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the samples from the atmosphere. In addition, over 90 researchers from several faculties use our SEM. Would a temporary setup like this with the argon cause any problems or concerns down the road? As I said, this is the fi rst time for me trying something like this, and I do not want any surprises. Pat Scallion Tue May 30 Your concept sounds feasible but I’ll let the experts on here comment further. I thought you might want to have a look at 2 other solutions that I have seen: 1) VacuShut sample transfer device - this was sold by Agar Scientifi c but I don’t see it on their website now. It was invented at Karlsruhe Inst for Tech. Here is a fl yer PDF showing how it works. Maybe the inventors listed on this know where you can acquire it now: . Also, Transfer Module from Kammrath Weiss - a more elegant solution (and probably more expensive): en/products/materials/transfer-module.html Mike Toalson mtoalson@ Tue May 30

It sounds like something I did back in 2002 on a similar SEM back at the Electron Microscopy Center at Argonne National Lab. Should work just fi ne and an inert gas like argon will not cause any problems. Science and research are all about having fun and trying new things. Roseann Csencsits Wed May 31

FIB: typical metallic purity for FIB source

I will have to replace my LMIS soon and was just wondering what they start as. Seems like the less pure, the less ideal your focused beam spot would become, and more ‘chromatic’ aberration probably. Just looking around I fi nd 99.99% pure through 99.99995% available. So where would these be relative to what precision FIB would commonly use? I would guess that for some applications, a custom ion mill could tolerate a wide range of purity (not that I can imagine one at the moment). It leads to the question of, do all impurities ionize, or would some remain as ‘slag’ that prevents transport (fl ow) of clean metal to the emission point. Nathan nmz787@gmail.comT u Jun 1 When I was at Drexel, I remember the FIB scientist discovered (with the help of another scientist at Applied Beams) a solution as to why all of our ion beam images and milling patterns had these ghostly shadows present. For example, if you tried to drill a very small hole into a silicon nitride membrane, instead of single hole you would get two! T is turned out to be because our ion source had two diff erent isotopes of gallium present, and each isotope experienced a slightly diff erent path through the optics and was focused to a crossover that was slightly laterally displaced with respect to each other. T e purity of the source is certainly one thing to consider but apparently the isotopic distribution of even a pure gallium source is another. T is doesn’t answer your question directly but I thought you might fi nd it interesting. I imagine the FIB source suppliers go to some extra lengths to make sure that the ion source is isotopically pure Ga-69. Chris Winkler T u Jun 1

EDS: parameter defi nition

We just got an up-date on our IXRF EDS system. One parameter we get from the semi-quant routine is MDL (3sig). We are not sure we know what that means. It has been suggested that is an actual lower detectable limit for that element, while others suggest it is a parameter defi ning detectable signal over background. T oughts anyone? Frank Karl Sun May 7

Not having seen any replies so far, I will jump in. I had an IXRF system for over ten years; indeed, we were one of the early customers. However, I cannot recall the specifi cs of their MDL numbers. MDL

68 • 2017 September

should mean the actual lower detectable concentration given the parameters of the collection. T erefore, it should drop with additional counts because the relative noise in the background is being reduced. If it does not change over time, then it could be a defi ned parameter which would not be correct in my opinion. You may also want to look into the practicalities of their system and its calculations. (Remember, my information is several years out of date.) An old version of their soſt ware fi tted the background and subtracted it and then rectifi ed the data. T at is, all of the negative counts in the spectrum were set to zero. T at resulted in a positive integral and result for virtually any element even when none was present. T e reported amount diminished over time (approached zero) for those cases where the element was not present. It may have been that the reported level was less than the reported MDL. I should have compared the number to the MDL and ignored results less than MDL. Many systems fl ag results that are less than statistically signifi cant, but some do it more clearly than others do. However, I think it would have been better if they had let the result wander around zero (both positive and negative) and settled in closer and closer to zero with time. I have heard from various soſt ware people that negative results are incomprehensible for many users so they (the developers) take steps which end up biasing the results. For the record, I reported this matter to IXRF on at least two occasions and it had not been resolved the last time I checked which was several years back. I was told it was going to be addressed. I certainly hope it has been fi xed by now, but we may all be able to cite soſt ware issues that languish on the do-do list. Maybe one of their engineers is following the list and can clarify the matter. Warren Straszheim Wed May 10

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