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

[Matt Newville]

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