Science method

X-Ray Absorption Spectroscopy - Science method

Analysis of the energy absorbed across a spectrum of x-ray energies/wavelengths to determine the chemical structure and electronic states of the absorbing medium.
Questions related to X-Ray Absorption Spectroscopy
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Similarly In XAS (X-ray absorption spectroscopy) spectra for 3d elements, why BE of the L3 edge has lower in energy than the L2 edge?
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Ah, yes. I just have never seen it as an acronym before.
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I recently tried to do a D-parameter calculation for reduced graphene oxide, and the value came out to be 21. This corresponds to >70% of sp2 contribution as per the available literature of XAENS. I doubt whether the same calculation can be applied to XPS? Any good literature suggestion is highly appreciable.
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Dontt forget that the X-ray induced Auger will have a different information depth to the C1s core level, so depending on how 'clean' your sample is from the reduction of GO may be more sensitive to the surface carbon. However to comment more it would be good to see the C1s and O1s spectra to comment on the values
See my recent paper discussing some analysis of carbon linked below
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Hello Researchers.
I am carrying 100slab calculations for 2*2*2supercell using fhi pseudo-potential. for supercell creation and slab i have used BURAI. in the slab i have kept 1 position mobile and 3 fixed. the problem is the supercell was simple cubic but when i changed to slab it changed to tetrahedral. and results of slab and supercell are not same. although matches with data. but there is split in the peaks.
anyone having any idea please comment.
Thanks in advance.
#DFT #QuantumEspresso
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Dear Fernando, please see the attached click.
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Hi,
Even though Artemis gives an error bar on the EXAFS fitting but it assumes the value to be zero at certain R values.
In the case of data with some experimental noise, the error bar needs to be corrected, weighted by the square root of the reduced chi-squared value, taking into account the experimental noise for each R-space spectrum from 15 to 25 Å, as described in
How do calculate the uncertainties in the coordination number when EXAFS is fitted using Artemis?
Thanks in advance
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Thanks, Gerhard Martens it was indeed insightful
I have one more case where relatively good data (up to k=14) gives the following fitting (see attached).
it still show a huge error bar? can it be solved somehow?
Thanking you,
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Assuming that we could probe using high enough energy XPS energy source,
How will be the binding energy of Au 2p3/2 will be different from the Au L3 absorption edge in XANES?
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It's simple just take a short look to this two techniques and pay attention to the mechanisms. In XANES the absorption of a monochromatic X-ray beam is probed as function of the X-ray energy. But In XPS one is analyzing the kinetic energy of the photoelectrons that are emitted due to the excitation by X-rays of well-defined energy.
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Starting from the bulk gold and going down to atomically precise metal cluster, we wanted to know how does the energy of excitation for 2p3/2 --> 5d transition will change with particle size
We have a range of atomically precise clusters say Au4, Au7, Au11, Au25 Au102, and Au nanoparticles of ~2 nm.
Thanking you
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Mr./Dr. Sharma, You need to first check Google and the RG also, before you put the query!
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How does the excitation energy of core energy levels (say 2p) to LUMO (or conduction band) of Au change with decreasing the particle size from bulk gold to nanoparticles and nanoclusters (<2nm) then to atomically precise clusters (say Au4).
Thanking you,
Yours
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I think chapter 4.1 of this dissertation from Berlin might be what you are looking for:
You can also check if the author has also published this in paper form.
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How can we find out coordination number using XANES and EXAFS ? I am using Artemis and Athena for the data analysis?
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Dear Shailendra, both XANES and EXAFS may be used for an estimation of coordination numbers, while XANES is more indirect, (because many details of the short range order structure such as coordination number, bond angles and distances, second and third nearest coordination, type of coordinating elements / ligands, ... all have an influence on the XANES, see the review by John Rehr and coworkers, Rev. Mod. Phys. 2000, DOI: 10.1103/RevModPhys.72.621), EXAFS is much more direct. Due to the fact that the backscattering phases and amplitudes are different for the envolved elements, even the type of neighbor atom can be resolved.
What you need is to have a structural model, calculate ab-initio the EXAFS (by using e.g. the FEFF software) and a fit software to fit the calculated data to the experimental data (e.g. Athena/Artemis, WinXas, LASE, or similar).
Come back if you need more help, however I may recommend to go through the information provided on Bruce Ravels github pages, for the adequate use of his software packages (check: i.e.
and related pages for Athena and Artemis!
Warm regards, Dirk
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Hi,
I have some molecules with known crystallography data (cif file) I wanted to calculate the EXANES and XANES for the material.
please suggest me the best way ?
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The problem for all kinds of EXAFS / XANES simulation is a correct and physically valid structural model. This not only includes the positions of the atoms, but also disorder parameters, site occupancies, and potential models. Here, in particular for XANES calculations, small changes may have a big influence on the calculated spectra. For EXAFS, the situation is more safe, as those type of calculations are much more straightforward ... see e.g. the review by John Rehr (Rev. Mod. Phys. 72 (2000) 621, DOI 10.1103/RevModPhys.72.621). Hope this helps, Dirk
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I am trying to generate a core-hole pseudopotential for the Ru atom using Quantum Espresso ld1.x. But as described in the attached document ( where they have generated pseudopotential for Si atom) I can not understand how they are taking the number of wave functions to be pseudized and the Number of projectors. So it will be beneficial if you can help me in understanding it.
Thank you for your time & attention.
