reactions. The spheres must be connected to stabilize the structure, and avoiding high temperature-treatment, reduces cracking.<br />
*This can be achieved with CVD deposition of silica as a interconnecting layer between the spheres. CVD deposition of interconnecting silica by alternating treatment in <math>SiCl_4</math> and water vapor onto the colloidal crystal, creates the interconnecting silica layer. An advantage of this method is good control of layer thickness, as it can be controlled/monitored by optical diffraction. A thicker layer red-shifts the diffraction peak.<br />
*Another strategy is heat treatment of the spheres before assembly. This may require pretreatment before assembly to give desired surface charges. Re-disperse and crystallize without volume contraction.<br />
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===Liquid crystal photonic crystal===<br />
A liquid crystal is neither a liquid nor a crystal, but an intermediate state of matter, so called mesophase. Lacks the long range order of the crystalline state and does not exhibit the randomness of the liquid state.<br />
*Themotropics are liquid crystals which consists of melted anisotropical shaped molecules (rods or discs) which are partially aligned. The order of the components in the liquid crystal is determined and changed by the temperature. <br />
*Two groups of thermotropics are ''nematic'', where the molecules have no positional order, but they have a long-range orientational order, and ''discotic'', which consists of disc-shaped particles that can orient in a layer-like fashion.<br />
*By applying electric- and/or magnetic fields the small crystals in the liquid will align along the E (electric) or H (magnetic) field direction, and this can control the refractive index of the film and hence it's optical properties. A change in temperature can switch the crystals between anistropic and isotropic states, where the properties of the crystal are the same in any spatial direction. Electric/magnetic fields or temperature changes can therefore change the structure from coherently aligned to random, which makes the film either transparent or reflective to incident light. Example of usage is privacy/smart windows.<br />
*By filling the voids in an inverse opal photonic crystal with a nematic liquid crystal we make what's called a Liquid Crystal Photonic Crystal (LCPC). Applying a field or changing the temperature makes the refractive index of the liquid crystal inside the voids change, by switching between anistropic and isotropic states. This means that other wavelengths will satisfy Bragg's criterion, which in practice means that the color of the LCPC changes (you alter the stop band frequency) See [[TMT4320_-_Nanomaterialer#Bragg-Snell_law | Bragg-Snell law]].<br />
*LCPC is thought to be used as tunable photonic crystal device and liquid crystal-colloidal crystal switch.<br />
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== Reactions that you need to know ==<br />
* Reaction of alkane thiolate with gold. Important to know that alkane thiols have a specific affinity for gold (also keep in mind that silver and gold have very similar properties): <math>X-(CH_2)_n-SH + Au^0 \rightarrow X-(CH_2)_n-SAu^1 + 1/2H_2</math><br />
* Reaction that occurs when during anodic oxidation of Al to produce porous alumina membranes (section 5.4): <math>2Al + 3PO_4^{3-} \rightarrow Al_2O_3 + 3PO_3^{3-}</math><br />
* Reaction that occurs when silica microspheres are formed from Si(OEt)4 and water (section 7.9): <math>Si(OEt)_4 + 2H_2O \rightarrow SiO_2 + 4EtOH</math><br />
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== Eksterne linker ==<br />
*[http://www.ntnu.no/portal/page/portal/ntnuno/AlleEmner?rootItemId=22934&selectedItemId=31007&emnekode=TMT4320 NTNUs fagbeskrivelse]<br />
*[http://www.ntnu.no/studieinformasjon/timeplan/h08/?emnekode=TMT4320-1&valg=emnekode&bokst= Timeplan Høst08]<br />
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[[Kategori:Obligatoriske emner]]<br />
[[Kategori:Fag 5. semester]]<br />
[[Kategori:Fag]]</div>Kenrogerhttp://nanowiki.no/index.php?title=TMT4320_-_Nanomaterialer&diff=869TMT4320 - Nanomaterialer2008-12-16T07:06:56Z<p>Kenroger: </p>
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<div>{{Infobox<br />
|Fakta høst 2008<br />
|*Foreleser: Fride Vullum<br />
*Stud-ass: Katja Ekroll Jahren og Ørjan Fossmark Lohne<br />
*Vurderingsform: Skriftlig eksamen<br />
*Eksamensdato: 18. desember<br />
}}<br />
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{{Infobox<br />
|Øvingsopplegg høst 2008<br />
|* Antall godkjente: 6/12<br />
* Innleveringssted: Utenfor R7<br />
* Frist: Tirsdager 16:00 (?)<br />
}}<br />
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Emnet skal gi en innføring i grunnleggende kjemisk prinsipper for å lage nanomaterialer. Stikkord: "Self-assembled" monolag ([[SAM]]) og hvordan disse kan formes ved myk litografi og "dip pen" nanolitografi, syntese av tredimensjonale multilag strukturer. Tynne filmer ved kjemisk gassfase deponering. Syntese av nanopartikler, nanostaver, nanorør og nanoledninger. Våtkjemiske syntese av oksidbaserte nanomaterialer. "Self-asembly" av kolloidale mikrokuler til fotoniske krystaller, porøse nanomaterialer, blokk-kopolymere som nanomaterialer. "Self assembly" av store byggeblokker til funksjonelle anordninger.<br />
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== Oppsummering av pensum ==<br />
Her vil det etterhvert vokse fram et lite kompendium i faget. Dette følger i utgangspunktet pensumlista som gjelder for høsten 2008.<br />
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===Chapter 1: Nanochemistry Basics ===<br />
Not terribly important.<br />
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===Chapter 2: Soft Lithography===<br />
====Self-assembled monolayers (SAMs)====<br />
*The typical example of a SAM is a layer of alkanethiols on a gold substrate. <br />
*The S-H bond is cleaved by oxidation on the gold surface and a covalent Au-S covalent bond is formed. <br />
*The alkanethiols are tilted off-axis from the normal. The angle depends on the surface. (30 ° for a {111} gold surface, 10 ° for a silver surface). <br />
*The end group on the alkanethiols can be tailored to achieve different monolayer properties, thus modifying the surface properties of the structure.<br />
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====PDMS stamp====<br />
* PDMS (PolyDiMethylSiloxane) is a soft elastic polymer.<br />
* A master (casting) of the stamp, with the desired pattern, is made with electron or UV-lithography. The master is silanized and made hydrophobic so removing of the stamp becomes easier.<br />
* Liquid PDMS is then poured into the master, after which it is cured and a finished PDMS stamp is removed from the master.<br />
* The critical dimensions of the stamp are limited by the lithography techniques used, and for [[photolithography]] the wavelengths of the light used to expose the [[photoresist]] limits the dimensions. Typical CDs given are, for lateral dimensions within the range of 500nm-200µm, and for the height of patterns 200nm-20µm. <br />
* The PDMS stamp can be dipped in alkanethiol solutions (or solutions of other molecules, collectively known as "chemical ink") and be stamped onto surfaces.<br />
* PDMS stamps work on both planar and curved surfaces.<br />
* For the stamp to properly print a pattern onto a surface, the molecules need to adhere to the stamp from the solution, but the affinity for binding to the surface has to be stronger.<br />
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====Hydrophilic / Hydrophobic stamps====<br />
* The endgroup/terminal group on the alkanethiols (or other molecules used) determine the properties of the monolayer, f. ex. a OH-terminal group makes the monolayer hydrophilic, while a <math>CH_3</math>-group makes it hydrophobic.<br />
* Wetability is determined by the polarity of the endgroups.<br />
* By introducing a wetability gradient or abrupt changes in wetability, different effects can be obtained:<br />
** Square drops, by having checkerboard square patterns of hydrophilic monolayers with hydrophobic lines inbetween, and condensating water onto the surface. This is called condensation figures and results from the condensation on the hydrophilic areas, when the substrate is cooled below the dew point. The diffraction pattern of the structure can be studied for obtaining information on the kinetics and structure of the water droplets. This can be used in biological sensing.<br />
** Droplets "running uphill" by having wetability gradients. The droplets are moving towards the more hydrophilic areas, against the force of gravity.<br />
** Nanoring arrays can be synthesized using the condensation figures as templates for molding. A solvent precursor which wets the regions between the microdroplets is added and then evaporated. Deposition of precursor occurs around the perimeter of the droplets. Finally, the water droplets is evaporated, and the precursor remains on the substrate as nanorings. <br />
** Solid state patterning by dipping a SAM-patterned substrate in a precursor solution. This creates microdroplets with a predetermined precursor concentration, which on evaporation and vertical drying leaves behind an array of size-tunable solid precursor dots.<br />
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====Printing thin films====<br />
* As long as the adhesion between the chemical ink and the substrate is stronger than the adhesion between the ink and the stamp, printing thin films is no problem<br />
* Metal thin films can be evaporated onto a PDMS stamp (f. ex. gold). Evaporation gives homogenous and directional coatings, and no covering of the side walls on the stamp. This pattern is printed onto a SAM-primed substrate with exposed thiol groups (gold adheres strongly to the metal layer).<br />
* This is a very gentle technique for metal film depositing, good for making contacts on fragile layers. Also good for making 3D stuctures by printing multiple layers. Also, there is no need for photoresist because the pattern is printed directly.<br />
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====Electrically contacting SAMs====<br />
* Molecular electronic devices need to make good electrical contact with SAMs.<br />
* Making electrical contacts by vapor deposition on the SAMs may sometimes be more convenient than thin-film printing with a PDMS stamp.<br />
* Other, less gentle methods of metal deposition than printing with PDMS stamps (sputtering, CVD, etc) can cause the metal layer to penetrate the SAM and deposit on the substrate, or even diffuse into the substrate, introducing defects to the structure.<br />
* Morale: Use stamps to deposit metals on SAMs!<br />
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====Patterning by photocatalysis====<br />
* Photocatalysis is used to remove parts of a SAM (making patterns)<br />
* Titania (<math>TiO_2</math>) can photocatalytically decompose organic molecules.<br />
* A quartz slide patterned with titanium dioxide in the required pattern using ALD is pressed against a wafer with the SAM on it. <br />
* The assembly is exposed to UV radiation, triggering the degradation of the (organic) SAM. When titania is exposed to UV, radiation free radicals are created, which react with the organic molecues, removing the parts of the SAM that is in contact with the titania. Thus, the substrate in these areas is revealed.<br />
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===Kapittel 3: Building layer-by-layer===<br />
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====Electrostatic superlattices====<br />
* LbL multilayer films formed by alternate immersion in suspensions of opposite charges. Electrostatic interactions are responsible for the LbL growth.<br />
* A primer layer with a charge adheres to the substrate. The substrate is then dipped in a solution of polyelectrolytes of opposite charge from the primer layer. This process can be repeated numerous times in order to get the desired thickness or functionality of the film.<br />
* Any species bearing multiple ionic charges can be layered, f. ex. an amphiphile.<br />
* The anionic layered materials can be exfoliated with bulky cations to create electrostatic superlattices.<br />
