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Since a cylinder lasts for years, it is easy to forget about. Dave Wilbur Headers David.Wilbur@tuſts.edu Tue Mar 8 I do not know the type of valve that you are discussing but


may I offer some general advice on trying to fix it? (1) Switch off the microscope at the wall. (2) Work with the idea that someone had to build it therefore there must be a way of taking it apart. (3) Have someone with you so that you can dictate what you did to take the unit apart, it will help when reversing the process. (4) Expect a spring under tension to be inside the unit so take great care when finally opening it. (5) A standard reason for such an item to jam is the “O” ring has dried out and it is sticking to the degraded grease within the chamber. (6) Give the chamber and the plunger a good clean and use a good quality vacuum grease on the “O” ring. Steve Chapman protrain@emcourses.com Wed Mar 9 I found the problem was that the piston of a mechanical valve


is slowed down, which prevented a complete the venting sequence. I helped the piston movement by pushing it gently, and the sequence could be completed. Now I hope it’s enough to clean the valve, though the dismantling won’t be that easy. Davide Cristofori dcristofori@ unive.it Wed Mar 9


EDS:


unexpected Si peak I use a 2000FX TEM at 200kV equipped with an Oxford Inca


EDS, ultra-thin window Si-Li detector. Sometimes I get Si K line from a sample which should have no Si at all. Can anybody please explain where the Si peak comes from? Zhou z.zhou@lboro.ac.uk Wed Mar 30 I can think of two reasons for seeing the Si K peak. First is the


silicon internal fluorescence peak, that is, the SiLi detector itself emits Si K x-rays from the “dead layer,” which are then detected by the “active layer” of the detector. I have experienced this in some detectors more than in others. Second may be contamination from Si-based vacuum grease, transferred from o-ring to loadlock wall to sample holder tip, during sample holder insertion and retraction. Of course, it could also be from sample contamination: We had an associate that habitually secured the TEM sample to the ion-milling stub with Si-grease. Tis got transferred to the TEM holder and appeared in all EDX spectra on that instrument. A thorough cleaning of the TEM sample holder eliminated the Si K peak due to this problem. Roger A. Ristau raristau@ims.uconn.edu Tu Mar 31 I ran into one additional source of Si. A specimen had been


placed on a glass slide and subjected to evaporation, then embedded and sectioned. Sure enough, there was a prominent Si peak. Bill Tivol william.f.tivol@aero.org Tu Mar 31 Most modern detectors have much better resolution that in the


past, but you may want to see if you have an overlap with a heavier element. If memory serves me Ta or W had m lines close to the Si K line. If your Si line is very high then this will be less likely. Your settings on the Oxford may be such that if you are using auto ID the soſtware is identifying it as Si to be sure you look for it. Tommy Derflinger gtuser@comcast.net Tu Mar 31 Tis is a good subject for discussion. A way to identify the Si


source is to collect the spectra at difference spots. If the Si is seen on the particle (or phase A), but not on the support film background (or phase B), then we can say the Si is from the sample itself. In the case Si is seen everywhere even on the hole without specimen, then it is from the TEM system—service is needed! Considering the spurious signals in the TEM, the different spots tested should be far away enough. Occasionally I receive the complaints about the Si that is not


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supposed to have, mostly from the chemistry users. I prove to them that it is the sample contaminated with Si, rather than the TEM. If the TEM is well aligned, the EDS is quite reliable. Zhiping Luo luo@mic. tamu.edu Tu Mar 31


EDS: ZnO


A recent paper in JACS (do not want to provide citation


intentionally) claims to have used EDS analysis in the TEM to determine presence of about 1% of Na in ZnO single crystals. Any comments on validity and prudence of such a claim? Krassimir Bozhilov bozhilov@ ucr.edu Wed Apr 20 1% is possible, but close to the limit of detectability. I presume


that the EDS system has an ultrathin window or no window. As to the prudence, if the spectra show a bump at the right position, and there is no possibility of interference from another element, (I don’t have access to a table of x-ray lines, but I know that Cu-L is somewhere near Na-K.) I see nothing wrong with reporting it as Na. At one time I was looking for chlorinated hydrocarbons in clay samples, and I could see a small bump where the Cl should be in some of the grains. I also saw the Ti-L alpha clearly and the Ti-L beta was the same size as the Cl and obviously must be there. Tis gave me confidence that the Cl bump was also real. Bill Tivol william.f.tivol@ aero.org Tu Apr 21 I have been posting replies privately. I suppose I should


summarize to the list. Tere should be no problem detecting Na with even a Be window detector, but I would assume this is a thin-window detector. Te big problem is an overlap with the Zn-L line, and they are measuring Na in ZnO. Tat will be difficult. It might be possible if they are using their own profiles for the elemental peaks under their exact conditions and calibration. If they are using the factory profiles, it is probably not feasible. We collect our spectra a little faster than the factory used for their profiles, so the peaks are a bit wider. Tat may be fine in the case of widely separated elements. It breaks down in cases of peak overlaps. A follow-on post indicated that this researcher had tried mapping for Na and found it uniformly distributed. It was not at all clear if the researcher considered the Zn-L overlap with Na-K. I know our system does not deconvolve peak overlaps for mapping. I don’t think it even does background corrections. Maybe new systems do with their spectral imaging. I make sure to label the Na map as Na/ Zn if there is any chance of the overlap. Warren Straszheim wesaia@ iastate.edu Tu Apr 21 Except of course for the possibility of the doublet of Oxygen K


(0.523 × 2 = 1.046 keV). Te sample is ZnO! Peter Ingram p.ingram@ cellbio.duke.edu Tu Apr 21 It is pretty obvious from the paper’s supporting documents that


the EDS/EDX spectrum is misidentified: http://pubs.acs.org/doi/ suppl/10.1021/ja908521s/suppl_file/ja908521s_si_001.pdf NaK 1.04KeV ZnL 1.01KeV Tis is a common overlap, that like many people, I experience


several times a week. I hope the authors print a retraction. Jim Quinn jquinn@ms.cc.sunysb.edu Tu Apr 21 Follow-up questions to Peter and Bill: (1) Would WDS give a


definitive identification? (2) Would using a variety of kV’s using EDS give a better identification? John Bozzola bozzola@siu.edu Tu Apr 21 Except of course for the possibility of the doublet of Oxygen K


(0.523 × 2 = 1.046 keV). Te sample is ZnO! Peter Ingram p.ingram@ cellbio.duke.edu Tu Apr 21


www.microscopy-today.com • 2011 July


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