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The number of pseudo wave functions depend on the number of atomic orbitals you want to treat as valence bands for the given atom. For example, for Si, you can pseudize 3s and 3p only and treat all the other orbitals as core states. Alternatively, you can include 2p or any other semi-core orbitals in the valence region as well. Bu this usually means you have to take a higher cut-off energy, as your pseudo waves are now harder.
As for the number of projectors, this is only needed if you want to generate a PAW pseudeopotential. They can allow you to reproduce the all-electron wave-function within the core region and thus would be essential for the studies involving the core states. The rule of thumb is the more projectors included the more accurate the pseudopotential becomes. There is no particular restriction on the number of projectors.
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Dear All,
I am a beginner of theoretical XANES calculation in Quantum Espresso (xspectra.x) code. For this I need GIPAW reconstructed pseudopotentials. Is there any step by step guidelines how to do it. Your help will be highly acknowledged.
I have tried some examples, but always end up with ghost states (warnings!).
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Sorry, not yet
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Hello,
I was looking for theoretical data of the Cu K-edge RIXS, I would like to plot the intensity versus the incident energy and transfer energy to obtain like a contour plot.
I tried starting from the Kramers-Heisenberg relation but I did not succeeded. I would like to plot some contour images like in this article.
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You can try to generate the spectrum through CTM4RIXS. Please see the attached link of the software
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Is there a post analytical methodology or experimental technique used to distinguish between overlapping energy edges in XAS?
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they are only 1,3 eV apart from each other: no chance.
Sorry for that answer....
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222Rn is a soil gaz that permit the localization of hydrocarbure in soil.
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Even if the soil were pure uranium-238,1g would contain only about 1e8 atoms of Rn-222. There are not many analytical techniques that can detect anything on that concentration level.
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Core hole effect plays an important role in determining X-ray absorption spectra (XAS) from first principles. Sometimes core hole effect is negligible as compare to spectra where core-hole is absent in the calculation. What are the physical reason behind this? Simply, what are the factors affecting the core-hole effects in any material?
Any help will be appreciated.
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Hi Soumyadeep,
Your question is very interesting, and I guess you are a theoretician.
I will try to shed some light on this issue as a experimentalist. But before that I am assuming that you know the reason behind the large core-hole effect in photo-electron spectroscopy (e.g. XPS) and negligible core hole effect in XAS.
Consider the case of L egdes XAS, for 2p6 3d9 system (spin orbit splitted 3d3/2 & 3d5/2 initial states). In the final state after excitation, in such system, you will end up with the spin-orbit splitted 2p3/2 & 2p1/2 states, and the usual selection rule will give you the features in XAS. This description comes from totally atomic point of view. In case of some oxide materials (for example with strong hybridization TM-O), it is energetically possible to transfer one electron from the O 2p band to the above mentioned atomic states of TM. Because of this so called "charge transfer effects" the additional contribution appears i.e. 2p6 3dn+1 L(bar) in the initial state and 2p5 3dn+2 L(bar) in the final state. And now the additional multiplets will appear in the atomic spectra. Similarly, other distortion and field (e.g. crystal field) will further modified the initial and final state and hence the spectra.
Finally, (your concern), because of this charge transfer the effect of 2p core hole (in this example) is screened well.
I hope this will provide you some information.
Regards
A. Ahad
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I tested a series of samples contained Cu (including CuO and CuO2 )by X-ray Absorption Spectra to determine the oxidation state. But the equipment did have Cu foil as reference. in this case, how can I normalize data? appreciate for all your help.
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Hello Peng,
so higher the oxidation state, so higher is the intensity of Cu-3d-states. In really pure copper, all 3d-states are occupied and you dont see this line. The CuO2 states (I assume you investigate high Tc superconductors) give an intensive signal. I would relate the 3d signal to the oxygen signal of an oxygen standard.
With regard
R. Mitdank
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Good Morning.
Iv'e made Fe K-edge XAS measurements on a mineral with Fe3+ and Fe2+ atoms, looking for the pre-edge feature and using gaussian curves to fit the pre-edge assuming 4 quadrupole transitions: 2 for Fe2+, 2Fe3+. Obviusly, each transitions has an excitation state lifetime, of 1.5eV from literature, which i have assumed to be the same for each absorbing atom.
My question is: Can the temperature (even 800°C) alter this lifetime? If it changes, does it equally changes? The lifetime can be altered also by the oxidation state of the absorbing atom?
ps: naturally, what i wonder is if the alterations is more than 5/10 % than the original.
Edit: the sample is a natural riebeckite crystal, measured from 270°C to 800°C continuosly, with normal atmosphere conditions.
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Hi Federico:
interesting question.
I would add a question but not an answer.
If there is observable change in the life time, you may see it in the broadening of of those absorption features, is that your case?
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Kindly suggest to me for the extraction of the pair distribution function from XAS (EXAFS) data.
Any software for that or any logarithmic code for that.
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Hello!
I use the Demeter package (athena+arthemis), you can find it here
You first need to extract the EXAFS data from your data. You can find clear explanation abount normalization, background substruction in the user guide of the Athena software. Then you need to put an input structure in an Ab Initio code that will calculate scattering amplitude (for example FEFF code). Finally, you can use the Arthemis software to fit your structural data (distances, number of atoms, Debye Waller factors...)
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The effect is observed to be dominant in glancing angles as compared to the normal incidence geometry and the measurements were performed in Total electron yield mode.
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Hello Mangalika
Could you show some data and provide more details on how the experiments where performed (which angles exactly, more details about the sample, ... ) ?
