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I have came across many research articles in which metal halide materials are dissolved in DMF or DMSO or combination of both solvents. Then the liquid is injected in isopropyl alcohol for getting halide perovskite nanocrystals. So now my question is can I use 1-propanol instead of isopropanol for getting halide perovskite nanocrystals?
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You are most welcome dear Chaitanya Limberkar .
Wish you the best always.
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Hello. I want to simulate the phase transitions of zirconia after doping with Y2O3 in the VASP package.
How and with the help of what program is it correct to create a surface from tetragonal ZrO2 nanocrystals and their structures stabilized by yttrium (ZrO2 + 3 mol.% Y2O3, ZrO2 + 8 mol.% Y2O3) for further study of water adsorption on their surface?
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RRAM device has metal/insulator/metal structure, in which insulating layer acts as an active switching layer. I am looking for any correlation between the crystllite size of the active switching layer's nanoparticles with resistive switching mechanism. Does the size of Nanoparticles control the switching mechanism?
Please share some relevant articles.
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I think the construction of such devices is metal amorphous semicondcutor metal
The amorphous material acts as insulator as its conductivity is very small. When it is it stressed by an applied voltage the current will not be distributed homogenously among the divide but the current finds the easiest path and it will be concentrated there. Such filamentation leads excessive heating of the material and melting where the resistance of the filament will be minimum and the device switches to the conduction state. when the current is reduced the material will be converted into polycrystalline material where its resistance will be much less than the amorphous sate. So, it is the heating effect which converts the material from the amorphous state of high resistivity to the polycrystalline state with low resistivity. This resistive switching is known in the chalcogenide glasses. Please see the paper in the link:
Best wishes
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I could not get any VESTA documentation nor any lectures for adding vacuum and removing boundry conditions for nanocrystals, especially defining their facets and in which directions the vacuum and periodic boundary conditions are to be added and destroyed respectively. Would be grateful if anyone provides any material related to this.
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In utilitues we can modify boundaries sir.. we can give 0 -1 then it will be one unit cell... -1to +1 boubdary limit also
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The s1 figure contains a CdSe quantum dot diagram/structure made from single unit cell of CdSe.
The s2 figure contains the powder diffraction simulation of CdSe quantum dot.
The powder diffraction simulation for a single unit cell of CdSe shows correct peaks.(s3 figure)
Here CdSe is taken as example.
The simulations are made in VESTA.
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I agree with Andreas Leineweber.
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Hello everyone. I have conducted PL measurements on CsPbBr3 nanocrystals at 10 K. I observed a significant power-dependent blueshift (~50 meV) and spectral broadening as the laser power was raised from 1 W/cm^2 to 30 W/cm^2. I estimated that the range of induced carrier densities is around 10^14 to 10^15 cm^-3.
Given the typical temperature-dependent shift of the PL energy in this material, a 50 meV blue shift could be explained by an increase in temperature of around 150 K. However, I do not have any feeling for how strong the laser-induced heating should be in this material, under the given conditions.
As such, I was wondering if there was a simple way to confirm or dismiss the laser-heating argument in this situation.
Any insight or suggestions of relevant publications on this topic would be highly appreciated.
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Dear Rüdiger,
Thank you for your answer. Indeed if this were a typical semiconductor like GaAs, I would expect a heating induced red shift. However, lead halide perovskites like CsPbBr3 exhibit a blue shift with increasing temperature. To my understanding, this is because the orbitals contributing to the valence and conduction band edges are reversed, as compared to typical semiconductors.
As such, there is no simple way to distinguish between band filling and laser heating.
However, band filling is unlikely at my excitation density, because the exciton binding energy is around 40 meV, meaning that there are no free carriers available, even up to room temperature. To observe band filling i would need to have significant exciton screening, which would require around 10^21 cm^-3, by my estimate.
Similarly, I believe I may be able to exclude laser heating as well, since the blue shift stops above a certain laser power (i did not mention this initially, to keep the discussion as simple as possible, but after a while I realised that this might just be my answer). So if the material were indeed around 150K, then i would still expect some further shift and broadening as I increase the laser power further. Since this does not happen, I can exclude laser heating as the reason for my observations.
I am wondering if the blue shift may be due to a filling of shallow trap states, as I expect the material to have a trap concentration somewhere between 10^14 and 10^17 cm^-3. Then, excitation from 10^14 to around 10^15 cm^-3 should be enough to observe some trap filling. However, I haven't found many examples of this in the literature so I cannot say if this always results in a blue shift and broadening, as I observed. Are you, by chance, familiar with shallow trap filling?
Kind regards,
Claudiu
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Most perovskite quantum dot/ nanoparticles are cubic while some are spherical also. What is the reason behind the cubic or spherical shape of the quantum dots? Why do they have different morphology or nucleation?
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Dear Arnab and Dr. Wand, thank you so much for sharing your knowledge and article about the morphology of the PQDs.
Dr. Wand, you are absolutely right about the change in morphology because of temperature, electronic structure, and used ligands. But for the same perovskite QDs, such as MAPbBr3, there are cubic and spherical morphology have been reported in many research articles. Even they used the same LARP method and temperature. On the other hand, if we think about the electronic structure of materials, the CsPbX3, MAPbX3, FAPbX3have different electronic band structures for the different halides, even their morphology is cubic. So, still, it is not clear to me, (i) why PQDs have cubic morphology? (ii) what is the mechanism behind spherical and square morphology?
Spherical PQDs
Cubic PQDs
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When Chitin and cellulose nanocrystals prepared using acid hydrolysis are mixed, I get two new peaks at 264 and 700. I have read some papers that indicate that these peaks correspond to aliphatic CC bonds but I not sure if that happens.
Note: these peaks do not show up on spectra when nanocrystals are are not mixed
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Hello Mohamed when you say 'mix' is it a physical mixture or a chemical interaction? if it is the former these peaks might be due to crystal(s) re-orientation in the new mixture. The latter could indicate the formation of a new bond.
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I am working on spinnel ferrite synthesis by hydrothermal and Sol gel route method
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Microstrain in nanoparticles can arise from the surface restructuring or due to the localized disturbances in the lattice omprakash rajpoot
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Some papers quoted that synthesized zinc sulfate nano particles having the solubility of 100%. As per my little knowledge of nano technology, once the particle soluble, it will not sustain its size as in the nano meter range and converted to angstrom range. And so called particle not called as nano particle. So kindly clarify my query?
