NetNotes
that describes what the various options are for each routine? Steven R. Spurgeon
steven.spurgeon@pnnl.gov Mon Jun 15
The JEOL EDS software works on both SEMs and TEMs and the three different quantification methods are tailored to those two different microscopy techniques. In short, the quantification routines are used to compute the k-factors for quantitative analysis. The ZAF routine is a method to compute matrix corrections for the effects of atomic number, likelihood of absorption, and characteristic fluorescence of emitted x-rays from your sample, and these corrections are generally only valid when you have the classic teardrop interaction volume (i.e. bulk samples). So this would be a good routine to correct maps acquired via SEM. The ratio technique is the appropriate technique for maps acquired via TEM as TEM samples are typically much too thin for the emitted x-rays to be influenced in any statistically significant manner by Z, A, or F (you might still need to worry about channeling effects induced by sample orientation, however). This routine uses precomputed k-factors or experimentally calculated k-factors as anchor points from which the quantitative composition of your sample is derived, as the ratio of peak intensities from a known material and an unknown material is directly related to the k-factor. Selecting the ratio routine fills in the peak intensity of a known material and the k-factor, allowing the software to calculate the concentration from the measured peak intensities of your unknown sample. Obviously your results will be much more quantitative should you experimentally calculate k-factors for the elements of interest (and under identical illumination conditions) than by using the software database. X-from the JEOL EDS software manual regarding the net intensity routine: “The net intensity map displays relative intensities after deconvolution and back-ground subtraction. The result of the net intensity map is different between with check in the “100%” and without. Check “100%” Concentration before correcting by Quant. Method displays. The summation of K-ratios for all elements is unified at each pixel. Uncheck “100%” Normalize the maximum net intensity to 255 in the all pixel of the element.” Practically speaking, you’ll want to be exceedingly careful generating quantitative EDS data without first experimentally generating appropriate k-factors. Without doing so, your quantitative numbers are going to be ballpark estimates for anything but the simplest samples. Such data might not be trustworthy by itself but it can be useful as a comparison between EDS data from different unknowns acquired under similar conditions. Masashi Watanabe and David Williams discuss the problems associated with acquisition of quantitative EDS data and an alternative to using k-factors in a series of papers (see M. Watanabe’s website at Lehigh) and in the second edition of the classic Williams and Carter intro to TEM text. Chris Winkler
microwink@gmail.com Mon Jun 15
STEM-EDS: beam broadening
I am looking for a program that will help me calculate beam broadening for STEM-EDS measurements. In particular, I’d like to figure out the maximum achievable spatial resolution given a known sample composition, zone axis, thickness, energy, and so on. Does anyone know if there is a freely available program that can help me with these calcula- tions? Steven R. Spurgeon
steven.spurgeon@pnnl.gov Thu Jun 11 David Joy wrote such a program some time ago. I hope someone else on the list knows how to get a hold of it. Bill Tivol wtivol@
sbcglobal.net Thu Jun 11
You can also try using the Monte Carlo programs by Gauvin and Demers group (WinXray and Casino) or DTSA-II (N. Ritchie, NIST). The cross-sections are more accurate for SEM work, but they should be good enough to give you an idea of your beam spreading. DTSA-II has an option for a thin film on substrate and you can define the substrate as “none”. Win X-ray MC X-ray
http://montecarlomodeling.mcgill.ca/ software/
softwareprojects.html Casino
http://www.gel.usherbrooke. ca/casino/
DTSA-II
http://www.cstl.nist.gov/div837/837.02/epq/
dtsa2/ Hendrik O. Colijn
colijn.1@osu.edu Mon Jun 15 I am one of the authors of some of the programs mentioned, and I want to add a warning. All MC programs mentioned do not take into account the crystal structure of the sample, they consider the sample amorphous. So you will get the beam broadening without channeling effect (or orientation effect). For more information, we published a paper on the lateral resolution in STEM mode with CASINO v3 in amorphous sample: Demers, H.; Ramachandra, R.; Drouin, D. & de Jonge, N., “The Probe Profile and Lateral Resolution of Scanning Transmission Electron Microscopy of Thick Specimens,” Microscopy and Microanalysis , 2012, 18:582-590 DOI: 10.1017/ S1431927612000232 Hendrix Demers
drix00@gmail.com Mon Jun 15 Good point! All the MC programs I mentioned assume an amorphous sample. I had missed the fact that Steve had included channeling in his requirements. I believe that Dave Muller’s group at Cornell has taken channeling into account in their atomic resolution STEM calculations. For non-atomic resolution work, channeling may safely be neglected in most cases. It is also likely that beam convergence angle will have a more significant effect on resolution than channeling. For example, in organic samples <100 nm, Muller’s group indicate that the beam convergence has a greater effect than the beam spreading (Ultra. v.109 p.1 2008). Hendrik O. Colijn
colijn.1@osu.edu Mon Jun 15
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