* As the amount and identity of constituents of each layer can be controlled, a composition gradient can easily be constructed throughout the structure. <br />
** Quantum dots (QD) with different size can be introduced in the layer structure, creating a gradient in fluorescent colours.<br />
*<br />
* The layer separation can be modified by varying the pH, salt concentration (screening of electrostatic interactions) or polyelectrolyte charge density.<br />
* Can be applied to curved surfaces, as coating of microspheres or rods.<br />
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====Some applications====<br />
* Electrochromic layers, used in "smart windows" for instance.<br />
** Electrochromism is a optical change (absorption of light in this case) in the material upon oxidation or reduction.<br />
** The absorption of light can therefore be modified by applying a voltage to a film of alternating polyelectrolytes.<br />
* Construction of cantilevers for chemical sensing, using photolithography and LbL.<br />
* Hollow spheres can be made by LbL growth on a templating microsphere.<br />
** The template can be dissolved by HF.<br />
** Chemicals can be encapsulated inside the hollow spheres (f. ex. medicine).<br />
** Layer separation can be modified by adding electrolyte solution, making it possible to tune diffusion in and out of the hollow sphere, thereby controlling release of encapsulated chemicals.<br />
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====Analysis, measuring film thickness====<br />
* Indirect techniques:<br />
** Optical spectroscopy: If the substrate is transparent, and the film absorbs light at a certain wavelength, the film thickness can be found by monitoring the optical absorption as a function of number of layers. A dye can be introduced to ensure absorption. Easy to perform but hard to interpret - must know the observation area and extinction coefficient of the absorbing group.<br />
** Ellipsometry: Film is probed by polarized light, and change in polarization in the reflected light is measured. This can be used to find the refractive index, thickness, roughness and orientation of a thin film. Ellipsometry works with films much thinner than the wavelength of light - down to atomic layers. A theoretical fitting must be done to extract the required parameters from the experimental data.<br />
** Quartz crystal microbalance (QCM): Quartz (piezoelectric material) in an alternating electric field contracts/expands with a characteristic oscillation frequency. When mass is added to a QCM the frequency decreases, which correlates directly with the amount of mass added. This allows real-time thickness measurements when the density of the material is known. Works well for hard materials like metals and ceramics, but not for viscoelastic materials.<br />
* Direct techniques: <br />
** Label each layer with heavy metal atoms and image by TEM. <br />
** Alternately, deposit a thin gold layer on top of the surface and image cross section by TEM.<br />
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====Non-electrostatic lbl assembly====<br />
* LbL doesn't need electrostatic bridges - can use hydrogen bonding, ligand-receptor interactions or even covalent bonds.<br />
* Example: DNA-multilayers by hydrogen bonding (adenine-thymine and guanine-cytosine bridges).<br />
* Hydrogen bonds can be broken again by changing the pH, or can be strengthened by UV irradiation.<br />
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====Low-pressure layers====<br />
* '''Molecular beam epitaxy (MBE)'''<br />
** Performed in ultrahigh vacuum, sources of constituents (elemental) are heated, and a thin film alloyed from the constituents is deposited. The result is a single crystal film with homogeneous thickness grown epitaxially on the substrate. <br />
** The substrate should have a similar lattice constant to that of the layer deposited. If the lattice constant of the substrate is substantially different from that of the deposited material, there will be a dewetting effect where the material can form quantum dots.<br />
** Because of the low pressure, there is no reaction between different precursors. <br />
** The advantages over CVD and ALD is that no impurities or contaminants exists, also there is a minimum of crystal defects. The grow-rate is very low (about 1 monolayer per second), thus this technique gives exact control of layer thickness and composition.<br />
* '''Chemical vapor deposition (CVD)'''<br />
** Volatile precursors are introduced in gas phase in a low-pressure reactor chamber. <br />
** Argon or nitrogen gas are usually used as carrier gas to dilute the precursor and achieve optimal pressure and concentration. <br />
** The substrate is heated, and the precursor reacts or decomposes at the surface to create a film, where the film thickness depends on amount of precursor and time allowed for reaction to occur.<br />
** There are several different types of CVD reactors, such as cold wall and hot wall reactors. There are also plasma enhanced reactors (PECVD) where the electric field in the plasma can force growth of nanowires in the direction of the electric field. <br />
** CVD can be used to make monocrystalline, polycrystalline, amorph and epitactic films. The disadvantage over MBE is greater risk of introducing contaminants and defects into the film.<br />
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====Lbl self-limiting reactions====<br />
* Atomic layer deposition: Similar to CVD, but usually carried out in solution (can use gas as precursors).<br />
* Iterative saturating reactions. ALD is a self-limiting process where only one layer at a time is deposited. When the first layer is deposited it needs to be reactivated in order to grow a second layer. It is therefore easy to control thickness down to the atomic scale.<br />
* Material can be deposited uniformly into deep trenches, porous structures and around particles.<br />
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=== Kapittel 4: Nanocontact printing and writing ===<br />
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====Soft lithography and microcontact printing ====<br />
* Sub 100 nm Soft Lithography: Previous chapters has covered printing on 10.000-100 nm scale. Need for further miniaturization because of demand for more power, efficiency, and density. This can be done by manipulating PDMS stamp, Dip Pen Nanolithography (DPN), Whittling Nanostructures or by Nanoplotters<br />
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====Manipulating PDMS stamp====<br />
* Manipulating PDMS stamp can be done in various ways, and seven of the basic ideas will now be explained. Illustrating pictures are in the book and in the slides.<br />
# Compress the stamp, mold to get a new stamp with inverse pattern, peel off and repeat. The new stamp has lower dimensions than the master.<br />
# Apply force perpendicular onto stamp when on substrate. The areas in contact with substrate will then increase, and spaces in between gets smaller.<br />
# Size reduction by reactive spreading of ink when in contact with substrate. The contact time + properties of the ink decide to which degree the ink spreads. The printed area is increased and the spacing between is reduced.<br />
# Size reduction by extraction of inert filler (just like removing water from a sponge).<br />
# Size reduction by swelling the stamp in toluene. The areas in contact with the surface are increased in size while the spacing between is reduced. <br />
# Size reduction by stretching stamp so that dimensions get smaller in one direction and larger in another.<br />
# Size reduction by double-printing.<br />
* Overpressure printing<br />
** Defect-free contact printing is restricted to a certain range of height-to-width ratios. If ratio is outside 0.2-2, the roof of the grooves on stamp will touch the substrate. Too high perpendicular force on stamp has the same effect, but overpressure can also be used to form new patterns such as micron scale discs and rings of ferromagnetic core-shell nanoparticles. Nanoparticles are then transferred to PDMS stamp by Langmuir-Blodgett technique (chapter 6) and then into contact with Au-coated silicon substrate. <br />
*** Low pressure => discs, high pressure => rings.<br />
*Limitations<br />
** Deformation can be a shortcoming if care is not taken with the dimensions of surface relief pattern in the stamp, as this can give unwanted deformations. Quality of printed pattern will not be good.<br />
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====Dip pen nanolithography====<br />
* Alkanethiols can be written on gold substrate with AFM tip. The alkanethiols are delivered to the tip via a water meniscus, and this can be adapted to suit other surface chemistries. The result is 10 nm fine patterns of molecules (biomolecules, polymers etc.) on metals, semiconductors and dielectrics. <br />
* Sol-gel DPN: patterning of solid-state materials. Nanoscale patterns are written using a metal oxide sol-gel precursor in a solvent carrier. The sol-gel precursors are hydrolyzed to metal oxide by use of atmospheric moisture and water meniscus at the tip-substrate interface. pH, substrate temperature and post treatment can be varied. Temperature treatment is necessary.<br />
*Enzyme DPN: A scanning microscope tip can be used to deliver an enzyme via a water meniscus to a specific site on a biomolecule with nanometer presicion. This can be used to control biochemical reactions locally. After patterning, the enzyme is activated by metal ions to start the reaction. Deactivation is achieved by washing with de-ionized water. This method leads to the possibility of bionanodegradable electronic and optical devices.<br />
*Electrostatic DPN: Like thin films can be made of charged polyelectrolytes, an AFM tip can "draw" lines or structures of charged polymers on a oppositely charged substrate, with for example specific electrical properties to build nanoscale electronic devices.<br />
*Electrochemical DPN: The meniscus that forms between surface and tip is used as a nanochemical reactor. Electrochemical deposition or etching (oxidation) can be done by applying voltage between tip and substrate. Ex: making platinum lines can be done by reducing Pt salt at -4 V, and silica lines can be made by oxidation of a silicon surface at +10 V.<br />
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====Whittling of nanostructures (section 4.19)====<br />
* Only be able to explain basic principle<br />
**The spatial extent of SAMs can be reduced by so-called "whittling". Whittling is an electrochemical desorption process where a voltage applied will cause ligands at the peripheries of a structure to desorb. The spatial extent of desorption is directly proportional with time. It has been found that the larger the accessibility of a molecule, the lower the desorbation voltage is (fig. 4.22).<br />
<br />
====Nanoplotters and nanoblotters====<br />
* The principle is to increase the low throughput DPN methodology, by using parallell DPN.<br />
*Nanoplotter: An array of parallel cantilevers can write SAM nanopatterns simultaneously.<br />
** The cantilevers are electrically driven by differential thermal expansion.<br />
*Nanoblotters: An PDMS inkwell has been created to deliver ink to the nanoplotter cantilever tips (fig. 4.26)<br />
** Inkwells are capped with a semipermeable PDMS membrane. By contacting the DPN tips to the membrane, ink diffuses to wet the tip.<br />
<br />
====Combinatorial libraries====<br />
*DPN can be used to put different materials together in the research of new material composition. With DPN, many different combinations can be made with small material amounts used (in theory only single molecules).<br />
*Parallel DPN can accelerate the analyzing of reactions, and increase the rate of discovery of new materials.<br />
<br />
=== Kapittel 5: Nano-rod, nanotube, nanowire self-assembly ===<br />
<br />
<br />
''Emily skriver på denne. Håper folk retter opp dersom de finner feil, og legg gjerne til flere ting:)''<br />
<br />
====Templating nanowires and nanorods====<br />