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Dear All,
I am trying to synthesize TiO2 sol using the hydrolysis technique with Titanium Butoxide as a precursor, the reference as attached below.
The process is very simple as follow,
Beaker 1: 5 ml DI Water + 70 ml Ethanol @ 80°C, Stir
Beaker 2: 5 ml Ethanol + 0.075 ml H2SO4 + 0.18 ml Ti(Butoxide)
Add beaker 2 in Beaker 1. The clear solution will start turning turbid with time and after 12 hours a TiO2 sol will be formed.
However, when I add Ti(butoxide) in ethanol, it instantly changes to yellow color, which in reality should remain colorless (transparent).
Can anyone give his/her feedback and suggestions on what can be causing this issue?
I will be really thankful for the feedback.
Thanks
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Dear Umar,
I tried to prepare TiO2 from titanium butoxide. I used 1 M HCl as a catalyst, distilled water and ETOH. I noticed that after adding few milliliters of water the color of the solution change from yellow to turbid. However, I used the sol for coating.
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I have encountered some studies doing this through some calculations involving FWHM values of PL bands but I couldn't figure that out. I am calculating radii by using the effective mass approximation. EMA predicts radii through bandgap energy, therefore, the output is unrealistically precise and doesn't have any error function. One of the reviewers especially asked for the size distribution calculation from the FWHM value of the PL band.
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There is Scherrer's equation for X-ray diffraction analysis of nanocrystals, which lets calculate average size of them from FWHM of X-ray peak. But I don't listen about similar calculation for PL spectra. Of course, the PL peak position depends on Eg, and Eg is a function of nanocrystal size. So, your calculations of radii by using the effective mass approximation looks quite reasonable, I believe.
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What are the values of γp and γd, and total surface energy for nanocellulose nanocrystals?
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Dear Hamta Kordbacheh, please check the following documents. My Regards
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Dear Researchers
I have synthesized gelatin stabilized ZnIn2S4 nanocrystals, I have obtained XRD patterns which is different from its bulk cubic and hexagonal phases. I assume there is some shift due to nanostructure. However i couldn't assign the patterns even though I spent a lot of time looking at many literatures. Can you please assist?
Thank you
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Harshit Agarwal Thank you so much for sharing the link. It is working. I will work on this.
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Usually, I mix silicon nanocrystals with polymeric compounds to create a nanocomposite for the purpose of studying changes in the photophysicsl properties. The problem is that I am still having trouble knowing the concentration of the silicon crystals added to the mixture. I hope to help me in whatever method you think is good in determining the amount of silicon crystal in the mixture.
With appreciation,
Mahmud Sefannaser
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Can you explain how do you build your composite.
It is so when you synthesize certain composite material you start with measured quantities of the components. If this is the case you know apriori the mixing ration between the different components of the complex.
You can use the absorbance of a specific wavelength to determine the content of the silicon.
Normally polymers are widegap and therefore they are transparent to the light with near infrared which is absorbed in silicon.
Then if you use light with wavelength of about 0.9-0.8 wavelength you can get information about the effective thickness of your silicon in the composite.
You can build yourself your spectrophotometer using LEDs as we introduced in the paper:
Best wishes
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I am working on making nanocomposites from silicon nanocrystals and thiolate. I get a massive change in the photophysical properties of some composites. However, other composites did not show me any change in photophysical properties. I hope anyone can go more in-depth and explain how the interaction between radical thiolate and the surface of silicon nanocrystals works. Let us focus on the chemistry point of view.
I appreciate your time in answering my question.
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would you please tell us what is the optophysiacl property which you assess after building the composites?
As Yuri hinted, the change of complex building is possibility of passivating the dangling bonds on the silicon surface.
It is known in order to improve the optoelectronic properties of the silicon grains , one passivates their active surface states by for example hydrogenation of oxidation. The mechanism is to saturate the dangling bonds.
Best wishes
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I am trying to synthesize ZrS2 in the liquid phase based on this paper, but it does not work.
For some reason ZrO2 is formed.
Please advise.
Well-Defined Colloidal 2‑D Layered Transition-Metal Chalcogenide
Nanocrystals via Generalized Synthetic Protocols
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Dear Toru,
Prof. Mirgorod is right. Moreover, you have to keep all components including the glass ware extremely dry to prevent hydrolysis. The formation of elementary sulphur points to the reduction of S2- which might be promoted by butanol.Please check the patent US 7,078,005 B2.
All the best,
Thomas
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I am working to detect the lifetime decay for silicon nanocrystal, so I read about the topic for more understanding.
Could you pick molicules as an example?. What will happen when a molecule is excited?.
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In order or fs.
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Suppose, nanocrystals of two or more compounds are obtained in the form of stable sols. Is it possible to control aggregation between different (but mainly not the same) nanocrystals expressed as plane-selective aggregation to obtain molecule-like nanocomposite which can be used either by itself or in the form of bigger aggregates as novel metamaterials?
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Hi, This seems to be possible, for example, with the help of a catalyst (especially moving catalysts) for the arrangement of materials or even the installation of special antibodies on the sides of the central material and the attachment of accessories to them.
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these images for tetragonal zirconia nanocrystals ?how these images can be correlated with xRD for the same structure?
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Nesreen Yahia You're looking at an incredibly small amount of material in each case. It is a very useful exercise to see how much material is being 'characterized' by each technique. Local inhomogeneities are easy to invoke in order to explain differences. Many of us have seen systems where one indication is of amorphous material and another of crystalline. You need to take far more images in order to reach a more reasoned statistically significant conclusion.
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Hi I'm interested in analyzing transport in nanodevices. I don't clearly understand how to properly set the number of k-points sampling in transmission spectrum computations. Is it possible, given a certain nanostructure (e.g. molecule, nanocrystal...) to understand which number of them (in x,y,z directions) leads to a reasonable accuracy?
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I use the Whatman 41 paper filter for filtering perovskite nanocrystals that synthesized by the Ruddlesden popper method but I have H3PO3 byproduct in the reaction equation which causes damage to the filter paper and led to defect within the synthesized crystals. what should I do to solve this issue?
If anyone knows an inexpensive anti acidic paper filter, I appreciate her/him for letting know.
