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.
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.