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I want to know the physical phenomena at the second peak of Fe K-edge XANES spectra.
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Sofi Suhail Majid This is not generally correct. There is indeed quadrupole 1s to 3d intensity in the pre-edge shown by many authors using e.g. linear dichroism. This is the case if the local geometry around the absorber Fe has inversion symmetry such that p and d fall into distinct point group symmetries. In the absence of inversion symmetry Fe p and d have partly the same symmetry in the relevant point group and thus mix. Fe p and O p may indeed have the same symmetry and thus also mix which may reflect in the pre-edge intensity.
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Hello,
I am about to perform XPS analyses in natural soil samples (mineral horizons) and compare these data to synchrotron derived XAS data. Now I wonder whether it makes sense to also analyze the corresponding leaf litter (foliage / L-horizon), too. I think I would need to mill the leaves and I wonder if I would still get "surface" Information at all? Is there anyone who has experience in working with XPS on foliage (and Of, Oh-horizons)?
Thank you for your answers,
Teresa
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I can only agree to what Artur Braun has mentioned above - if you don't try, you wíll never know. We did some XPS studies of paper materials (coated, non-coated), and there is a huge amount of data in this business (related to cellulose, lignin and other wood derivatives, and wood-related materials) available from the group of Leena-Sisko Johannson (Espoo Finland), Laurent M. Matuana & Pascal Kamdem (Michigan State Univ.) - you may also check the Springer Journal of "Wodd science and Technology" - maybe there you'll find some hints as well. If you are not successfull, come back to me, I can provide a list of references, maybe there are good ideas for you as well? Good luck in any case, Dirk
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I have done X-ray absorption spectroscopy (XAS) on my sample and collected the Fe L edge spectra. Now that I'm doing the simulation to compare it with the experimental result using CTM4XAS software, I'm confused whether the crystal field parameters which i have used are correct or nor, however the calculated spectra is more or less superimposed with the experimental spectra. Also I could not exactly understand the contribution of Dtau and Dsigma for D3d symmetry and how it affects the energy levels.
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Hello Abdul,
Thanks for sharing your view, of course it will help.
As you have mentioned that the relation for x2-y2 and z2 in D4h symmetry, is there any relation for xy and xz/yz of T2g splitting (delta) in D3d symmetry except the notations -4Dq+1/2delta and -4Dq-2/3delta respectively. Because I want to check the energy levels using 10Dq, Dsigma and Dtau values as De Groot has mentioned in J. Am. Chem. Soc. 2012,134, 13708-13715 for D4h symmetry.
thnQ.
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I have a collection of *.NXS files got from the Diamond Light Source and I need to open and see the plots of the contained data. Can anyone advice an easy to use reader software for MS windows?
Thanks in advance to all of you
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My peaks are shifted from reported data as 883.6 and 901.7 eV as 893.3 and 912.7 eV. how can i determine correct position ? If C 1s correction is needed then how to find position of peak from C data.
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You seem to have very nice pre-edge feature, so finding the inflection point may prove difficult.
The best way to have correct energies is to use reference materials with well known edge or features energies, before and after the samples (to detect eventual energy shifts during recording). However, I do not know if such material exists for this energy range.
Without this, you may
1) try to model the molecular orbitals of your sample and deduce from that the allowed electronic transitions and their energies (but not sure if a 10 eV difference can be resolved this way)
2) try to find other references in the literature for this edge in other Ce compounds, and check if the E0 energy is closest from yours or if literature is consistent
3) as suggested by Artur, but without the option "I'm correct, literature is wrong" (which may occur but is also the last resort ;), you well may be in a setting where absolute energies are not needed, only relative energies. For instance, if the aim is to detect oxidation state changes by edge shifts. This assume however that all samples were recorded during the same experimental session, otherwise you cannot decide if the shift is due to the sample or to the beamline...
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Dear all,
I am wondering which X-ray absorption spectroscopy mode (transmission, fluorescence, electron yield, or auger electron yield) suitable for insulating samples and why?
Thank you very much in advance.
Best Regards,
Efi
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Dear Efi,
in x-ray transmission as well as x-ray fluorescence processes there are no free electrons involved; so charging of samples does not affect the XAS measurement.
For Auger and total electron yield mode things are quite different. Here charging has severe influences which in addition are be time dependent.
Special techniques have to be applied to overcome these shortcomings
For example please have a look at:
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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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The coordination number of the 1st shell of a metal (Pt, Pd, etc.) derived from fitting EXAFS data has long been use to estimate the average particle size of metal nanoparticles. I wonder if the same method is applicable to oxide nanoparticles (PtO2, PdO,etc.)? If it is applicable, what is the correlation?
Thank you all for the kind help in advance.
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Dear Son,
the 1st  coordination shell  of the above mentioned oxides consits of O atoms. Their backscatter amplitude is a strongly decreasing function of k.
In contrast to that  the 1st shell of the metals are the metal atoms themselves. For high atomic number  scatterers (such as Pt or Pd ) the backscatter amplitude extends over a quite large k-range having significant scatter strength.
So I fear that for the oxide case  the first peak  in the radial distribution function of EXAFS might be too small in order to determine  a coordination number precisely enough to have a reliable  estimate of the particle size. I think this also holds when EXAFS evaluation is done by fitting as you mentioned above.
But it is only a guess.
May be other colleagues comment on that more positiv.
P.S. You might request full-text of the attached paper at G. Tolkiehn or me.