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Mohammad,
welcome
Best wishes
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I want to do compositional analysis of doped colloidal CsPbBr3 nanocrystals, by STEM-EDX.
However, even for short exposures, the electron beam induces carbon buildup on the sample, which dominates the EDX signal, and it becomes impossible to measure anything else.
Can someone indicate if and how they managed to do this type of measurement? Is the carbon buildup due to the organic ligands which are not attached to the nanocrystals? is there a simple way to remove them form the solution, to enable the measurement? Please note that I am not doing the measurement myself, so my knowledge of the technique is not very extensive.
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I would expect that you can detect the elements in the sample. Especially because you have high atomic numbers, the X-rays are hardly absorbed by carbon. The other condition is the energy used. To excite the sample volume you need low energies. To excite the elements you need high energies. I assume, you try to detect the M-lines or L-lines. The best chance, I believe is to look for the Pb-lines due to their high absorption you need a lower sample thickness. The M-alfa energy is 2,34 keV transition energy (so you need only 5 keV excitation) or L-alfa (10,5 keV). This is well to excite with 15 keV electrons. With such energies you penetrate the carbon layer and the X-rays do so. Perhaps it helpes.
With Regards
R. Mitdank
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please suggest me how make sample for XRD.
I've tried with spin coating on a glass substrate, but it didn't work.
Sampling will be done on a glass substrate.
I had made sample for nanocrystals in toluene as solvent.
#nanocrystal #perovskite #xrdsampling #MAPbI3 #colloid
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Perhaps the dip-coating also works. To enhance the adhesion of your particles, surface modification of the glass substrate with the opposite charge requires. Or if you have a possibility, try to make a thin film using the Langmuir-Blodgett technique.
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Dear all
I read one literature in past, which discusses selection of solubilization technology based on the melting point and log P of active pharmaceutical ingredient.
The faint content back of the mind is:
There were two graphs, Log P on X-axis and Melting point on Y-axis
[1] Dose is less than 100 mg, what are the zones, where you choose (1) nanonization (2) liquid filled capsules and (3) solid dispersion as solubilization enhancement technology
[2] If dose is greater than 100 mg, then the similar selection based on zones
COuld you please help me find this reference?
This article is really a good read.
Thank you
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Dear Dr. Andrei Blasko
yes, I do agree with your comment. Solubilization of pharmaceutical compounds is a complex phenomenon and there are factors other than MP can affect the solubilization.
Moreover, in vivo conditions that include but not limited to presence of bile salts, pH of different parts of GIT, and mechanical movements can have further impact on the same.
You may check the paper that I mentioned in previous comment to this thread (link copied below). This publication summarizes various tools to support formulation development based on physicochemical properties of poorly water-soluble pharmaceutical molecule(s).
Sincerely
Samarth
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Why are there a lot of approach to exfoliate graphene using nanocrystal cellulose rather than using microcrystal cellulose?
Is there any advantages of using nanocrystal rather than using microcrystal? If yes, what is the advantages?
also, it would be very kind if you can give the link for the supported statement/answer.
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I don't have a firm answer but my guess is that nano-crystals are easier to penetrate between graphene layers than micro-crystals due to their small sizes, so the exfoliation is favored.
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Dear reader,
I am trying to perform Rietveld refinement with irf function for crystalline nanoparticles. During the refinement, I get "Resolution limited" message for apparent size and strain in Fullprof mic file. Why does this happen?
Please find attached an example of mic file.
Best regards,
Nevena Celic
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generally the "Resolution limited" message appears when the breadth of the diffraction line calculated using the instrumental resolution is larger than that measured in the analyzed sample. It is quite strange in this case because you have nanoparticles (are you sure of this?). did you put NPR=7 in the *.pcr file? have you put U=V=W=0? maybe your *.pcr file could help for identifying the problem
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Please suggest me how make sample for TEM. I have no idea how sample for TEM colloidal nanocrystal prepared. I had made sample for nanocrytals in toluene as solvent.
#Nanocrystals #Solvents #Imaging #TEM sample preparation
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Perovdkite QDs are very senstive with temperature and humidity. In my openion, after drying TEM Cu grid with QDs at 70 to 100 C, it can damage the QDs. I am working on MA based PQDs. For my sample, I just droped 20micro litter of QDs solution ( in toluene) on Cu TEM grid dried in glove box or vaccum chamber for 2-3 hr at room temperature. Through this approch we got very good QDs TEM images but with heating at 50C for 30 min I got larger and aglomerated particles. So in my case I am not using heating for drying the sample.
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I have to do synthesis of W doped VO2 for which the oxalic acid dihydrate was used as reducing agent according to research paper :
i am limited to the access of oxalic acid dihydrate, Can I use oxalic acid anhydrous instead for my synthesis?
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Lokesh Murali i think this paper is useful for you
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Does anyone know of any literatures where the hydrodynamic size range of cellulose nanocrystals and nanofibers would fall within? The literature I have seen indicates actual lengths and diameters, however I am going to be using a zetasizer and obviously this gives the hydrodynamic diameter so I am trying to see what size the transition from nanocrystal to nanofiber would occur.
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The DLS method gives the average hydrodynamic size of nanoparticles. If you measure the size of a nanoparticle in the shape of a ball, then you get the exact diameter. If you measure the size of a nanoparticle in the shape of a tube, then you get the average size between the size of the diameter of the tube and the length of the tube. The average fiber diameter you will not get. You need to use an optical microscope.
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A DSC run at a heating rate of 10K/min of nanocrystalline Y2Ti2O7 powders showed a broad exothermic peak spreading from 350 - 950 C. No such signature in the cooling curve! Can you please help us decipher this? Could crystallisation or relaxation of the nanocrystals result in such a peak? Simple crystallisation should have resulted in sharper peaks, isn't it?
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whether the nano crystalline powder synthesized by ball milling If so then such a broad peak is due to the release of stored energy as a result of thermal relaxation. It is definitely not due to the crystallization. crystallization peaks normally occurs over smaller temperature range.
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Im having issues with interpreting the CV graph produced by my experiment.
Here are the details:
Metrohm spe gold disposable electrodes. Chemically cleaned then electrodeposition of palladium chloride with hcl mixture (-100 mV) to form nanocrystal on the surface - done using potentiostat. Then the electrodes are plasma cleaned with oxygen at med rf for 5 min. Then CV scans are taken using a sodium chloride and sodium phosphate buffer (25/25 mM) as a blank before dna immobilization.
