NetNotes
can use a FE SEM with a good BSE detector just above the sample (some millimeters) you may obtain a good result. More than lateral resolution, the precision of the measure may be affected by the calibration of magnification. For such job it could be interesting to check the accuracy of the magnification with an appropriate standard. You can easily simulate how far is the interaction volume for your sample by using software like CASINO for example. If you are lucky, you may find a good value for acceleration voltage; not too deep on the sample to avoid resolution problem but deep enough to get BSE from all the volume of the particles. In that case, probably you will see the diameter of the particle and not only the diameter of the sectioned disk on the surface. Of course, it supposes good correlation between several factors: Z number of particles, Z number of matrix, size of particles, etc. Nicolas Stephant
nicolas.stephant@
univ-nantes.fr Tue Jun 2
Why do you like a complicated approach to a simple question? Remove the bulk substrate! The easiest would be to cast a water or ethanol suspension of your particles on a TEM C-film/Cu 200 mesh grid, then go to see a colleague who runs a TEM or STEM microscope! Too far? Too expensive? No friend? Be self-standing. 1. First obvious solution: stick your TEM grid on top of a 10 mm deep, 2 mm diameter hole drilled in any light conductive material block (Al alloy is fine). Look at it in SE mode as usual, you will avoid all the trouble of electrons spreading in the substrate, BSE backscattering and secondaries of type 2. Of course, the W cathode is not as good as a FEG for ultimate resolution, but nevertheless will give a better resolution than BSE. 2. Assuming you have a semi-conductor BSE detector, you can easily transform your SEM in S(T)EM microscope. With a bit of manual skill you can carefully mount your BSE detector on the sample table (upside-down to receive the primary probe!), then with a light U-shape jig hold the TEM grid some 10-15 mm above the center of the BSE detector. The BSE signal becomes a STEM one. However the contrast is not well defined as both directly transmitted (bright field) and scattered electrons (dark field (DF) + high-angle annular dark field (HAADF)) are detected together. 3. To improve the contrast, you may add a beam stop to catch the transmitted beam and let only the scattered electrons to reach the BSE detector (DF + HAADF). Or you may cover the BSE detector, letting only a 2 mm hole to get the directly transmitted beam and BF contrast. Lazy? You may even more easily mount the BSE detector off-center to block the directly transmitted electrons on its edge and detect only electrons scattered in 2 quadrants (DF + HAADF, 50% signal). The efficiency of detection is high, which means you may use lower beam currents than usual and certainly much lower than for BSE. Expect a better resolution in this STEM mode than in SE. Beware! Contamination may be a limiting factor depending on your vacuum quality and require you to work fast, even to record pictures on fresh areas adjacent to that used for focusing. Philippe Buffat
philippe.buffat@epfl.ch Tue Jun 2
Image Processing: convert to .dm3 files
Digital Micrograph records EEL spectra as .dm3 files. While there are scripts that can export the data to a text file - I am wondering whether the reverse is possible. I have a two column.txt file of my EELS data - will it be possible to import that data into Digital Micrograph for further processing? Debangshu Mukherjee
debangshu@psu.edu Wed Jun 3
There is a feature in the GMS “File” menu called “Import Data...”. This is a fully functioned import tool that handles most data types. For importing EELS data, the spectra must be represented in equally spaced energy bins. If it is just a single row of data with the
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intensity values, you can convert this to EELS and calibrate using the “Spectrum” menu items. If the data is in energy / intensity format, there is no simple way to convert it to EELS data. I have written a short DMScript that handles imported data where the first row (or column) contains the energy values and the second row (or column) contains the EELS counts. I hope this helps, Ray Disclosure: I work for Gatan but I am not a programmer. I am sure the code below breaks a dozen rules. I learned scripting as a user of Gatan equipment and continue to use it when analyzing data, trying out new ideas or prototyping. This is unsupported script code. Interested readers can e-mail me to receive copy of the code. Ray D. Twesten
ray.twesten@
sbcglobal.net Wed Jun 3
Image Processing: Photoshop
We’ve updated our free image processing instructions from the NUANCE Center at Northwestern University. A few additions have been made to include explanations of file types, how to resize images the right way, and even some new coloring instructions. All of which are designed to be super easy and will walk the user step-by-(sometimes painful) step to do all sorts of normal image processing procedures, to several different procedures to apply false color to an image. The extra special part is the chapter on what I call Multi-Detector Color. Now I know I did not invent this technique, but I’ve worked out some pretty simple procedures that will allow you to make these really fantastic color images, even if you only have 1 SE detector in your SEM. It’s totally free, so please check it out and let us know what you think.
http://www.nuance.northwestern. edu/docs/epic-pdf/Basic_Photoshop_for_Electron_Microscopy_06- 2015.pdf Eric Jay Miller
eric-miller@northwestern.edu Tue Jun 9
EM: Gauss meter
I was thinking of buying a portable Gauss meter last week to try and track down some electrical interference in our lab. Comment from a colleague – ‘oh, just download a free app for your phone’. So I did; I think there are several ones available but I got Teslameter. It looks really good - and seems to work with reading levels down to 0.1 mG. Does anyone know if these apps actually work as well they appear to? Are they accurate? Richard Beanland
contact@integrityscientific.com Fri May 22
There are I think two dimensions to this question. The first is technical. If you are trying to track down sources of interference in your lab, you are probably concerned with time-varying magnetic fields - often at 60 Hz. The sensors in a phone will give DC readings, and thus they are not useful to you. I bought a Tenmars TM-192 3-axis EMF meter (<$200), which I compared to a $2000 Hall effect probe, and I found it to compare nicely for purposes of walking around a space and seeing where “hot spots” are. The second dimension is economic. Do you want to base expensive decisions such as room design, instrument selection, instrument placement or interference abatement on an app you got for free? Be sure your investment in information gathering is in proportion to the commitments you make based on the information. Larry Scipioni
les@zsgenetics.com Fri May 22
EM: high dynamic range
I was wondering if anyone has ever come up with a good repeatable technique for making high dynamic range (HDR) images using SEM or TEM micrographs. I think this could be a useful technique to use on low contrast samples and just to make a cool image. But I can’t seem to get it to work on my own. Eric Jay Miller
eric-miller@northwestern.edu Wed Jun 17
www.microscopy-today.com • 2015 September
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