June 2005 - Ifeffit - millenia.cars.aps.anl.gov

Debye-Waller factors for metal oxides ?
by Ian James Drake 16 Apr '09

16 Apr '09

Hi, There is little discussion over the significance of fitted Debye-Waller factors (ss2) found for metal centers in metal oxides of heterogeneous catalysts. I am searching for a better way of determining how reasonable these values are in the fits I get. 1. Are phenomenological models like the correlated Debye model and Einstein model appropriate? It seems that Debye temperatures are hard to find for oxides. 2. Is there an equivalent value for ss2 in x-ray crystallography data that I can refer to for comparison in these materials? What should I look for in reviewing published x-ray crystallographic data? 3. Is the temperature dependence reported for the ss2 for some metals (like Cu and Al) similar to their respective oxides? For example, in Debye-Waller factor calculations reported for Al metal by R.C.G Killean (in J.Phys.F: Metal Phys., v. 4, pg. 1908, 1974), the ss2 changes by a factor of three between 25C and 300C. Would I expect a factor of three increase in crystalline zeolites (AlO4 structural units). 4. Specific to my work: I have studied Al containing oxides at temperatures between 25 and 300 C. I would like to quantify coordination changes by doing EXAFS fitting of the Al K-edge data. The EXAFS was taken at temperature and I observe no change in the broadening of the data. Likewise, the fitting shows no sensitivity in the Debye-Waller factor. It is nearly constant at 0.001 A over the temperatures of interest. Since ss2 and the coordination number (CN) are correlated, I would like a way to bind the error on the fitted CN by modeling real physical changes in the Debye-Waller factors. Do you have any suggestions? Looking forward to your thoughts. Ian Drake Graduate Student UC Berkeley

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Artemis- Loading up error
by Zohair Hussain 16 Apr '06

16 Apr '06

Hi! I recently had to install ifeffit software package on our network computer. The first time I ran Artemis I was asked to update which I did. However, Artemis did not start after that. The error message that I got is shown in the attached figures artemis-error1a and 1b. Please note that only Artemis doesn't work, all the other softwares (Athena, Hephaestus, TKAtoms etc.) work fine. I tried running the .bat file from the Ifeffit folder but that didn't work either. I also tried to run the artemis.exe file and received the error shown in figure "artemis-error2". Later I unisntalled and re-installed Ifeffit and chose not to do the updates and Artemis is now running fine. I was wondering if anyone has any idea why this is so or if there is a way around installing the updates and still being able to use Artemis??? Thanks, Zohair

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RE: [Ifeffit] feff data
by Barton, David (DG) 23 Jun '05

23 Jun '05

Steven, Sorry for the duplicate....I sent the previous message as HTML (shame on me) beta-Ga2O3 files are attached. I attached the CIF (crystallographic information file) and an Artemis project that has the FEFF.inp inside it. CIF files can be opened directly in Artemis by choosing the File option, Import ATOMS files, and then select *.CIF in drop down box. If you need just the FEFF.inp for another purpose you can just cut it out of Artemis project and paste it to a text file. Dave Barton -------------------------- Dear all, Does anyone out there, by any chance, have feff data or .inp file of Gallium oxide (any of GaO, Ga2O, and Ga2O3)? I tried to create an .inp file but it was out of my ability. If somebody has one or can give me an information where or how to get, I will do appreciate it. Thank you. Steven Steven Sangyun Lim Associate Research Scientist Dept. of Chem. Eng., Yale University Tel : 203-432-4365

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RE: [Ifeffit] feff data
by Barton, David (DG) 22 Jun '05