Having trouble replicating data and understanding the shape of CV
Have also tried CVs without electrodeposition and getting similar shapes but with lower max current peaks
Thanks
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I agree with both previous answers. As Andreas Heyn points out, move towards a reliable reference electrode, this will make it easier to analyse the CVs and should rule out a secondary reaction occurring.
Can you show a set of scans to demonstrate how the response evolves?
Jules
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I have an HRTEM image of CuInSe2/ZnS core/shell nanocrystals where small individual dots can be seen. The size of the dot is roughly 0.2 nm. I summed up the ionic radius of Cu(+) +In(3+) 2* Se(2-) from the literature which is 0.616 nm. This means these small sized dots are the individual elements/ions as their size is lower than sum of ionic radius. So i assume that its possible to identify the individual elements (like Cu, In Se) based on the size of dots. However, i found it difficult to measure the exact size of the dots in picometer resolution using image J. So how do i do this? Is it possible?
Also is it possible to draw the crystal structure based on the position of these elements?
Note:
Ionic radius of Cu+ =140 pm, In3+ = 80 pm, Se2- = 198 pm
I have excluded the capping agents from this calculation
Thanks in advance
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Oh sorry. the Name is quite unsurprising: Transmission electron microscopy. It has several subchapters also one exspecially for HRTEM.
We had it in our library and it was very useful for me.
I think in one chapter was a case where it was not clear if the "dot" you saw in the image was a doting ion, an error in the lattice or a vacancy.
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Hello Users
I want to extract an optical gap from the spectra of my work, I found a way to do that from other works " we took the absorption edge as the energy threshold at which the absorption is 2% of the total absorption. The same criterion was used previously for determining optical gaps in Si sRef. 31d and CdSe sRef. 32d nanocrystals and was found to yield good agreement with experiment. ". But I did not know how to implement this method practically Can you help me?
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2% is ambiguous so is Tauc plot. This topic has been discussed multiple times in ResearchGate. Please search for the old discussions.
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Is it reasonable to state that Stokes shift for core-shell nanostructures (e.g. CdSe/CdS) is smaller in comparison to bare core (e.g. CdSe)? If so, why this phenomenon occurs? Thanks in advance for your help!
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If the absorption/emission is due to the crystal itself, rather than surface states, then the Stokes shift is due to electron lattice coupling and lattice relaxation in the excited state. It is conceivable that this lattice relaxation is constrained in Core/shell structures, compared to core structures of the same core dimensions.
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How to select the concentration of the core for the preparation of a colloidal core shell nanocrystals?
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Dear Sir,
many thanks for your replies. They have been really helpful. One last question: i have core shell nanocrystals of the same material (lets say material X) and the core is doped with a rare earth material, will TEM or HRTEM helpful to identify the formation of the core shell structure?
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A major infant formula manufacturer was forced to recall supplies from Australian supermarkets after their dry milk product was found to contain hazardous nanocrystals of Fluoride doped Hydroxyapatite.
I am currently most interested in the formation of covalently bound Fluoride attached to protein, heme centres and especially Phosphorus in food.
I have not found any literature with data for 19F NMR of milk samples containing Fluoride, either as a result of pollution, or the deliberate addition, as occurs in some human experimental locations in the UK or South America.
If anyone has access to NMR facilities, this could make the basis of a refereed paper reporting results of incremental addition of Fluoride to milk and measuring the effects of high temperature treatment as occurs in pasteurization.
31P NMR looking for 19F coupling could also prove useful.
Would anyone like to collaborate?
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Hmmm, I am not sure solid state NMR will help. What is understood today by "solid state NMR" is a technique involving magic angle spinning and cross-polarization. It is suitable for 13C studies and allows molecular structure studies without dissolving the sample. It is not a trace analysis technique, and it is not suitable for measuring traces of mineralized 19F.
When I said that the fluorine traces in hydroxyapatite are probably solid and that I was detecting concentrations of 0.1% of CaF2 (not really "traces") in processed gypsum, I was not recommending the use of "solid state NMR" (that would be useless). I meant old-fashined, direct "NMR of solids", a very different thing , with broad-band, short dead-time probes. Not a routine NMR spectroscopy stuff.
You should also consider another option: a chemical transformation of the sample to convert any fluorine that it might contain into soluble species and then apply usual liquid state NMR spectroscopy. Not being a chemist, though, I am not sure whether any such chemical processing is possible (I am rather skeptical).
Also, since this problem might well be totally beyond the reach of NMR, you should think about other methodologies for the essays.
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After quench the as-synthesised InP nanocrystals in toulene, I have tried to use methanol:crude product in ratio of 2:1 and centrifuge it with 4000rpm for 30 mins. However, the nanocrystals cannot be completely purified. Is there anyone have the experience on purifying InP in 1-octadecene? Please do drop some advices and opinion. Thank you.
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1-Octadecene high viscosity hydrocarbon. Wash it with a lower viscosity hydrocarbon with hexane.
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I'm using a Delsa Nano (Beckman-Coulter) with a scattering (detection) angle fixed at 165 degrees to determine de size distribution of colloidal nanocrystals. Is there any problem if I choose a glass cuvette with two opposite clear sides instead of a typical one with four clear sides?
Thanks!
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Hi Diego,
It depends at which angle your detector is suited. If it is suited at 90 degree to the incident light then you need 4 clear sided.
So have s look and check the angle between the laser and the detector and then you can decide
If you are not sure, measure a sample using 4 clear sided cuvette and then measure the same sample using the 2 sided cuvette. If they are more or less the same then the type of cuvette is irrelevant.
Hope this help
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I want to synthesize CdSe nanocrystals with high temperature colloidal technique. I have some set up. But I want to buy a Temperature controller (temperature range upto 400 oC is fine) with J thermo-couple. Also I want to buy heating mantle 100 ml size. Please suggest the cheapest one and some website where I can buy?
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We use Omega https://www.omega.com/ for all our temperature controllers and heaters purchases. They have very good, not too expensive, controllers and various heaters.
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If a nanocrystal sample is too small, for example, <5 nm. Is it possible to yield a smooth powder XRD pattern which is similar to that of an amorphous one?
