[Ifeffit] Very large exafs amplitude in collected data - cause unknown (Jason Alvino)

[Jason F. Alvino]

Hi Matt,

As I pointed out before, in the attached zipfile, there is a file called
"AuNP_anatase_Au.D" which has the data in two columns of energy vs mu,
comma separated underneath the "EV RAW" header.

It also already has all the bad channels removed from the averaged data.

Cheers,
Jason

Hi Jason,
>
> On Fri, Jun 7, 2013 at 9:25 AM, Jason F. Alvino
> <jason.alvino at adelaide.edu.au> wrote:
> > Hi all,
> >
> > There seemed to have been abit of a misunderstanding with the data
> format,
> > sorry about that. I was not really sure what format was going to be best
> to
> > share with people, I thought the raw data would have been useful so that
> > people were able to see all the channels.
> >
> > I have attached a data file from average (AuNP_anatase_Au.D) which has
> the
> > data in columns of energy vs u(E).
> >
> > The second data format (.ssrl) has data in the following columns;
> >
> > 1 = real time clock
> > 2 = Mono angle (requested)
> > 3 = Energy (eV)
> > 4 = I0
> > 5 = I1
> > 6 = I2
> > 7-9 = blank
> > 10-44 - fluor channels (SCA)
> > 45-79 - ICRs for the det element
> >
> > I have attached these two data sets to this new email.
>
> I still am completely unwilling to work with that file.  Send a file
> with no more than 5 columns, and do not expect anyone to add columns
> together or know how you would use the different columns in your file.
>  It's best to send a file with only energy and xmu.
>
> > Now to try to answer some of the questions that have been asked of the
> data.
> >
> > The samples are chemically synthesised Au8, Au9, Au11 clusters protected
> by
> > PPh3 ligands. We then support these samples on various oxides, in this
> case
> > anatase at a % weight loading of 0.17% cluster/anatase. The loading is
> > typically quite low as we discovered that higher loadings lead to greater
> > levels of Au agglomeration. The samples can then undergo various
> treatments,
> > in an attempt to remove the protective ligand groups, however harsher
> > treatments can also lead to agglomeration of the Au clusters. The
> currently
> > attached example is of Au9 on anatase at 0.17% loading after being
> calcined
> > at 200 C under an oxygen atmosphere. There was potentially an issue
> > initially about releasing all the info of the samples which has  now been
> > sorted out.
> >
> > "Perhaps there is some sort of coupling in the signal chain between the
> Ge
> > detector and IO" - I wouldn't really know how to start with that one,
> > however I could have another chat with the beamline scientists over this
> and
> > see if they may have some ideas as to the cause.
> >
> > We were actually analysing some of the data as we went, but unfortunately
> > not all of it. However this problem of large k2 or k3 weighted exafs
> > amplitude only occurs in samples that we know begin to agglomerate into
> > larger particles of gold (this has been determined from a similar study
> we
> > have done at the SXR). We have multiple samples that display this
> behaviour.
> >
> > The values I get for sigma2 when trying to fit using XFIT are 2 or
> greater,
> > if I maintain debye waller factors greater than 0.001 and maintain
> sensible
> > coordination numbers <=12.
> >
> > The samples were cooled to 12 K using a cryostat, however the Au foil
> data
> > is not cooled.
>
> That alone could explain the difference.
>
>
> --Matt
>
>
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> End of Ifeffit Digest, Vol 124, Issue 8
> ***************************************
>



-- 
Jason F. Alvino
PhD Candidate (Chemistry)
School of Chemistry and Physics
University of Adelaide, AUSTRALIA 5005
Ph     : +61 8 8313 3707
E-mail: jason.alvino at adelaide.edu.au
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