[Ifeffit] Linear Combination Fitting using ATHENA

Wed Aug 14 03:46:48 CDT 2013

Yup.  That's consistent.  That sort of thing is why every XANES paper should state clearly
the basis of the energy calibration.  With Newville's database, you can often figure that
out yourself because many of the spectra were done with a reference foil.
    mam
----- Original Message ----- 
  From: Teck Kwang Choo 
  To: XAFS Analysis using Ifeffit 
  Sent: Wednesday, August 14, 2013 1:07 AM
  Subject: Re: [Ifeffit] Linear Combination Fitting using ATHENA

  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 
      To: XAFS Analysis using Ifeffit 
      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>>

                    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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  PhD Student
  Department of Chemical Engineering
  Room 225, Building 36
  Monash University
  Mobile No.: 04-11489904

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