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One issue will be the extremely weak scattering of particles < 5 nm combined with the line broadening. Almost certainly you'd need long exposure times (maybe even 24 hours) under the x-ray beam in order to get anything of value. What material are you talking about?
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how can we calculate the work function of 0-D (quantum dot or nanocrystal or molecules) and 3-D (bulk) materials using density functional theory?
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Dear Askari,
The following article will answer your question:
Langreth, D.C., Dion, M., Rydberg, H., Schröder, E., Hyldgaard, P. and Lundqvist, B.I., 2005. Van der Waals density functional theory with applications. International journal of quantum chemistry, 101(5), pp.599-610.
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We have synthesized MAPbX3 (I, Br & Cl) and CsPbX3 perovskite quantum dots but MASnX3 and CsSnI3 quantum dots are not synthesized yet.How can we synthesize Pb replaced quantum dots perovskites?
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After a long time I got the some explanation about my question. I have tried to synthesize MASnBr3 perovskite QDs but I did not get good emission (got very low blue emission). So 100% replacement of Pb from perovskite system is very challenging with Sn due to lower ion conductivity of Sn. Low ionic conductivity of perovskite QDs caused surface defects and makes the material unstable. I think that,s why it is challenging task to prepare MA/CsSnBr3 PQDs.
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I had prepared some polyhedral alloy nanocrystals by using PVP( Polyvinyl pyrrolidone ),then washed them by using water and
ethyl alcohol for several times. But a layer of PVP was found adsorbed on the nanocrystals' surface under the SEM. How to wash it completely?
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PVP is not a surfactant. Maybe you can remove it only by oxidation. Depending on chemistry of nanocrystals variation of pH might also help.
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What is nucleation energy? If I am making hybrid nanoparticles (metal oxide/metal), the reaction mixer contains both precursors (metal and metal oxide) and allowing to grow both nanocrystals simultaneously to make hybrid nanoparticles. Which nanoparticle can grow faster than the other? Does nucleation energy determine growth rate of nanoparticles?
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The Gibbs energy (delta G) of nucleation of a new phase with homogeneous nucleation has three components: bulk, surface, and elastic deformation energy during the structural change of solids. The surface energy acts as a potential barrier to condensation.
The kinetics of formation of a new phase is determined by two stages: the rate of formation of nucleus centers and rate of delivery of the substance to the nucleation center, which ensures the formation of a stable nucleus. . The rate of formation of condensation centers is proportional to the probability of its nucleation.
I =A exp(- delta G/RT). (1)
The rate of delivery of a substance to the nucleation center is proportional to the probability of the “survival” of the nuclei that have emerged
U = B exp (- E/RT) (2)
E - activation energy of a viscous flow or energy of transition of a substance to the surface of a nucleus. A, B - proportionality coefficients.
The overall rate of formation of centers of condensation nuclei is proportional to the product of the above probabilities.
As can be seen from equation (1), the growth rate of the nucleus of the nanoparticles depends on the Gibbs energy.
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How can I process the SAED TEM images to determine the crystalline planes of my nanocrystals?
I can see in the images the concentric cones of diffraction and marked atomic positions. But I do not know how to process the image to obtain the interplanar distance using the scale bar (5 1 / nm). How to use the Fourrier transform in this case?
Thank you for your attention.
Best regards,
Felipe Leon
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I have been working on ternary and quaternary Cu based chalcogenide nanocrystals. I have measured the UV-vis-NIR absorption spectrum to calculate the band gap. From literature I came to know that the well known method to calculate the band gap is to use the (αhν)2vs hν graph. Where "α" is the absorption coefficient. 
How to calculate the absorption coefficient of colloidal nanocrystals from absorption spectra?
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The absorption coefficient α is expressed from the Beer-Lambert law
α =2.303A/d
Where A is known as the absorbance, d is the thickness
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I'm researching about Li absorption with hydroxide nanocrystal.
my hydroxide always perfect change crystal structure by absorb Li, fixed time.
but, When i refluxed 10M of LiCl long time until 2 weeks at 120'C, hydroxide didn't react 100%.
What's happening about 10M of LiCl solution when it was boiled 2 weeks?
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If there are indeed good reasons to expect 100% (complete) conversion ― reactions are often not complete in the experimental practice ― you may want to consider the possibility of contamination of the salt by previous exposure to atmosphere (hydration and/or carbonation), ion exchange with the vessel material, and carbonation of the aq. sol. by exposure to atmospheric CO2. Also note that the salt is hygroscopic, what may induce weighing errors, particularly if the salt is not conveniently dried, so that either the anhydrous salt or a single pure hydrate is weighted.
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I have read papers about nano-crystals but how I can differentiate that they are single crystals.
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Yes, there is. There are two aspects there which may establish a difference between both.
First, Single Crystall = Monocrystal:
This means; the crystall (solid structure of periodically repetition of the same atomic structure) is not composed by grains, which means, it has no grain boundaries. all its atomic planes extend in the same orientation one next to the other , the solid grows and arranges itself continuously with no change in orientation (or direction) of its planes.
but a Nanocrystall, could be a Single Crystall, o a Poly Crystall
Here the other aspect which defines the term "Nanocrystall" is the size.
The former definition of the prefix nano in material science and nanoscience is:
An atomic structure exteded along its three dimensions, while its size along each direction (x, y, z) should n't be greater than 100 nm
:) hope it helps
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Suppose we have a metal core surrounded by organic ligands. In that case, can a ligand act as/can be termed as a shell or is there any obvious difference between the two?
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Ligands and shell are two very different things, with ligands you can perform a functionalization between two incompatible materials, it's not a shell because don't act like as a physical barrier, it's only an attachment with others particles. Usually shell growth in all the nanoparticle's surface.
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I have been asked to support an intern with the development of a ultrananocrystaline thin film MOS device. We have some already developed ultrananocrystaline thin films of Si-substrates, but i need to deposit a insulative thin film to form the MOS structure.
His project has a close deadline, so I need to find an insulative material that is easily compatible with ultrananocrystaline. My department currently has access to RF magnetron sputtering, evaporation and spin coating, I could access other resources. but the deadline is limiting my options.
 I myself have developed MOS devices before using insulative Bismuth based aurivillius structures, but these require annealing at temperatures above 550OC, and do not know how the diamond films would be effected by this condition.
