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Thin Films and Nanotechnology - Science topic

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Questions related to Thin Films and Nanotechnology
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I am currently trying to emulate a process known as Glancing Angle Deposition (GLAD) by manufacturing sculptured thin films of different compositions of alloy. I am just wondering has anyone else tried to do this to form an array of nanostructures on either a seeded or unseeded substrate.
I am using DC Sputtering (PVD) and would like to know what base pressures the chamber should be at. then what differential pressure the chamber should be at during the Argon flow (i.e the Argon pressure) and what throw distance should be used between the target material and substrate.
Any suggestions are very welcome; as I can quickly change the set-up of my equipment to investigate any augmentations to my current set-up.
Regards,
Christopher Quinn
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First of all, the way that a film grows on a substrate depends on the material (i mean growth type, like layer-by-layer, island formation or stranski-crastanov). maybe you can drive the deposition to the result you want by calculating the effective area of the sputtered material...let's say that the deposition at the edges of the plasma plume (let me call it this way) is way too different to the centre. Different kinetic energy and a lot different deposition rate (leading to different relaxation time and diffusion).
As it has to do with gold and gallium, they are two different materials with different catalytic properties. I think that's why using Ga leads to unsuccessful growth.
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I am working on dilute magnetic semiconductors, cobalt doped ZnO prepared using sol gel spin coating method. when I use DMF (dimethylformamide) as solvent , I get easily dissolving up to 15% without heating and without any stabilizer. Is there any way that I could use DMF as solvent instead of traditional ethanols? And can I use my thin film samples to study them for magnetic characterization?
I have not seen any paper reporting magnetism with DMF as far as my survey is concerned, only with methoxyethanol.
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Indeed the solubility of zinc acetate in ethanol is low, and it increses gradually with the addition of water. I do not think there is any restriction of water addition for the synthesis of DMS (speially for Co-doped ZnO). The magnetic behavour of the sample should not change substantially on adding water in the sol.
On the other hand, fabrication of metal oxide NPs using DMF as solvent has been demostrated by Prof. Diaz´s group (Prof. David Diaz, Facultad de Quimica, UNAM, Mexico; e-mail: david.nanochemist@gmail.com). However, selection of solvant affects the grain size, and the final size of NPs (in case of coolidal samples). The princpal reason for using a particular solvent for thin film fabrication (using sol-gel technique) is to adjust the viscocity of the gel.
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I need to know what substitution site for Co2+ in ZnO is good for magnetism in Cobalt doped ZnO thin films. Also, please suggest how to get that preferred site occupation for Co2+ in ZnO?
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ZnO can be crystallized into two crystal phases, namely : hexagonal (wurtzite, C6V-symmetry) and cubic (zinc blende, Td-symmetry). In both cases, the Zn and oxide are tetragonal. Cobalt relate to the transition elements with unfilled 3d-electron shell. He have such electron configuration s2d7. Zinc did not relate to the transition elements since its have fulled 3d-electron shell. Its electron configuration is s2d10. However, both Zn and Co are two positive charged in ZnO (Zn2+). Thus, Co2+ replace Zn2+. Such replacement is very favorable since the ionic radii both elements are same (0.74 A).
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Can anyone please help me to select a proper organosilane combination or titanates with inorganic nanoparticles which will form thin film (monomolecular) on glass surface in short time span and at room temperature. It is important that there is no effect on its optical transparency and that it cures at room temperature.
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Superhydrophilic is quite easy, just treat the glass with O2 plasma. However, you cannot make a surface "super"hydrophobic just by coating with an organosilane, you need to create a texture like the lotus leaf. To hydrophobize you can use either alkyl-chlorosilanes (better trichlorosilanes) or perfluoroalkyl-trichlorosilanes.
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NaClO3 has cubic structure (P213 (n.198) space group). NaClO3 crystals can possess the left or right symmetry.
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You won't be able to recognise left or right NaClO3 by XRD as this crystallise in a non polar space group meaning to impossible absolute structure determination.
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I used Zinc acetate dehydrate and cobalt nitrate as precursors, methanol as solvent and monoethanolamin as additive, the sol was refluxed for one hour at temperature around 60 degree of Celsius.
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Hi,
Blue color is due to tetrahedral Co2+ inside ZnO atom network. Pink color is due of octahedral Co2+
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Is there any online portal where I can upload the uv vis spectra and get the size statistics of nanoparticles?
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Hello Raj,
You can use Brus equation for this. It is quite simple, here: http://en.wikipedia.org/wiki/Brus_equation . In this page, the example is for CdSe, but there should be no problem to find correct parameters for CdS,
Just keep in mind that deltaEgap=Egap(nano)- Egap(bulk), and that Egap(nano) can be calculated from the onset of your absorption spectra as 1240/lambda(onset in nm). Hope this helps!
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I want to do XPS studies of TiO2 for surface analysis so what else i can get from the XPS studies
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Dear Colleague Burlu,
X-Ray photoelectron spectroscopy, XPS was used to investigate the chemistry at the surface of the samples. The basic mechanism behind an XPS instrument is that  the photons of a specific energy are used to excite the electronic states of atoms at and just below the surface of the sample.
There are several areas suited to measurement by XPS:
1. Elemental composition
2. Empirical formula determination
3. Chemical state
4. Electronic state
5. Binding energy
6. Layer thickness in the upper portion of surfaces
XPS has many advantages, such as  it is is good for identifying all but two elements, identifying the chemical state on surfaces, and is good with quantitative analysis. XPS is capable of detecting the difference in chemical state between samples. XPS is also able to differentiate between oxidations states of molecules.
XPS  has also some limitations, for instance, samples for XPS must be compatible with the ultra high vacuum environment.  XPS is limited to measurements of elements having atomic numbers of 3 or greater, making it unable to detect hydrogen or helium. XPS spectra also take a long time to obtain. The use of a monochromator can also reduce the time per experiment. 
Hope this helping
Have a very good day
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Argon and N2 are standard gases for BET surface area measurements for powders. For thin films adhered to the surface of a substrate such as silicon, however, the mass is below the threshold of the sensitivity of the device. Krypton, very expensive, has been shown to work for low sample masses. I would like to understand how the adsorption process is different for each that results in higher sensitivity. The literature mentions sublimation but to me that doesn't get at the core reason.
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Dear Michael,
The cross sectional area of Kr and N2 are 0.202 nm2 ans 0.162 nm2 respectively. Kr molecules are larger by about 25% and so, Kr should not be more suitable that N2 for the low specific surface area measurement. But… it is more suitable!
The reason of using Kr is due to its lower vapour pressure (267 Pa) compared to N2 (101325 Pa) at 77 K. The gas adsorption amount in the volumetric method is calculated from the difference between the number of dosed molecules and number of unadsorbed gas molecules at equilibrium pressure. In other words, by assuming both molecular sizes equal and adsorption pressure equal to 50 Pa, it is necessary to measure the pressure change of 0.16% (=50/30450) for N2 and 38% (=50/130) for Kr at the same relative pressure (P/Po=0.3, N2=30400Pa, Kr = 80Pa).
Obviously, it is easier to measure larger pressure change, and therefore, the accuracy of the measurement is better. For this reason, the lower the saturation vapour pressure at the adsorption measurement temperature, the more accurate the measurement of low surface areas and so Xe, with vapour pressure equal to 0.23 Pa at 77K, is still a better gas to measure low surface areas. Unfortunately, Xe is much more expensive than Kr…
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Thin film electrical characterization
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For dielectric (insulating) films in the ideal case, no current should flow when a voltage is applied. However, in real situations, a small current does flow, as detected by the I-V curve measurements. This current is the leakage current (without any corrections for extrinsic effects, such as those due to the electrodes, etc.) Leakage current is usually reported as a leakage current density (amps per centimeter squared), which is the current divided by the electrode area, at a given applied voltage (or electric field). So, all you have to do is divide by the electrode area and be sure to mention that the leakage current value is specified at a specific electric field value.
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Methods other than Ellipsometry to determine the refractive index of the film which varies with the depth profile.
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We use XRay Reflectometry under N2 flux to avoid water condensation (see http://onlinelibrary.wiley.com/doi/10.1002/smll.200800894/abstract; some links to basics in http://www.mendeley.com/tags/x+ray+reflectometry/). From here you can obtain film density then model the refractive index. Another very nice technique is ellipsometric porosimetry, see works by Mogilnikov and Boissiere.
Good luck!
G
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The samples are annealed in air or O2. Is the grey due to O2 vacancies? For the yellowish-brown or pinkish tint due to excessive O2 (O2 doped) as I see in some O2 annealed samples. Hope someone can help. Thanks.
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Colors are often difficult to explain. Of course oxygen vacancies may be the reason for the color. Use different oxygen partial pressures for the annealing and see if there is an effect.