Templates can be used for making solid nanorods and nanotubes of controlled size. Examples of templates are alumina, silicon, zeolites and lipid bilayers. If the holes are completely filled nanorods and nanowires result, while a partial filling with continuous coating gives rise to nanotubes.<br />
<br />
====Making modulated diameter silicon templates====<br />
A p-doped silicon wafer is put in aqueous HF and an oxidizing potential is applied. The result from this is nanoporous silicon with a random network of pores. The diameter of the pores can be tuned by controlling the voltage or current. The higher the current is, the wider the channels get. If the current is modulated during oxidation, the resulting structure is an array of modulated diameter nanochannels. If perfectly ordered pores are desired, the wafer can be lithographically patterned with regular array of nanowells in advance. The electric field will then be focused at the tip of these wells.<br />
<br />
====Making porous alumina membranes====<br />
Porous alumina membranes can be made by anodic oxidation of lithograpically embossed aluminum sheet in phosphoric or oxalic acid electrolyte (the almunium sheet functions as the anode).<br />
<br />
<math> 2Al + 3PO_4^{3-} \rightarrow Al_2O_3 + 3PO_3^{3-}</math><br />
<br />
The residual Al and <math>Al_2O_3</math> is removed by mercuric chloride and phosphoric acid. The diameter is controlled and can be 20-500nm. Mechanisms that give ordered channels are the fact that electric fields created by applied voltage (which is concentrated at the tips of the growing tubes) repell each other, and that we have volume expansion when aluminum becomes alumina. Temperature is also a factor that affects the reaction.<br />
In this process oxygen diffuses through the alumina layer from the electrolyte and alumina grows at the alumina/aluminum interface, while alumina is slowly dissolved at the alumina/electrolyte interface. This growth/dissolution comes to an equilibrium at the bottom of the pore, giving a specific thickness for a certain current/voltage. The growth of alumina is still allowed to continue upwards (along the pore walls) where the electric field is weaker, giving longer pores. Growth continues until the electric field is quenced or there is no more aluminum left.<br />
<br />
====Modulated diameter gold nanorods====<br />
With use of silicon template. The back surface of the silicon membrane is subjected to a local thermal oxidation which formes silica. The silica is then removed by HF. By proceeding with a KOH anisotropic etch on the same area, and a dip in HF, the pores in the template are opened. A gold sputter deposition can then be done on the backside. This gold layer acts as a catalyst for continued electroless deposition of gold. Finally, the silicon membrane is etched away, and the gold nanorod dispersion can be collected.<br />
<br />
====Modulated composition nanorods/nanobarcodes====<br />
Modulated composition nanorods can be made by electrochemical deposition of different metal segments within the channels of an alumina template (electrodeposition will be better explained in the following section). Any type of material that can be electrodeposited can be used in the nanobarcodes. One synthesis route is to evaporate thin metal film to one side of an alumina membrane. This metal film function as the cathode, and metal deposition begins at the bottom. Bath can be switched between different metal salts to grow several segments. The lenght of the metal segments scales directly with the current. The alumina membrane is dissolved using sodium hydroxide, and the metal backing is dissolved using acid. <br />
<br />
Nanobarcodes can be used to tag molecules in analytical chemistry and biology. Characteristic of metals are optical reflectivity, which means that different segments of the barcode nanorod can be distinguished in optical microscopy. Probe molecules must be anchored to different segments, and the rods must be dispersed in analyte containing target molecules which bear a luminescent label. By molecular recognition, the target molecules bind to the probe molecules (ex: ligand-receptor binding for biological applications). By looking at the segments that light up, it can be decided which molecules exist in the solution.<br />
<br />
====Electroplating/electrodeposition====<br />
The part to be plated is the cathode, while the anode is made of the material to be plated. Both components are immersed in electrolyte solution. The dissolved metal ions (cations) are reduced at the interface between the solution and the cathode when current is applied.<br />
<br />
====Electroless deposition====<br />
This is an auto-catalytic plating method that involves several simultaneous reactions in an aqueous solution. The reaction involves plating of a metal onto a conductive surface and occurs without the use of external electrical power. This is accomplished when hydrogen is released by a reducing agent and thus producing a negative charge on the surface of the metal. There is no direct control over length or thickness of the deposited layer. This needs to be calibrated with regards to concentration of precursor and amount of time that reaction is allowed to run.<br />
<br />
====Nanotubes====<br />
Nanotubes can be made by partial filling of the membranes radially. This means that a uniform coating must be deposited on the pore walls. One way to do this is by letting fluid spontaneously wet inside the template pores. Fluids that can be used are molten polymers, polymer solution or sol-gel preparation. These are coated onto template using capillary forces resulting from small diameter channels with a large available surface. Solidification of these fluids can be done by heating, cooling, waiting or using a catalyst. With this method it is difficult to control the wall thickness. <br />
Another way to make nanotubes is by using LbL growth procedure inside the pores. This can be done by CVD of gas phase species, solution phase ALD or LbL electrostatic assembly. Wall thickness is easier to control with these methods. <br />
Finally, the membrane is dissolved. It can also be deposited other material inside the remaining void to get coaxially coated rod or wire. <br />
<br />
Nanotubes can also be made from LbL electrostatic coating of nanorods. The rods can be dissolved afterwards, and will leave a closed-ended tube. This method is applicable to any material that can be coated onto a nanorod and not be affected by the etching step. <br />
<br />
====Magnetic Nanorods====<br />
Magnetic metals such as iron, cobalt or nickel can easily be deposited into membranes. Magnetic properties are direction and size dependent. By applying a magnetic field, the segments become permanently magnetized and there will be attractions between the rods. If the thickness of the magnetic segments on a nanorod is smaller than the diameter, magnetization is perpendicular to the rod axis, and they will self assemble into 3D bundles. If the thickness is bigger than the diameter, magnetization is parallel to the rod axis, and they will align in chains of rods. If the thickness is the same as the diameter they will be in random aggregates. <br />
<br />
Magnetic nanorods can be used for separation of molecules. A tri-segmented Au-Ni-Au nanorods can be used as affinity template for histidine- tagged proteins. Nickel selectively captures the labeled protein, and a magnetic field can be used to separate the rod with the captured protein from the rest of the solution of biomolecules. After this, the proteins can be chemically released from the magnetic nanorod. The gold segments must be in the rod to protect nickel from the etching during dissolution of alumina template after electrodeposition, and also to prevent aggregation.<br />
<br />
====Making Single Crystal Nanowires====<br />
Single crystal nanowires can be made by Vapor-Liquid-Solid (VLS) synthesis, Supercritical Fluid-Liquid-Solid (SFLS) synthesis or by Pulsed laser deposition. <br />
<br />
*VLS Synthesis<br />
A catalyst droplet first melts on a substrate, then becomes saturated with precursors. Elements extrude out of the catalyst droplet as a single crystal nanowire in a furnace where the temperature is controlled to maintain liquid state of the catalyst droplet. Micrometer length with diameter less than 10 nm can be done. The diameter is controlled by the diameter of the catalyst droplet, and growth stops when the nanowire pass out of the hot zone, if the precursor is depleted or the catalyst droplet no longer is in liquid state. One example is to use laser ablation of Fe-Si target to evaporate the precursors and to create a Fe-Si nanocluster catalyst droplet. The Si nanowire grow with the (111) lattice planes perpendicular to the growth axis due to epitaxy at the nanocluster-nanowire interface. Doping can be done by controlling stoichiometry of the target, or by introducing dopant into gas phase during growth.<br />
<br />
*SFLS Synthesis<br />
Similar to VLS, but used for materials with a higher eutectic temperature. This technique increases the variety of available source materials. The solvent is pressurized above its critical point to reach higher temperatures. Can be applied to semiconductor/metal combinations (Ga/GaAs, In/InN) with eutectic temperature below 600 degrees. Au is used as catalytic seed, and diameter depends on this. <br />
<br />
*Pulsed laser deposition<br />
A high-power pulsed laser is used to ablate a target (pulsed laser ablation) in a vacuum chamber, meaning that the pulsed laser vaporizes small parts of the target for each pulse. This creates a plume of vaporized precursor material which is allowed to deposit as a thin film onto a substrate that is placed in the reaction chamber. When small catalyst particles are placed on the substrate, small single crystal nanowires can be grown. The diameter of the nanowires are determined by the diameter of the catalyst particles. <br />
<br />
====Nanowires branch out====<br />
Can create branched nanowires by VLS growth. The catalytic nanoclusters from solution placed on specific point on the body of a parent nanowire before growth. The process can be repeated for a hyper-branched construction. This could be the future development of nanowire electronics in 3D. <br />
<br />
====Quantum Size Effects (QSE)==== <br />
QSE appear when the particle size becomes smaller than the exciton size for the material (about 5 nm for silicon). Exciton is a bound state of an electron and an electron hole in an insulator or semiconductor, which is defined by the energy gap between the valence band and the conduction band. Color of the emitted light is determined by the size of gap energy. Gap energy increases with decreasing nanowire diameter. This can be used for LEDs and lasers. Both quantum confined nanoclusters and nanowires show QSE, but anisotropy make them different. Luminescent nanoclusters emits plane-polarized light, while nanorods exhibits linearly polarized light. <br />
<br />
====Alignment methods==== <br />
Alignment methods include electric field based alignment, microfluidic alignment and Langmuir-Blodgett technique. <br />
<br />
*Electric Field Based Alignment<br />
Apply voltage between two micropatterned electrodes to produce electric field. Charges within a nanowire in solution become polarized, creating an attraction between the electrodes and the nanowire. The electric field is quenched when the gap between the electrodes are bridged by a nanowire. This eliminates absorption of a second nanowire at the same electrodes. Metal spots can be evaporated onto insulator surface to focus the electric field.<br />
<br />
*Microfluidic Alignment <br />
A PDMS stamp with a series of parallel rectangular grooves is used for this purpose. The channels are aligned under a microscope with electrodes that have been previously patterned on a substrate (these will function as metal contacts for the conducting or semiconducting lines made by this method). A drop of nanowire suspension is flowed into the microchannels by capillary forces, and solvent evaporation aligns the wires at the edges of the channels. <br />
<br />
*Langmuir-Blodgett Technique<br />
