- Ifeffit - millenia.cars.aps.anl.gov

Differences between fluorescence and transmission of the same sample
by Ditty Dixon 14 May '10

14 May '10

Hello ifeffit users, I am working in the area of In-situ XAS analysis of Fuel cell catalyst. The heart of the fuel cell, MEA(membrane electrode assembly) consist of nafion membrane and the catalyst sprayed on both sides which act as Cathode and Anode(the whole max thickness 1mm). I have a system where Platinum is a common metal catalyst for both anode and cathode, with anode made of alloy of Pt and Ru(nano) ,and Cathode pure Pt(both 2mg/cm2 metal loading). An In-situ transmission XAS measurements on such a system gives no information as the transmission signal will contain both Pt signal from anode and cathode and two different process taking place oxidation and reduction. So we deal with the situation by removing the catalyst from one side. But when we did our measurements in fluorescence(without removing any catalyst) we got two different signals when we turned the cell 180 degree. If the anode was facing the fluo detector we got characteristic signal for Pt/Ru alloy(dampening in FT) and when cathode was facing, that of pure Pt. Is this a solution to separate the signals from anode and cathode without removing any catalyst?. I have attached the file for the fluorescence measurements for my MEA. Thanks in Advance, Ditty On Wed, May 5, 2010 at 5:43 PM, <ifeffit-request(a)millenia.cars.aps.anl.gov>wrote: > Send Ifeffit mailing list submissions to > ifeffit(a)millenia.cars.aps.anl.gov > > To subscribe or unsubscribe via the World Wide Web, visit > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > or, via email, send a message with subject or body 'help' to > ifeffit-request(a)millenia.cars.aps.anl.gov > > You can reach the person managing the list at > ifeffit-owner(a)millenia.cars.aps.anl.gov > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Ifeffit digest..." > > > Today's Topics: > > 1. Re: Differences between fluorescence and transmission of the > same sample (Bruce Ravel) > 2. Re: Ifeffit Digest, Vol 87, Issue 4 (Bruce Ravel) > 3. Differences between fluorescence and transmission of the same > sample (Andrew Campos) > 4. Re: Differences between fluorescence and transmission of the > same sample (Ditty Dixon) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Wed, 5 May 2010 10:30:18 -0400 > From: Bruce Ravel <bravel(a)bnl.gov> > To: XAFS Analysis using Ifeffit <ifeffit(a)millenia.cars.aps.anl.gov> > Subject: Re: [Ifeffit] Differences between fluorescence and > transmission of the same sample > Message-ID: <201005051030.18579.bravel(a)bnl.gov> > Content-Type: Text/Plain; charset="iso-8859-15" > > Andrew, > > I suspect that you are seeing what Grant refers to in his tutorials as > "leakage". That is, your transmission data appears to my eye to be > what happens when you have a wide spread in sample thickness under the > beam, ranging from gaps to very thick particles. > > If you go to > > http://gbxafs.iit.edu/training/tutorials.html > > And follow the link to the "Sample preparation" presentation, the > effect of leakage is shown on slide 16. > > On the following slide, Grant points out that this thickness effect > always reduces amplitudes. That is the case above the edge for your > data. And if you normalize data distorted in that way, you end up > with an artificially enhanced pre-edge peak, again as in your data. > > My US$0.02, > B > > > On Wednesday 05 May 2010 09:55:16 am Andrew Campos wrote: > > Hi everyone, > > > > My lab mates are running in-situ H2 reduction of Cobalt/SiO2 catalysts > > using the Co K-edge and are obtaining differences between the > > fluorescence and transmission signals. The in-situ cell does have > > quite a bit of sample thickness (2-3 mm approx) and I was wondering if > > the fluorescence signal only has a penetration depth of a few > > micrometers. If this is the case that would explain it where the side > > that is further away from the heating element is more oxidized than > > the rest of the sample. > > > > Has anyone run into this problem before? We're using the basic > > furnace/cryostat unit (in-situ cell manufactured by the exafsco) and a > > 13 element fluorescence detector (germanium diode). > > > > I appreciate any insight into the issue, I have attached a > > fluorescence and transmission spectrum collected at