[Ifeffit] Linear Combination Fitting using ATHENA

Wed Aug 14 03:07:40 CDT 2013

Yes Matthew, I used 7112 eV for my Fe K-edge calibration. I am guessing
that is the reason a ~+1 eV shift in your maghemite spectrum is required is
required to fit mine. Both pre-edge features match in the sense that they
are roughly bound by the same energy values.

On 14 August 2013 17:30, Matthew Marcus <mamarcus at lbl.gov> wrote:

> **
> That depends on the way you did your calibration.  If it really matches,
> including the
> pre-edge features, with a 1eV shift, then that's what you probably have.
> Did you take
> into account my calibration, which puts the Fe K-edge at 7110.75eV?  Some
> people use other
> values like 7112eV.
>     mam
>
> ----- Original Message -----
> *From:* Teck Kwang Choo <teck.kwang.choo at monash.edu>
> *To:* XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> *Sent:* Tuesday, August 13, 2013 9:20 PM
> *Subject:* Re: [Ifeffit] Linear Combination Fitting using ATHENA
>
>  Also Matthew, I have found that my sample spectrum is an almost exact
> replica of the maghemite spectrum, the only differences being the
> absorbance height of the edge-peak (highest peak), which is ok but more
> importantly
> I have found that there is a +1eV shift of my spectrum relative to the
> maghemite one, probably due to slight differences in beamline. Do you think
> it is alright to make a +1 eV shift to the maghemite spectrum (or -1eV
> shift to my sample spectrum)?
>
> Thanks.
>
> Kind regards.
>
> Teck Kwang
>
>
> On 14 August 2013 10:07, Teck Kwang Choo <teck.kwang.choo at monash.edu>wrote:
>
>>  Thanks Matthew for the spectra.
>>
>> Is it correct to use the spectra that was taken in transmission mode (the
>> one you did) to fit those taken in fluorescence mode (my case)?
>>
>> Teck Kwang
>>
>>
>> On 14 August 2013 01:37, Matthew Marcus <mamarcus at lbl.gov> wrote:
>>
>>> Here are reference spectra.  The calibration is defined with the Fe
>>> metal edge at 7110.75eV.  The maghemite spectrum has been corrected for mild
>>> overabsorption by reference to magnetite, which is very similar.  The
>>> magnetite is synthetic Fe3O4 from Aldrich, and done in TEY, so no
>>> overabsorption.
>>> The maghemite is from oxidation of Fe oxide nanoparticles and has been
>>> verified by XRD and comparison with the ETH group's maghemite spectrum.
>>>         mam
>>>
>>>
>>> On 8/13/2013 1:33 AM, Teck Kwang Choo wrote:
>>>
>>>> Hi all,
>>>>
>>>> @Drew Latta: I was wondering why the end members should be magnetite
>>>> and maghemite. Is it because they are both of inverse-spinel structure, the
>>>> difference only being that the latter has all Fe completely oxidized into
>>>> Fe(III)? Would you be able to provide the standard spectra to me if that is
>>>> the case? Thanks very much!
>>>>
>>>> Previously I have only thought of using hematite (alpha-Fe2O3) and FeO
>>>> as end-members, both representing Fe(III) and Fe(II) respectively without
>>>> giving much thought to the structure Fe takes. I also had my doubts using
>>>> magnetite (Fe3O4) as a standard as it is a mixture of both Fe (II) and Fe
>>>> (III). But thanks to the insights Drew has given, I now think I should take
>>>> the Fe-coordination environment into account with the use of magnetite and
>>>> maghemite as standards.
>>>>
>>>> @Alexandre and Matthew: I have obtained Mossbauer spectra of some of my
>>>> samples but like Drew said, it is not straightforward at this point in
>>>> time. Will see what I can do with the data I have!
>>>>
>>>> Thanks for all your responses! It is greatly appreciated! This forum
>>>> has been more helpful than I thought!
>>>>
>>>> Teck Kwang
>>>>
>>>>
>>>> On 13 August 2013 01:34, Matthew Marcus <mamarcus at lbl.gov <mailto:
>>>> mamarcus at lbl.gov>> wrote:
>>>>
>>>>     While it's true that Mossbauer is the gold standard for Fe valence
>>>> determination, access to the technique isn't all that common, and I don't
>>>> know
>>>>     of any facility that can do it on a micro scale.  Is there one?
>>>>              mam
>>>>
>>>>
>>>>     On 8/12/2013 7:01 AM, Alexandre dos Santos Anastacio wrote:
>>>>
>>>>         Hello,
>>>>
>>>>         maybe that fingerprinting technique would be Mossbauer
>>>> spectroscopy. The Fe(II)/Fe(III) ratio comes easily and also there are lots
>>>> of papers about Mg-ferrite, an example:
>>>>
>>>>         10.1109/TMAG.2009.2018880 <http://dx.doi.org/10.1109/__**
>>>> TMAG.2009.2018880 <http://dx.doi.org/10.1109/__TMAG.2009.2018880> <
>>>> http://dx.doi.org/10.1109/**TMAG.2009.2018880<http://dx.doi.org/10.1109/TMAG.2009.2018880>
>>>> >>
>>>>
>>>>         Alexandre.
>>>>
>>>>
>>>>
>>>>
>>>>
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>>>>
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Teck Kwang Choo
>>>> PhD Student
>>>> Department of Chemical Engineering
>>>> Room 225, Building 36
>>>> Monash University
>>>> Mobile No.: 04-11489904
>>>>
>>>>
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>>
>>
>> --
>> Teck Kwang Choo
>> PhD Student
>> Department of Chemical Engineering
>> Room 225, Building 36
>> Monash University
>> Mobile No.: 04-11489904
>>
>
>
>
> --
> Teck Kwang Choo
> PhD Student
> Department of Chemical Engineering
> Room 225, Building 36
> Monash University
> Mobile No.: 04-11489904
>
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-- 
Teck Kwang Choo
PhD Student
Department of Chemical Engineering
Room 225, Building 36
Monash University
Mobile No.: 04-11489904
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