A Langmuir film is created when hydrophobic molecules float on a water-air surface, and an aligned monolayer is formed at the interface when external film pressure is applied. The balance of surface tension forces determines the profile of the meniscus formed when a substrate is pushed into this liquid. If the substrate is hydrophobic it will experience deposition of the amphiphiles during immersion. If it is hydrophilic it will experience deposition during retraction. A nanowire array can be made by firstly compressing the interface to increase the surface density of nanowires (so they align parallel to each other), and then do a double dip. The second dip must be done so that the wires align normal to the previous once. It is important that the film pressure is mantained at a constant magnitude during the immersion.<br />
<br />
Application areas for these methods are in LED’s, transistors and in nanowire UV photodetectors. <br />
<br />
====LED====<br />
A LED can be made by assembling an n-doped and a p-doped semiconductor nanowire perpendicular to each other. This is done by [[TMT4320_-_Nanomaterialer#Alignment_methods|electric field based alignment]] with two electrode pairs aligned perpendicular to each other where voltage is applied to one pair at a time. They can also be assembled by using the microfluidic approach. When a potential is applied across the junction, light is emitted when electrons recombine with holes at the junction between the differently doped wires. Color of the emitted light depends on composition and condition of semiconducting material used. The LED can only conduct current in one direction. With positive voltage current flows. With negative voltage current is inhibited. The key for success is to achieve abrupt and uncontaminated junction between n- and p-doped wire. Efficiency can be improved by using core-shell-shell nanowire axial heterostructure. The greatest challenge is to make arrays of closely spaced junctions because the nanowires are so thin. This leads to the pitch problem, how to pack light sources into smallest possible area.<br />
<br />
====Transistors====<br />
A transistor can switch or amplify signals, and has three terminals (n-p-n). The n-type region attached to the negative end of the battery sends electrons into p-region, and the n-type region attached to the positive end slows the electrons down. The p-type region in the middle does both. Because of this, a depletion layer develops between the base and the emitter, and the base and the collector. The thickness of the layer is varied by the potential in each region. Active bipolar n-p-n transistor can be built from heavy and lightly n-doped nanowires crossing a common p-type wire base. <br />
<br />
====How can nanowire transistors be used as sensors?====<br />
Si nanowires are naturally coated with silica through VLS synthesis. This makes it easy for surface silanol groups to attach to the wire. If probe molecules are anchored to the surface silanols, highly sensitive real time electrically based sensors can be made. Low levels of chemical and biological species can be detected. Boron doped silicon nanowire is used as a FET. The wire is self assembled across electrodes (source and drain), and aminoethylsilane anchored to SiOH surface groups. The conductance of the wire changes with pH linearly due to protonation or deprotonation of the amine. An increase of the surface negative charge (deprotonation) attracts additional holes into the p-channel and the conductance is enhanced. The reverse action at low pH, an increase of surface positive charge causes protonation which repell holes from the channel. The conductance is decreased. Almost any type of molecule can be anchored to silica, so sensors can be designed to detect almost anything. For example, a biotin could be strapped to the surface amine groups to detect streptavidin. <br />
<br />
====Nanowire UV photodetector====<br />
The conductivity of ZnO nanowires is extremely sensitive to ultraviolet light exposure, which means that UV light can switch the nanowires between ON and OFF states. ZnO nanowires are highly insulating in the dark, but UV light with wavelength less than 380 nm decreases resistivity by 4 to 6 orders of magnitude. These nanowire photoconductors exhibit excellent wavelength selectivity. Green light (532nm) gives no response, while less intense UV light increases conductivity 4 orders. The response cut-off wavelength is at about 370 nm. <br />
<br />
====Simplifying complex nanowires====<br />
Complex oxides with superconducting, ferroelectric and ferromagnetic properties can not easily be made as nanowires by conventional methods. MgO nanowires must be used as templates. Firstly, single crystal orthogonal MgO nanowires are grown on single crystal MgO substrate. Oxygen is flowed over <math>Mg_3N_2</math> at 900 degrees as precursor for VLS, using Au catalyst. After the MgO nanowires have been made, the complex metal oxide is deposited by pulsed laser deposition to create a shell on the surface of MgO wires. Another approach to simplify complex nanowires is to use hydrothermal synthesis. This can be used to make <math>PbTiO_3</math> nanorods which is a ferroelectric material and potentially useful as building blocks in nanoelectrochemical systems. (Amorphous <math>PbTiO_{(3-X)}OH_{2X}</math> (mulig jeg rettet feil/misforstod?) precursor is mixed with sodium dodecyl benzene sulfonate surfactant and reacted at 48 h at 180 degrees at alkaline conditions in the presence of a substrate.) The nanorods obtained have a squared cross section 35-400 nm, and up to 5 um long. The rods grow in the (001) direction by self-assembly of nanocubes to anisotropic mesocrystals, which is ripened into nanorods.<br />
<br />
====Electrospinning====<br />
Electrospinning is nanofiber extrusion in a capillary jet. A polymer solution or polymer sol-gel pass through a high voltage metal capillary to create a thin charged stream. The stream undergoes stretching, bending and solvent evaporation. The charged nanofibers are driven to ground electrodes. The dimensions of the fibers depend on solvent viscosity, conductivity, surface tension and precursor concentration. The collector electrodes can be patterned to make organized arrays between them by electrostatic self assembly. The electrodes can be grounded simultaneously or sequentially. This can be used to make single layer or multilayer nanowire architectures. <br />
<br />
====Hollow nanofibers by electrospinning==== <br />
Hollow nanofibers can be made by co-axial double capillary electrospinning that creates heavy mineral oil core with inorganic polymer around (Ti and PVP). The core-shell nanofibers are collected on an aluminum or silicon substrate and hydrolyzed. The oily core can be extracted with octane, which creates nanotubes with amorphous <math>TiO_2</math> + PVP. To crystallize <math>TiO_2</math> and oxidate PVP, the tubes can be calcined in air at 500 degrees.<br />
<br />
====Dual electrospinning====<br />
A side by side spinneret can be used to make bicomponent fibers. Ex: two solutions containing <math>TiO_2</math>/<math>SnO_2</math> are simultaneously jetted. This is calcined. A heterojunction of <math>SnO_2</math>/<math>TiO_2</math> can create devices with extremely high quantum efficiency and photocatalytic activity for treatment of organic pollutants in water and air. <br />
<br />
====Dette mangler:====<br />
* Carbon nanotubes (sections 5.41, 5.42, 5.44, 5.45-5.48 and lecture notes)<br />
** What are carbon nanotubes? Be able to describe the three different structures they can have and how their properties are different.<br />
** Be able to describe briefly (basic principles) at least two of the three main methods used to synthesize carbon nanotubes<br />
*** Arc discharge<br />
*** Laser ablation<br />
*** CVD<br />
** How can the different structure nanotubes be separated from each other and from other carbon particles.<br />
** Be able to say something about their properties<br />
*** Mechanical<br />
*** Electrical<br />
*** Chemical<br />
** Know some about carbon nanotube chemistry (reactivity on the surface vs the ends etc.)<br />
** Aligning of carbon nanotubes<br />
*** Evaporation induced self-assembly<br />
*** Patterned hydrophilic SAM on substrate – carbon nanotubes will assemble only on the hydrophilic patches.<br />
*** Alignment by pre-existing patterns<br />
**** Perpendicular to substrate<br />
**** Parallel to substrate<br />
*** AC/DC electric fields<br />
** Applications of carbon nanotubes<br />
*** Sensors<br />
*** Strengthening of materials (composites)<br />
*** Added to materials to improve conductivity<br />
<br />
=== Kapittel 6: Nanocluster Self-Assembly ===<br />
<br />
<br />
====Capped nanoclusters====<br />
<br />
A capped nanocluster is a nanometer scale particle with well-defined positions of the constituent atoms. They nucleate from atoms and enter a size range where they behave electronically as molecular nanoclusters. As the number of atoms increases further, they cross over into the nanoscale size domain where quantum size effects dominate, they become quantum dots. A capped nanocluster has a monolayer of a capping ligand on the surface, which can be a polymer or an alkane thiol (if the surface is silver or gold) or some other molecule with an end group that will bind to the surface of the nanocluster. The capping molecules will prevent further growth of the nanocluster. Capping groups serve multiple purposes:<br />
*Change solubility properties<br />
*Enable size-selective crystallization<br />
*Surface functionalization<br />
*Protect nanoclusters from luminescence or charge-carrier quenching<br />
<br />
====General principles for synthesis of capped nanoclusters (arrested nucleation and growth)====<br />
<br />
One general synthesis method is the arrested nucleation and growth synthesis. The basic idea is to rapidly create a large number of nucleated seeds (of desired materials) and then allow these to grow at the same rate below supersaturation conditions. This method can be described by the following steps: <br />
* Desired precursors are added to a solution containing a proper capping agent, which is held at an intermediate temperature (200-400 °C depending on the materials. Temperature needs to be high enough to overcome the activation energy for the reaction.). <br />
* Precursors need to be added at an amount that is over the saturation point for the materials in that specific solution. <br />
* Materials will rapidly nucleate (precipitate) and start growing. Once the first molecules have reacted and created a small seed, the energy required for further growth is smaller than the initial activation energy. The nucleated seed can therefore continue to grow below the saturation concentration for the precursor materials. <br />
* Once the nanoclusters reach a certain size range, which may vary from one material to the other, the capping agents will adsorb on the surface of the nanoclusters and prevent further growth. The nanoclusters that are formed will not all have the same diameter, but a range of different diameter clusters will be formed. This can be due to for example concentration gradients in the reactor or reaction medium.<br />
<br />
====Minimize size dispersity by confining the reaction space====<br />
<br />
The size of the capped nanoclusters can be controlled by growing them in nanowells made by the methode in figure x. The nanowells are obtained by patterning a silicon wafer with a layer of well-ordered microspheres. By pressing the microspheres against a the wafer and at the same time melt the surface of the wafer with a pulsed laser molten silicon will flow into the voids between the spheres. The size of the nanowells depend on the size of the spheres, the energy density of the laser pulse and applied mechanical pressure, while the size of the crystals depend on the well volume and concentration of the reactants. The crystals can be removed by ultrasound. The downside of the approach is that the amount of nanocrystals obtained will be quiet small. <br />
<br />
====Tuning properties through physical dimensions rather than chemical composition (QSE)====<br />
<br />