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I m working in chlorine alkaline plant. We are analysing gas (H2, O2) in chlorine gas by GC system manually. But this method is really take many time and labor force. We have analysed 24 point every day and there are 304 points in the plant. We have took samples with injector and then get in to lab and analysed it by GC chromatography.
I think, online system processor could be good choice for this process analysis.
Have you any idea?
Thanks in advance,
Umut BASTURK
QC Supervisor
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you may use O2 detector device instead of GC
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Now, I'm studying on KNbO3-based ceramic material.
I need to know the change of lattice parameters with calcination temperature variation. My samples (powders) was calcined (heated) from low to high temperatures. After that, I took the samples to measure in many techniques.
The results from XRD and XAS (including XANES and EXAFS) techniques were measured at room temperature. I found the difference between two results.
The lattice parameters obtained from XRD tends to change from cubic to tetragonal structure with some parameter is increase and some parameter is constant. However, XAS result revealed that the atomic bonding in the local structure (up to 3rd shell) tends to decrease all. Meaning, I obtained the strange result from XAS, which the atomic bonding should be increased (expansion) with temperature increases following the XRD result (same result as a conventional material) but now it decreases (contraction).
Can I interprete these results?
I have known that XRD measures in overall (global) lattice and XAS measures in an atomic scale. There has the difference behind them but I still don't know how to analyze these results.
I have searched from many researches. However, It is very hard to find the explanation and some explanation is not clear. For examples, it might be occurred from the reformed-impurities at high temperauture or occurred from the local tilting of the center atom inside the unit cell.
Thank you very much for the valuable answers
Best Regards,
Saichon Sriphan
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In EXAFS, the E0 energy shift and the bond length are strongly correlated parameters. So I suggest performing the fittings keeping an eye on the E0 shift value. If it is too large (let say, more than +/-5 eV), you should try to make a constrain to keep it smaller than +/-5 eV, or even fix it to 0 eV, and look what happens to the bond lengths.
For more information, discussions and more you can go to:
or ask to:
Best wishes,
Leandro.
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In the neodymium absorption spectrum, there are several peaks correspond to two energy level (transition overlaps), but to do the Judd-Ofelt parameter calculation I have to choose one certain energy level. So, how can I decide which energy level to choose? 
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Read this paper
Joao Azevedo et al.
Physica B Condensed Matter 405(22):4696-4701 · November 2010
DOI: 10.1016/j.physb.2010.08.066
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I have a sample which shows multiple phases ( BCC, FCC, Tetragonal, Orthorhombic) at room temperature obtained from the XRD measurement. Now how can I generate the EXAFS input paths for the sample including all the structures? 
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It's hard enough to constrain an EXAFS fit for a single unknown phase - four phases will be a real challenge! What specific questions are you trying to answer with EXAFS?
Here are some suggestions for your analysis:
  • If some of the four structures are known, input paths can be generated from published atomic coordinates or .cif files. If not, you can construct a guess structure or duplicate selected paths from a known structure.
  • In order to fit the EXAFS, you'll have to fix as many parameters as possible, guided by your XRD data. If the Scherrer broadening of the XRD peaks indicates sufficiently large crystallite sizes for the phases with known structures, then you may be able to constrain the bond lengths, coordination numbers, and sigma^2 values of those phases to published bulk values.
  • If you have an accurate measurement of the fraction of each phase, you can constrain the ratios of the path amplitudes of each phase to those ratios, similar to Gerhard's suggestion.
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Why not consider the delocalized pi-subsystem as nano-wires, which absorbs only parallel E-vector?
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Yes, I have the spectra of oriented carbyne, where pi-resonance is weak whereas sigma has good anisotropy and magnitude. Thanks for good book...
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I am using Artemis to analysis EXAFS data, and the figure produced by the software is not very suitable for publishing. How could I get the data to replot using Artemis?
I have known "Save next plot to a file", but it can only save one column data.
Thanks a lot.
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Dear David, which version or Artemis do you use?
In the older versions, you may use the "save current group(data) as ... function"
In the newer versions, there is an option in the plot window  - save next plot to a file"
Both should work out!
Cheers, Dirk
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The spectrum of a beam of therapeutic x-rays (megavolt) or diagnostic x-rays (kilovolt) cannot be measured precisely. And it seems that an estimation of spectra using deconvolution of attenuation data is the most common method to get such spectra. The method of estimating x-ray spectrum using measured attenuation data is an ill-posed problem on itself (a situation where we solve for larger number of unknowns with fewer number of equations). Using an estimated or derived spectra we can calculate back the attenuation data. A comparison of the calculated attenuation data with the measured attenuation data is the only method that I use and know so far.
Besides this, could anyone please suggest me any other idea to check the accuracy of a spectrum?
Thank you in advance.
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Dear Rajesh Panthi
You can get the HVL of your beam in a high purity Al or Cu according to the kV of you x-ray beam.
From the HVL, calculate the corresponding attenuation coefficient and so the effective x-ray energy can be calculated by the aid of winxcom of NIST as Heyang explain.
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I synthesized CeTi2O6 which contains Ce4+ at 1200 and 1325 so from Ce L-edge XANES spectra, I found all of Ce+4 convert to Ce3+ for sample which heated at 1325c and there is a mixture of both in the sample which heated at 1200c, I know  higher temperature is more favorable for Ce3+ and makes this change in the oxidation state of Ce but why all of Ce4+ convert to Ce3+, there is no sign of the presence Ce4+ in the sample which heated at 1325?
