On 11/27/2014 04:13 AM, kaziz sameh wrote:
Dear All, I look for advice or document that can help me to fit the FT EXAFS data of Pd2Au36(SR)24. The situation is as follows: In the sample there is 3 sites of the Pd ( in staples, in surface or in the core). the spectrum that I have presents a first bond of Pd_S and second bond of Pd_Au, so the palladium should be in the staples or in the surface because in core we cannot see Pd-S, but other results of the same sample confirm that the palladium is in core. I concluded that there is a mixture of some nano (x ) with Pd in staple and another nano(y) with Pd in core such y>x. Note that I fit the data with Pd2Au36(SR)24 structure in which I put the 2 palladium in the staple and I have got a good fit (attached) but I think that is not logical. If you can help me with an idea how to fit this mixture, I would be very grateful.
Kaziz, I don't really understand your question. You use a lot of jargon. I don't know what a "staple" is this context. I don't know what "SR" means in this context. I don't know what "x" and "y" are or how they might enter into your analysis. And I do not know anything about the nature of the sample you are measuring or what you did to measure it. When you ask a question in a forum like this mailing list, it is helpful to remember that those reading your question know a lot about XAS, but probably don't know anything about your specific research problem. You need to ask a question that can be answered in that context. Reading between the lines, you seem to have a problem that is similar, at least conceptually, to the question that Pushkar Shejwalker asked last night. That is, you seem to be anticipating one thing, but coming to a different conclusion in your EXAFS analysis. That happens sometimes. In fact, that can be the exciting part of doing research. If our measurements always turned out exactly the way we anticipate, then the synchrotron would be a much more boring place. You need to first ask yourself if your expectation is merited. What is the evidence from other measurements supporting your expectation? Have you been very careful to control the state of your sample throughout its entire lifetime? Is there any chance that the sample could be damaged by exposure to the beam? If you have convinced yourself that the sample is in the state you expect, then you need to evaluate the result of your EXAFS analysis. Is the R factor small? Are all the fitting parameters of values that make sense physically? Are the error bars small? If you are finding the sample in a different state that you anticipate, do you think that the results you obtained are defensible? If so, then maybe you have discovered something new about your sample! If not, then you need to critically evaluate all the steps of the experiment all the way from sample prep until pressing the fit button in Artemis. I encourage you to, as Matt suggested, figure out how to ask a more targeted question. Broad, open-ended questions are hard for the rest of us to answer. Well-focused questions tend to get better answers. HTH, B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS-II Building 535A Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/