Since it are nanostructured particles it may also be a size effect. From a certain size of the particles and, thus, from a certain number of the atoms building this particles the band gap scales with the particle size.
So it may be a good idea to search for a correlation between color and particle size.
You can eliminate contamination of your product? Doping of the material (starting materials, the material of the shuttle in which the powder is annealed and so on) of course can alter the band gap.
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Maybe tetraethylorthosilicate?
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Yes, I use tetraethylortosilicate (TEOS) dissolved in ethanol. In order the reaction to take place I put the solution for 12 h at 60 degree
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I want to prepare thin polymer films by spin coating technique. Therefore, I need flat substrates like Si wafers, mica, etc., e.g. those with negligible roughness in comparison to film thickness. I was wondering, if anyone has any suggestions for a suitable substrate of reasonable price. Thanks!
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i would say quarz glass. it is not very expensive, you may order wery thin one, its absorption and emission properties are known and /or easy to measure by yourself.It is not changing any properties of your material so you may measure everything up to 240nm ( int the 160-240 nm quarz glass absorbs) -this is for PL. For electrical properties, try to use quarz glass with ITO. It is eanugh that you will look for details in any OLED paper. they are all doing EL and electrical curves.
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Could anyone provide values or references to a protocol?
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Ya i have synthesized the ZrO2-TiO2 nanomaterial by sol-gel method. What u wanna know
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For example, increasing the thickness of the film causes a decrease in grain size, as a result of the increase in energy band gap.
So how does the grain size depends on energy band gap?
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Dear Jaymin Ray, Once grain size falls below ~100 nm, quantum effects manifest themselves. Small grains work as quantum wells, and bandgap depends on the grain size. Many examples available, look eg. fig. 5.4, p. 111, Nanophotonics and Nanofabrication. Edited by Motoichi Ohtsu, Copyright 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 978-3-527-32121-6 (just the first thing I got from the Web).
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I prepared MgO nano for use in removing dyes from water, but it needs many days to remove the dyes. How can I speed up the process of removal dye from wastewater using nano-MgO?
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Dear Mr. Afifi
First of all , let me explain for you the reson why your dyes did not completly Removed ( as you said )
MgO nano or bulck or even broader sence Metal Oxides nanostructures they do not remove dyes.
What they do simply is they Decompose them to small organic molecules or even smallar entities
Meal Oxide used as Photocatlyst to decompose dyes, in the Presence of Activating sorce of Light
For example if the metal Oxide absorbe below 400 nm then it only activated using the Ultra violet light
and if they absorb light beond 400 nm to the visible region they can be activated by Sun light and this is
the most important region since the sun is every where and free
Also, the above mentiond process can be accelarated in some cases by adding superoxide salts or even Hyderogen Peroxides
Good luck
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Which are the most important conditions in electrodeposition of ZnO?
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I think it has to do with the surface area where you deposit: 0-500 s might be formation of small nuclei growing from the sides of the pores to the inside (along diameter), 500-1000 s might be steady growth in the center of the pores (aong the length) and then 1000-1700 s might be the decrease in diameter of the pores (Whatman makes cigar-shaped pores). The increase after 1700 s looks like you completely filled your pores... If your curve can be explained like this, it's in agreement with what my colleage wrote in the paper "Microstructure development..."
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What is the benefit of FTIR (spectroscopy) test for semiconductor thin films and can we find out what kind of semiconductor we can test with it?
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hai it is basically to know what kind of functional groups and their bonding between individual elements present in the sample .u can characterize semiconducting thin films using FTIR for their optical properities such as transmittance,reflectance.etc.
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I need to clean glass flasks after synthesis. Usual liquid detergent does not work much.
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try chromic acid. sonicate after adding chromic acid and leave it undisturbed for a week
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I have synthesized the above nanocomposites but we are trying to know the magnetic properties and couldnt find any easiest method.
Please suggest some from your experience!
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You can defeinitely try a Vibrating sample magnetometer measurements for M v.s H or B v.s H curve. it would give you a hysteresis loop with saturation magnetization and coercivities and remnant magnetization values. this would be usually the basic properties one would like to understand before going ahead. Its available in IITM and one in Madras University also.
How many atoms has a copper nanoparticle of 1 nm?
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How can I assess the number of atoms in metallic nanoparticles with different sizes?
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I agree with the answer above. However, you can use Van Hardeveld and Hartogs publication (1969) on the statistics of metal nanoparticles. There you can estimate not only the total amount of atoms with nanoparticle size, but also the type of surface atoms present on the nanoparticle. Furthermore, you can do this for several different nanoparticle shapes which will make it much more accurate.
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I have a thin film of palladium acetate which when annealed at a high temperature should leave behind metallic palladium. However, I do not have a good way to verify whether what I get is metallic palladium or not? I have done UV-vis on the film but do not see any specific absorption/extinction.
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Carbon monoxyde and/or hydrogen adsorption are good techniques to determine quantity of mettalic atoms on a substrate. These techniques are common on catalysts characterization because the adsorption is seletive and happens only on metal state. Other way is benzene hydrogenation that is seletive too.
But, these techniques detects only the mettalic atoms that are available on surface of your film. So, I suggest MEV or MET to investigate the particles diameters. If you have only small particles very good, but for big ones you will have wrong results because of the hidden particles.
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In CBH, charge carriers hop from one hopping site to another on application of an external electric field. The energy required for a carrier to jump from one site to another is the polaron binding energy (thats my understanding. Any correction will be appreciated). Now I want to know if the ac conductivity will be higher for a material with higher polaron binding energy, or are they inversely proportional, or not related at all?
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Hello!
Thank you for attracting attention to this question. I think this will be quite interesting for those, who (like myself) have worked with hopping conduction mechanisms described by Efros, Shklovskii, Mott, Ionov, Shlimak, Pollak, and many-many-many others...
I have looked quickly through the papers [S.R. Elliot "A theory of AC conduction in chalcogenide glasses" // Philosophical Magazine Volume 36, Issue 6, 1977, page 1291 ] and [Samuel M. Soosen et al. "Samuel M. Soosen" // JAP 109, 113702 (2011)] and have the following ideas:
1. There are three energy scales considered by Elliot (see p. 1295-1296):
Wm - "the energy that would be required to take two electrons from the D(-) state to the continuum (the conduction band)"
W - "The potential barrier, over which carriers must hop (this is the random variable in the problem)."
E - the energy of excited levels, from which the hopping itself occurs.
From this I see that Wm is the best candidate for interpretation as a polaron binding energy (although this may be not in a strict sense).
The infer perfomed by Elliot leads to the expression for AC conductivity that depends on Wm in the following way: \sigma \prop Wm^{-6} (see Eq. (13) on page 1298).
2. The model presented in the above mentioned paper by Elliot seems to me to be too phenomenological. Very little considerations are performed ab initio. Probably, it can help in interpretation of some experimental results, but as soon as one needs to go deeper or to relate this model with other hopping conductivity models, one should develop the model itself.
3. I have just looked through the problem and do not know if there are some recent developments of this model.
best regards
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* XTEM will show the thickness of each layer. Is there any possible way of finding the approximate total thickness and thickness of each layer for an initial confirmation? The deposition has been done by pulsed laser deposition.
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Normally you have to cross techniques, as Andreas says, XRR and ellipso might be excellent, but model-dependent. I typically use cross section SEM or TEM to have an approximate idea and use these values as seeds for the ellipso and XRR calculations. XRR can be tricky if your low-density film is below your high-density one, ellipso does not have that limitation.
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I have read some papers
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Another way to look at this ... a surfactant lowers the surface tension at the interface between materials. Your nanoparticles can only grow bigger than a few tens of nanometers by successfully growing larger than their Kelvin barrier. This barrier is determined by the available surface energy and the radius of curvature of the particle. So when the particle is too small and doesn't have enough surface energy to exceed the Kelvin barrier, the low surface tension due to the high radius of curvature won't allow the particle to grow any larger. But if the particle successfully grows larger than the barrier, then the radius of curvature decreases, making a flatter particle with a larger radius, and the surface tension allows the particle to grow even larger into the mesoscopic domain.
The surfactant modulates the available surface energy of the particles so that the surface tension decreases, and the Kelvin barrier moves, allowing more particles to escape the aggregation process and generally lowering the mean particle size.
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Can one please tell me or give me the link to the mechanical properties of pure poly(acrylic acid). I made a bio composite film of chitin whiskers, poly(acrylic acid) (mw =2,000) and poly(ethyl glycol) at a constant ratio of PAA:PEG=7:3. I noticed that tensile stress at different % of chitin content (10-50%) were far below the pure chitin. What could be the possible explanation. I was expecting better properties. I also want to know the properties of pure PAA and pure PEG.