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yes but I expected to have a mixture of both not  Ce3+ only, so what factor cause all Ce4+ reduced to Ce3+?just change in temperature?
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I want to get valence band maximum of my sample. To do this, ı tried to use xps measurement in small binding energy region and also UPS measurement. But ı do not know how to calibrate my spectra. Is it right that the calibration should be done according to zero count should be Ef=0 binding energy? 
In my laboratory, there is XPS system and we use CASAXPS pragramme. I know to peak fitting and obtain the atomic ratio of each element of my sample But ı do not know how ı can  get valence band maximum from the spectra.
If any one want to do collaboration with me, ı can share my measurement. 
I am waiting your valuable comments and helps...
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you write: "Is it right that the calibration should be done according to zero count should be Ef=0 binding energy?"
answer: maybe, maybe no. Much depends on what your sample is (polycristalline, textured, single crystalline), what you know about it (band structure, band gap, n- or p-doped). From what you write, I reckon it's a semiconductor.
This may become a difficult task, for several reasons. But that also depends on the level of accuracy you want to achieve. What is the goal and what is current practice in the lab you're working at? (so what's the opinion of the pro's around you?)
If you have a single crystal, you can do ARUPS and determine the band dispersions. It is then tempting to associate the peak at smallest binding energy you can find with the VBM. However, with standard He lab sources, you don't actually know whether your spectrum picks the right momentum vector along the surface normal.
To give you an idea how this could be done with a single crystal, you can have a look in the paper I linked below. It's not recent and measured with "old style" instrumentation (channeltron detectors in analysers, no 2D detectors). But it should be instructive. You will notice that measurements with synchrotron radiation (variable photon energy) were required to assign the VBM. (Note that newer, work with better resolution yields a different conclusion about the location of the VBM).
When measuring a polycristal (truly random) you may run into the problem to have too little intensity near the VBM to actually find it in your spectrum. But you can do cross-checks. If you know the band gap of your material, then the VBM cannot be off by more than that from the Fermi edge position of a metallic sample (gold or silver, preferably) measured under the same consitions. That would give you a first indication. If you know the character of doping, then you also know, whether you expect the VBM or the CBM nearer to the Fermi level (btw.: do you know, whether you have Ohmic contact to your sample? If it's a Schottky contact there may occur extra shifts, rendering the latter conclusions invalid!)
With XPS, you have much worse energy resolution. Therefore the intensity will usually extend over the Fermi level and it is hard to know what to do.
OK, I'll leave it at that for the moment.
P.S.: why is your question tagged with "SPM" and "XAS"?
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I am working on the synthesis of WSe2 by CVD, and I want to know the degree of crystallinity of the sample. The sample, which is less than 1nm, is too thin to be characterized by XRD. Thus, I am looking for other method to check the degree of crystallinity. Some paper mentioned that it is possible to calculated the crystallinity degree of Si film from Raman spectra. So I wonder whether it is also suitable in case of WSe2.
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Dear Yanan Liu,
Raman spectroscopy can be used to estimate the crystallinity.
But if your samples are only 1 film of 1nm thick then it could difficult to measure it because of the laser penetration. If the penetration is much bigger that the film, can happen you don't enough Raman scattering from the film.
You need to have in consideration the wavelength vs absorbance of the material and calculate the penetration in the WSe2.
Three methods can be used to enhance the Raman scattering from the film: resonance Raman, the used of shorter wavelengths and increase the volume of material mesuared.  If you use a laser with a wavelength close to the energy to an electronic transition of a compound then the resonance Raman will greatly enhanced the scattering. Shorter wavelength like UV can offer less penetration (in general the absorption is higher for short wavelenths) and also enhance the Raman scattering but can result in photoluminescence that can be of higher intensity than the Raman scattering. If you can make a structure of multi layers or thicker films then your Raman scattering from the WSe2 can also be enhanced.
You should also have in consideration that the same material in amorphous stage have less intensity that in the crystalline stage.
My experience with epitaxial quantum wells of group IV material tell me that is possible to measure films with thickness as low was 1nm, but in my case the signal was very weak to extract precise information.
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The XRD peaks of cubic and tetragonal ZrO2 are almost same, thus, we cannot identify the crystallinity of Zirconia using XRD. Same with TEM, I know.
Is there any useful method to clearify the crystallinity of ZrO2?
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The (200) peak (and others) of the cubic phase shows a splitting into two peaks when the tetragonal phase appears while the (111) peak shows no splitting. Depending on the crystallite size, the quality of the scan and other parameters this splitting may be seen or not. This is also valib for a lab goniometer. Pawley- or Rietveld-Analysis may be helpful. Are you able to provide a scan?
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I am trying to find a table of X-ray mass attenuation coefficients for SiO2 in the energy range 4 keV to 7 keV. I expected this information to be easy to find, because ionizing dose is a concern for electronic devices exposed to radiation, but the only tables that I found so far apply to various biological materials. I have to estimate dose in silicon dioxide and I need this data.
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Use XCOM from NIST: http://physics.nist.gov/PhysRefData/Xcom/html/xcom1.html. It's very simple to use.
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Hello All,
For materials that exist in different phases depending on temperature, how can I determine the phase of the material base on XRD data?
Can I also determine the atomic composition of different elements in a  compound (for example Ti0.4C0.6) from XRD data? 
