[Ifeffit] Give me some advices

[Leandro Araujo]

Hi Kefan,

I'll risk some comments here since I've worked with Ge nanocrystals
before. Keep in mind that these are comments based on the belief you
measured at a synchrotron facility (essential when working with
nanostructures, I guess) and on the information you gave, which does
not mention how dilute your samples are, if you measured in
transmission or fluorescence mode, if the samples are solely composed
of Ge or not (and they are very likely not to be - is there any Si in
your samples?), if there is a matrix around the QDs or if they are in
solution with surfactant atoms, ect. Such circumstances might make my
comments dubious (or even more dubious), but I'm sure more experienced
users would warn you should that happen.

1 - The first thing I noticed when opening your project is that you do
not have any standards! You should have at least one bulk crystalline
Ge standard when working with Ge nanostructures. Having bulk amorphous
Ge and bulk GeO or GeO2 standards would also be very useful. Just by
comparing the spectra of your QDs to the spectra of the bulk standards
(check the attached project) we can infer that your QDs are very
unlike to be crystalline like bulk Ge, even after annealing. You can
tell this by the complete lack of oscillations at higher k in your
spectra (from k ~ 8 inverse angstrom onwards the signal looks like
noise-only). In fact, even the amorphous Ge standard has more
oscillations at higher k. Further evidence is given by the XANES
structure after the white line, which does not resemble either
crystalline or amorphous bulk Ge. And it does not resemble the bulk
crystalline oxide as well. I know this was not your question but I
mention it here to warn you that your data goes against the assumption
that you have "elemental Ge QDs"; it actually suggests that you have
"Ge-something QDs".

2 - You surely have an awful lot of glitches (sharp spikes) in the
spectra with higher numbers (i.e., Ge23, Ge24, etc), which I assume to
be the QDs annealed at the highest temperatures. Interestingly, the
glitches do not appear always in the same places, so I'd guess that
they are not originated from harmonic reflections or monochromator
issues. They might be related to the sample preparation method; Grant
Bunker has elaborated a very good presentation on EXAFS sample
preparation that you can check at
http://gbxafs.iit.edu/training/XAFS_sample_prep.pdf . It might be of
help for future measurements. As for your spectra now, I guess you can
try and deglitch them. Deglitching in Athena is easy, as you can
verify in the Athena manual (the one you mentioned a few days ago).
Keep in mind that when deglitching you should remove the sharp spikes
without changing the oscillatory features in your spectra.
Nevertheless, it seems to me that even after deglitching it will be
pointless to try and fit something beyond k ~ 10 inverse angstrom.
Good luck, anyways.

3 - Finally, I'd advise you (since you asked for advice ;) ) to mind
the title of future emails. "Give me some advice" does not sound well
in English, I guess. It sounds like giving and order, which I believe
(and hope) was not your intention. A "Please" at the begging (or end)
would help making people more prone to help you...

Hope all this babbling helps,
Leandro


On Dec 17, 2007 9:22 PM,  <wang.kefan at gmail.com> wrote:
> Hi
> I have used the Athena 0.8.054 to processing the EXAFS data of Ge quantum
> dots. You can find the .prj file in the attachment. In fact, they are a
> seriers of samples with or without annealing at high temperature. Surely,
> the data after annealing is difficult to deal with. Please do not hesitate
> to give me some advices! Such as the issues on normalization, deglitching,
> truncating, etc. Thanks a lot.
>
> PS, I think this is a good way to exchange experiences and learn knowledges.
> Kefan
> --
> Kefan Wang
> School of Physics and Electronics
> Henan University, 475004
> E-mail: kfwang at henu.edu.cn; wang.kefan at gmail.com
> _______________________________________________
> Ifeffit mailing list
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>
>
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