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

current-amp recommendation
by Matthew Marcus 14 Nov '17

14 Nov '17

I've gotten involved with a project in which stabilization of the position of a monochromatic, soft X-ray beam is needed. The offending frequencies seem to be vibration frequencies like 57 and 116Hz. We have in mind to use a thin Au film with a gap in the middle, measuring the drain current from the films, much as people normally use the jaws of slits. Now, I'd like to find a couple of current amplifiers which are small enough so that they can be connected with very short cables to the BNC connectors on the air-side of this detector, and which would have decent frequency response and low noise with inputs of the order of 0.1-1nA. Although this topic is outside the realm of XAFS analysis with IFEFFIT, I figure that people on this group might have some good experience. mam

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Re: [Ifeffit] Consult a few questions about XAS data analysis
by fred.mosselmans＠diamond.ac.uk 14 Nov '17

14 Nov '17

Hi Jun, Two points so Bruce doesn't get two upset. If you included the Athena project you used for the lcf and maybe an excel file of the results you got, then someone could Check what you did, as it is there is almost no way to offer an opinion on that. Bruce gave a course at Dimaond several years ago now, but most of what he shows is relatively as true as it was the day he said it. The videos can be found here. http://www.diamond.ac.uk/Beamlines/Spectroscopy/Techniques/XAS.html The VLC media player works well with them. Regards Fred J.F.W. Mosselmans Principal Beamline Scientist I18 Diamond Light Source Ltd Diamond House Harwell Campus Didcot OX11 0DE P + 44 1235 778568 M + 44 7785510211 E fred.mosselmans(a)diamond.ac.uk orcid.org/0000-0001-6473-2743 [cid:image002.png@01D27563.28EDA240] -- This e-mail and any attachments may contain confidential, copyright and or privileged material, and are for the use of the intended addressee only. If you are not the intended addressee or an authorised recipient of the addressee please notify us of receipt by returning the e-mail and do not use, copy, retain, distribute or disclose the information in or attached to the e-mail. Any opinions expressed within this e-mail are those of the individual and not necessarily of Diamond Light Source Ltd. Diamond Light Source Ltd. cannot guarantee that this e-mail or any attachments are free from viruses and we cannot accept liability for any damage which you may sustain as a result of software viruses which may be transmitted in or with the message. Diamond Light Source Limited (company no. 4375679). Registered in England and Wales with its registered office at Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom

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Consult a few questions about XAS data analysis
by Jun Ge 14 Nov '17

14 Nov '17

Hi Bruce I'm a learner for XAS data analysis because of the need of scientific research. I have been to SLAC in San Francisco three times last year and collected some XAS data of samples and models in Beamline 7-3. This summer, I began to learn how to analyze these XAS data. My professor used to use WinXAS to analyze data. But this time he asked me to learn Athena. He thinks use two different softwares can double check the result. After the data pro-processing, including background remove and data normalization, etc., I save each spectrum in the form .txt. However, *in the same energy range and same file of sample and models, the result of LCF performed by WinXAS and Athena was totally different!* I try to solve this problem for a long time but no progress was made. So I turn to you and Ressler (the author of WinXAS) for help. I guess may be the algorithm is different between your Athena with WinXAS, but I'm not sure. With great experience in XAS data analysis, I think it's easy for you to solve this problem, isn't it? By the way,* I don't know how to fit the Coordination Number in another software called Artemis* in the software package of Demeter. I was told by Artemis that the coordination number can only be a number not alphabet. So I have no idea how to do this (yeah, I'm really a noob orz). And I don't know how to set the parameter more correctly to run a excellent Feff fit. So could you please help me? Finally,* I want to learn XAS data analysis systematically. So could you please recommend me some references like books or papers?* Anyway, thanks a lot for your help and your precious time! Sincerely, Jun Ge

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Re: [Ifeffit] Hephaestus: Absorption Data Source
by fred.mosselmans＠diamond.ac.uk 14 Nov '17

14 Nov '17

Hi Apologies for turning this into a social network, but Robert scanning Krause and Oliver, reminded me of when several decades ago, as a PhD student I typed all the K and L shell values from that paper into a table for Norman Binsted to use in his latest version of Excurve , probably Excurv88. Regards Fred -- This e-mail and any attachments may contain confidential, copyright and or privileged material, and are for the use of the intended addressee only. If you are not the intended addressee or an authorised recipient of the addressee please notify us of receipt by returning the e-mail and do not use, copy, retain, distribute or disclose the information in or attached to the e-mail. Any opinions expressed within this e-mail are those of the individual and not necessarily of Diamond Light Source Ltd. Diamond Light Source Ltd. cannot guarantee that this e-mail or any attachments are free from viruses and we cannot accept liability for any damage which you may sustain as a result of software viruses which may be transmitted in or with the message. Diamond Light Source Limited (company no. 4375679). Registered in England and Wales with its registered office at Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom

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Hephaestus: Absorption Data Source
by Daniel Przyrembel 13 Nov '17