When electrons are confined in space the size invariant continuum of electronic states of bulk matter transformes into size dependent discrete electronic states in a quantum dot. At the 1-5 nm length scale, which is the CdSe nanocluster size range, the parent continuous electron bands of the bulk semiconductor becomes discrete. The nanoclusters then belong to the quantum size regime, and the properties begin to scale in a predictable fashion with size. By looking at the Schrödinger wave equation it can be seen that there is a blue quantum size effect shift in the energy of the first exciton band or band gap that scales with the reciprocal of the square of the radius of the nanocluster. The wavelengths absorbed change, and the colors of the nanoclusters can be alterd from yellow to red, by changing the physical size of the clusters<br />
<br />
====How can different phases occur for smaller size particles?====<br />
<br />
Similar to temperature and pressure, phase transformations in bulk materials are dependent on size. Phase transitions that are prohibited or slowed down by activation energies in the bulk can occur much more readily in nanocrystals of same material. Because of the small size of the crystal the influence of bulk and surface-free energies are different from in a bulk matter. Phase transformations show a distinct dependence on nanocrystal size. It can be shown that phase of nanoclusters can change just by exposing them to a different chemical environment at room temperature.<br />
<br />
====Makeing nanoclusters water soluble====<br />
<br />
Why? Water is cheap, widely available and use of it avoides the disposal o organic solvents, which can be quiet harmful for the environment. (Green chemistry). You can use the same principles as for the SAM surface chemistry. A hydrophilic SAM is made by choosing a hydrophilic group such as a carboxylate, ammonium or oligo ethylene glycol. In the case of a gold nanocluster, a thiol with a terminal carboxyl group gives an ionized, water loving carboxylate when in aqueous solution. Hydrophobic nanoclusters can be wrapped by amphiphilic polyers. The polymer coating is stabilized by partially cross linking the anhydride gropuos with bis(6-aminohexyl)amine. Can also coat with silica. Often, the resulting crystals bear a surface charge, which allows their use in electrostatic layer-by-layer deposition.<br />
<br />
====Separation of nanoclusters by size using using a non-solvent and centrifugation====<br />
<br />
Nanoclusters can be dissolved in toluene and by gradually adding a non-solvent (e.g. acetone) the nanoclusters will precipitate. The largest clusters precipitate first. Every time a bit of acetone is added the solution is centrifuged and the precipitate collected. The result is highly monodisperse nanoclusters collected in each fraction.<br />
<br />
====Superlattice====<br />
<br />
A superlattice is a material with periodically alternating layers of several substances. Such structures possess periodicity both on the scale of each layer's crystal lattice and on the scale of the alternating layers.<br />
<br />
====Assembling of superlattices====<br />
<br />
A superlattice can be assembled by means of these techniques: <br />
*Tri-layer solvent diffusion crystallization - Three immiscible solvents are arranged to form separate layers in a test tube. Bottom layer →capped CdSe nanoclusters dissolved in toluene. Middle layer →buffer layer of 2-propanol selected for poor solvent properties wrt the nanoclusters. Top layer →non-solvent for the nanoclusters such as methanol. The process involves slow diffusion of the nanoclusters from the toluene bottom layer and the methanol from the top layer into the buffer layer. The change in solvent properties causes a slow and controlled nucleation and growth of capped CdSe nanocluster crystals.<br />
*Sedimentation – <br />
*Evaporation induced self-assembly – Strong capillary forces in an evaporating water meniscus drives the nanocomponents into close-packing.<br />
*Langmuir-Blodgett – A dilute monolayer of capped silver nanoclusters is spread on an air-water interface. Using Langmuir – Blodgett “equipment”, this monolayer can gradually be compressed until a compact monolayer is formed. <br />
<br />
<br />
<br />
====Gjenstår====<br />
<br />
*Why do we want to make superlattices? (change of properties, properties of superlattice does not necessarily equal the sum of the properties of the individual constituents)How can capping agents (different type and length) affect the properties of a superstructure? (section 6.15)Alloying core-shell nanoclusters<br />
<br />
* Nanocluster-polymer composites<br />
** What is it?<br />
** How can it be used for down-conversion of light?<br />
* Be able to give one or two examples of how different size nanoclusters labeled with different fluorescent molecules can be used in biology.<br />
* What is a tetrapod and what is the main priciples of the synthesis behind the tetrapod?<br />
** Using a material that has two common crystal polymorphs where growth of one over the other can be controlled by synthesis temperature.<br />
** Use of a long chain molecule which selectively binds to specific facets of the structure and hinders growth in those directions. This confines the growth of the material to one spatial dimension.<br />
* Photochromic metal nanoclusters (section 6.31)<br />
** Be able to explain what happens to silver nanoclusters embedded in a titania matrix when it is exposed to either UV-light or visible light.<br />
* What is a buckyball and what can it be used for? What special properties does it exhibit? (Do not need to know specific details of synthesis or assembly techniques.)<br />
<br />
<br />
=== Kapittel 7: Microspheres – Colors from the Beaker ===<br />
<br />
<br />
Nå ferdig med så mye som forfatteren greide, men finn gjerne ut resten og del det med alle!<br />
<br />
<br />
====What is a photonic crystal (PC)? ====<br />
*It is a crystal consisting of a material with high dielectric contrast and periodicity at the light scale<br />
*Wavelengths of light that are allowed to travel are known as modes, and groups of allowed modes form bands. Disallowed bands of wavelengths are called photonic band gaps (PBG).<br />
*Vullums definition: Natural gratings that diffract light are based on dielectric lattices with periodicity at optical wavelengths. 3D optical diffraction gratings have dielectric lattices that are geometrically complimentary.<br />
*1D PC (planes) is a crystal which only inhibit light to travel in one direction<br />
*2D PC (rods) inhibits light to travel in two directions<br />
*3D PC (spheres) inhibits litght to travel in any direction and has a full photonic band gap, whilst 1D and 2D only have so called stopgaps<br />
<br />
====Photonic Crystal defects====<br />
*Point defects: Holes, missing spheres, in a 3D PC can trap light inside the crystal <br />
*Line defects: Many holes which make a line can guide light through a crystal<br />
*Plane defects: A missing plane or a defect in a plane can make photons slip through to the other side. Planes consisting of another type of material can cause the perfect reflection curve of a PBG-crystal to drop at certain wavelengths depending on the size of the defect.<br />
<br />
<br />
====Making defects==== <br />
*Writing defects: Multiphoton laser writing using a confocal optical microscope induced polymerization of an organic monomer in the colloidal crystal to create small line inside the photonic lattice. Then you treat the crystal and remove the polymer. In reversed opal structures you can use laser microwriting where you attach a laser to a scanning optical microscope which again changes the phase (which again changes the refractive index) of the inverse opal by annealing.<br />
*Synthesizing planar defects: Introducing a dense layer or a layer with spheres of a different size than the surrounding colloidal crystal. Dense layers can be introduced by either CVD, electrolyte LbL, PDMS-stamps or maybe another deposition technique. The process consists of growing a photonic crystal, then using electrolyte LbL-deposition or PDMS-stamp make a thin film before making another photonic crystal. It's like a sandwich.<br />
<br />
<br />
====Manipulating photonic crystals usage==== <br />
*Color of the structure is partially determined by the size of its spheres, where small spheres give blue/purple colors and larger spheres goes towards red (from yellow to green and then red).<br />
*Non-close-packed polymerized colloidal crystalline arrays can be made to swell or shrink by external influence. As the diffraction colors of the crystal depend on the spacing between microspheres you can place a hydrogel between the spheres and this gel will swell or shrink depending on external environments. This will make the color change when the gel shrinks or swells as the pH, temperature, water concentration or ionic strength changes.<br />
*The dielectric constant can be changed by changing the material, the structure of the crystal ''or something else that others edit in here''<br />
*An example: Removal of cation causes a hydrogel to shrink, which can be detected at even very small concentrations. The order of cation complexation determines how sensitive the sensor is. Cation selectively binds covalently to the polymer network, sol-gel or hydrogel.<br />
<br />
<br />
====Core-corona, core-shell-corona and multi-shell microspheres====<br />
Core-corona and core-shell-corona can be made by both re-growth and one stage growth as multishell microspheres probably is better off being made by the re-growth process. The purpose of making these spheres is to put a lot more functionalities into just one sphere. The shells can be fluorescent, magnetic , photoactive, semiconductive, sacrificial or something else pulled out of a hat.<br />
<br />
<br />
====Growth synthesis==== <br />
*One stage: Reagents are mixed and the microspheres are obtained in solution by a nucleation and growth<br />
*Re-growth: First a sees is produced. The seed is then allowed to grow in several steps. Surface tension controls the shape, where low surface tension gives spherical particles.<br />
<br />
<br />
====Self assembly of photonic crystals==== <br />
*Sedimentation (be able to explain in more detail): Use Stokes equation to make the radius as you want it by changing the viscosity very slowly. Let the spheres sink to the bottom and assemble, where the viscosity of the liquid decides the speed(?) '''Fill in some more...'''<br />
*Electrophoresis '''– noen som veit?'''<br />
*Hydrodynamic shear '''– same ballpark as LB-LbL or EISA?'''<br />
*Spin coating '''– noen som veit?'''<br />
*Langmuir-Blodgett layer-by-layer (be able to explain in more detail) '''– as other L-B-techniques?'''<br />
*Parallel plate confinement: Force spheres to assemble by placing them between two parallel plates and slowly moving one plate closer to the other. Important with slow movement to prevent defects. This can be done both dry and in fluid. It is necessary to increase density and viscosity of solvent so that settling occurs slowly in order to control structure and shape, and to avoid defects.<br />
*Evaporation induced self-assembly, EISA (be able to explain in more detail) Capillary forces drive the assembly of spheres in a solution as you remove a wetting plate out of the solution. These the need to be dried and this can cause cracking. Vertical substrate is placed in a dispersion of microspheres. As solvent evaporates, the microspheres are driven by convective forces (forces from movement in solvent towards wall, surface, water meniscus) to the solvent-air meniscus. The layer thickness is determined by the diameter of the microspheres, their volume, concentration and the wetting properties of the solvent on the substrate.<br />
<br />
====Colloidal aggregates==== <br />
*CA are made either by templated pattern in a surface or by aggregation in a homogeneous emulsion.<br />
Emulsion-way:<br />
*They are disperse microspheres in a solvent such as toulene.<br />
*Add dispersion to solution of surfactant and water<br />
*Stir or shake to get emulsion<br />
*Toulene evapourates and as toulene droplets shrink, microspheres are pulled together in a stable cluster through capillary forces.<br />
Photonic crystal marbles:<br />
*Aqueous dispersion of microspheres is forced, under pressure, through a small syringe in the presence of an electric field. Surface charge on the liquid jet make it break into homogeneously sized spherical particles. Each droplet (sphere) contains a preset quantity of microspheres.<br />