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You should do the SEM of the fractured samples. May be the whiskers are acting as a point of stress concentration in the matrix and consequently site of crack initiation leading to early fracture.
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Some literature describes nanorods as 1D and some other 2D? Can anyone explain?
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Nanorods are considered 1D dimensional materials.
One easy way to decide the dimension is to think how many sides of the structure are bigger than the others.
The dimension of nanomaterials can be summarizes as:
- 0D = espherical nanoparticles (all dimensions are the same and in the in the nanometric behavior)
- 1D = nanorods, etc (1 dimension bigger than the other 2)
- 2D = nanosheets, etc (2 dimensions bigger than the other 1)
- 3D = other nanomaterials
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By CVD or PVD processes
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Look up Zheng Yan et al., Growth of Bilayer Graphene on Insulating Substrates, ACS Nano 5, 10, pp 8187, 2011. Basically, graphene forms by CVD on both sides of a Nickel film, so deposit Nickel, do CVD and then remove the Nickel.
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I need to deposit a thin film of Tin (Sn) with grain size less than 300 nm.
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Hi! you need to vary the deposition variables. E.g, use low substrate temperature <300C and deposition time <1min. Optimising the substrate temperature, source temperature and deposition time or annealing the films should be helpful!
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I'm working on the oblique angle deposition of metals and I would like to quantify the density of the films deposited at different angles.
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Another simpler method (but not as accurate), weigh substrate prior to deposition, deposit film and reweigh. Subtract substrate mass, thus you now have mass of deposited film. Measure columnar height of structures on film using SEM, calculate the mass of a solid cubic volume using the columnal height as the thickness and using the density of the material calculate the mass of the solid volume. You now have a mass difference between the actual film and the calculated solid volume, you can use this to get a relatively accurate porosity value. My original method is more accurate though.
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Thin film technology
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Try Sol Gel Electro Spinning.
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Is there any literature which explains computation of refractive index etc from the ellipsometry data in a simple way?
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Dear Dr. Palakkandy,
Are you trying to perform point-by-point fitting? If so, the point-by-point method should be used with great caution. First of all, the correct initial model must be used for such direct data inversion, i.e., all other parameters, except the n&k values for the material under study, need to be known with high accuracy, otherwise those modeling errors can lead to unphysical dispersion or discontinuities in the optical constants. Moreover, existing measurement noise will be directly translated into extracted n&k values. In addition, the method does not enforce Kramers-Kronig (K-K) consistency between the real and imaginary part of the obtained optical constants (or, dielectric function) and, therefore, can result in unphysical shape of the (n,k)-curve in the considered spectral range.
Many analytical physics-based and Kramers-Kronig consistent expressions have been developed which describe various types of materials – amorphous and crystalline semiconductors and dielectrics, metals, organic films, optical metamaterials, etc. One of the first oscillator models, widely used for the optical modeling of metals and other conductive materials (for instance, indium tin oxide (ITO)), is simple phenomenological Drude–Lorentz (DL) oscillator model [for instance, see R.W. Collins, A.S. Ferlauto, Optical physics of materials, in: H.G. Tompkins, E.A. Irene (Eds.), Handbook of Ellipsometry, William Andrew Publishing/ Noyes, Norwich NY, 2005, p. 93]. Another well-known optical function parameterization has been developed by Forouhi and Bloomer for amorphous semiconductors and dielectrics [A.R. Forouhi, I. Bloomer, Optical dispersion relations for amorphous semiconductors and amorphous dielectrics, Phys. Rev. B 34 (1986) 7018] and later for crystalline materials [A.R. Forouhi, I. Bloomer, Optical properties of crystalline semiconductors and dielectrics, Phys. Rev. B 38 (1988) 1865]. Although the FB model fits satisfactory certain materials, in many cases it provides reasonable fit only in very limited spectral range or even yields unphysical results. Because of that some modifications of the original FB model have been derived by McGahan et al. [W.A. McGahan, T. Makovicka, J. Hale, J.A. Woollam, Modified Forouhi and Bloomer dispersion model for the optical constants of amorphous hydrogenated carbon thin films, Thin Solid Films 253 (1994) 57], Liu et al. [Y. Liu, G. Xu, C. Song, W. Weng, P. Du, G. Han, Modification on Forouhi and Bloomer model for the optical properties of amorphous silicon thin films, Thin Solid Films 515 (2007) 3910] and Laidani et al. [N. Laidani, R. Bartali, G. Gottardi, M. Anderle, P. Cheyssac, Optical absorption parameters of amorphous carbon films from Forouhi–Bloomer and Tauc–Lorentz models: a comparative study, J. Phys.: Condens. Matter 20 (2008) 015216]. More realistic Tauc-Lorentz (TL) and Cody-Lorentz (CL) parameterizations for the optical functions of amorphous materials have been proposed by Jellison and Modine [G.E. Jellison, Jr., F.A. Modine, Parameterization of the optical functions of amorphous materials in the interband region, Appl. Phys. Lett. 69 (1996) 371–373; Erratum: “Parameterization of the optical functions of amorphous materials in the interband region” [Appl. Phys. Lett. 69, 371 (1996)] idid. 69 (1996) 2137] and Ferlauto et al. [A.S. Ferlauto, G.M. Ferreira, J.M. Pearce, C.R. Wronski, R.W. Collins, X. Deng, G. Ganguly Analytical model for the optical functions of amorphous semiconductors from the near-infrared to ultraviolet: Applications in thin film photovoltaics, J. Appl. Phys. 92 (2002) 2424].
Those analytical models describes the imaginary part of the complex dielectric function and the real part of the dielectric function is obtained by the Kramers–Kronig integration, - therefore, those models are K-K consistent and can be used to fit the experimental data.
An alternative approach to express the dielectric function of the thin film is to use a parameterization by polynomial spline functions, which does not required any assumptions about the film properties and interaction of light with the material. Recently, Johs and Hale suggested a Kramers-Kronig consistent B-spline representation for the dielectric functions which has been successfully utilized to multiple applications [B. Johs, J.S. Hale, Dielectric function representation by B-splines, phys. status solidi (a) 205 (2008) 715]
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Thanks in advance.
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There are many methods for cleaning substrate materials. One method that many people use is to place the wafer in acetone and use ultrasonication for at least 15 minutes. Then, when the film is removed from the acetone, it should be IMMEDIATELY rinsed with ethanol and/or methanol and dried with a dry N2 gun, if possible. Compressed air can also be used for drying, but I think the N2 gun is better. When using this method, you must watch for residue left on the surface by the solvents - this can be an issue.
If you are using spin-coating, I would recommend "spin-cleaning." In this method, a few drops of a strong solvent (such as 2-methoxyethanol) are dropped onto the wafer using a syringe, and then the wafer is spun to remove the excess solvent and dried on a hot plate to remove any remaining organics. I like this method; however, make sure you are doing this in a fume hood as stronger solvents (like 2-methoxyethanol) are quite toxic.
There are many other methods out there, and the best one for you will depend on your deposition technique, materials, applications, etc.
Good luck!
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Usually you can use those studies indicated by Tejabhiram, but using a lower field, like 20 or 50 Oe (you can read a review that I wrote about superparamagnetism, 7. “Superparamagnetism and other magnetic features in granular materials: A review on ideal and real systems”, M. Knobel, W.C. Nunes, L. M. Socolovsky, E. De Biasi, J. M. Vargas, J. C. Denardin; Journal of Nanoscience and Nanotechnology 8 (2008) 2836–2857). But in your system, assess magnetism is not an easy task. First i will recommend a carefully inspection on the whole fabrication process, looking for possible sources of magnetic contamination. You will need a SQUID with RSO head to see if there is magnetism in your sample. Make your measurement at very low temperature.
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How should I prepare my samples in this case?
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Dear Gloria,
1.Basically RGO is in the form of colloidal form in-order to get the uniform film up to the single layer is possible by spin coating, controlling by RPM and time
2. Choose the appropriate substrate because RGO basically hydrophobic, you can use cronning glass, quartz even Si/SiO2 substrate.
I hope you get good morphology, quality films, since I have done.
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Thin film coating methods
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That depends on your application. We can study optical properties by Spectroscopic Ellipsometry, magnetic properties by VSM, we can see its structure with SEM and AFM and definitly XRD and so on...
What does stacking (transparent) thin layers of a metal oxide mean in terms of transparency ?
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So what happens if I stack those layers, let’s say with one layer thin glass between each layer of oxide ? Is it exactly as transparent as if I would leave out the glass layers (so then I just have a thick layer of the oxide) or is there a difference?
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if you stack number of thin layers or Multi layers when light passing through each layer experience change of medium and hence Refractive index so that you can get selective Transmission and Reflection. for example if you need 50 % Reflection and 50 % Transmission etc. of course that depends on application and material of interest.