22 Jun '05

Steven, beta-Ga2O3 files are attached. I attached the CIF (crystallographic information file) and an Artemis project that has the FEFF.inp inside it. CIF files can be opened directly in Artemis by choosing the File option, Import ATOMS files, and then select *.CIF in drop down box. If you need just the FEFF.inp for another purpose you can just cut it out of Artemis project and paste it to a text file. Dave Barton _________________________________ David Barton, PhD. The Dow Chemical Company Catalysis R&D 1776 Building Midland, MI 48674 USA -----Original Message----- From: ifeffit-bounces(a)millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Steven S. Lim Sent: Wednesday, June 22, 2005 10:14 AM To: ifeffit(a)millenia.cars.aps.anl.gov Subject: [Ifeffit] feff data Dear all, Does anyone out there, by any chance, have feff data or .inp file of Gallium oxide (any of GaO, Ga2O, and Ga2O3)? I tried to create an .inp file but it was out of my ability. If somebody has one or can give me an information where or how to get, I will do appreciate it. Thank you. Steven Steven Sangyun Lim Associate Research Scientist Dept. of Chem. Eng., Yale University Tel : 203-432-4365

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feff data
by Steven S. Lim 22 Jun '05

22 Jun '05

Dear all, Does anyone out there, by any chance, have feff data or .inp file of Gallium oxide (any of GaO, Ga2O, and Ga2O3)? I tried to create an .inp file but it was out of my ability. If somebody has one or can give me an information where or how to get, I will do appreciate it. Thank you. Steven Steven Sangyun Lim Associate Research Scientist Dept. of Chem. Eng., Yale University Tel : 203-432-4365

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IFEFFIT for OS X 10.4
by Ann Liang 21 Jun '05

21 Jun '05

Hi all, I just recently upgraded my computer from Mac OS X 10.3 to 10.4 (Tiger). I was not able to open programs in the IFEFFIT package. Please help. Thanks, Ann -- ANN LIANG Bruce. C. Gates Catalysis Research Group Chemical Engineering & Materials Science University of California at Davis One Shields Ave. Davis, CA 95616 530-752-3544 (office) 530-752-1031 (fax)

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EXAFS mean free path in small particles
by Laurent Menard 21 Jun '05

21 Jun '05

Disclaimer: I'm an experimentalist and not a theorist. I'm not sure that Zhao and Montano's calculations are correct. I think their calculation for the transition probability assumes that the electron density is constant when, in actuality, there is a spatial dependence resulting from quantum confinement effects. As a result, the energy of the surface plasmon peak as calculated by Zhao and Montano is constant for all cluster sizes at approximately the classical value of omega(bulk plasmon)/3^0.5 and shows an increase with decreasing particle size. Including quantum confinement results in a blue shift of the surface plasmon resonance with decreasing particle size and a decrease in transition probability for decreasing particle sizes (as suggested by Anatoly). This change in the calculation will also impact the bulk plasmon and I don't know what that trend will be. As far as their experimental demonstration with Fe nanoparticles is concerned, I really can't make an assessment about the experiment since they don't indicate how the nanoparticle size was determined and I'm not familiar with their preparation of the nanoparticles. I'm not sure from this paper what the impact on the MFP will be although there very well could be some effect on the EXAFS. Personally, when I began working on EXAFS of nanoparticles and small clusters (Au13), I was leery of using the bulk phase and amplitudes to fit the data. My experience to this point has been that there have not been observable deviations of coordination numbers for nanoparticle systems using these FEFF inputs. That being said, I tend to agree with Matt that this is something that people working in this area need to think about a bit more than it seems they have judging by the literature. I would like to see some (correct) theoretical assessments that support the assertion that bulk phases and amplitudes are ok for nanoparticles that I think has been demonstrated by validating EXAFS results with other techniques (mostly electron microscopy). -Laurent

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EXAFS mean free path in small particles
by matthew marcus 20 Jun '05

20 Jun '05

I'm working on a couple of projects involving nanoparticles, and a collaborator pointed out an old paper by Zhao and Montano (PRB 40,3401(1989)) which claimed theoretical reasons why the electron mean free path in nanos should be smaller than in bulk. This would cause coordination numbers to be underestimated. The effect is supposedly due to a surface plasmon which grows in importance as particle size shrinks. I have reasons why I think this paper exaggerates the possible effects, but I'm posting this to see what other people think about this effect. The paper seems to have gone down into obscurity, but that doesn't mean it isn't right. Thanks. Matthew Marcus