*Electrospraying - '''noen forslag?'''<br />
<br />
<br />
====Bragg-Snell law==== <br />
*The reflected light has a wavelength depending on Bragg's and Snell's law. This then tells us that the wavelength of the first stop band is proportional to distance between the lattice plains. This gives that the longer the distance between the plains (bigger microspheres) gives longer wavelength.<br />
<math>\lambda_{c(hkl)} = 2d_{hkl}\sqrt{\langle \epsilon \rangle - sin^2{\theta}} </math><br />
der <math>\langle \epsilon \rangle</math> is the effective dielectric constant of the colloidal crystal.<br />
<br />
<br />
====Cracking====<br />
This happens when the thin hydration layers around the crystal spheres dry out. This creates capillary stress and thermal expansion. To prevent cracking you can dry the crystal slowly, use hydrophobic spheres. Methods for preventing this is:<br />
*<math>SiCl_4</math> reacting within the hydration layer to create a <math>SiO_2</math> layer between the spheres. Rehydrate to form multiple layers. Advantages as good control of layer thickness as it can be controlled/monitores by optical diffraction as a thicker layer res-shifts the diffraction peak.<br />
*Necking at room temperature using vapor phase alternating chemical reactions<br />
*Heat treatment before assembly. This may require pretreatment before assembly to give desired surface charges. Redeisperse and crystallize without volume contraction<br />
<br />
<br />
====Liquid crystal photonic crystal==== <br />
A liquid crystal is neither a liquid nor a crystal, but an intermediate state of matter, so called mesophase. Lacks the long range order of the crystalline state and does not exhibit the randomness of the liquid state.<br />
*Themotropics are liquid crystals which consists of melted anisotropical shapes (rods or discs) where they ar partially alligned. The order of the components in the liquid crystal is determined and changed bu the temperature. <br />
*Two groups of thermotropics are ''nematic'', where the molecules have no positional order, but they have a long-range orientational order, and ''discotic'', which consists of disc-shaped particles that can orient in a layer-like fashion.<br />
*By applying electric- and/or magnetic fields the small crystals in the liquid will align after the applied fields and this can control the refractive index of the film or whatever you have made out of this liquid crystal. Electric/magnetic fields or temperature changes can make it go from nearly transparent to reflective. Eksample of usage is privacy/smart windows.<br />
*By filling the voids in an inverse opal photonic crystal with liquid crystal we make what's called a Liquid Crystal Photonic Crystal. (LCPC) Applying a field or changing the temperature makes the refractive index of the liquid crystal inside the voids change. This means that other wavelengths will satisfy Bragg's criterion, which in practice means that the color of the LCPC changes (you alter the stop band frequency) See [[TMT4320_-_Nanomaterialer#Bragg-Snell_law | Bragg-Snell law]].<br />
*LCPC is thought to be used as tunable photonic crystal device and liquid crystal-colloidal crystal switch.<br />
<br />
=== Reactions that you need to know: ===<br />
* Reaction of alkane thiolate with gold. Important to know that alkane thiols have a specific affinity for gold (also keep in mind that silver and gold have very similar properties).<br />
* Reaction that occurs when during anodic oxidation of Al to produce porous alumina membranes.<br />
* Reaction that occurs when silica microspheres are formed from Si(OEt)4 and water (section 7.9): <math>Si(OEt)_4 + 2H_2O \rightarrow SiO_2 + 4EtOH</math><br />
<br />
== Eksterne linker ==<br />
*[http://www.ntnu.no/portal/page/portal/ntnuno/AlleEmner?rootItemId=22934&selectedItemId=31007&emnekode=TMT4320 NTNUs fagbeskrivelse]<br />
*[http://www.ntnu.no/studieinformasjon/timeplan/h08/?emnekode=TMT4320-1&valg=emnekode&bokst= Timeplan Høst08]<br />
<br />
[[Kategori:Obligatoriske emner]]<br />
[[Kategori:Fag 5. semester]]<br />
[[Kategori:Fag]]</div>Kenrogerhttp://nanowiki.no/index.php?title=TMT4320_-_Nanomaterialer&diff=674TMT4320 - Nanomaterialer2008-12-12T14:57:26Z<p>Kenroger: </p>
<hr />
<div>{{Infobox<br />
|Fakta høst 2008<br />
|*Foreleser: Fride<br />
*Stud-ass: ?<br />
*Vurderingsform: Skriftlig eksamen<br />
*Eksamensdato: 18. desember<br />
}}<br />
<br />
{{Infobox<br />
|Øvingsopplegg høst 2008<br />
|* Antall godkjente: 6/12<br />
* Innleveringssted: Utenfor R7<br />
* Frist: Tirsdager 16:00 (?)<br />
}}<br />
<br />
== Kort om faget ==<br />
Emnet skal gi en innføring i grunnleggende kjemisk prinsipper for å lage nanomaterialer.<br />
<br />
Stikkord: "Self-assembled" monolag ([[SAM]]) og hvordan disse kan formes ved myk litografi og "dip pen" nanolitografi, syntese av tredimensjonale multilag strukturer. Tynne filmer ved kjemisk gassfase deponering. Syntese av nanopartikler, nanostaver, nanorør og nanoledninger. Våtkjemiske syntese av oksidbaserte nanomaterialer. "Self-asembly" av kolloidale mikrokuler til fotoniske krystaller, porøse nanomaterialer, blokk-kopolymere som nanomaterialer. "Self assembly" av store byggeblokker til funksjonelle anordninger.<br />
<br />
== Et lite kompendium i faget ==<br />
Her vil det etterhvert vokse fram et lite kompendium i faget. Dette følger i utgangspunktet pensumlista som gjelder for høsten 2008.<br />
<br />
===Chapter 2: Soft Lithography===<br />
====Self-assembled monolayers (SAMs)====<br />
*The typical example of a SAM is a layer of alkanethiols on a gold substrate. <br />
*The S-H bond is cleaved on the gold surface and an Au-S covalent bond is formed. <br />
*The alkanethiols are tilted off-axis from the normal. The angle depends on the gold surface. (30 °C for a {111} surface). <br />
*The end group on the alkanethiols can be tailored to achieve different monolayer properties.<br />
<br />
====PDMS stamp====<br />
* PDMS = PolyDiMethylSiloxane<br />
* A master (casting) of the stamp, with the desired pattern, is made with lithography. The master is silanized and made hydrophobic so removing the stamp becomes easier.<br />
* Liquid PDMS is then poured into the master, after which it is cured and a finished PDMS stamp is removed from the master.<br />
* The critical dimensions of the pattern are limited by the lithography techniques used, and for [[photolithography]] the wavelengths of the light used to expose the [[photoresist]] limits the dimensions. Typical CDs given are, for lateral dimensions within the range of 500nm-200µm, and for the height of patterns 200nm-20µm. <br />
* The PDMS stamp can be dipped in alkanethiol solutions (or solutions of other molecules, collectively known as "chemical ink") and be stamped onto surfaces<br />
* PDMS stamps work on both planar and curved surfaces<br />
* For the stamp to properly print a pattern onto a surface, the molecules need to adhere to the stamp from the solution, but needs to adhere more strongly to the surface to be printed on.<br />
<br />
====Hydrophilic / Hydrophobic stamps====<br />
* The endgroup/terminal group on the alkanethiols (or other molecules used) determine the properties of the monolayer<br />
* By introducing a wetability gradient or abrupt changes in wetability, different effects can be obtained<br />
** Square drops, by having checkerboard square patterns of hydrophobic/hydrophilic monolayers, and condensating a vapor onto the surface<br />
** Drops "running uphill" by having wetability gradients<br />
====Printing thin films====<br />
* As long as the adhesion between the chemical ink and the substrate is stronger than the adhesion between the ink and the stamp, printing thin films is no problem<br />
* Metal thin films can be evaporated onto the stamp (evaporation gives homogenous and directional coatings, not covering the side walls on the stamp) and printed onto a substrate that has been primed with a SAM with exposed thiol groups (adheres strongly to the metal layer)<br />
* This is a very gentle technique for metal film depositing, good for making contacts on fragile layers. Also good for making 3D stuctures by printing multiple layers.<br />
====Electrically conducting SAMS====<br />
* Electronic devices will always need to make electrical contact with SAMs<br />
* Other, less gentle methods of metal deposition than printing with PDMS stamps (sputtering, CVD, etc) can cause the metal layer to penetrate the SAM<br />
* Morale: Use stamps to deposit metals on SAMs!<br />
====Patterning by photocatalysis====<br />
* Photocatalysis is used to remove parts of a SAM (making patterns)<br />
* Titania can photocatalytically decompose organic molecules.<br />
* A quartz slide patterned with titanium dioxide in the required pattern is pressed against a wafer with the SAM on it. <br />
* The assembly is exposed to UV irradiation, triggering the degeneration of the (organic) SAM<br />
<br />
===Kapittel 3: Building layer-by-layer===<br />
''Gøran er på saken.''<br />
<br />
=== Kapittel 4: Nanocontact printing and writing ===<br />
<br />
''Dag H. jobber med kap.4''<br />
* Soft lithography and microcontact printing (sections 4.1-4.3 + lecture notes)<br />
** Explain basic principles and explain advantages and limitations.<br />
** Explain how a patterns printed with a PDMS stamp can be made smaller by manipulating the stamp or using other tricks.<br />
** Explain how the properties of the ink and the contact time (reactive spreading) can influence the size of the patterns.<br />
* Dip pen nanolithography<br />
** Be able to explain basic principles and give a couple of examples of what it can be used for (no need to know exact details of each example). Examples that are good to know are that you can write for example solutions that can be transformed into metals or metal oxides by post-treatments such as temperature.<br />
** Sol-gel DPN (section 4.10)<br />
** Enzyme DPN (section 4.15)<br />
** Electrostatic DPN (section 4.16)<br />
** Electrochemical DPN (section 4.17)<br />
* Whittling of nanostructures (section 4.19)<br />
** Only be able to explain basic principle<br />
* Nanoplotters and nanoblotters<br />
** What are these and what can they be used for?<br />
** Be able to explain basic principles.<br />
* Combinatorial libraries<br />
** Be able to explain the basic principle and how it is used to find new and improved materials.<br />
<br />
=== Kapittel 5: Nano-rod, nanotube, nanowire self-assembly ===<br />
* Templates for synthesis of nanorods<br />
** How to make Si and Al2O3 templates<br />
*** Straight pores vs modulated diameter pores.<br />
** Need to know basic principles behind both synthesis methods. Which parameters determine diameter, ordering, length etc?<br />
<br />
* How are these templates used to make nanorods and nanotubes<br />
** Complete filling gives nanorods – electrodepositionI (also called electroplating) and electroless depositionII. Be able to explain the synthesis route for these two methods.<br />
** Partial filling gives nanotubes – spontaneous wetting using sol-gel or grow layer-by-layer using CVD or ALD.<br />
** Modulated composition nanorods.<br />
* Magnetic nanorods (sections 5.7 and 5.8)<br />
** Explain how they assemble based on the geometry of the magnetic segment.<br />
** Explain how magnetic nanorods can be used to separate specific molecules from a solution.<br />
* Be able to explain how you can make nanorods with both axial and radial composition profiles. Which methods can be used? Also be able to explain how nanorods with a radial composition profile can be used to make nanotubes.<br />
* Single crystal nanowires<br />
** Synthesis methods<br />
*** VLS synthesis (section 5.15)<br />
*** SFLS synthesis (section 5.17)<br />
*** Pulsed laser deposition<br />
** How can you make them branch out?<br />
** Nanowire quantum size effects (section 5.18)<br />
** Alignment methods<br />
*** Electric field based alignment<br />
*** Microfluidic approach<br />
*** Langmuir-Blodgett<br />
** How can you get the nanowires to grow in ordered arrays either parallel or perpendicular to the substrate? (Identical to methods used for carbon nanotubes)<br />
** Application areas<br />
*** LED – be able to explain briefly how to make a nanowire LED and what the important factors are to make a good quality device.<br />
*** Transistors – be able to explain briefly how you can make a simple transistor and how it can be used as a sensor by exploiting adsorption dependent conductivity.<br />
*** Nanowire UV photodetector (section 5.35)<br />
* Simplifying complex nanowires (section 5.36 and lecture notes)<br />
