[Ifeffit] Ti data problem

[Carlo Segre]

Hi Jia:

For the first one of the spectra, I chose the shoulder in the derivative 
at 4974 instead of the large peak.  I consider the lower energy peak to be 
a pre-edge feature due to the 3d quadrupole transitions and I generally 
don't choose that.  If the analysis later tells me that I am wrong, I move 
it accordingly.

In this case, the 4974 positoin withthe other parameters I mentioned gives 
a very reasonable FT.

Carlo

On Mon, 8 Aug 2016, Qingying Jia wrote:

> Hi Carlo,
>
>  In many transition metal oxide cases like this, what would be the more
> proper E0, the position of the apex of the first derivative peak or the
> second one that is usually higher than the first peak, or it really
> depends? I have seen people using either. In this particular case, it seems
> like using E0 of 4967 eV (the first derivative peak position) gives cleaner
> and more reasonable FT-EXAFS.
>
>  Regards,
>  Jia
>
> On Mon, Aug 8, 2016 at 5:05 PM, Carlo Segre <segre at iit.edu> wrote:
>
>>
>> Hi Siliang:
>>
>> The first thing is that you have misidentified the edge position.  Itis
>> way too high in all the data sets.
>>
>> Put it at the inflection point of the main rise in the absorption curve
>> and you will find that the problem is much reduced.
>>
>> The second thing is that you have a very bad backgrund problem in your
>> data and, in my estimation your usable data range is no moe than k=2 to
>> k=8.  In fact, my suggestion is that you truncate the data by setting the
>> spline range to end at 8.  The FT range should probably be set at 2-8 or
>> even 2-7 (somewhere in that range and put a window sill of dk=2 to get rid
>> of some of the ringing.
>>
>> Once you do those things the data will look much more reasonable.
>>
>> These data could probably have used some longer counting times.  Where did
>> you take the data?
>>
>> Carlo
>>
>> On Mon, 8 Aug 2016, Siliang Chang wrote:
>>
>> Dear all,
>>>
>>>
>>>
>>> I am new to XAFS data analysis. I?m currently working on the XAFS data of
>>> atomic layer deposited mixed oxide thin film: SnTiOx. I have both Sn and
>>> Ti
>>> K edge data, and was able to fit Sn edge using a model of (Sn,Ti)O2 solid
>>> solution. However, Ti data really confuses me (please see attached file).
>>> With Rbkg set to 1, there is a doublet in 1-2 Å region in every data, this
>>> is something I have never seen in the literature. I?m wondering if this is
>>> normal? Does this mean I should set a larger Rbkg value, say, around 1.5?
>>>
>>>
>>>
>>> I?ve tried to fit the abovementioned Ti data using several models:
>>> anatase,
>>> rutile, (Sn,Ti)O2 solid solution, perovskite (N is fixed at 6 for all of
>>> those), so far no success. I would really appreciate if you can comment on
>>> my data processing, any suggestions are welcomed, as I?m new to this, I?m
>>> not sure if I?m doing it the right way.
>>>
>>>
>>>
>>> Thank you very much.
>>>
>>>
>>>
>>> Best regards,
>>>
>>> Siliang Chang
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>> --
>> Carlo U. Segre -- Duchossois Leadership Professor of Physics
>> Interim Chair, Department of Chemistry
>> Director, Center for Synchrotron Radiation Research and Instrumentation
>> Illinois Institute of Technology
>> Voice: 312.567.3498            Fax: 312.567.3494
>> segre at iit.edu   http://phys.iit.edu/~segre   segre at debian.org
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>>
>

-- 
Carlo U. Segre -- Duchossois Leadership Professor of Physics
Interim Chair, Department of Chemistry
Director, Center for Synchrotron Radiation Research and Instrumentation
Illinois Institute of Technology
Voice: 312.567.3498            Fax: 312.567.3494
segre at iit.edu   http://phys.iit.edu/~segre   segre at debian.org