[Ifeffit] Ifeffit Digest, Vol 172, Issue 15

Thu Jun 22 11:35:05 CDT 2017

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 at 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, <ifeffit-request at millenia.
> cars.aps.anl.gov> wrote:
>
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>> Today's Topics:
>>
>>    1. Self absorption or Ce4+ reduction in the CeO2 film? (Weizi Yuan)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Thu, 22 Jun 2017 10:11:05 -0500
>> From: Weizi Yuan <weiziyuan2015 at u.northwestern.edu>
>> To: ifeffit at millenia.cars.aps.anl.gov
>> Subject: [Ifeffit] Self absorption or Ce4+ reduction in the CeO2 film?
>> Message-ID:
>>         <CAKT5DaU1U2UX7bVUx9ffhvTfE7txqnZDgGu3cNujM6ceQyp6Hg at mail.gm
>> ail.com>
>> 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>
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>> End of Ifeffit Digest, Vol 172, Issue 15
>> ****************************************
>>
>
>
>
> --
> Regards,
> Weizi Yuan,
> Graduate Student,
> Northwestern University,
> Ph:(+1)312-560-9619 <(312)%20560-9619>
>
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