Dear Pushkar,
1) The priority is the mass, i.e. the number of absorbing atoms of the
measured element, because that determines the edge jump. The thickness
mostly depends on the type of sample and amount of BN (or cellulose) used
and is usually important for the stability and homogeneity of the pellet.
0.5 mm to 1 mm thickness is fine. The thickness affects the total
absorption, so do not use too much BN. If your pure material makes good
pellets without BN, great!
2) You have a bimetallic Cu-Pd alloy. Yes, treat Pd as a neighbour of Cu.
In the feff-input, replace some of the Cu with Pd and calculate the
scattering paths. For the Cu K-edge spectrum, refine the Cu-Cu and Cu-Pd
paths and for the Pd K-edge spectrum refine the Pd-Pd and Pd-Cu paths.
Prior to that, refine the spectra of the pure metals (Cu and Pd foils) to
get an idea of the S02, deltaE0 and sigma2 values that you should expect
for the alloy.
Googling "exafs bimetallic" gives many nice articles.
3) Using linear combination analysis (e.g. in Athena) the fraction of Pd
and Pd2+ can be easily determined.
All the best!
Alexey
2017-02-01 7:19 GMT+01:00 pushkar shejwalkar
Dear All, I have some basic questions that are more related to the practical handling of the samples rather than the concept. 1) Recently we had to prepare for the Cu and Pd samples and I had carried out the calculations of how much material will be needed for such measurement to get relatively good uT and deltauT values. For such purpose, I used the program developed by SPring-8 (on their website) dedicated for BL-14 beamline. In this program we can put in the cell diameter and what kind of BN thickness is needed. Since my samples are metal immobilized heterogeneous organic materials, it has a lot of background in terms of C,H,Si,N etc. Thus, I use material directly and I do not use BN at all. So my BN thickness is 0. How do I change this mass of material needed into the thickness of cell? What I do, is I use density of material and for the cylinder of pellet I calculate the thickness. My question is, WHAT GETS THE PRIORITY, THICKNESS OR MASS of material that goes in? Becuase thickness of pellet governs the XAFS equation, whereas mass governs the absorption peak (height and high uT). It is difficult to comprehend everything written on website, Since the website is in Japanese and I am not. Also it is kinda difficult to communicate with the authorities directly in free English, I am asking this question here. 2) Secondly, In the mixed metal case of type AB, If I focus the energy for A, how will the B have effect on the scattering of A. A=Cu and B=Pd. I will be measuring Pd in later days. Would it be possible to consider Pd (in this case) as a neighboring atom and purely treat it like I would otherwise e.g. N or O like that? Since this is my first time with mixed metal situation, any reference publications or material to read would be very helpful. 3) In another case of mine, I have Pd and Pd2+ mixture in my sample. Would it be possible to estimate the exact concentration of each of them? Using two analytically pure Pd and Pd2+ salts to make calibration curve would it be possible to get the exact concentration? What will be the independent variable on the graph? . Thank you for your kind help and information, in advance Best Pushkar
-- Best Regards, Pushkar Shejwalkar. Post-doctoral -Researcher, Tokyo Engineering University, Tokyo-to Japan
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