Dear All I would like to grow UO2 thin films on STO (SrTiO3) substrate but I found that Sr K-edge 16105 and U L3-edge is 17166. Do you think there will be any interference? Best, Mohamed
Dear Mohamed,
I think you will have some kind of "over" or "self" -absorption from the
substrate, specially in geometries other than grazing incidence. I have
performed that kind of experiments in fluorescence and in transmission. The
result was that the absorption coefficient signal I was interested in,
really was of 2nd or 3rd order of magnitud less that the "tail" of
absorption of the substrate. I would not do that again. Maybe somebody has
better experience.
Regards
Maria Elena
2010/11/16 mohamed sobhy
-- María Elena Dra. María Elena Montero Cabrera Centro de Investigación en Materiales Avanzados (CIMAV) Miguel de Cervantes 120, Compl. Ind. Chihuahua Chihuahua CP 31109, Chih. México Tel (614) 4391123
I'm assuming that the desire is to measure the EXAFS of the UO2, not the SrTiO3 substratem right? The ratio of the signal from the SrTiO3 to the UO2 would depend on the thickness of the UO2 and the incidence and takeoff angle (assuming you do fluorescence). There shouldn't be much interference with the EXAFS signal from the substrate because you're a keV away, so the EXAFS from the substrate will be substatially damped and will show up as slowly-varying background. The real issue will be if the fluorescence from the Sr swamps that of the U. The fluorescence energies are pretty close. Some things to try include going to grazing exit or incidence, depending on the film thickness, and doing the measurement in electron yield, which won't see much of the substrate. mam On 11/16/2010 2:16 PM, María Elena Montero Cabrera wrote:
Mohamed, The answer to that would depend on the relative amounts of U and Sr that you probe simultaneously with the beam, as well as what you mean by "interference". By 1000 eV above the edge oscillations from the EXAFS are largely gone (relative to the edge step). So I would say that Sr K-edge oscillations are unlikely to interfere with your U L-edge oscillations, unless your U L-edge step is say 500x smaller than your Sr edge step or the Sr atoms are in a very tight binding environment (not sure if STO qualifies) and you decide to measure the spectra at LN temperature. Your bigger problem will likely be collecting the U EXAFS data with sufficient signal-to-background ratio. Attached is an XRF spectrum from a U-contaminated sediment containing Sr (not sure what the Sr:U ratio is, but I think it is small), measured in a relatively high energy resolution mode of a Ge detector. You can imagine the Sr line being many many times bigger in your system, so the U line may end up being a small blip on the left shoulder of the Sr line. A solid state detector will probably not be able to sufficiently separate the two signals. You may have to use grazing incidence geometry to minimize the substrate Sr signal and/or use a high energy resolution detector to separate the U and Sr lines (e..g a bent Laue analyzer). Both of the latter will make the experiment non-trivial, so be prepared for some extra work :-). Finally, the answer will depend on the level of detail you are hoping to get from the measurement. If all you are interested in is proving the formation of uraninite then the U-U coordination should be relatively easy to see in a Fourier transform in spite of all the possible "interference" effects discussed above. Cheers, Max. _____ From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of mohamed sobhy Sent: Tuesday, November 16, 2010 3:38 PM To: ifeffit@millenia.cars.aps.anl.gov Subject: [Ifeffit] UO2 thin films on STO Dear All I would like to grow UO2 thin films on STO (SrTiO3) substrate but I found that Sr K-edge 16105 and U L3-edge is 17166. Do you think there will be any interference? Best, Mohamed
participants (4)
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María Elena Montero Cabrera -
Matthew Marcus -
Maxim Boyanov -
mohamed sobhy