[Ifeffit] Question about shift in E0

[Brandon Reese]

Ahh, it sounds I wasn't entirely clear on what I doing. The measurements
were at the In edge, so I aligned all the scans such that the peak in the
first derivative of the reference foil was at 27940 eV. The peak of the
first derivative in the samples was ~27944 eV. The 1st derivative peaks of
samples grown without additional oxygen ("conducting") compared to the
samples grown with additional oxygen ("intrinsic") were ~0.5 eV different or
less.

Using the peak of the first derivative in Athena for the background
subtraction, the refined E0 in Artemis was ~7 eV for conducting samples and
~5.5 eV for intrinsic samples. I also tried setting the E0 in Athena to the
peak of the whiteline, which was about 27950 eV. Again the spread between
the white line peak values was ~0.5 eV between samples.  With this value for
the background subtraction in Athena, Artemis refined the E0's to be ~1.5 eV
for the conducting samples and ~0 eV for the intrinsic samples.

Another piece of information is that the refined CN's for the samples had an
inverse correlation to shift in E0. So the conducting samples with a higher
E0 (by 1.5 eV) had a lower CN of about 0.1. The calculated correlation in
Artemis for the two variables was ~35%.

I didn't intentionally change anything on the beamline setup. I measured all
of the conducting samples and then all of the intrinsic samples. So if there
was a sudden change in *something* in between the sample groups, it would be
consistent. The sample changes took ~10 minutes at most, so the change would
have to happen on that time scale. The only other consistency I noticed is
the conducting samples had to be shifted ~0.7 eV to get the metal foil to
line up, and the intrinsic samples only had to be shifted about 0.1 eV.

Brandon

2011/6/6 "Dr. Dariusz A. Zając" <kicaj at ifj.edu.pl>

> **
> Hi Brandon,
> before someone gives you correct answer, could you shortly inform us, what
> is the E0 for reference foil, for each experimental data. As I understand
> you have a shift of 7eV between samples, but measured on samples, thus would
> be nice to see what is the shift for reference.
> The second question comes for me automatically - have you done something
> with the beamline set-up between experiments ?
> kicaj
>
> W dniu 11-06-06 08:56, Brandon Reese pisze:
>
> Hi all,
>
> I am looking at EXAFS of thin film metal oxides.  I am varying both metal
> content and the oxygen content of the films. I aligned the scans with a
> metal reference foil collected simultaneously.  In Artemis, I have noticed
> that when changing between films with no extra oxygen versus those with
> extra oxygen there is a shift in the fitted E0 of ~1.5 eV (after aligning to
> the foil). I tried setting the E0 in Athena to the peak of the 1st
> derivative and the peak of the white line with the same result (~7 eV
> difference). I was a little surprised by the offset because in Athena the E0
> values varied by <0.5 eV. I am not sure if the argument could be made that
> this shift is a result in a changing oxidation state because it doesn't show
> up in the XANES (at least qualitatively).  Are there other experimental
> effects that could cause a shift like this, or is this likely something real
> in my material? If anyone want to see a representative group of data, let me
> know.
>
> I also have an unrelated quick (I think) question on the EXAFS equation. In
> some references I see a term 1/(k R)^2 and in others it is 1/(k R^2). I
> couldn't really see any reason for the difference, unless it is to correct
> for subtle differences in how the other terms are defined.
>
> Thanks
> Brandon
>
>
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