On Wednesday, February 15, 2012 01:52:50 am 陈娟 wrote:
However, for the pure standards without dilution by BN, How to do the self-absorption correction? For example, I try one, but cannot get the credible spectra. ForDibenzyl Disulfide, the formula should be (C14H14S2)0.5435(BN)0, no dilution. I put (C14H14S2)0.5435(BN)0 in, but the spectrum I got is
So can you tell me how to do the pure standards self-absorption correction using Athena?
The self-absorption corrections are not particularly robust algorithms. For pure materials, they tend to be quite sensitive to errors in tabulated values, small errors in stoichiometry, and so on. I don't really know what dibenzyl disulphide is or how you prepare the sample for measurements. I would guess that, when specifying the stoichiometry, you will need to do something to account for the sample holder. For example, if you have a thin piece of polyimide tape between the beam and the sample, that will have the effect of "diluting" the sample, at least as far as the correction algorithm is concerned. This (along with Matthew's point about particle size and many other issues) is one of the reasons why self-absorption correction is such a tricky business. You could try making the coefficient for the (BN) something non-zero to approximate the effect of the tape (or of any water that might have been absorbed, or whatever). I suspect that if you do so, you will find that the correction will be numerically stable. Will it be right? Who knows! B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/ifeffit/Demeter