Thanks
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The manufacturer of most XRD equipment provides computer software to assist in the analysis of the XRD pattern.  The software available varies from the major manufacturers will often attempt to analyze the area beneath the curves and then compares that to the known peak intensities to try to establish an estimate of the concentrations of each compound that is present.  This calculation can never be precise because some compounds act as better reflectors than others.  XRD also assumes a random orientation of the crystals, so if there is any sort of physical ordering of the orientation, then that can skew the results and change the assumed "measured" concentrations.  XRD can therefore be good for estimating whether you have a lot or a little, but not actually providing a true measurement of how much of each compound is present.
And yes, XRF is not going to work if you are looking for a direct measure of hydrogen.  As long as you are not looking for dissolved molecular H2, you can get an idea of the hydrogen content by using XRD to identify the exact compounds present (must include water(s) of hydration, and then use XRF to look for the atomic content of the other ions in the sample.  If you are looking for dissolved H2, you should probably try a hydrogen analyzer that measures H2 released while "baking" the sample.
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I would plan to make a Doctor Thesis and focused with Heterogeneous catalyst characterization. There are ATR - IR Spectroscopy and XAS should be offered to support the research.
Could anyone help to briefly describe based on experiences, what could we work with the help ATR - IR and XAS for characterizing Heterogeneous Catalyst.
Many thanks for help
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ATR can easily be used  to spectroscopically characterize different types of sample systems. This includes heterogeneous catalysts, electrode-interfaces but also bulk solution phase systems. There is in fact a vast literature on this topic available. Possibly important for you is that different tricks can be empolyed to make ATR advantageous for surface-sensitive spectroscopy, the most prominent thereof is the surface-enhancement effect employing metal-coated surfaces. 
Depending on the particular scientific question that you have, and the system that you want to investigate, you may find some important examples for applications in the following overview articles:
Chem. Soc. Rev., 2010, 39, 4571–4584 (http://pubs.rsc.org/en/content/articlepdf/2010/cs/b919544k)
Chem. Rev. 2012, 112, 2920–2986 (http://pubs.acs.org/doi/pdf/10.1021/cr2002068)
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It will be used for x-ray absorption studies in the human body as well as the dose fall off with depth.
I am using a PMMA container volume 35x38x40
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Darrion, you can find here an example of pelvic cavity phantom: http://www.cirsinc.com/file/Products/002PRA/002PRA_DS_070113.pdf
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For instance, the 4s ->5p transition around 170 eV or 3d ->5p around 573 eV. Their intensities are expected to be very low though. I haven't succeed to find anything about it in the literature so far. Thanks in advance.
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Hi, T.R.F.!
Perhaps the following reference is appropriate as well (see link).
Regards,
Daniel
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Can anyone explain how does such a relaxation process effect the XAS or XPS peak position, I have tried to obtain materials online however those available seems to be filled with mathematical complexities. I need some help!
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Dear Kumar,
In brief:
Initial-state effects, it is the charge on the atom prior to photoemission that plays the major role in the determination of the magnitude of the chemical shift. 
Final-state effects that occur following photoelectron emission, such as core hole screening, relaxation of electron orbitals and the polarization of surrounding ions are often dominant in influencing the magnitude of the chemical shift.
More detailed it is explained in the attached review and  second manuscript on the base of theoretical background.
Hope it will be useful.
With the best regards,
Dmitry
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I would like to know if it is possible to calculated an quality index to determine the best calculated XANES spectrum.
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The question is interesting and challenging and in principle the answer is quite easy.
You can run a fit as already possible with some SW packages. However, because at variance of EXAFS, for the XANES technique there are no equation associated, to answer to your question properly I need to know why you need a single parameter to evaluate XANES simulations. Can you clarify what is the problem you need to solve with a comparison based on a single parameter? 
Take care that just changing the range of the XANES you can weight different contributions (e.g., electronic vs. structural) and get a different feeling about the comparison.  
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  1. Synchrotron radiation
  2. XANES and XEOL
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Dear Yuting, X-ray absorption spectroscopy is generally associated with the creation of a photoelectron, that can be treated as an electron wave propagating through a sample, and the interaction of this photoelectron wave with neighboring atoms modifies the absorption probabilty if the energy of the incident radiation is varied in the vicinity of an absorption edge. You may in many cases directly measure this absorption coefficient by means of a transmission more experiment, however, in several situations you may not penetrate your sample and measure the transmitted intensity., for example in the case of a bulk material sample or if you are working with very low energies, for which the attenuation length in solids is very small (in the order of some 100 nm, see e.g. http://henke.lbl.gov/optical_constants/atten2.html).
In those cases, you may use different other signals, that are closely related to the absorption coefficient. For example, the X-ray fluorescence, i.e. the number of excited characteristic X-ray photons of a considered transition of an element. The fluorescence originates from the relaxation of the created core hole, and its intensity is proportional to the number of core hole, and thereby to the absorption coefficient.
Other signals are the absorbed current, the X-ray excited luminescence, the total electron yield, ... - all these quantities are directly linked to the photoabsorption process itself!
Differences in PL and FL may originate from the fact that the fluorescence is usually not site-selective, while the XEOL is, which has implifications especially for magnetic materials, or complex crystallographic structures, where different optical transitions are representative for specific sites in the crystal lattice.
For the XEOL, check the following article published in
EXAFS and Near Edge Structure III, Springer Proceedings in Physics Volume 2, 1984, pp 490-495 by J. Goulon et al.,
"X-Ray Excited Optical Luminescence (XEOL): Potentiality and Limitations for the Detection of XANES/EXAFS Excitation Spectra"
If you compare fluorescence and 
Hope this short explanation helps, Dirk
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Has anyone worked on nanoparticles using either X-ray absorption near edge structure (XANES) or Synchrotron radiation? I would appreciate an enlightenment on better techniques out of the two to examine biotransformation/speciation of nanoparticles in plant parts after uptake.
