[Ifeffit] copper 1st shell coordination number

[Scott Calvin]

You're thinking about this the right way, Zhaomo Tian.

The measurement should come primarily from the bulk portion--even electron yield, which is most surface sensitive, will probe deep enough for that, and fluorescence or transmission certainly would.

Are you getting a reasonable value for sigma2? If you have a negative sigma2 and a coordination number that is too small, that suggests some sort of data problem. If, on the other hand, you're getting a more typical value for sigma2 (in the 0.001 to 0.01 angstrom^2) range, then that suggests you're seeing something structural in the sample. Could there be vacancies? Some sort of non-close-packed structure? A modest degree of oxidation or other impurities?

--Scott Calvin
Sarah Lawrence College

On Jan 1, 2013, at 4:57 PM, Zhaomo Tian wrote:

Dear all!

Really thanks for your kind and helpful reply to my previous questions about confusion between CN and degeneracy number.I understand it now.

Now another problem happened is that when I tried to fit the first shell of Cu, the CN would never be 12(initial guessed value), but turned out to be some value around 8. At first, I thought something might be wrong such as choosing bad value of S02, but after I set different values for S02 in a certain range, the CN won't change too much and remains around 7~8. Then I suddenly realized that the guessed CN of Cu first shell should be closed to 8 rather than 12, I do not know if it is correct so I am asking if it is possible. The reason is : actually, my copper data is not from copper foil but from a copper thin film(thickness around 300nm deposited on silica substrate), the EXAFS data I wanted is also the surface copper atom, For surface copper atom, there is only 8 nearest neighbors(the upper 4 nearest neighbors do not exist). So I think if the EXAFS signal came mainly from the surface copper atom, then the ideal CN for 1st shell is 8, but since there is only one single! top atomic layer and the rest are all bulk, I think the major EXAFS signal should come from bulk, in this case the CN for 1st shell should be 12.

Maybe I am thinking in a wrong way, I am waiting to be corrected.

Thanks so much!
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