[Ifeffit] Peakfitting CeO2 data in Athena

Matthew Marcus mamarcus at lbl.gov
Wed Dec 7 14:22:53 CST 2016


Ce(OH)4 is probably not a well-defined compound.  I wouldn't use it.  I suspect that "Ce(OH)4" is really hydrated CeO2 nanos.  I've measured 30nm CeO2 nanos and they look like bulk.
	mam

On 12/7/2016 11:53 AM, Stephanie Laga wrote:
> I had started with LSQ but switched to peak fitting because I was worried about the Ce(IV) reference. I have data for bulk CeO2 and Ce(OH)4, but doesn't this have some Ce(III) impurity in it? I'm not quite sure how to account for this when I do LSQ.
>
> Another challenge I've had is in using the Ce(IV) refs for our nanoparticles, which are about 2-5 nm in diameter. Is there a good Ce(IV) ref for nanos that are in this size range?
>
> On Wed, Dec 7, 2016 at 2:37 PM, Matthew Marcus <mamarcus at lbl.gov <mailto:mamarcus at lbl.gov>> wrote:
>
>     Instead of doing a bunch of peak fitting, try LSQ.  Use CeO2 (bulk or nanos) for one reference and some Ce(III) for the other.  Consistency check: see that the Ce(III) fraction is consistent over some set of Ce(III) references.
>     Ce(III) has an assymetric white line, so it doesn't really fit a single gaussian.  CeO2, unlike other Ce(IV), has a shoulder on the first peak, and the first peak is shifted left a little with respect to other Ce(IV).
>             mam
>
>
>     On 12/7/2016 10:33 AM, Stephanie Laga wrote:
>
>         Dear all,
>
>         I am trying to extract the % Ce(III) from some CeO2 nanoparticle XAS data. I have been using moved the peak fitting function in Athena to model the XANES with an arctan background function and a series of gaussians.
>
>         Looking through the literature I haven't seen too many specifics to using this approach (rationale for choosing the widths of peaks or how to define the background function). Similarly, doesn't seem to be much rationale for choosing a 4 vs 5 peak fit for the XANES.
>
>         My main question is then...1) Is there a rational for picking the background function, specifically the height and width (can I let the height vary or should I be keeping a constant arctan through all samples)?
>
>         Any advice is greatly appreciated!
>
>         Stephanie
>
>
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