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Is there any free software that can calculate optical constants from thin films reflect and/or transmetance spectra data in txt or excel files? My films are semi transparent with a unknown thickness but between 50nm and 2minron deposited on glass slides or metaliques substrates
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For people who can’t afford the software or have difficulty with the spreadsheet that was given I would recommend the papers by Swanepoel (which I think was briefly mentioned in an earlier post) The citations are listed below. The formulas can easily be used and put into a computer. They also allow you to vary your parameters and easily plot them on top of your experimental data. This is very useful to do at least once since it can give you a good intuition as to how your data changes with respect to varying a parameter in an intuitive way. Even more importantly, it can help understand the importance of scattering or surface roughness on your data and give you an idea of how much that impacts your measurement. Finally, you have to remember that the index and absorption is a function of wavelength and the Swanepoel formulas let you input dependencies in a natural way.
The other thing that is missing from the discussion is that depending on the nature of the material, that for measurements around the bandgap, one really should have some idea of the fundamental properties of the material. i.e. in GaN or ZnO the exciton can have a significant impact. For alloys of those materials alloy broadening can alter the spectra. Thus the dispersion can be changing rapidly.
For routine measurements where you know what you are depositing, the Swanepoel method should work pretty well.
Title: DETERMINATION OF THE THICKNESS AND OPTICAL-CONSTANTS OF AMORPHOUS-SILICON
Author(s): SWANEPOEL, R
Source: JOURNAL OF PHYSICS E-SCIENTIFIC INSTRUMENTS Volume: 16 Issue: 12 Pages: 1214-1222 DOI: 10.1088/0022-3735/16/12/023 Published: 1983
Times Cited: 1,850 (from Web of Science)
Title: DETERMINATION OF SURFACE-ROUGHNESS AND OPTICAL-CONSTANTS OF INHOMOGENEOUS AMORPHOUS-SILICON FILMS
Author(s): SWANEPOEL, R
Source: JOURNAL OF PHYSICS E-SCIENTIFIC INSTRUMENTS Volume: 17 Issue: 10 Pages: 896-903 DOI: 10.1088/0022-3735/17/10/023 Published: 1984
Times Cited: 372 (from Web of Science)
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My purpose to use them in STM analysis.
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Crystalline Si(111) substrates are available commercially. These substrate contains oxide layer on top of it. If you carry out standard cleaning procedure to remove the oxide layer from the top in an ultra high vacuum chamber, you will get Si (111)7x7 surface.
What is done in the standard substrate cleaning steps is as follows.
The Silicon substrate first cleaned in ultar high vacuum pressure (~10^ -10 mbar). Resistive heating at 400-500°C is done for two and half hour to decrease the resistivity of the Si substrate.
After completion of resistive heating, Direct Heating is done for degassing the substrate. This time current is passed through the Silicon substrate. By this direct heating the absorbed gases is degassed out of the substrate. This process continues for 14-16 hours during this time sample temperature is around 600 °C.
After keeping the sample at a temperature of around 600 °C for 14-16 hours, the sample temperature is swept to quickly 1100 -1200 °C for 60 second. This is called Sample Flashing. By sample flashing the top oxide layer on the surface of silicon substrate is removed. As the oxide layer is removed from the surface, it becomes clean silicon substrate with (111)1x1 surface.
Then it is again lowered at a temperature of around 850 °C for 30 minutes, cool it down to RT. During this time the silicon atom on the cleaved surface gets reconstructed to saturate the dangling bonds to lower the surface free energy.
Due to this rearrangement of atoms the unit cell of this reconstructed Si (111) surface becomes seven times larger than that of the bulk silicon (111)1x1 unit cell. So, we call this surface as Si(111)7×7 surface.
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I am working in the field of sensors and for that I need to monitor the change in resistance. Currently I am having the KD 106 LCR meter only, so with that I want to finish my work.
Otherwise tell me what other methods available to measure the resistance of thin film.
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Hi Dhivya,
Resitance measurement is pretty straight forward.
You can measure the resistance by just putting 4 contacts on your thin film sample. You can pass known current (I) through two outer contact leads and measure voltage (V) across middle two leads. Then, your sample sample resistance is just R = V/I.
If you don't have current source and voltmeter, you can make use of LCR meter itself. Just pass low frequency (less than 100kHz - this is to avoid the contribution from the impedance of the sample) current through two outer leads i.e., connect I+ and I- to outer leads, and measure voltage across the middle two leads i.e., connect V+ and V-. The in-phase component of impedance Z, i.e., X gives the resistance of your sample. If you use higher frequency, the value of R contains the contribution from Y i.e, out-of phase of component of Z. So, try to use low frequency for measurement.
Hope this helps.
Good Lcuk!
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There are several methods to measure and determine specific heat such as DSC, and calorimeter. How do you do it?
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You can find tens or even hundreds of papers on this; all standard methods such as DSC have been used. However, as your question indicates, this is not a trivial matter. First, one has to be extremely careful in preparation of the nanofluid to guarantee proper dispersion (by controlling the zeta potential by acidity or surfactants). Second, the experiment should not generate phase separation of the fluid and particle phases. It's conceivable that large thermal gradients might induce thermophoresis, as the particle size distribution functions can be relatively broad (this must be controlled by DLS or TEM).
I think a good practical guide is to use at least two different methods and make sure that the data are mutually consistent.
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I will be working with the Titanium etching and is going to use Hydrofluoric acid to etch, but now I wanted to replace it with some other etchant because of its hazardous nature. Can anyone suggest an Etchant which does not involve HF acid?
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I'm not sure an oxygen plasma would work on Ti. I think it would just form a TiO2 passivation layer. Oxygen plasma works on carbon substances because it forms CO or CO2 that can be pumped off.
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What in-depth physical attributes apply to the change in band gap, and is it related to grain size, or particle size?
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I would like to say about the bandgap, thickness and grain size of the THIN FILM. The grain size mainly depends on the film thickness and IN ADDITION OR in other words, chemical composition of the thin film is responsible for the grain size distribution. So, if the film’s composition is not varying with the film thickness, you will get a linear relation between the grain size and the film thickness. it may increases or decreases, but the band gap never changes in this case. If the composition changed with thickness, it will directly affect the material (thin film) band gap. Lastly, The grain size of the thin film affect the average transmission of the film, due to the scattering, but not affecting the energy band gap until the composition is not varying.
On the other hand, once grain size falls below ~100 nm, quantum effects manifest themselves. Small grains work as quantum wells, and bandgap depends on the grain size.
Many examples available, look eg. fig. 5.4, p. 111, Nanophotonics and Nanofabrication. Edited by Motoichi Ohtsu, Copyright 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 978-3-527-32121-6
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Why could the the grain size calculated by XRD be larger than the grain size calculate by UV-Vis method for the same sample?
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Grain size measurement by XRD is not an accurate determination of particle size because the formula used is assumed as there is no strain at all (Schrer fromula). For accurate particle size measurement use TEM.
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I am preparing a thin film of cadmium Sulfide (CdS) in powder form using the thermal evaporation technique (closed sublimation). I have problem in that
1) the films are not uniform and
2) some times my crystal monitors gives me readings of the progress of thin film thickness but when I open the chamber the films are blank.
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can i use the pallets or ingot of CdS cadmium sulfide for thermal evaporation ? i wants to take the film fo 1000 to 5000 arms strong. i had maintain the pressure 10-5 torr. source to substrate distance is 15 cm. and substrate temperature is room temp. but i already try for 50 to 150 degree centigrade.
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I am trying to bind gold nanoparticles to functionalized glass surfaces (optical fibers in particular) and the simple protocol I use works GREAT with 3-aminopropyltrimethoxysilanes, but fails regularly with 3-mercaptapropyltrimethoxysilane! The protocol is as follows:
Clean fibers in pirhana (30min)
Rinse with anhydrous ethanol.
Immerse in anhydrous ethanol, add MPTMS/APTMS at 1% by volume for 1 hour.
Remove and rinse with ethanol.
Store fibers in ethanol until use.
The weird part is I've had at least one trial where the MPTMS worked great. (I evaluate the efficacy by monitoring nanoparticles depositing on my fibers in realtime with UV-Vis). I am amenable to any suggestions and really have no idea why this protocol worked really great once, but mostly fails. I have tweaked most parameters such as immersion times, heating vs. non-heating etc.
It's really confusing to me why this doesn't work since the only difference in these molecules is the headgroup.
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In Addition, you should let hydrolyze your 2 % MPTS solution for 5 min prior to silanization. After Silanization, wash it with the same solvent, never with water! The Silane-layer is not stable before it is heat-polymerized. Cure it at 110 °C for 15 min. Wash then with water to remove non-stable Multi-Layers.