I am currently investigating depositing SiO2 by RF-Magnetron sputtering, but I do not know if it will need post deposition annealing. Also my RF-sputter is only equipped with a pure Ar gas capabilities, and I understand O2 partial pressures are necessary for Oxides.
If anyone can suggest any easily formed insulative thin films for use on ultrananocrystaline diamond films. I would be extremely grateful.
Best wishes
David Coathup
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Electrical insulators as a new phase state of quantum matter with some bulk gap and some odd number of Dirac formations have recently been entangled with a two-dimensional model by us through an external magnetic field. The magnetic field used has its own impurities so much so that the eccentricity resulting from the turning point of magnetic critical insulation leads to aspects of compilation that have never been revealed by the “approximate approximation calculus” mostly used in a run under such circumstances.
Crystal and electronic structures have given us the topology that have made it likely for us to depend more on over-stuck service rather than on projections that go into manifolds and submanifolds of various dimensions. In additions, fulton heaters in this specific setting of complex systems where technique does not exist for efficient approximation, has led us to find even lower than submanifolds: something like up-submanifolds and down-submanifolds whereby the cloesed set of combining topological insulators itself has become the target in insulating the whole bulk without any regard for the gapless and/or edge services states. This means that the topological insulators that we are working on have been both gapless at surface and without such states so that they might be able to carry a pure spin current. However, this pure spin current is the point where we have made our own initiative provided through the closure of those areas where points cannot satisfy every path from one origin-set of the insulator to another point of it simulacrum. Therefore, we are actually depending on, so to speak, closure models for creating metainsulators, giving yet more models of simulations of magnetic insulators.
The surface of state of spin resolved ARPES works so that the focus of one direction is in Riemannian contrast to the zones that consequently appear throughout the folding holes as borderlines between submanifolds. For this, without any doubt, means that the dimensions of submanifolds where we are working on our different froms have been entangled with ergodicity as the totality of anisotropy that rises from insulation through coupling strength. The simplest form is, of course, happening within a two-dimensional partially anisotropic plane. In the most complex forms, they can even go into the quantum mechanic levels such as N-Hilbert dimension.
Roya Attarzadeh
Don Senior Prof. Reza Sanaye
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Recently, I have investigated vibration modes in NaGdF4 nanocrystal, and I came across of some bands in the resulting spectrum , somewhere at ~250, 300, and 360 cm-1. Somehow, I could not able to find any references to quantify and back the analysis. I would be grateful, if anyone insight me with your great knowledge related to this situation.
Thanks in advance and hope to hear from someone soon.
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Thanks a lot Mr. Abdur and I appreciate your efforts.
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Which solvent should I use for testing?Study of UV vis and fluorescence characteristic of YAG.
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Dear Rishabh, The experimentally determined optical band gap of YAG is at about 7.1. eV = 175 nm (Cryst. Growth Des., 2017, 17 (4), pp 1863–1869
DOI: 10.1021/acs.cgd.6b01822), which means that your absorption band at about 210 nm is not related to the optical band gap of YAG. I assume that the solvent ethanol is already strongly absorbing below 220 nm and thus governing the shape of the absorption spectrum. The decline of the band below 210 nm is caused by the deviation from the Lambert-Beer law due to the large ethanol concentration. The absorption edge of clean and dry ethanol is at about 205 nm. Advice: The best solvent for the deep UV range is water (~ 190 nm), but this is yet not good enough for the determination of the optical band gap of YAG.
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Could anyone please suggest some easy-to-prepare samples for DLS measurements for practice? The perfect system would be the one were you could vary the size of almost monodisperse nanoparticles, that could be comparatively easily and quickly obtained in the lab and stable enough to measure at the DLS.
A side similar question concerns the easy systems for zeta-potential measurements - the ones were you could have abs(z)>30 mV.
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Hi Leonardo,
An example of its use is here:
I'm not aware of a peer-reviewed article concerned with the use of Coffee-mate. Its use is more of something known in the instrument trade as an easily available and reliable sample to check/demonstrate the general performance of an instrument. I learned the "trick" from a former employee at Brookhaven Instruments many years ago.
John.
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I have not seen any reports based on shelling of semiconductor nanocrystals with metal. In your opinion, do you think shelling a semiconductor nanocrystal(CdSe, CdS, CZTS) with metal(say Au or Ag) can improve a thin film solar cell?
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I think the p-type semiconductor for core may be more efficient to abrove metal SPR and formation of e-h pair .
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Hello. I want to standardize a platform to prepare micrometric (900-1200 nm) drug nanosuspensions (nanocrystal dispersions), at my laboratory, of curcumin and other hydrophobic drugs. I have read about preparation methods and we are going to select first a bottom-up procedure since we don't have the equipment to employ a top-down approach. So, I know the main steps: dissolve hydrophobic compound in organic solvent and then mix it with an aqueous solution with a stabilizer. In my laboratory I have a bath sonicator, would that be enough to produce a narrow PDI? What's the setting and the procedure of the mixing of the phases and the stirring/sonication? Do you have any specific protocol paper about this? Thanks a lot.
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Hi David,
Regarding to your above question;
3 transdermal curcumin formulations and their ingredients are described below:
Curcumin propylene glycol liposome (PGL) preparation. Hydrogenated phosphatidylcholine 10 mg (HPC), cholesterol 5 mg (Chol), Tween-80 1 mg and curcumin 3 mg were added into propylene glycol. Then 7 ml 5% trehalose solution was added slowly into 3 ml propylene glycol solution with constant rotation of 750 r/min. Curcumin PGL was formed in solution after 10 min constant rotation.
Curcumin liposome preparation. Curcumin liposomes were prepared by ethanol injection method with the same component proportion as curcumin PGL. HPC, Chol, Tween 80 and curcumin were dissolved in 3 ml anhydrous ethanol. Then ethanol solution was added slowly into 10 ml distilled water with constant rotation. Ethanol in final liposome solution was removed by vacuum rotation evaporator. Curcumin liposome was formed after the removal of ethanol.
Curcumin ethosome preparation. Curcumin liposomes were prepared by ethanol injection method with the same component proportion as curcumin PGL. HPC, Chol, Tween 80 and curcumin were dissolved in 3 ml anhydrous ethanol. Then ethanol solution was added slowly into 7 ml distilled water with constant rotation with constant rotation of 750r/min. Curcumin ethosome was formed in solution after 10 min constant rotation.