the same time > > where the transmission and fluorescence are in the .prj file. > > > > Thanks so much! > > Andrew > > > > -- > > Bruce Ravel ------------------------------------ bravel(a)bnl.gov > > National Institute of Standards and Technology > Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 > Building 535A > Upton NY, 11973 > > My homepage: http://xafs.org/BruceRavel > EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/<http://cars9.uchicago.edu/%7Eravel/software/exafs/> > > > ------------------------------ > > Message: 2 > Date: Wed, 5 May 2010 10:39:14 -0400 > From: Bruce Ravel <bravel(a)bnl.gov> > To: XAFS Analysis using Ifeffit <ifeffit(a)millenia.cars.aps.anl.gov> > Subject: Re: [Ifeffit] Ifeffit Digest, Vol 87, Issue 4 > Message-ID: <201005051039.14501.bravel(a)bnl.gov> > Content-Type: Text/Plain; charset="iso-8859-1" > > On Wednesday 05 May 2010 07:56:47 am baran yildirim wrote: > > My problem is similar; I am trying to simulate a doped crystal > > (different than chp 10 in Atemis doc, this time impurity atom is > > subjected to XAS) and the host is similar to inverse-spinel type: > > include both tetrahedral and octahedral sites in its structure. The > > dopant may settle in tetrahedral or octahedral sites. > > Indeed. Similar enough that you also should read the paper by Scott > Calvin that I suggested to Maria Elena. > > > 1- I managed to simulate the doped structure as changing the FEFF inp > > file manually (first I run Atoms as if impurity ions settle in all > > sites and then keep it in 0 potential and change the 1st potential > > with the original atom) and did it for both sites, thus i have 2 batch > > of paths and then fit it. It seems it works (Question: Do you think > > what i am doing is logical? or any other suggestion? ) > > I think that's a good approach. > > Question 15 at > > http://cars9.uchicago.edu/ifeffit/FAQ/FeffitModeling > > gives a bit more information. The link to the page authored by Scott > is quite useful. > > > > 2- But problems do not end :) Another problem is impurity ion may > > take different valences: it can be trivalent or divalent. In FEFF 9.0 > > i found kinda solution using ION command, it doesnt do what i > > exactly want but i can get some idea on what happens if the charge > > distribution changes. But unfortunately, i cant try it in ARTEMIS > > since i can not install FEFF 9.0 in ARTEMIS. As far as i understood > > the program structure is changed completely. But I didnt give up :)I > > generated the chi file in FEFF 9.0 and load it in ARTEMIS and continue > > to analyze but the results are not promising. (Question: Is there any > > way to run it together? and any suggestion in changing the valance? ) > > Artemis does not support Feff9 at this time. > > I actually have not played around with Feff9 yet, myself, so I won't > be able to help with the rest. Perhaps one of the Seattlites can help > .... > > B > > > -- > > Bruce Ravel ------------------------------------ bravel(a)bnl.gov > > National Institute of Standards and Technology > Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 > Building 535A > Upton NY, 11973 > > My homepage: http://xafs.org/BruceRavel > EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/<http://cars9.uchicago.edu/%7Eravel/software/exafs/> > > > ------------------------------ > > Message: 3 > Date: Wed, 5 May 2010 11:24:16 -0400 > From: Andrew Campos <acampo2(a)tigers.lsu.edu> > To: ifeffit(a)millenia.cars.aps.anl.gov > Subject: [Ifeffit] Differences between fluorescence and transmission > of the same sample > Message-ID: > <z2md94177571005050824k8abda3a0n708eaada202fdc6e(a)mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > Dr. Ravel, > > Thanks so much for the link and the advice! I appreciate it greatly. I > will advise my lab mates as such and may have to only use the > fluorescence data if that is indeed the case. > > I also included the file where the lower temperature is included and > you might come to the same conclusion. The samples that I ran were > pre-sieved, and the ones included in the .prj file aren't so that > should be pursued prior to running the experiment. If they crush the > particle and sieve the sample, I think that we can be more certain > that this is not the case. This was very helpful! > > Andrew >

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fitting
by mohamed sobhy 14 May '10