Good Luck!
By the way: Always use fresh silane solution, never store ist for more than one hour.
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I want to know the procedure of dip coating for the synthesis of tin oxide thin film
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What is the application? 10µm is very thick as mentioned.
You can do solgel from a precursor such as Tin tert-butoxide (Sn(OtBu)4), or possibly should look at electrodeposition if your substrate is conductive so you can deposit thick and highly crystalline layers quickly.
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Can anybody tell me the the influencing factors of preferred orientation, especially in aqueous solution?
Energy minimization? Kinetic factors? Or something else.
Can anybody recommend reviews or books about this problem?
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Microstructure of thin film deposited by sputtering: preferred growth and texture.
All these cosiderations refer to metallic thin film deposited in high vacuum. I do not have any specific experience on growing films fro acqueous solutions, but I think that these considerations hold true.
PREFERRED GROWTH
The microstructure of a thin fims can be evaluated by X-ray diffraction, e.g. using the Bragg-Brentano geometry. I find that in a poor vacuum all the diffraction peaks for a given system are present, i.e. the film is “powder like”, as reported for instance in the JCPDS files; even amorphous films can be obtained, if the vacuum is “bad” enough.
However, in a very good vacuum a ”preferred growth” is observed; in the extreme case only one family peak is present; for instance, only the (111) an (222) peaks are observed for f.c.c. elements, like Al or Au. This is due to the fact that the (111) oriented surface are the lower energy ones .
Very good vacuum means that the adatoms can migrate on the surface long enough to find their lower energy position before the arrival of another adatom I used the term “preferred growth” instead of the “preferred orientation” because the latter is an artefact experienced when preparing a sample by compactation of powder, and is caused by the relative arrangement of the various crystallites; by contrast the “preferred growth” has a pregnant physical meaning, as described above. The vacuum is “good” when thermodinamics dominates over kinetics: the probability of the growth of an already nucleated grain is larger than the probability of the nucleation of a new grain.
TEXTURE
Another characteristics of deposited thin films is the “texture”, i.e. the spatial distribution of the (hkl) directions; a partial – but significant enough – information on the film texture can be obtained in the B-B scheme by setting the detector at the 2 theta angle for the selected diffraction peak, and “rocking” the sample from zero to 2 theta. The angle between the (hkl) planes is different for different textures.
In one of my work I characterized a lot of Al films deposited by sputtering on different substrates and different systems. As already stated above, in a very clean deposition system, i.e. for a system with a very low base pressure, and used without exposing it to the atmosphere and hence with a very low partial pressure of un wanted contamination (like oxygen, water vapour, etc) the films exhibit for all the substrate a very pronounced “preferred growth” along the lower energy (111) surfaces. However, the texture was different for different substrates, even if deposited in the same batch or in sequence when dealing with a single wafer deposition system. In addition, differences were observed on the same substrate by changing the deposition temperature.
For instance, in Al films deposited on silicon dioxide substrate the (111) directions are distributed along a cone, whit an aperture of some 5-10 degrees; while for films deposited on TiN all the (111) directions are aligned along the sample normal, with a FWHM as low as 1° or less, of the same order of magnitude of the width of the slits used to obtain the rocking curve.
Why the nature af the substrate affect so much the deposited thin film structure? What is changing when the nature of the substrate is changed? Changing the substrate the film/substrate energy is changed.
When the film start to grow, grain to grain interfaces are formed, and grain/grain energies are born. At the surface-grain boundary three forces are acting: the ones related to the G1 (grain1)/G2 (grain2), and G1/substrate and G2/substrate interfaces energies. In addition there is the constraint of an already defined film/substrate interface shape, so these forces cannot modify the shape in order to approach the minimum energy configuration. As, for instance at the the free surface of the growing film, or – in a very differen world – on the skin of an old man.
What is then left to the growing film in order to make the condition in which a given flat shape of the film/substrate interface is as near as possible to the equilibrium one? The only way is to change the grain to grain energy. But how this can be obtained? Only by changing the angle between the (111) planes (for f.c.c. metals) in adiacent grains. That means by changing the thin film texture.
IN CONCLUSION:
PREFERRED GROWTH DEPENDS ON THE ENERGY OF THE DIFFERENT CRYSTALLITES, AND ON THE BALANCE BETWEEN THERMODINAMICS AND KINETICS.
TEXTURE DEPENDS ON THE FILM/SUBSTRATE INTERFACE ENERGY, AND CAN CHANGE BY CHANGINg THE SUBSTRATE NATURE AND DEPOSITION TEMPERATURE.
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What are the best materials for 3D Isotropic nanoCatalysts?
Can you suggest a reference to similar applications and source?
I need to study electrolysis using 3D Isotropic nano Catalysts.
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Maybe the following two books will help making your question a bit more specific:
1) catalysis and electrocatalysis at nanoparticulate surfaces, A. Wieckowski et al (Ed.), 2003
2) surface and nanomolecular catalysis, R. Richards (Ed.), 2006
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can any one please help in telling how to prepare colloidal TiO2 suspension for dye synthesized solar cells.
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You can use commercial powder of TiO2 (P25) and mix aqueous solvent. It is easy to get TiO2 suspension. Else you can start with Ti- precursor ( like iso propoxide or chloride etc) and obtain the colloidal solution.
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Hi everyone. I'm currently trying to link some I-V measurements obtained on my oxide thin films to a electrical conduction mechanism. It's been told to me that it can be donc quite easily, but I haven't been able to find any list/summary of such models. Another way to phrase my question would be : "Can we deduce (and if so, how) a conduction mechanism from I-V curves ?"
Any thought/comment would be highly welcome.
If my description is not precise enough, I'd try to give more details if it can help.
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Hi, You can think to make impedance measurements at different temperatures. The dependence of the conductance on frequency measurement and temperature allows you, more easily, to deduce the conduction mechanism through your sample. If possible, please specify your samples or structure.
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Dear All
Can any one explain the term Optical conductivity?
Thanks
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Optical conductivity is a powerful tool to measure electronic states of materials. Take a material sample. It can be graphene for example.Put it it an electric field. Electronic charges in it get redistributed-polarised in other words. Currents are induced. Fields small? Then induced polarization and currents are proportional to applied field. Experimentally one can measure optical reflectivity and deduce optical conductivity. Let me know if you want more details. CSS
What is sol gel method?
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dear researchers will any one of u plz tell me that What are the requirements in preparing yttrium vanadate using sol gel method?
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One has to search carefully for details.Here is one useful ref. Soft Chemistry Routes to Oxide Nanostructures by Joshua Furman PhD Thesis UCSB 2007 High aspect ratio nanostructures of conductive oxides were prepared through a two step route. V2O5−_ nanoscrolls were prepared by intercalating V2O5 with long chain primary amines such as dodecylamine. . If u give me your e-mail ID I can send the full file. CSS can send a file. The mixture was treated hydrothermally at 180_C for one day. This reaction formed nanoscrolls with a diameter of around 150nm and many microns long. These were then heated to 500_C for 2 h in flowing 5%H2:95%N2. X-ray diffraction shows a transformation from a lamellar vanadium oxide phase to crystalline monoclinic VO2. Thermodiffractometry shows that the metal-insulator transition known to be present in bulk VO2 at 68_C is also present in the reduced nanotubes. Nanoparticles of the oxide phosphor Y3Al5O12 doped with 2%Ce were prepared by emulsion synthesis. Metal nitrates were dispersed by sonicating in cyclohexane with sorbitan monooleate as a surfactant. The emulsions were refluxed for 2 days at 90_C followed by hydrolysis with tetraethylammonium hydroxide. These precipitates were then calcined in air at 1300_C for 2 h. Phosphors were also prepared by mixed oxides and molten salt synthesis methods, and were characterized using scanning electron microscopy, X-ray diffraction, and photoluminescence spectroscopy.
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There is a minimum energy requirement of substituting the host atom as compared to the interstitial position for the host atom. On which basis this is correct.
Plz explain it.
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If you're asking about the physical position of a host atom it's simply determined by the minimum (free) energy site.
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Hi! What thickness of the Cu shield layer is better to use in order to prevent the underlying thin structure from oxidation ?
I found somewhere that oxygen penetrates inside Cu films over the distance 20 - 25 nm ? Is it true ? Because i have a problem that 10 nm of Cu layer is not enough for preventing the rest of the layers from oxidation.
Thanks!
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It depends upon the way you deposit your Cu films as well. Sputtering is always a better way to deposit metals compared to evaporation. With sputtered 8-10 nm of Cu, it is enough to protect underlying layers.
