Re: [Ifeffit] Ifeffit Digest, Vol 172, Issue 15

Weizi, Self absorption occurs in the transmission measurement of the powder because it is a concentrated sample and it has to be exceedingly well made to eliminate the thickness effect. Because it was shown in your previous email to be lower than the film that decrease in intensity was caused by self-absorption (if I remember your old email correctly). The fact that your new data shows such decrease (compared to the powder or compared to other conditions, such as an angle or a graphite dome) it is likely the same effect (because it is exactly what self absorption would do with Ce L3 edge). . Thin films should not have it because 200 nm is much lower than one absorption edge of Ceria at Ce L3 edge energy. The reason you see it in your films is because you chose a strange geometry to fight self absorption (which should not exist in thin films). You make your angle grazing incidence angle and you are making it effectively a very thick sample, thus you create a condition for over absorption. Instead, you should have used normal incidence and grazing exit, which is what needs to be done to eliminate self-absorption in concentrated sample (which is not the case here). Anatoly On Thu, Jun 22, 2017 at 12:12 PM, Weizi Yuan < weiziyuan2015@u.northwestern.edu> wrote:

Hi Anatoly, Thanks for your quick response. Yes, I actually asked the self absorption question about CeO2 a few weeks ago. And your answer that it is due to self absorption leads me to study more about it and I appreciate it. In that last question, the strong attenuation of signal occurs in the incident angle = 0.6 o . However, when the incident angle is 3 o under room temperature ,air, the peak intensity is stronger than the CeO2 measured in transmission mode, which leads me to think that no over absorption correction needed here. And I try to conduct the correction which gives me crazily high (~9 after normalization) peak intensity. This makes me further confirm that no strong self absorption effect here. And if no strong self absorption in RT, air ,then why strong attenuation in RT, vacuum condition(case ii in my question)? For your answer,I am a little confused. Are you saying self absorption occurred in only case ii or in both cases, even though the result of case i spectrum has a higher signal than the transmission mode data? Thank you, Weizi

On Thu, Jun 22, 2017 at 10:16 AM, wrote:

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Today's Topics:

1. Self absorption or Ce4+ reduction in the CeO2 film? (Weizi Yuan)

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Message: 1 Date: Thu, 22 Jun 2017 10:11:05 -0500 From: Weizi Yuan To: ifeffit@millenia.cars.aps.anl.gov Subject: [Ifeffit] Self absorption or Ce4+ reduction in the CeO2 film? Message-ID: Content-Type: text/plain; charset="utf-8"

Dear all, I have measured some spectra of a CeO2 film(~200nm) grown on Yittria stablized Zirconia(YSZ) substrate under 2 conditions. (i) room temperature, ambient atmosphere (ii) room temperature, vacuum (pO2~1E-6 atm) inside a graphite dome of the DHS 1100 anton paar, The spectra are collected in fluorescence mode. The incident angle is 3 o and the fluorescence collection angle is 90 o.

My questions are: (i) From the theory behind the FLUO program developed Dr. Daniel Haskel, CeO2 spectra collected with a 3 o incident angle *would have a strong self absorption effect and need*

correction , however, *the signal *is not attenuated compared with the CeO2 powder taken in a transmission mode, shown in attached plot. I've gone through many literature and people sometimes tell that whether they have a successful self absorption correction by comparing the spectrum with a spectrum taken under a transmission mode. So I'm wondering if I can say that I don't need a self absorption correction in this case? (ii) The Ce4+ peak in the spectrum collected under condition (ii) has a much lower intensity. I think it is due to the reduction of Ce 4+ under vacuum, however, the Ce3+ peak does not show an increased signal here. Which makes ma doubt whether this is simply reduction of Ce *or might be from over absorption? *

Thanks for any response.

[image: Inline image 1] -- Regards, Weizi Yuan, Graduate Student, Northwestern University, Ph:(+1)312-560-9619 <(312)%20560-9619>