Source:
Zhao YZ, Lu CT, Zhang Y, Xiao J, Zhao YP, Tian JL, Xu YY, Feng ZG, Xu CY. Selection of high efficient transdermal lipid vesicle for curcumin skin delivery. International journal of pharmaceutics. 2013 Sep 15;454(1):302-309.
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I've been searching for cationic materials to stabilize a suspension of drug nanocrystals. We want to prepare curcumin nanocrystals (with a bottom up approach, probably) but we need them to be cationic for application purposes (targeting to dendritic cells - immunotherapy). I've found chitosan, cationic surfactants, and other cationic polymers to be a good choice to stabilize nano and microcrystals for this highly hydrophobic drug. Do you have any information about this topic or do you personally know which one would be better in term of prevent changes in size and polydispersity of the system? Thanks a lot!
PD: do you also think cellulose nanocrystals with curcumin are also a good option?
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dear
i dont have any idea about this but share your question with 2 man that are specialist in this.
i hope it will help you.
good luck
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How to calculate the amount of strain generate in Si nanocrystals from Raman spectrum ? Is there any way to distinguish the component of strain and phonon induced Raman peak shift ?
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I am attaching an article , it will help you to calculate strain from Raman data.
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It is a common phenomenon for most of the nanoparticles to aggregate especially when they are in dried form. For example, the morphology of freeze-dried cellulose nanocrystals was observed to be flake-like compared to the rod/needle-like morphology of never-dried cellulose nanocrystals. Several studies suggested using longer stirring time (24 h or more), tip sonication with higher amplitude considering lower concentration (1wt% or less) of nanocrystals in aqueous suspension as well as use of appropriate surfactants to achieve improved dispersion. However, still, the freeze-dried nanocrystals were found hard to re-disperse in an aqueous medium and get the similar rod/needle-like morphology (like never-dried cellulose nanocrystals).
Any thoughts/suggestions/comments/discussion on this issue????
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"breaking the bonds" is exactly what you are doing when producing the nanomaterial. H-bonding is a van der Waals force. Regards
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I always get nucleation of metals onto the facets or on the defect sites or they just form separate islands. Any suggestions to achieve homogeneous nucleation?
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What I have understood so far that the rate of charge transfer at semiconductor surface is slower than the metal surfaces due to the lower surface electron density which could be a potential reason for metal deposition in the form of 3D island on semiconductor surfaces or self-nucleating island.
Feel free to add more, I am keen to know more about the interaction of two different class of materials.
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I have seen few reports for the binding of silver ions to sulfur and forming silver sulfide when depositing silver on a semiconductor nanocrystals such as CdS, PbS, CZTS. Why? What are the factors associated with it? Is it a cation exchange process?
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Free ions always have counterions. Therefore, if you measure the free energy of the silver ion in solution with respect to metallic compact silver, you will see that the free energy of compact silver is higher. That is, compact silver is more likely to enter into a chemical reaction than the silver ion in the solution. Nanoparticles have even higher free energy due to excess free surface energy. This, in particular, is the driving force for nanoparticle coagulation. Therefore, silver nanoparticles are an even more effective reducer of lead than silver ions in solution.
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Dear community,
I'm looking for bibliographic reports that clearly stablish and explain the existence of band bending in very small nanocrystals of semiconducting materials, i.e. quantum dots. There are reports that claim there is no band bending in nanocrystlas while some others explain their results in terms of band bending. While the pictorial view would be not important, it became a bottle neck when quantitative electron transport in this materials is evaluated. I will apprecaite any deep and clear report that can pave the way. Than you very much!
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Dear Iglesias
For semiconductor nanocrystals of size smaller than around 10nm energy gap increases dramatically for exampl energy gap for Si increase to about 1.6eV for nanoparticle size of about 4nm So if that is bulk crystal aband bending may occure since there will be a transition energy from 1.1eV for a bulk to that of the nanocrystaline.
for mor information you can see the following presentation
"Solid Surface and Nanoscale materials Structure"
Presentation · July 2016 with 156 Reads
DOI: 10.13140/RG.2.2.31947.59684
Charmo, University of Charmo, University of Salahaddin, DOI:10.13140/RG.2.2.31947.59684
Cite this publication
Omar M S at Salahaddin University - Hawler, Arbil, Kurdistan, Iraq
Omar M S
39.98Salahaddin University - Hawler, Arbil, Kurdistan, Iraq
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CsPbI3 nanocrystals crude solution can not be separated, precipitates have a little nanocrystals and nanocrystals are always left in supernatant.
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Which nanocrystal have high luminescence, 3D or 2D nanocrystal of lead based perovskite ?
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3D has good Luminescence, but 2D layer with Pb(SCN)2 good stability
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Hello,
How can I have a nanocrystal from a organic crystal?
is there a specific technique ?
Thanks
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Hello Youssef Ramli
Ball milling is one way of getting your desired size as Adrian Radon mentioned. One thing i'd recommend is avoid excessive ball milling in one time. Start with low RPM and little milling time and increase step-wise as excessive milling can leads to disappearance of some of the properties correlated to magnetism.
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According to the literature method, the hot injection method cannot be repeated. The yellow phase was always obtained.
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@ Rajan K. Singh
I want to prepare nanocrystals,but thank you all the same.
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When ternary compounds are synthesized, it is challenging to control the growth and crystallinity. As it gives impure phase. Is it possible that the diffusion of copper is happening? Due to which reason i am not getting pure CuCr2Se4 nanocrystals.
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The reason is not in the diffusion of copper, but in thermodynamics. You need to calculate the standard Gibbs energy of this substance. If it is positive, then such a substance can not be obtained under normal conditions.
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Following figure (see attachment of curve) is showing the time-resolved PL decay curves of Nanocrystals (red one is sample and black one is standard sample). I want to eliminate the hump, which is due to instrumental response, in the sample spectrum. But I don't know how to eliminate it. Does anyone have any idea? Any type of help will be appreciated...thanks!
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Do you have checked the way I suggested. I think it can be.....
