On 01/25/2016 09:13 AM, Aditya Shivprasad wrote:
I was looking at the XANES standard for Fe foil from Hephaestus and I noticed that there was a small, curved feature at the edge (7112 eV), another inflection point at 7116.4 eV, and then the edge step at around 7131 eV. My question is: why is the feature at 7112 eV considered as the edge and not as a pre-edge feature? Are they due to fundamentally different phenomena? I would like to understand where this type of feature comes from so as to be consistent in the current paper that I am writing. I have attached the standard, just in case.
Hi Aditya, That's a great question! In Athena, you are looking to identify the "threshold" or the "zero of wavenumber" as the value for E0. In a metal, this is probably not hard to identify. In a compound, which might have localized, unoccupied states, the question is a bit harder. As a practical matter, you want to process your data consistently and in a way that yields defensibly normalized data so that you can use XANES methods (e.g. LCF or PCA) and EXAFS analysis in a defensible way. As a practical matter -- almost any point on the main rising edge tends to be adequate for either XANES or EXAFS analysis. I was going to go on and talk about how to think about the Fermi energy, but I was going to say basically the same thing that Matt said in his email that arrived while I was typing. Matt's comment about the "XANES industry" is quite right and I encourage you to read up on that. But as a practical matter, these choices should be consistent such the normalization is done in a consistent manner. What do I mean by "consistent"? Well, I believe you said you are doing some kind of LCF analysis of your data. Well, if you were to make a synthetic sample with known quantities of Iron standards, then your methodology for the analysis of the standards and the synthetic sample should yield the same ratios that were used to make the sample. 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/