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Hi everybody,
I hope all of them do their research effectively. I am beginners of thin film technology. I am doing research in Ferromagnetic shape memory alloy in thin film using sputtering method. I want to prepare free standing thin film, for these i didn't know which material is used as substrate and then how to separate the film from the substrate. If anyone knows please help me.
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I have worked with Ferromagnetic films for over 5 years, if you are wanting to create films for direct analysis using TEM, the simplest method we use is to grow the film on a cleaved piece of NaCl (Sodium-Chloride or Rock-salt). The salt can then be put into warm water where it dissolves and the film will float upon the water - a TEM grid can then be used to pick up the film and it is ready for analysis in your Transmission electron microscope.
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Dear All
Is there any difference between electrical band gap and optical band gap?
If so can we relate them?
Please answer
Thanks
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Well, it seems that Ilias Katsouras refers to organic materials (I don't know a lot about this kind of semiconductors). In the case of inorganic materials, direct optical band gap is ALWAYS greater than the electrical band gap. Electrical band gap is simply the difference between the top of the valence band, and the bottom of the conduction band. For the optical band gap, you need to know where the higher energetic electrons are in the valence band, and determine the energy they need to reach the lowest energy level AVAILABLE on the conduction band. As you can expect, usually the higher energetic electrons on the valence band are the top of this band. But, for the lowest energy level AVAILABLE on the conduction band, the history is different. Depending on the doping level and the band structure, you fill the bottom of the conduction band until a limit. This filling of the lowest energy levels at the conduction band is a constant for your doping level. Thus, if you supply any external energy (electric field or ligth illumination mainly), the excited electrons that could reach an unoccupied level at the conduction band need an energy HIGHER than the electrical band gap, because of the already occupied levels due to doping. This is the so called OPTICAL BAND GAP (because of the main effect related to this phenomena is the hopping of electrons due to the illumination). And there is a lot of theory behind the behavior of the optical band gap, and here it is not the place to discuss about. Dear Sriram Subramanian, as you're working on a subject that I'm working on more than a 25 years ago, I'll be glad to discuss on it if you like. The same goes on to Chandra Shekhar Prajapati (I've see that you're working on ZnO thin films).
any method to produce thin films from PVA/alginate complexes? or any other natural polymer or its complex with a synthetic polymer?
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I need to produce biodegradable thin films...any suggestions on the possible methods which would not alter the properties of the polymers?
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post a comment
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I have tried it but it didn't worked out. So, please help me to give me the synthesis of PbS thin film.
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I have done it by using lead acetate, thiourea and ammonia.
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How to prepare iron oxide nanopartcles by sol gel method?
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I understand that you planning for free-standing Nanoparticles of Iron Oxide . But it is important to note that Iron Oxide can be useful in form of Fe3O4 or Fe2O3 (alpha or gamma) either. It can be decided depending on your application.
Mostly starting Fe- precursor is deciding factor of the end product . Well iron oxide is much studied system and there are several good reports. It can be discussed further if needed. I already see some useful replies.
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I am depositing thin films on metal substrate such as nickel and copper. The films are very thin. I could not get thickness using cross sectional SEM. Please suggest way. Also how to check surface SEM of samples deposited on metal substrate.
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Another way to measure film thickness is Spectroscopic Ellipsometry. Especially, if you have Ni/Cu system it's quite easy, quick and non-destructive technique. But, i have to agree that the most accurate method is XRR.
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i am doing indium oxide thin film by resistive heat method.
now looking for a anti-reflection coating in VU region only.can anybody tell me, how i can get transmittance only in the visible region (ie,anti reflection coating in VU region) for indium oxide(not in ITO). from the deposition i got the transmittance till IR. for that what i have to do?
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2 options:
- absorb the UV as proposed by Amir : TiO2 is good because it is more transparent than ZnO (higher band-gap, ZnO can give you a yellowish coloration) and reflect the IR
- reflect UV and IR: again TiO2, or multiples layers TiO2/SiO2
in both case, you have to do intereferential optics simulation to adjust the thicknesses of each layer.
Is optics the only one function you need (for example, no need of protection ? I think In2O3 is sensible to humidity ? )
Choicie of the solution will also depend on your process, because it influences the possibility to have one material or the other, and the ability to control at +/- 1 nm the thickness or not .
I would recommand to specify: what is the precise spectra you want to reach (or which value of transmissivity in the different regions) ?
If you don't have done it yet: make the optical spectrum of your current films (transmissivity and reflectivity)
Depending on your deposition process: make the list of the materials available (among materials transparent in the visible, there shouldn't be that much)
use an interferential optics software to see the performances achievable with those materials, or combination of those as well as the thickness required.
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Hi!
If someone experienced in making substrate/Pb/Fe thin films let me know.
1)Ultrahigh vacuum system
2)Knutsen cell - Pb
3)e-beam source - Fe
MgO(100) substrate at room temperature.
there is no problem with Fe but with Pb
Problem : I've get the Isand like grow of Pb on Fe layer when I use ~6-8A/s rate (840 C of the Material) and a dirty film (RRR~2).
What is the optimal deposition conditions for Pb (40 nm) to avoid the island structure and make the film uniform ?Is there any sense to increase the deposition rate which should increase the epitaxy?
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I am agree with Pavel Leksin. You have to check the other parameters...............The film quality also depends upon the deposition rate.
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I am fabricating a thin film transistor using high-k dielectric material. I need easy steps to coat a thin film on the substrate.
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It depends on what variables you need to control in this process.
1) Is the film thickness of importance ?
2) Is the material a conductor, semi-conductor or insulator ?
3) Is the material or substrate susceptible to temperature variations (i.e. low melting point) ?
4) Is film flatness an issue ?
If you can answer these I can probably suggest a suitable method to do this.
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characterization of thin films
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What kind of semiconductor your material is (p or n type)?
What do you mean by saying "with the help of the same material "? A homo-junction? Usually a Scottky diode consists of a semiconductor, either a n- or a p-type and a metal. Depending on the relative magnitudes of the workl functions, the junction may be a diode of Ohmic in both directions.
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Can anyone guide me how to select Nano material for preparing a nano suspended particles with water as medium.
We need to basically study effect of electromagnetic field on water molecule in presence of suspended nano particles.
Thanks.
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As mentioned the particle size is important, one experiment I would suggest would be to study the difference between a nonmoving and a very slowly moving fluid (i.e. strongly laminar) with nanoparticulate. This is because the B-field component of your EM field can obviously do no work on the particles while the fluid is still. However with a moving fluid, the B-field can potentially polarize the particulate to a degree, as the flow combined with the B-field presents the opportunity to do work on the particles due to the Lorentz force, assuming the particles develop a charge in the E-field. By varying the flow with Reynolds numbers between zero and about 1000, you should be able to build up a profile of how the particles move in the EM field. Your measurement might include the voltage perpendicular to flow direction, which indicates the potential in the charge separation. If you have any questions, please feel free to contact me.
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I use vacuum 10-8mbar, e-beam gun and Knutsen heating ceel. What is the best solution for preparing Fe0,5Mn0,5 thin films (thickness about 5 nm). Is it right to prepare thin film with cross-deposition of Fe and Mn. Or it is better to deposit them right from one cell (e-beam ot Knutsen cell)? thank you. I beg a pardon for my english
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By making compound ingot or by co evaporation technique are the best solution for making thin films
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I Prepared a nano crystalline thin films but due to its high resistance i can not get conductivity. how i prepare a device from these thin films with a lower conductivity. please help me on this problem.
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I Prepared a nano crystalline thin films but due to its high resistance i can not get conductivity. how i prepare a device from these thin films with a lower conductivity. please help me on this problem.
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I Prepared a nano crystalline thin films but due to its high resistance i can not get conductivity. how i prepare a device from these thin films with a lower conductivity. please help me on this problem.
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You may anneal them and check again. But first, refer to the type of the thin films: e.g. metal oxides or else.....
Why colours changes at nanoscale?
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As we reach nanoscale, the color of nanoparticles go on changing depending upon their size. Why?
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Hi Deepali, It's because the energy bands. The color of a bulk material depends on its electrons that absorb photons energy, they are excited and finally go back to relaxation. The final energy is being released as photons and depends on the allowed states that electrons can be excited. So when they go back to their primary state they emit that energy as photons. When you have a bulk material, the energy levels are bands (because of the large amount of atoms inside the material). When you go to nanoscale, the bands become more finite and the specific energy that electrons are excited and relax changes. I don't know your physics level, but i'm sure that you can find some help in: http://wiki.answers.com/Q/Why_different_materials_have_different_colors and about energy bands in solids or free atoms in this pic: http://universe-review.ca/I13-03-energyband.jpg Hope i've helped you. For any other answer just feel free to ask.
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Does anyone have any experiments about growth of NiO nanowires using thermal evaporation method?