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EXAFS mean free path in small particles
by Matthew 17 Jun '05

17 Jun '05

A couple of notes on this group treat the Zhao&Montano Al-plasmon results as if they were experimental truth. They are in fact theoretical, based on what I think is a jellium model, though that word isn't used. Their only experimental data is on matrix-isolated Fe particles. mam

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RE: [Ifeffit] EXAFS mean free path in small particles
by Frenkel, Anatoly 17 Jun '05

17 Jun '05

Matt, In their paper, Zhao and Montano studied Al particles that showed surface plasmon activity for sizes as small as 10 A. I had no idea that Al does it, and it is very peculiar. However, I have been dealing most heavily with gold nanoparticles. According to literature (here is another article: Sarathy et al, J.Phys.Chem. B, 1997, v. 101 pp. 9876-9880, and ref. 14 within), Au nanoparticles show no surface plasmon activity below 20 A. Our recent experiment, where we have taken UV-vis. measurements of several samples of Au nanoparticles that were very small (13 to 100 atoms) and monodisperse, did not show any surface plasmon band around 525 nm where it appears at larger particles. In fact, Zhao and Montano say in p. 3403: "we would like to point out that based on the experimental results for noble metals [Cu, Au, and Ag] no evidence of a substantial change in the electron MFP value between bulk and small particles was found". That, to my mind, is an indirect but a fair reason to reuse bulk amplitudes, at least for Cu, Au and Ag. I also think, if HRTEM and EXAFS agree, it says for itself (that bulk FEFF amplitudes are correct). If they do not agree, AND if other reasons for discrepancy can be ruled out (e.g., broad size distribution, or electron-beam caused growth of particles), AND if the discrepancy is in the right direction (EXAFS-determined size is smaller than the HRTEM-determined size), then surface plasmon and other losses should be looked into. And, I agree, it is an important issue to be aware about. Anatoly -----Original Message----- From: ifeffit-bounces(a)millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov]On Behalf Of Matt Newville Sent: Tuesday, June 14, 2005 9:47 PM To: XAFS Analysis using Ifeffit Subject: RE: [Ifeffit] EXAFS mean free path in small particles Anatoly, > The point is, to my opinion, that since In the most > interesting range, below 2nm, the plasmon activity decreases, > therefore its effect on EXAFS interpretation, if any, should > be negligible. I think I may not understand your point. The Zhao and Montano paper shows very pronounced changes in the plasmon spectra between each of 10,3,2, and 1 nm for Al. At 1 nm, the surface plasmon is definitely dominating -- not going away. So their conclusion, that lambda changes substantially below 10 nm due to the changing relative importance of surface-to-bulk plasmons seems well-argued to me (not to say its correct). I agree (I think) with Matthew that the Zhao and Montano work shouldn't be too easily dismissed, though it might not be completely correct. I don't know of any other work on how lambda might depend on particle size, and never really thought about this. The Rao paper seems broader in scope and not necessarily addressing plasmons and mean free path, but I only skimmed it, so maybe I missed something. Their fig 8 definitely shows a size dependence of O K-edge, though I didn't immediately see a clear interpretation for this -- it could have several explanations. Again, I only skimmed this paper, so maybe I missed something: perhaps the electron diffraction literature has more information?? > ... There are other evidences that small particles have DOS > similar to molecules, not typical metals. Most notable is the > evidence that HOMO-LUMO band grows to more than 1 eV at sizes > of 1 nm range. Hmm, I'm not sure I see that becoming more molecular and less metallic indicates that using the bulk mean-free-path is OK. . The 'universal mean free path' that Feff uses and the fact that S02 is still has to be a fitting parameter even for excellent data with Feff8 suggests to me that there may be many hidden sins in Feff's mean-free-path calculation. Sadly, we seem to be a little short on theorists these days. --Matt _______________________________________________ Ifeffit mailing list Ifeffit(a)millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

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