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From which number there is no need for correction?
Single crystal X-ray, absorption coefficient, absorption correction.
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You can do Absorption Correction of your crystal data directly by using software which  already installed in single crystal X-ray diffraction (SCXRD) instrument. Which company SXCRD are you using?  
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Mercuric nitrate monohydrate can easily take water from air, so is it really difficult to obtain a uniform layer of salt.
I know that people can prepare Hg sorbed on goethite from Hg(NO3)2 solution. However, I was having hard time to find reference materials that were made of Hg(NO3)2. I was wondering if I need to make Hg(NO3)2 reference material, should I consider to let Hg(NO3)2 precipitate from solution instead of directly using salt?
Thank you very much  
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Hg(NO3)2.H2O can readily be bought from chemical suppliers such as Alfa Aesar relatively inexpensively. Mixing with a diluant such as BN, Alumina, Silica or  cellulose should provide best results. A glove box or glove bag could be used in you have issues with water uptake. As mentioned above Kapton tape will seal the sample for measurement.
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Hallo Monu is the coverage needed as submonolayer, monolayer, or is it an average whose meaning, interpretation depends on the growth mode (as indicated by Amdrew) and which in turn depends on the growth conditions (A good reference here "Introduction to Surface and Thin Film Processes, John A. Venable, Cambridge University Press (2000)".  The information obtained depends on the escape depths  and geometry so having different energies e.g. Augers, photoelectron peaks can help in the interpretation. 
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I have Nb-doped MoS2 samples. How reliable is XPS for determination of Nb content? What other techniques could be used for that? Thank you.
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Sure you can use XPS. It can see down to 0.5 atomic %, which depends somewhat on the cross-section. The only principle trouble with XPS - it's sensitive to the first 1 nm of the surface. Among other methods are Rutherford backscattering (RBS), SIMS, EDX.
Have fun!
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 Most of the papers that I have seen involves a MC simulation where the exact formula to be used is not mentioned. 
There was another paper which states that the MC calculation was based on K value where the K value is defined as the ratio of x ray absorption by the element to the x ray absorption of the same element in bulk. Could someone kindly explain how this is calculated?
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Du you ask for EDS resp. EDX:  energy dispersive X-ray spectroscopy?! If yes, see for instance:
Notthoff, C. , Winterer, M., Beckel, A., Geller, M., Heindl, J.: Spatial high resolution energy dispersive X-ray spectroscopy on thin lamellas, Ultramicroscopy Volume 129, June 2013, Pages 30-35
or some other.
Use this link. if you have free accsess:
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Hi, I have a simple question. I have a bilayer (A & B) material with 2mm each thickness, and I want to calculate X-ray absorption final intensity. The layers have different properties. If top layer is A and Bottom is B and incident x-ray is at A, the final intensity that I will have, will that be similar if I have B as top layer and A as bottom layer and the incident x-ray is at B. I mean interchanging the layers whether effects the final intensity or not. It would be a great help for me if anyone could explain. Thanks in advance.
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Will be no effect of the order A and B. You could easly check it by using the following equation: I = I0 e-kd there k - is absorption coeff. and d - thickness.  
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Can any one explain physically why the refractive index for x-rays is less than one? Mathematically in many books it has been explained using the Lorentz oscillator model, but can some one explain it physically?
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Sorry, folks, but the three comments (by Wasim, Marek, Manohar) all touch on the topic, but none are the answer (I think). Wasim describes a nonlinear behavior of the oscillating electrons in the material that are also mentioned, more correctly in my opinion, by Manohar: the oscillating electrons (in the classical approximation, considering electrons as infinitely small points of charge) achieve the same frequency   as the electromagnetic wave that sets them in motion. They then radiate their own waves, and these combine with the incoming wave. The phase between the incoming and the induced wave determines what the index of refraction is.
If the incoming wave oscillates relatively slowly, the electrons can follow the wave: they are in phase. So, what is 'relatively slowly'? This is in relation to the oscillation frequency of the electrons themselves: in this picture the electrons may be bound to some equilibrium position and oscillate back and forth around this location, always with a small enough amplitude that nonlinear effects can be ignored. Now, when the incoming wave's frequency exceeds that of the electrons, the electrons can no longer follow the wave, and they get out of phase. Then, the waves radiated by the electrons are out of phase too, and the index of refraction is less than unity.  
What Marek says is true, but not an explanation, it's a description. Mine is also a description but it describes the mathematics that models the underlying physics, in the classical approximation.
Interestingly, you can make lenses for x-rays with this refractive effect: they have been used on synchrotron radiation sources since 1996. In some ways the best material for these lenses is lithium metal, because for many interesting x-rays this material is little more than a bag of otherwise free electrons: one problem is that an electron bound to some equilibrium location can get into some higher energy state when you take quantum mechanics into account, and when it does the electron takes the necessary energy from the wave which is then absorbed. Not good, for a lens. 