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Hi everybody
I have a good nanowires sample. I have done several characterizations for it. I can submit it to an ISI journal, but I want to submit it to a high impact journal. Therefore, I need to HRTEM. So, I am looking a researcher as collaborator who can do HRTEM for this sample. Everybody are interested for this collaboration please contact me by my email: yousefi.ramin@gmail.com
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I'm starting my research in catalytic thin films, deposited by magnetron sputtering. I would like to read your opinion about the materials can be used or any other thought about the subject...
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i'm thinking of single layer films and yes, i'm going to use Ti target, rf reactive magnetron sputterring with O abient gas
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How it can be prepared (with procedure)? Is it possible with the help of PECVD thin film of PbTe? Please, specifies with detail.
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Abhay,
R u working on PbTe thin film or any other thin film technique?
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I Have tried it but it will come out while touching
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With some experience on the hydrothermal synthesis of MoO3 and combustion synthesised Co3O4 films I feel that the secret of forming peelable oxide thin films has to do with the morphologies that develop on crystal growth. Just compare MoO3 with MoS2(which is a famous layered structure used as a lubricant). You would see the difficulty of making MoO3 by poor man's techniques. Ultimately it boils down to the strength of the Mo-O bond. CSS
How to prepare thin films of silver?
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I have tried using silver nitrate but didnt succeed.
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Silver films could be prepared by spray pyrolysis too. The conditions depend on the type of substrate and the thickness of the film that you want. I have done it with sputtering and with spray pyrolysis. If you want some collaboration, please let me know. Good luck!
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Im having trouble making a decent dispersion of graphene oxide (from a solution of 5mg/ml in ethanol or water) in THF diluted down to around .25mg/ml and casting a uniform film. The mixtures tend to settle upon centrifuging even as slow as 3K RPM
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Yeah im trying to avoid surfactants... Literature suggests that it should be easy. Im starting to worry that my sm is contaminated
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Has someone information on formation and growth of thin films polymerized acetylene, and some recommended article on the subject
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Its possible to obtain thin films of DLC from acetylene using dc magnetron technic see J, Libardi at sciencedirect " Comparative studies of the feed gas composition effects on the characteristics of DLC films deposited by magnetron sputtering"
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Are there any simple, cheap methods to grow Si or ZnO wafers? Say for example using enzymes or Sol-gel or Spin techniques etc
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If you want high quality or single-crystalline growth, then physical vapor deposition wont work for silicon, but you can get fairly high quality biaxial ZnO using sputtering or ebeam evaporation. Silicon will grow amorphous and slightly porous using these methods. For ZnO, if you employ oblique angle deposition during growth, you can partially control the crystal orientation and quality.
Teki, R., Parker, T., Li, H., Koratkar, N., Lu, T., & Lee, S. (2008). Low temperature synthesis of single crystalline ZnO nanorods by oblique angle deposition. Thin Solid Films, 516(15), 4993-4996. doi:10.1016/j.tsf.2007.10.024
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Dear every one,
I’m student of polymer Engineering (MS degree) and besides I’m working at HDPE production company. This semester I have to submit my proposal and I want to work on my working field (HDPE-film grade)
Can anyone give me the Idea for using Nono materials in HDPE film? or other subjects.
Thank you very much in advance.
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Thank you so much my friends, I will raise your Ideas to my Teacher .
Actually, My teacher is waiting for my proposals to select one for my thesis.
Im looking forward to recieving your suggestions.
Thank you.
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E.g. crystalline YIG films appear yellow, whereas amorphous YIG is black.
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This is explained by the concept of "color centers" in Solid State Physics which has some complex tensor-based math to quantitatively explain something which is a lot easier to understand in words ...
A perfect crystal (like a high-grade diamond or quartz) is optically transparent, light moves through the crystal without any particular absorption of any specific frequency. But of course, that would make for a boring world, so Mother Nature gives us a gift when she makes crystals, in the form of defects. Luckily everything in the world isn't perfect, and as those crystals grow, the randomness which is a part of the quantum world begins to take its effect, which creates point defects in the crystal lattice. One defect leads to another, and these defects begin to show a pattern all on their own.
As the light passes through this otherwise perfect volume of the crystal and then meets these defects, light responds to the defect in different ways. If the defect is significant enough and shaped in the right way, all of the visible light is trapped in it, and that part of the crystal, (or even the entire crystal) appears opaque. But when the defect is slight, it will absorb certain light frequencies, but not others. This produces the effect of color, because the whitish light that goes in may appear reddish or bluish or greenish (etc.) coming out, due to the fact that some of the light energy that went in was captured, and the light that came out was missing some bands.
To make things even more interesting, these defects in the crystal can be enhanced or cleared with more radiation (usually high energy radiation). So a clear crystal left in sunlight may absorb enough UV energy over the years to become slightly clouded, or even a bit yellowish. On the other hand, a colored crystal left in the sunlight with enough UV energy may gradually lose its vibrancy. Very high energy radiation can make this happen much faster, for instance inferior diamonds can be irradiated with high energy to make them appear clear, or else clear crystals can be placed in a high energy neutron flux or x-ray beam to give them a beautiful color.
To take this even further (and this is the really mind-blowing part) some seemingly unchanging materials can and will change dramatically for very (very) brief periods of time when exposed to light. Take a pencil out of a dark drawer, and hold it in the sunlight ... for a few femtoseconds, some of the graphite in that pencil actually converted to diamond due to the light absorption. Similarly, that expensive diamond when taken out of a drawer and exposed to light actually changed to nearly worthless graphite for a few femtoseconds. This doesn't last though (and the pencil graphite and diamond change back because these states are metastable, and they prefer to fall back to their more stable energy configuration.
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Does anybody have experience (or references) on measurements of viscosity of nanofluids (solute size less than 100 nm) with different methods - are results significantly different using different techniques?
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the polymers are both 4% functionalized and I was asking if with QCM I was able to see the ongoing crosslinking reaction and variations on LbL films properties once the crosslinking reaction is complete.
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Organo-modified mica nano-particles possessing higher aspect ratio than montmorillonite nanofillers could have pronounced effect on barrier properties of polymers. Especially in low concentrations which could result in higher level of exfoliated morphology and less agglomerate formation.
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My original work is to build a Schottky diode but I have to do some simulations in COMSOL for some IV curves.
As shown in the page 422 of the attached work
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thank you, Goodarzi
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I have a paper claiming that a specific material was found to have piezoelectric coefficients e31,f = –27 coulombs per square meter, and I want to use this material in a MEMS device. I would like to know an expression to find the maximum transverse axial force that can be generated for some voltage, and material dimensions, x,y,z. Am I missing a parameter? Could someone point me in the the right direction?
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I was actually looking for a specific function that would be help me calculate this value.
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I have found some work (not much) with sputtering and PLD, but none so far with reactive-MBE (i.e MBE with O2, O3, ...)
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Are you trying to synthesize superconducting films ?
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I need a mono-layer graphene oxide! The conditions have been mentioned in several papers in general (temperature, dipping times, concentration of dip solution), but the exact conditions is not mentioned.
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yeah im struggling with this too. the best references i found are:
"transparent, conductive graphene electrodes for [DSSC]"
Nano Lett. 2008 (8) #1 p323-327; wang et al
"evaluation of a solution processed reduced graphene oxide film as transparent conductors"
ACS nano 2008 (2) #3 p463-470; Becerril et al.
one is dip coating the other is spin coating. that said i cant get either one to work out quite right. im starting to think that the size and morphology of the graphene oxide SM might be important. tell me if you manage to make it work
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Whether we can find Plasma frequency by calculating Dielectric Properties.... Pls share some clear info abt it....
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It's simple: if you have the spectra, at the crossover point of both!
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Nickel doped zno thin film prepared by silar method.
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The crucial interaction between the transition metal ion and ZnO that can tune the bandgap of the latter is sp-d exchange. Which TM ion can produce optimal coupling? Mn? Co? Ni? It turns out that Mn does it best.
(See Bhat et al, Solid State Communications, 135(2005)345). Better than Co or Ni. This doping is important for inducing ferromagnetism for example.
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Nanotechnology and layer by layer technique
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Hi Angela,
The layer-by-layer (LbL) polyelectrolyte assembly was introduced in the 1990s by G. Decher, Y. Lvov, H. Möhwald and M. Rubner. See website: http://www.pharmafocusasia.com/research_development/layer-by-layer-micro-nano-drug-encapsulation-eolyelectrolytes.html
You can find the answer for your question by using KWs: layer-by-layer (LbL) polyelectrolyte assembly.
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For calculating the band gap we need the thickness of the thin film.