** Template method<br />
** Hydrothermal synthesis<br />
* Electrospinning (sections 5.39, 5.40 and lecture notes)<br />
* Carbon nanotubes (sections 5.41, 5.42, 5.44, 5.45-5.48 and lecture notes)<br />
** What are carbon nanotubes? Be able to describe the three different structures they can have and how their properties are different.<br />
** Be able to describe briefly (basic principles) at least two of the three main methods used to synthesize carbon nanotubes<br />
*** Arc discharge<br />
*** Laser ablation<br />
*** CVD<br />
** How can the different structure nanotubes be separated from each other and from other carbon particles.<br />
** Be able to say something about their properties<br />
*** Mechanical<br />
*** Electrical<br />
*** Chemical<br />
** Know some about carbon nanotube chemistry (reactivity on the surface vs the ends etc.)<br />
** Aligning of carbon nanotubes<br />
*** Evaporation induced self-assembly<br />
*** Patterned hydrophilic SAM on substrate – carbon nanotubes will assemble only on the hydrophilic patches.<br />
*** Alignment by pre-existing patterns<br />
**** Perpendicular to substrate<br />
**** Parallel to substrate<br />
*** AC/DC electric fields<br />
** Applications of carbon nanotubes<br />
*** Sensors<br />
*** Strengthening of materials (composites)<br />
*** Added to materials to improve conductivity<br />
<br />
=== Kapittel 6: Nanocluster Self-Assembly ===<br />
* What is a capped nanocluster? What does it mean that it is capped?<br />
* Be able to explain general principles for synthesis of capped nanoclusters (arrested nucleation and growth). How would you explain the synthesis from the nucleation process to the final capped nanocluster? What type of chemicals (i.e. capping agents, surfactants and precursors) are needed? Do not need to know specific names of chemicals, only whether it’s a capping agent, a surfactant, complexing agent etc. and what the purpose of these different chemicals are.<br />
* How can you minimize size dispersity by confining the reaction space? (section 6.6)<br />
* Be able to explain how you can tune properties through physical dimensions rather than chemical composition (quantum size effects).<br />
* Be able to explain briefly how different phases can occur for smaller size particles, similar to temperature and pressure dependent phase transformations in bulk materials. (section 6.8)<br />
* Need to know how to make nanoclusters water soluble. (section 6.13)<br />
* How can nanoclusters be separated by size using a non-solvent and centrifugation?<br />
* What is a superlattice, how can it be assembled and why do we want to make superlattices? (change of properties, properties of superlattice does not necessarily equal the sum of the properties of the individual constituents)<br />
** Assembly techniques include tri-layer solvent diffusion crystallization, sedimentation, evaporation induced self-assembly, and Langmuir-Blodgett technique.<br />
** How can capping agents (different type and length) affect the properties of a superstructure? (section 6.15)<br />
** Alloying core-shell nanoclusters<br />
* Nanocluster-polymer composites<br />
** What is it?<br />
** How can it be used for down-conversion of light?<br />
* Be able to give one or two examples of how different size nanoclusters labeled with different fluorescent molecules can be used in biology.<br />
* What is a tetrapod and what is the main priciples of the synthesis behind the tetrapod?<br />
** Using a material that has two common crystal polymorphs where growth of one over the other can be controlled by synthesis temperature.<br />
** Use of a long chain molecule which selectively binds to specific facets of the structure and hinders growth in those directions. This confines the growth of the material to one spatial dimension.<br />
* Photochromic metal nanoclusters (section 6.31)<br />
** Be able to explain what happens to silver nanoclusters embedded in a titania matrix when it is exposed to either UV-light or visible light.<br />
* What is a buckyball and what can it be used for? What special properties does it exhibit? (Do not need to know specific details of synthesis or assembly techniques.)<br />
<br />
=== Kapittel 7: Microspheres – Colors from the Beaker ===<br />
* What is a photonic crystal (combination of high dielectric contrast and periodicity at the light scale)<br />
** 1 dimensional<br />
** 2 dimensional<br />
** 3 dimensional<br />
* Be able to explain how photonic crystals can be used to confine and guide light by the controlled synthesis of different defects<br />
** Point defects<br />
** Line defects<br />
** Plane defects<br />
* Be able to explain at least two different methods used to induce defects in a material<br />
** Writing defects<br />
** Synthesizing planar defects by introducing a dense layer or a layer with spheres of a different size than the surrounding colloidal crystal.<br />
* Be able to explain how you can tune the color by changing size of the structure and changing dielectric contrast. What happens if the spheres are embedded in a shrinkable and swellable matrix? How can this be used as a sensor to detect different cations?<br />
* What are core-corona, core-shell-corona and multi-shell microspheres, how can you make them and what is the purpose of making these spheres?<br />
* Know the differences between one-stage and re-growth synthesis.<br />
* Know what the basic principles of self assembly are. Be able to name and explain the following self-assembly techniques for microspheres<br />
** Sedimentation (be able to explain in more detail)<br />
** Electrophoresis<br />
** Hydrodynamic shear<br />
** Spin coating<br />
** Langmuir-Blodgett layer-by-layer (be able to explain in more detail)<br />
** Parallel plate confinement<br />
** Evaporation induced self-assembly (be able to explain in more detail)<br />
* What are colloidal aggregates? Need to be able to explain different techniques for manufacturing different shapes of these, such as template confinement, aggregation in homogeneous emulsion, and electrospraying.<br />
* Need to know that the basic principle behind optical quality of colloidal crystals is based both on Bragg’s law of diffraction and Snell’s law of reflection. Need to be able to understand and explain how the color of the diffracted light changes with the distance between lattice plains.<br />
* Cracking: Why do colloidal crystal films crack and what can you do to prevent it? Need to be able to explain briefly one or two methods of how you can stabilize a colloidal crystal lattice without causing cracking.<br />
* What is a liquid crystal photonic crystal? How can the colors of such a crystal be altered and what can it be used for?<br />
Reactions that you need to know:<br />
* Reaction of alkane thiolate with gold. Important to know that alkane thiols have a specific affinity for gold (also keep in mind that silver and gold have very similar properties).<br />
* Reaction that occurs when during anodic oxidation of Al to produce porous alumina membranes.<br />
* Reaction that occurs when silica microspheres are formed from Si(OEt)4 and water (section 7.9).<br />
<br />
== Eksterne linker ==<br />
*[http://www.ntnu.no/portal/page/portal/ntnuno/AlleEmner?rootItemId=22934&selectedItemId=31007&emnekode=TMT4320 NTNUs fagbeskrivelse]<br />
*[http://www.ntnu.no/studieinformasjon/timeplan/h08/?emnekode=TMT4320-1&valg=emnekode&bokst= Timeplan Høst08]<br />
<br />
[[Kategori:Obligatoriske emner]]<br />
[[Kategori:Fag 5. semester]]<br />
[[Kategori:Fag]]</div>Kenrogerhttp://nanowiki.no/index.php?title=TMT4320_-_Nanomaterialer&diff=668TMT4320 - Nanomaterialer2008-12-12T08:40:01Z<p>Kenroger: </p>
<hr />
<div>{{Infobox<br />
|Fakta høst 2008<br />
|*Foreleser: Fride<br />
*Stud-ass: ?<br />
*Vurderingsform: Skriftlig eksamen<br />
*Eksamensdato: 18. desember<br />
}}<br />
<br />
{{Infobox<br />
|Øvingsopplegg høst 2008<br />
|* Antall godkjente: 6/12<br />
* Innleveringssted: Utenfor R7<br />
* Frist: Tirsdager 16:00 (?)<br />
}}<br />
<br />
== Kort om faget ==<br />
Emnet skal gi en innføring i grunnleggende kjemisk prinsipper for å lage nanomaterialer.<br />
<br />
Stikkord: "Self-assembled" monolag ([[SAM]]) og hvordan disse kan formes ved myk litografi og "dip pen" nanolitografi, syntese av tredimensjonale multilag strukturer. Tynne filmer ved kjemisk gassfase deponering. Syntese av nanopartikler, nanostaver, nanorør og nanoledninger. Våtkjemiske syntese av oksidbaserte nanomaterialer. "Self-asembly" av kolloidale mikrokuler til fotoniske krystaller, porøse nanomaterialer, blokk-kopolymere som nanomaterialer. "Self assembly" av store byggeblokker til funksjonelle anordninger.<br />
<br />
== Et lite kompendium i faget ==<br />
Her vil det etterhvert vokse fram et lite kompendium i faget. Dette følger i utgangspunktet pensumlista som gjelder for høsten 2008.<br />
<br />
===Chapter 2: Soft Lithography===<br />
====Self-assembled monolayers (SAMs)====<br />
*The typical example of a SAM is a layer of alkanethiols on a gold substrate. <br />
*The S-H bond is cleaved on the gold surface and an Au-S covalent bond is formed. <br />
*The alkanethiols are tilted off-axis from the normal. The angle depends on the gold surface. (30 °C for a {111} surface). <br />
*The end group on the alkanethiols can be tailored to achieve different monolayer properties.<br />
<br />
====PDMS stamp====<br />
* PDMS = PolyDiMethylSiloxane<br />
* A master (casting) of the stamp, with the desired pattern, is made with lithography. The master is silanized and made hydrophobic so removing the stamp becomes easier.<br />
* Liquid PDMS is then poured into the master, after which it is cured and a finished PDMS stamp is removed from the master.<br />
* The critical dimensions of the pattern are limited by the lithography techniques used, and for [[photolithography]] the wavelengths of the light used to expose the [[photoresist]] limits the dimensions. Typical CDs given are, for lateral dimensions within the range of 500nm-200µm, and for the height of patterns 200nm-20µm. <br />
* The PDMS stamp can be dipped in alkanethiol solutions (or solutions of other molecules, collectively known as "chemical ink") and be stamped onto surfaces<br />
* PDMS stamps work on both planar and curved surfaces<br />
* For the stamp to properly print a pattern onto a surface, the molecules need to adhere to the stamp from the solution, but needs to adhere more strongly to the surface to be printed on.<br />
<br />
====Hydrophilic / Hydrophobic stamps====<br />
* The endgroup/terminal group on the alkanethiols (or other molecules used) determine the properties of the monolayer<br />
* By introducing a wetability gradient or abrupt changes in wetability, different effects can be obtained<br />
** Square drops, by having checkerboard square patterns of hydrophobic/hydrophilic monolayers, and condensating a vapor onto the surface<br />
** Drops "running uphill" by having wetability gradients<br />
====Printing thin films====<br />
* As long as the adhesion between the chemical ink and the substrate is stronger than the adhesion between the ink and the stamp, printing thin films is no problem<br />
* Metal thin films can be evaporated onto the stamp (evaporation gives homogenous and directional coatings, not covering the side walls on the stamp) and printed onto a substrate that has been primed with a SAM with exposed thiol groups (adheres strongly to the metal layer)<br />
* This is a very gentle technique for metal film depositing, good for making contacts on fragile layers. Also good for making 3D stuctures by printing multiple layers.<br />
====Electrically conducting SAMS====<br />
* Electronic devices will always need to make electrical contact with SAMs<br />
* Other, less gentle methods of metal deposition than printing with PDMS stamps (sputtering, CVD, etc) can cause the metal layer to penetrate the SAM<br />
* Morale: Use stamps to deposit metals on SAMs!<br />
====Patterning by photocatalysis====<br />