13 Nov '17

Dear All This might be a stupid question, but I have not been able to track this down myself: What is the data source of the "core-hole lifetimes" (i.e. the energy widths "gamma(ch)" in eV) of the "Absorption edges" in the "Absorption" panel of Hephaestus? As far as I could see these lifetimes/widths are not given in the 'Elam database'. Other XAS data tools based on the Elam database (like e.g. 'XrayDB') claim to be using values from 'O. Keski-Rahkonen and M. O. Krause, Atomic Data and Nuclear Data Tables 14, pp139-146 (1974) (http://dx.doi.org/10.1016/S0092-640X(74)80020-3)' for this. Because that reference does not give tabulated values but rough data plots only, it is difficult to compare those with the values in Hephaestus. If someone knows the respective data source used in Hephaestus, the answer/information is deeply appreciated! Best regards Daniel

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E0 in Co3O4
by Jesús Eduardo Vega Castillo 30 Oct '17

30 Oct '17

Dear list, I enclose an Athena project with a XAFS spectrum of Co3O4 with a metallic Co reference. Athena by default has chosen E0 at the absolute maximun of the derivative curve (at 7727.8eV) which in my opinion is too high because it is at the white line zone. I believe that E0 should be the previous maximun in the derivative at around 7722eV, which would be at the rising edge. Am I wrong? I would appreciate some help with the criterion to determine the right value. Yours, Jesús

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Re: [Ifeffit] iron carbide fitting with Artemis
by fred.mosselmans＠diamond.ac.uk 27 Oct '17

27 Oct '17

Dear Yunyun, I don't think Mike has written anything particularly incorrect , but he didn't point out why this approach is necessary. I believe there are two things you should definitely be aware of. An EXAFS dataset has a very limited amount of information. Approximately deltak.deltaR no of variables can be fitted To any spectrum as an absolute maximum and preferably quite a lot fewer than this (where deltak and deltaR are your fitted data range in k and R space respectively. Because of this if say you know you have N C atoms at ca G angstroms around your central atom. It is best not to use a variable for fit the degeneracy for that path but set it at the number you know is correct. And secondly because an EXAFS spectrum is effectively a collection of Sine waves there is a limited resolution, i.e. you cannot resolve paths of the same atom type that are less then Pi/2k(max) A apart, where k(max) is the maximum range of your dataset in k space, and Pi is Pi. Hence to separate two paths of the same atom that are 0.1 A apart you need about 15k worth of data. Regards Fred -- This e-mail and any attachments may contain confidential, copyright and or privileged material, and are for the use of the intended addressee only. If you are not the intended addressee or an authorised recipient of the addressee please notify us of receipt by returning the e-mail and do not use, copy, retain, distribute or disclose the information in or attached to the e-mail. Any opinions expressed within this e-mail are those of the individual and not necessarily of Diamond Light Source Ltd. Diamond Light Source Ltd. cannot guarantee that this e-mail or any attachments are free from viruses and we cannot accept liability for any damage which you may sustain as a result of software viruses which may be transmitted in or with the message. Diamond Light Source Limited (company no. 4375679). Registered in England and Wales with its registered office at Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom

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iron carbide fitting with Artemis
by Yunyun Zhou 27 Oct '17

27 Oct '17

Hello All, I am having trouble fitting my sample with both Fe5C2 and Fe3O4 as standards. Hopefully somebody could help me out and I really appreciate it. My iron sample was mainly iron carbide in the core and iron oxide on the shell. Fe5C2 has a monoclinic structure and generated complicated FEFF paths. Many of the paths have similar distances. I have found some paper reported their results as follows, which apparently combined several paths together and assume they have similar path length. My first question is does someone know how they did it? It seems that combing similar paths makes fitting much easier, but I am not sure whether this is a correct way to do the fitting. My second question is regarding fitting with the two combined models of Fe5C2 and Fe3O4. I haven't fit with two models before. Is it just like what I did in the attached Artemis file? Shall there be any restrictions between the two models and do I have to fix some of the parameters? Thank you very much in advance for your help! Best, Yunyun Zhou Fe5C2 FEff paths: [image: Inline image 1] Literature reported results: [image: Inline image 2]

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monoclinic elemental selenium data
by George Sterbinsky 26 Oct '17

26 Oct '17

Hello, I am trying to help someone locate XAFS data collected from the red allotrope (monoclinic) of elemental selenium. Does anyone have a data set they are willing to share? Thank you, George

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flattened norm export issues
by Robert Gordon 22 Oct '17

22 Oct '17

Hi, Encountered a difference on export of normalised data. Flattening does not seem to be preserved when saving current group as norm(E) but is when saving marked group. Example in norm.prj attached. original data set normalised and flattened...displaying "Normalized" as current group or as marked group looks the same: current: marked: On saving current or marked group as norm(E), re-importing and plotting as mu(E) marked is still flattened, but the set exported using "save current group as" is not flattened. Similar difference saving "marked" versus saving "each marked" So it seems only "Save marked group as..." preserves flattening for norm(E). -R.

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