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Refractive index (n)and film thickness(t) we can calculate by making envelope on transparent curve..
n = [N + (N2 – ns2)1/2]1/2,
N = (ns2 +1)/2 + 2ns (Tmax -Tmin)/ Tmax.Tmin
and t = λ1λ2/ 2[n1 λ2 – n2 λ1]
where n1 and n2 are the refractive indices at the two adjacent maxima (or minima) at λ1 and λ2, ns is the refractive index of the substrate, Tmax and Tmin are the transmittance values for a given wavelength taken from the envelopes....let me know if u hv any doubt
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What are application pathways you can deduce from RMS roughness value like using film as hydrophobic surface, in coatings or other platforms in electronic devices etc. Please suggest me the suitable roughness value ranges for different applications.
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My background is in thin film materials for electronic applications, specifically as the dielectric material in thin film capacitors. For this application, we needed the RMS roughness value to be as low as possible, typically below 10-20nm if possible. A low roughness in the case of our thin films ensured that good electrical contact could be obtained between the dielectric film and the metallic electrodes. However, in other applications, I think the tolerance for surface roughness is larger, ie: above 20nm RMS roughness may be acceptable in certain applications.
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It has been reported that ZnO when doped with various dopants (N,P) become p-type but none is long-lasting. This maybe due to, I believe, diffusion of atmospheric oxygen and interstitial Zn, but I'm not sure. Does anybody have any idea?
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Dear Devendra,
In order to obtain p-type of ZnO it is necessary provide the compensation of native donor defects such as oxygen vacancies and interstitial zinc atoms by doping. Usually the concentration of these defects in ZnO is very large. Thus that demands very high concentration of acceptors. However there is their low solubility in ZnO. I think that it is one of reason that p-type ZnO it is difficult obtain.
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SnO2 and TiO2 both are n-type , in some papers i have seen that Sn is doped with TiO2 how can it be possible when both are n-type?
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In an ideal semiconductor at low temperature the valence band is completely filled and the conduction band is completely empty. No conduction is possible. If the temperature is increased to the order of magnitude of the band gap, some electrons from the valence band go into the conduction band due to Fermi statistics. Now there are free states in the valence band and electrons in the conduction band, electric currents can flow. The number of electrons in the conduction band and the number of holes (missing electrons) in the valence band is equal.
There is another way to allow conductivity: Doping. It adds energy levels to the band gap. Acceptors are located below the Fermi energy, but above the valence band. If an electron from the valence band has enough energy, it can go into the acceptor level. This creates a hole in the valence band, which provides a free state into which any onther valence band electron can move. That is why the hole is moving like an electron with positive charge. This is called p-doping or p-conduction.Donators are located above the Fermi energy and below the conduction band. They can release electrons into the conduction band. There are many free states in the conduction band so that the electrons can move. This is n-dopind or n-conduction.
Resistivity measurements cannot show the type of conductivity, since it depends on the sum of the number densities n and p of the electrons and holes, respectively. You need to use the Hall effect. If you have an electric current flowing in x direction and apply a magnetic field in y direction, the charge carriers will see a Lorentz force in z direction. This is sensitive to the sign of the charge carriers (electrons or holes). The force will move the charge carriers to the edge of the sample. This inhomogeneous distribution creates an electric field opposing the Lorentz force. You can measure this voltage, its sign shows which charge carriers are in majority. With the formulae of the Hall effect you can even calculate the charge carrier density.
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Heavy fermion
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Could you pose your question in a sensible way?
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I have absorbance, reflectance% and transmittance% data. How to calculate refractive index from this.
I tried with R = [(n - 1)^2 + K^2 ] / [(n + 1)^2 + K^2] where K is extinction coefficient.
Calculation was done by numerical method. It shows large deviation from reported value.
Kindly suggest how to proceed.
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The complex refractive index n∗ is defined as:
n∗ = n − i k,
The refractive index n is determined from reflectance R using the relation:
n =[(1 +√R)/(1 −√R)]
and extinction coefficient k is given by the relation:
k = αλ/4π
Absorption coefficient α is determined from transmittance T by the relationship:
T = exp(−αx), or α = [ln(1/T )]/x
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Nanotechnology is talked about recently very much but not visbible in our everyday life.
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Nano technology used for - Self cleaning coatings, Quantum dots for drug delivery, Aluminium nano particles for rocket propulsion, gold nano particles are used to catalyze chemical reactions, magnetic nano particle Iron oxide acts as contrast agent in MRI ,Food and gas sensors, Infrared Micro bolometer detectors and magnetic materials for storage devices, Superior implant materials, Magnetic Hypertheramia for cancer treatment, Bio sensors and for Biomedical applications etc.
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Is there any possibility to prepare MnS thin films using spin-coating technique Or spray technique?
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Mariya, Just out of my curiosity want to know what piezoelectric polymer you used. I spun coated PMMA for my waveguide applications on Silicon wafers. thin films are really excellent and we are able to get films upto 2 micron with uniformity all over the wafer. But for inorganic materials I did not know what will work out.
Kiruthigaa, mostly for inorganic compounds you did not get a uniform over the entire surface. so try to minimize your area of the substrate which means not more than 1 sq cm or use adhesive agent to make good quality films.
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Can you please tell any articles on the study of surface morphology with the RHEED
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go to giga pedia and search for RHEED e-books you will get information . otherwise search any book regarding surface sensitive techniques
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We are working on developing CIGS solar cell process in our lab and have encountered presence of CuSe phases - KCN is reported as a good element to remove it - but is it safe to use?
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I guess that KCN would be difficult to replace, because CN- forms a number of very stable Cu(I) complexes. Copper in Cu(In,Ga)(S,Se)2 has the oxidation number (I), but in CuSe it has the oxidation number (II). Cu(II) in contact with CN- is a pretty strong oxidizer. The driving force is the stability of the Cu(I) complexes with CN-, in contrast to the unstable Cu(II) complexes. That means, the copper has to acquire an electron from somewhere in order to form the very desirable CN- complex, which means it is an oxidizer (= something that absorbs electrons).
Selenium and sulfur form compounds with cyanide, i.e. selenocyanate and thiocyanate. Without cyanide, the selenium resp. sulfur would have to be oxidized from the -II oxidation number either to +IV or +VI in order to be soluble in water. With CN- present, it (perhaps) only has to be the oxidation number 0, as in selenocyanate and thiocyanate.
This together gives the selective etching of CuSe vs. Cu(In,Ga)(S,Se): In CIGS, the copper is not oxidizing and the compound remains stable despite the stable Cu(I) cyanide complex, because Se and S are not oxidized and remain in place. In CuSe, the copper is oxidizing and oxidizes the Se, which can in turn form selenocyanate (or selenite, I am not 100% sure). This destabilizes CuSe in the presence of cyanide, but leaves CIGS in place.
In conclusion, replacing KCN would be difficult due to the unique chemistry at work here that gives SELECTIVE etching of CuSe vs. CIGS.
The danger of KCN comes from the fact that extremely toxic HCN gas can emanate from the solution easily (mixing with acids, for example, like your gastric acid in case of ingestion). If you can smell it, it may already be too late! And not everybody can smell it at all, there are genetic differences.
It is possible to work with KCN if a number of precautions are made:
- Get help from a professional at your lab/institute!
- Discuss every single step of the procedure with someone competent, don't try anything by yourself, work with someone else present at all times.
- Make yourself familiar with symptoms and treatment in case of cyanide poisoning and who you should call for medical help at your institute in case you or someone else get poisoned.
- Generally: Follow lab safety rules at all times. They were made exactly for work with dangerous stuff like KCN.
- Work under a fumehood in a proper chemistry lab at all times.
- Wear gloves that are ok for KCN. (look it up somewhere, I am not sure if thin nitrile or latex gloves are sufficient)
- Wear a lab coat and safety goggles.
- Wash hands after work.
- No eating, drinking or smoking at the work place or with gloves on etc.
- Don't touch your face or your clothes while wearing gloves.
- Clean up spills immediately and dispose separately (NOT normal trash).
- Avoid making the KCN solution acidic at all times! This would free toxic HCN gas from the solution. Maybe buffer the solution to an alkaline pH if that is OK with the etching. An ammonia buffer could work, but I am not quite sure if that would interfere with the etching. KCN solutions should naturally be somewhat alkaline due to the weak acidity of HCN, but I would make it more alkaline if that is possible. The more alkaline, the more likely the HCN stays in the pot where it belongs.
- NEVER EVER dispose of the KCN solution in the acid waste (see above why). A disaster would be inevitable. Figure out how to dispose of the solution according to the rules of your lab. Probably collect it separately in a clearly labelled bottle.
Good luck to you!
Note: This are only hints, not a conclusive list of safety precautions. Get help from someone at your institute and don't blame me if you mess up! Well, maybe it will be your loved ones who will complain... ;-)