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With the availability of high-flux monochromatic x-ray beams from the synchrotron radiation ‎sources, x-ray absorption spectroscopy techniques (XAS) has developed into a widely used tools ‎for the local structural analysis around a selected atom. Extended X-ray Absorption Fine ‎Structure (EXAFS) provides us information about the number and species of neighbor atoms, ‎their distance from the selected atom and the thermal or structural disorder of their positions. My ‎question is about, what is the best real space resolution achieved by a synchrotron radiation based x-ray ‎absorption spectroscopy techniques till today. Is still a difference in bond length of order of 0.01 ‎‎Angstrom too small to detect by XAFS?‎
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I'd add that resolution, relative bond length, and absolute bond length are three different questions with different answers.
"Resolution" would be the possibility of distinguishing between having a pair of bonds at a single length and two bonds with slightly different lengths (e.g., a distorted local environment). As Paolo said, this kind of resolution is largely determined by the k-space you measure: the Rayleigh criterion gives delta R = 1/2 pi/(delta k), where delta R is the resolution and delta k is the k-range measured.
"Relative bond length" is the ability to detect a change in a bond length when the structure is otherwise similar; for example, an expansion with temperature or the effect of doping. Relative bond length can often be determined with high precision by EXAFS, although there's no single formula. Under 0.01 angstroms is not uncommon if data quality is reasonably good.
"Absolute bond length" is the ability to measure the length of a bond accurately. Because EXAFS models often have a variety of systematic errors, this is often not nearly as good as relative bond length, although for reasonably good models with reasonably good data, accuracies better than 0.03 angstroms are not uncommon.
You asked for the best, and I gave you typical values, but the distinction between the three kinds of length accuracy still applies.
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Can anyone explain me how we can calculate the electron temperature from the x-ray absorption spectrum?
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If you are asking electron temperature, Boltzmann plot and saha equation can be the solution...another way to measure the electron temperature is using interferometer.
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I would like to measure the throughput of the diffraction.
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I really need it!
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X rays
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I could provide more information about scintillation crystals desire sustancuas a project of fluorescent in dental organs
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I have L2-Pt edge spectra of a sample measured at SSRL in Stanford, but I don't have reference spectra for that exact absorption edge. I only have L3-edge reference spectra of PtCl2 and a liquid Pt(IV) solution. I have two questions:
1. Can I use reference spectra for XANES evaluation of other beamlines?
2. If so, can someone provide me with either the reference spectra or a website/online database?
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Depends on what you want. A reference spectra can be used for: a) calibration b) oxidation state comparison c) other more involved electronic structure comparison. If your purpose is a) (which is unlikely) then you are out of luck. More likely you want to compare oxidation state or other electronic properties. If it is oxidation state then, yes you can use reference spectra for XANES evaluation (be careful about calibration differences). I agree with the comment that beamline to beamline data quality will change but if you are measuring at one of the better beamlines, your data should not be that different. One way to compare beamlines is to compare your L3 PtCl2 data with that from the other beamline that you are considering comparing your L2 data with. I would stay away from comparing data with simulations.
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The question is not to distinguish between mono- and polychromatic radiation, rather it is about which X-ray diffraction experiments require monochromatic radiation and which require polychromatic radiation? What is the purpose of narrowing the wavelength range?
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I think there is no simple answer to the question as the answer largely depends on source (tube vs. synchro for instance), specimen (mono vs poly vs powder) and detector system (point vs line vs area and angle vs energy dispersive).
If I'd have to give a quick answer: Laue -> polychromatic, Bragg -> monochromatic.
From my experience, polychromatic is in general used when the size of the grains is larger than the size of the beam and monochromatic in the other cases. But there are exceptions (e.g. coherent imaging).
As in using a polychromatic for powder diffraction (with a traditional instrument): the resulting profiles are the convolution of the emission profile and the specimen broadening profile so if your emission profile is a single delta function (ideal monochromatic), all what you see is your specimen (and with sufficiently large grains this means high resolving power). If your emission profile is broad (polychromatic) then the pattern will be dominated by the instrument. Of course this does not happen if you have a single crystal (and in that case you can directly image the reciprocal lattice).
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Dear Mr Sanjay,
Xray crystallography captures just one snap shot of many possible conformation that a protein can adopt in solution whereas MD although dynamic and explores conformational space but it is important to understand that MD can sample very less diverse conformation. It will dwell around the starting conformation. Neither Xray nor MD could explore all possible intermediate state of protein.
For example consider a receptor protein which binds to a ligand by induced fit affect. Using X-ray crystallography you can capture both apo (Ligand unbound) or holo form (Ligand bound) of same receptor. Lets assume that there is a drastic conformational change occurs upon ligand binding i.e. apo and holo receptor conformation are very different.
If we try to explore the above using MD and if we start our MD simulation with the apo receptor conformation, MD will sample around this equillibrium apo form. It is difficult to land from apo to holo receptor conformation using MD.
Another point is the experimental condition is rather difficult to mimic.
Last point is the time scale !!! ns? microSec? miliSec?
Lots of point we could consider when we compare Expt with Comp tech.
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I have a solution of gold branched nanoparticles and I need to measure the mass concentration. I'm thinking to use X rays scattering and/or absorption to calculate the amount of gold in solution.
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As always there are limits, but in general the answer is yes. You could use XRF and measure the concentration of gold from the fluorescence light emitted from Au atoms in a well defined volume. This is a standard procedure used in many commercial XRF devices for the analysis of concentration in galvanic cells. Click the link for a picture of a sample measuring cell (http://www.helmut-fischer.com/independent/31/Accessories_XRAY.asp). For a first try you could think of sending a sample to one of our application labs or simply visit an application lab.
Cheers,
Joerg Leske