14 May '10

Dear all I am trying to use artemis to do fitting to CeO2. But really I cant get the right way to do that. During the fitting, I am using amp as set and change in N degeneracy of the path. attached is the best fit i got but it still not good and the chi-square is 41.109065479 so can you suggest me what to do thanks Mohamed

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Debye model on Artemis
by Kleber Daum Machado 12 May '10

12 May '10

Hi Matt, Concerning the third cumulant, my problem is to use a particular model for it. Some articles (Frenkel and Rehr, PRB 48 (1993) 585; Araujo et al, PRB 74 (2006) 184102) show how to use the Einstein model on Artemis, since these articles show the expressions that should be defined for sigma^2(T) and C3(T) for this model in Artemis (eqs. 11 and 18 of Frenkel and eqs. 2 and 3 of Araujo). In fact, I have already tested them on my analysis, using the eins function for sigma^2 and defining the C3(T) expression given in those articles in Artemis. I'd like to test Debye model too, and my problem is to use Debye model for sigma^2(T) and C3(T). For sigma^2(T) Artemis has the debye function already predefined. I'd like to use/write an expression for C3(T) considering Debye model, but I didn't find anything about such expression on the literature. Kleber

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Debye model on artemis
by Kleber Daum Machado 11 May '10

11 May '10

I'd like to use the third cumulant option in Artemis, but considering the Debye model. Artemis has a Debye function for the second cumulant (Debye-Waller factor) but not to the third. How could this be done in Artemis? Kleber

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values of f(k),δ(k) and λ(k)
by Neetu parsai 11 May '10

11 May '10

Hello, Can some one give me the values of theoretically calculated functions f(k),δ(k) and λ(k), that can be used in EXAFS equation to calculate structural parameters. If these values are given in FEFF, how can I get those. I require it to use in EXAFS equaiton using some another computer program. Thanks Mrs.Neetu Parsai Head Department of Engg.Physics Sanghvi Innovative Academy Indore. Residence: 130 Hemu colony, New G.D.C.Road, Indore-452015(M.P.) India.

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Re: [Ifeffit] atoms.inp files
by csr019＠latech.edu 10 May '10

10 May '10

Yes I am new to EXAFS, so no offense taken. Thanks for the link on how to do it. ~Corisma ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.

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asking for model compound data
by María Elena Montero Cabrera 10 May '10

10 May '10

Hello to all! I have looked to Matt Newville's data for model compounds, and I have not found those for gamma-Fe2O3, so called maghemite. Carlo Segre has provided me those from Litle Library, I thank very much his kindness. He has suggested me to obtain this way newer data. Would any of you provide me that, please? Thanking in advance -- María Elena Dra. María Elena Montero Cabrera Departamento de Medio Ambiente y Energía Centro de Investigación en Materiales Avanzados (CIMAV) Miguel de Cervantes 120, Compl. Ind. Chihuahua Chihuahua CP 31109, Chih. México Tel (614) 4391123

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Re: [Ifeffit] atoms.inp files
by csr019＠latech.edu 10 May '10

10 May '10

Thanks for responding Mohamed. I previously had looked at the website that you mentioned (http://cars9.uchicago.edu/~newville/adb/search.html) but did not see either files (TiAl or TiAl3) on there. Do you or anyone else know of another place I can look? ~Corisma Robinson ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.

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Fwd: All that old figures
by Eugenio Otal 10 May '10

10 May '10

Hi, when I was writing my thesis I get bored to see the old figures of photoelectrons scattering in the classical books (*Konigsberger *, etc). So I decided to make them again. Hope it is useful. Regards ,euG 8<- - - - - - 8<- - - - - - 8<- - - - - - 8<- - - - - - Dr. Eugenio H. Otal Solid State Chemistry and Catalysis Laboratory, Empa - Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland, Tel +41 44 823 41 31, Fax +41 44 823 40 19, eugenio.otal(a)empa.ch, www.empa.ch/abt131, 8<- - - - - - 8<- - - - - - 8<- - - - - - 8<- - - - - -

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atoms.inp files
by csr019＠latech.edu 07 May '10

07 May '10

Hello, Does anyone have an atoms.inp file prepared or know where I can find one for: 1) TiAl and 2) TiAl3 Thanks!! ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.

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