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I am studying the effects of ion irradiation on Iron Phosphate Glass (IPG). We have earlier reported that ion irradiation leads to stress induced crystallization (nano sized crystals) in IPG, observed from TEM. Now I am comparing the Oxygen K edges of EELS and XAS recorded from as prepared IPG and ion irradiated one. The O K-edges from the asprepared sample have comparable shapes. But EELS and XAS spectra taken from irradiated samples do not match. I understand XAS has poor spatial resolution but EELS has good spacial resolution. But the area probed by the ebeam while taking EELS is definitely more than that of the nanocrystals. Can anyone tell me what difference can we expect in between Oxygen K edges from XAS and EELS?
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I agree with Artur - why don't you show the data?
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After conducting PL lifetime measurements on nanocrystals of different sizes (3 and 8 nm), I observe that the smaller particles have a longer lifetime than the bigger ones (especially the faster component: 3 vs 8 ns). It is unexpected, since a larger exciton band gap and a higher trap density should lead to faster recombination. Am I missing a mechanism here which could explain this phenomenon?
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Dear Victor
The PL intensity is proportionnal to the Oscillator strength (OS) of exciton , i.e the Coulombic bounded electron-hole pair . The OS is proportionnal of recover integral of electron hole wave function . OS increases with decreasing quantum dot or nanoparticle size. OS is inversely proportionnal to the PL nanocrytals lifetime !
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I have been working with oxygen reduction reaction (ORR), using Pd nanocrystals. I found that the in my case, the half-wave potential observed in the reverse scan (1.0 V vs. RHE while sweeping from more –ve potential to less negative potential) is better than in the forward scan (0.9 V vs. RHE). However when I do chronomperometry, I observe a value corresponding to the forward scan. I have not been able to find any literature justifying which scan value should be reported. Can anyone please advise or guide to the right literature. Thanks.
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Thank you for your answer. But reverse scan (more negative potential to less negative potential) gives better half wave potential value. Why can not we consider the reverse scan result? If you can refer me some references it will be very helpful.
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Respected Researchers !!! I have observed remarkably enhanced (282-fold) PL emission from Bi2Te3 nanosheets. However, its bulk counterpart being a narrow indirect bandgap semiconductor exhibits almost zero photoluminescence. Normally, SPR enhanced PL originates in the vicinity of metallic nanocrystals (The Purcell effect) .
I wonder if this pronounced signal originates solely from indirect to direct bandgap opening/transition or there might be the possibility of surface plasmon resonance (SPR) enhancement in photoluminescence from a single semiconductor ??? It should be noted that 2D nanostructure of Bi2Te3 also support SPR. Your answers would be highly appreciated.
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Thank you all. Dear Thomas Walther , structural and chemical composition are examined by Raman, XPS, XRD, TEM/HRTEM analysis. We found no such evidence,other than pure Bi2Te3 nanosheets. since its a layered lattice structure, so it does not need necessary dangling bond formation to stabilize the surfaces. Moreover, Bi2Te3 and other family members exhibit Negligible Surface Reactivity towards Oxygen and Water (ACS Nano, 2013, 7 (6), pp 5181–5191 DOI: 10.1021/nn400908b). Therefore, we were able to rule out the presence of moisture or oxidation. Nevertheless,Si/SiO2 substrate was used in all PL measurements. We never tried to support Bi2Te3 nanosheets on an inert wide-bandgap semiconductor or heat treatment under UHV though. we will try this as well.
Based on above answers and suggestions, i can safely rule out the phenomenon of surface plasmon enhanced PL phenomenon in a single semiconductor system (Bi2Te3). Right ???
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We are investigating the hydrophobicity of modified CaCO3 nanocrystals. Is there any practical and simple way to measure the contact angle?
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Stefanus - it can be as simple as taking a close-up photo of the drop on the crystal (take the image a few seconds after applying the liquid due to evaporation) and using a protractor (software-based or physical) to measure the angle manually from the picture. Adjust the lighting beforehand so you can get good contrast between the drop and the background. It may even be possible to do the whole thing by smartphone by taking a picture and using an angle measure app. Won't be the most accurate but will give you an idea.
Good luck.
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In theory, cobalt doped TiO2 thin film should be conductive. So, I was preparing cobalt doped TiO2 thin film on microscopic glass substrate to measure the conductivity. Samples contain different percentage of cobalt as dopant within the nanocrystals. Different rpm (500, 1000, 2000, 3000) were used to prepare film containing up to 20 layers of samples. Any idea why the samples aren't showing any conductivity. I tried to measure the resistance using two point probe.
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There may be a number of reasons for not measuring any conductivity in your film. Some of them can stem from structure of the same film, some from the measurement (you can face a combination of such problems too).
First, your film is not continuous, perhaps at the micro-scale, which may depend on the pre-deposition conditions of the substrate surface or on the spinning solvent and parameters, or also on post-deposition thermal treatment (if any).
You can use a planar SEM or FESEM analysis to easily check for any crack or lack of the coating.
Another possible cause is the presence of sizable residues of the spinning solvent. This may occur, for example, when organic solvents and additives are used and anot totally removed after spinning, which may lead to extended residue even at grain-to-grain scale. This could be not so easy to check, being yours a thin or very thin film. A FESEM expert may give some indication with a skilled use of the chem microprobe 
Turning to the IV measurement, you definitively can not use a std two-points configuration, where the contact resistance contribution dominates. Even the four-point probe (linear or Van der Pauw configurations) may be insufficient if too large current crowding occurs around  the contact between tip and film. This happens when you have ohmic contacts... but you could even face rectifying (diode-like) contacts which means no or very low conduction within some V range.
If you are not lucky with a simple 4-point measurement on bare film,I suggest you to check for a possible masked coating with a metal which is expected to give an ohmic contact with your doped film, so to have 4 small contacts (large enaugh to assure the probe tip touch only  the metal pad, small enaugh to leave most of the space to your free film).
I just cited some possible major causes of your conductivity problem... There may be other and more tricky ones. But I hope I gave some help
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I am trying to obtain nanocrystals of dexamethasone by nanoprecipitation using acetone. I am able to precipitate the drug, but the crystals are really big (5 - 25 um). How can I optimize the precipitation process?.
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Hi Airama, 
it depends probably on the way you precipitate.
Typically, the faster - the better.
You can think of applying (high) shear forces during the precipitation and to add a stablizer (e.g. Poloxamer 188 or Tween 80) to the water phase.
Milling of coarse material is another simple approach to obtain the nanocrystals.
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Where are the transition metal (TM) ions when TM is doped into ZnO nanocrystals? What are the most possible sites for these TM ions? 
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