* Photocatalysis is used to remove parts of a SAM (making patterns)<br />
* Titania can photocatalytically decompose organic molecules.<br />
* A quartz slide patterned with titanium dioxide in the required pattern is pressed against a wafer with the SAM on it. <br />
* The assembly is exposed to UV irradiation, triggering the degeneration of the (organic) SAM<br />
<br />
===Kapittel 3: Building layer-by-layer===<br />
''Gøran er på saken.''<br />
<br />
=== Kapittel 4: Nanocontact printing and writing ===<br />
* Soft lithography and microcontact printing (sections 4.1-4.3 + lecture notes)<br />
** Explain basic principles and explain advantages and limitations.<br />
** Explain how a patterns printed with a PDMS stamp can be made smaller by manipulating the stamp or using other tricks.<br />
** Explain how the properties of the ink and the contact time (reactive spreading) can influence the size of the patterns.<br />
* Dip pen nanolithography<br />
** Be able to explain basic principles and give a couple of examples of what it can be used for (no need to know exact details of each example). Examples that are good to know are that you can write for example solutions that can be transformed into metals or metal oxides by post-treatments such as temperature.<br />
** Sol-gel DPN (section 4.10)<br />
** Enzyme DPN (section 4.15)<br />
** Electrostatic DPN (section 4.16)<br />
** Electrochemical DPN (section 4.17)<br />
* Whittling of nanostructures (section 4.18)<br />
** Only be able to explain basic principle<br />
* Nanoplotters and nanoblotters<br />
** What are these and what can they be used for?<br />
** Be able to explain basic principles.<br />
* Combinatorial libraries<br />
** Be able to explain the basic principle and how it is used to find new and improved materials.<br />
<br />
=== Kapittel 5: Nano-rod, nanotube, nanowire self-assembly ===<br />
* Templates for synthesis of nanorods<br />
** How to make Si and Al2O3 templates<br />
*** Straight pores vs modulated diameter pores.<br />
** Need to know basic principles behind both synthesis methods. Which parameters determine diameter, ordering, length etc?<br />
<br />
* How are these templates used to make nanorods and nanotubes<br />
** Complete filling gives nanorods – electrodepositionI (also called electroplating) and electroless depositionII. Be able to explain the synthesis route for these two methods.<br />
** Partial filling gives nanotubes – spontaneous wetting using sol-gel or grow layer-by-layer using CVD or ALD.<br />
** Modulated composition nanorods.<br />
* Magnetic nanorods (sections 5.7 and 5.8)<br />
** Explain how they assemble based on the geometry of the magnetic segment.<br />
** Explain how magnetic nanorods can be used to separate specific molecules from a solution.<br />
* Be able to explain how you can make nanorods with both axial and radial composition profiles. Which methods can be used? Also be able to explain how nanorods with a radial composition profile can be used to make nanotubes.<br />
* Single crystal nanowires<br />
** Synthesis methods<br />
*** VLS synthesis (section 5.15)<br />
*** SFLS synthesis (section 5.17)<br />
*** Pulsed laser deposition<br />
** How can you make them branch out?<br />
** Nanowire quantum size effects (section 5.18)<br />
** Alignment methods<br />
*** Electric field based alignment<br />
*** Microfluidic approach<br />
*** Langmuir-Blodgett<br />
** How can you get the nanowires to grow in ordered arrays either parallel or perpendicular to the substrate? (Identical to methods used for carbon nanotubes)<br />
** Application areas<br />
*** LED – be able to explain briefly how to make a nanowire LED and what the important factors are to make a good quality device.<br />
*** Transistors – be able to explain briefly how you can make a simple transistor and how it can be used as a sensor by exploiting adsorption dependent conductivity.<br />
*** Nanowire UV photodetector (section 5.35)<br />
* Simplifying complex nanowires (section 5.36 and lecture notes)<br />
** Template method<br />
** Hydrothermal synthesis<br />
* Electrospinning (sections 5.39, 5.40 and lecture notes)<br />
* Carbon nanotubes (sections 5.41, 5.42, 5.44, 5.45-5.48 and lecture notes)<br />
** What are carbon nanotubes? Be able to describe the three different structures they can have and how their properties are different.<br />
** Be able to describe briefly (basic principles) at least two of the three main methods used to synthesize carbon nanotubes<br />
*** Arc discharge<br />
*** Laser ablation<br />
*** CVD<br />
** How can the different structure nanotubes be separated from each other and from other carbon particles.<br />
** Be able to say something about their properties<br />
*** Mechanical<br />
*** Electrical<br />
*** Chemical<br />
** Know some about carbon nanotube chemistry (reactivity on the surface vs the ends etc.)<br />
** Aligning of carbon nanotubes<br />
*** Evaporation induced self-assembly<br />
*** Patterned hydrophilic SAM on substrate – carbon nanotubes will assemble only on the hydrophilic patches.<br />
*** Alignment by pre-existing patterns<br />
**** Perpendicular to substrate<br />
**** Parallel to substrate<br />
*** AC/DC electric fields<br />
** Applications of carbon nanotubes<br />
*** Sensors<br />
*** Strengthening of materials (composites)<br />
*** Added to materials to improve conductivity<br />
<br />
=== Kapittel 6: Nanocluster Self-Assembly ===<br />
* What is a capped nanocluster? What does it mean that it is capped?<br />
* Be able to explain general principles for synthesis of capped nanoclusters (arrested nucleation and growth). How would you explain the synthesis from the nucleation process to the final capped nanocluster? What type of chemicals (i.e. capping agents, surfactants and precursors) are needed? Do not need to know specific names of chemicals, only whether it’s a capping agent, a surfactant, complexing agent etc. and what the purpose of these different chemicals are.<br />
* How can you minimize size dispersity by confining the reaction space? (section 6.6)<br />
* Be able to explain how you can tune properties through physical dimensions rather than chemical composition (quantum size effects).<br />
* Be able to explain briefly how different phases can occur for smaller size particles, similar to temperature and pressure dependent phase transformations in bulk materials. (section 6.8)<br />
* Need to know how to make nanoclusters water soluble. (section 6.13)<br />
* How can nanoclusters be separated by size using a non-solvent and centrifugation?<br />
* What is a superlattice, how can it be assembled and why do we want to make superlattices? (change of properties, properties of superlattice does not necessarily equal the sum of the properties of the individual constituents)<br />
** Assembly techniques include tri-layer solvent diffusion crystallization, sedimentation, evaporation induced self-assembly, and Langmuir-Blodgett technique.<br />
** How can capping agents (different type and length) affect the properties of a superstructure? (section 6.15)<br />
** Alloying core-shell nanoclusters<br />
* Nanocluster-polymer composites<br />
** What is it?<br />
** How can it be used for down-conversion of light?<br />
* Be able to give one or two examples of how different size nanoclusters labeled with different fluorescent molecules can be used in biology.<br />
* What is a tetrapod and what is the main priciples of the synthesis behind the tetrapod?<br />
** Using a material that has two common crystal polymorphs where growth of one over the other can be controlled by synthesis temperature.<br />
** Use of a long chain molecule which selectively binds to specific facets of the structure and hinders growth in those directions. This confines the growth of the material to one spatial dimension.<br />
* Photochromic metal nanoclusters (section 6.31)<br />
** Be able to explain what happens to silver nanoclusters embedded in a titania matrix when it is exposed to either UV-light or visible light.<br />
* What is a buckyball and what can it be used for? What special properties does it exhibit? (Do not need to know specific details of synthesis or assembly techniques.)<br />
<br />
=== Kapittel 7: Microspheres – Colors from the Beaker ===<br />
* What is a photonic crystal (combination of high dielectric contrast and periodicity at the light scale)<br />
** 1 dimensional<br />
** 2 dimensional<br />
** 3 dimensional<br />
* Be able to explain how photonic crystals can be used to confine and guide light by the controlled synthesis of different defects<br />
** Point defects<br />
** Line defects<br />
** Plane defects<br />
* Be able to explain at least two different methods used to induce defects in a material<br />
** Writing defects<br />
** Synthesizing planar defects by introducing a dense layer or a layer with spheres of a different size than the surrounding colloidal crystal.<br />
* Be able to explain how you can tune the color by changing size of the structure and changing dielectric contrast. What happens if the spheres are embedded in a shrinkable and swellable matrix? How can this be used as a sensor to detect different cations?<br />
* What are core-corona, core-shell-corona and multi-shell microspheres, how can you make them and what is the purpose of making these spheres?<br />
* Know the differences between one-stage and re-growth synthesis.<br />
* Know what the basic principles of self assembly are. Be able to name and explain the following self-assembly techniques for microspheres<br />
** Sedimentation (be able to explain in more detail)<br />
** Electrophoresis<br />
** Hydrodynamic shear<br />
** Spin coating<br />
** Langmuir-Blodgett layer-by-layer (be able to explain in more detail)<br />
** Parallel plate confinement<br />
** Evaporation induced self-assembly (be able to explain in more detail)<br />
* What are colloidal aggregates? Need to be able to explain different techniques for manufacturing different shapes of these, such as template confinement, aggregation in homogeneous emulsion, and electrospraying.<br />
* Need to know that the basic principle behind optical quality of colloidal crystals is based both on Bragg’s law of diffraction and Snell’s law of reflection. Need to be able to understand and explain how the color of the diffracted light changes with the distance between lattice plains.<br />
* Cracking: Why do colloidal crystal films crack and what can you do to prevent it? Need to be able to explain briefly one or two methods of how you can stabilize a colloidal crystal lattice without causing cracking.<br />
* What is a liquid crystal photonic crystal? How can the colors of such a crystal be altered and what can it be used for?<br />
Reactions that you need to know:<br />
* Reaction of alkane thiolate with gold. Important to know that alkane thiols have a specific affinity for gold (also keep in mind that silver and gold have very similar properties).<br />
* Reaction that occurs when during anodic oxidation of Al to produce porous alumina membranes.<br />
* Reaction that occurs when silica microspheres are formed from Si(OEt)4 and water (section 7.9).<br />
<br />
== Eksterne linker ==<br />
*[http://www.ntnu.no/portal/page/portal/ntnuno/AlleEmner?rootItemId=22934&selectedItemId=31007&emnekode=TMT4320 NTNUs fagbeskrivelse]<br />
*[http://www.ntnu.no/studieinformasjon/timeplan/h08/?emnekode=TMT4320-1&valg=emnekode&bokst= Timeplan Høst08]<br />
<br />
[[Kategori:Obligatoriske emner]]<br />
[[Kategori:Fag 5. semester]]<br />
[[Kategori:Fag]]</div>Kenrogerhttp://nanowiki.no/index.php?title=University_of_Waterloo_(UW)&diff=275University of Waterloo (UW)2008-10-06T20:26:24Z<p>Kenroger: </p>
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<div>{{Infobox<br />
|Fakta<br />
|*'''Land:''' Canada<br />
*'''Beliggenhet:''' Waterloo, ON<br />
*'''Studenter:''' 35000<br />
*'''Nettsted:''' [http://uwaterloo.ca/ University of Waterloo]<br />
}}<br />
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[https://www.intersek.ntnu.no/letsgo/FMPro?-db=letsgo.fp5&-format=record%5fdetail.htm&-lay=internet%20database&-op=cn&university%20name=Waterloo&-max=20&-recid=32795&-find= Litt generell informasjon].<br />
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