NetNotes SEM:
materials demo In a turn of events that will make many of you smile knowingly,
I’ve been asked to give a half day, hands-on “workshop” on “EM” as a professional development activity for some local high school science teachers. It’s a great idea, but, as you all well know, there is just no such thing as throwing something on the SEM or TEM for a “quick pic”! Tankfully, we have an SEM with LV capabilities so that we can look at unfixed samples! Some of these teachers are physics teachers and so probably not so excited about looking at the biological samples with which I am well-acquainted and bringing the micrographs back to their students. Do any of the materials scientists out there have a suggestion for an easy and easily available materials sample to look at with these teachers? Kristen Lennon
kamlennon@yahoo.com Mon Jun 21 Several years ago a group from Dupont in Delaware gave a
presentation at the Philadelphia Society for Microscopy, mostly biological focused. Tey showed SEM images of failure analysis that was of interest to all in that they could not show failure analysis of their work projects. Some that I remember were a screw that had to top twisted off and a broken flusher handle from a toilet. Tese showed force and corrosion. Perhaps you have something broken like these at home. Patricia Stranen Connelly
connellyps@nhlbi.nih.gov Mon Jun 21 Two low prep samples that show a nice fusion of biology and
physics/engineering principles are a butterfly wing scale and the structure of a chicken eggshell. I have images on my website. Neither requires critical point drying; just mount and sputter. Te eggshell is the surface exposed when the inner tough membrane layer is peeled off (bet someone knows the official name...), but both sides are interesting— outer surface shows the various fine CaCO3 beads that scatter light so nicely... Te xylem image is a confocal one, but could be prepped for SEM. It is made by finding the nice weed common here - Plantago - and nicking the petiole with a razor or fingernail and pulling apart - stripping out the vascular bundles (like celery strings - that would do also...); these wall thickenings support the xylem from collapsing due to atmospheric pressure when there is greatly lowered pressure from transpiration in the leaves (how much pressure does it take to get water to the top of a redwood?)
http://www.bio.umass.edu/microscopy/ gallery.htm Dale Callaham
dac@research.umass.edu Mon Jun 21 According to your web site, your University has a Materials
Engineering department. Tey probably have a tensile tester and may have a Charpy Impact tester. In any case, they have the capacity to break steel samples. So ask for two pieces of the same steel, one fractured at room temperature and one at depressed (LN) temper- ature. People realize that things can get brittle at low temperature. Te vivid difference between microvoid coalescence (overload) and cleavage (brittle) as seen in the SEM, at relatively low magnification, is something a Physics teacher or student will find immediately captivating. And if they ask you why the steel behaves like that, just look smug and inform them that they need to attend classes to find out. Andrew Werner
werner1@slb.com Mon Jun 21 I am not a materials person, but I did have a project looking at
sediment from river bottoms. Te samples are very easy to prepare— just suspend the mud in a fairly dilute suspension, let the larger particles settle, then put a drop (a few µl will do) onto a carbon/ Formvar coated grid and let dry. If my experience was typical, you will see diatom skeletons, mineral fragments, crystalline and not, and other items in a TEM image. EDS (if available) will also show some surprises for some of the particles. I saw U and Au in addition to the usual suspects, Na, K, Si, Al, Ti, Ca, etc. Bill Tivol wtivol@verizon. net Mon Jun 21
68
You can use paper. Place on the stub two pieces of paper: writing
paper and filter paper. You can see paper fibers and filler particles in writing paper (no particles in filter paper). You can check distribution of filler with BSE and composition with EDS (usually some salts of Ca2+). Vladimir Dusevich
dusevichv@umkc.edu Mon Jun 21 When I was at PPG’s Glass Technology Center, we had an open
house for family members. We did a demo on the SEM that was kind of neat. We set them up for a punch line at the end of the demo. Here’s what we did: We took a dead fly and heavily coated it with gold. It was a really thick layer of gold. Tis was done prior to the demonstration. Our real sample was a cross section of enamel on glass that we wanted to show the layers and components and measure the different phases with the XEDS to show how we measure composition. To introduce them to the SEM, we showed them the fly. Scanned it all over and explained how the image was formed. We did not tell them it was coated. Of course, they thought that it was neat. Ten we moved to the cross section sample and showed how we measured the composition of the different phases with the X-ray system. Oh-hum, kind of boring. Ten we asked them “what was the composition of the fly?” Some would say C,H,O or whatever their guesses were. We then said, “Well, let’s find out for sure.” And, of course, the only thing that came up was gold in the spectrum. We then asked, “Why is it gold?” and then let them guess. At the end, if they didn’t know, we asked them if we could interest them in stock certificates in the “PPG Lost Gold Bug Mine” which were certificates that we made up with a big yellow faux colored SEM image of the fly, the X-ray spectrum in the background, and the signed signatures of our group members as officers in the “PPG Lost Gold Bug Mine Corporation”. I think that it went over fairly well and the kids were carrying around their stock certificates all day. Scott Walck
swalck@southbaytech.com Tue Jun 22
SEM:
air sensitive sample I am challenged with the task of performing SEM on air sensitive
catalysts. Can anyone share their method for doing this? I have seen SEM images of the catalysts that I am interested in analyzing. However the company that generated those micrographs can not share their procedure with me. I can provide more information regarding the catalyst off-line. Jackie Ayotte
jacqueline.ayotte@ticona.com Somewhere I saw people using air-tight box with a cover that
was kept in place by suction (atmospheric pressure), so that specimen in the box was kept under vacuum. Small spring, attached to the cover, was used to move it away when air pressure in a SEM specimen chamber was low enough. Specimen was conductive and the box was made from metal. Vladimir Dusevich
dusevichv@umkc.edu Mon Jun 21 I have recommended the following procedure to people using our
SampleSaverTM storage containers. Tese containers are compatible with glove boxes, so if you are using a glove box, you simply close your sample up in the container without the need to purge the unit. Te SampleSaverTM container is used to transport the sample from wherever you are processing/preparing the sample under shielded conditions to the microscope. Tere are glove bags with large open ends that you can place the unopened SampleSaverTM container in and then tie the glove bag over the open end of the SEM. You then can fill the glove bag with nitrogen and then take the sample out of the SampleSaverTM container in the glove bag, place the sample in the SEM stage, close the stage and pump it out. I would, of course, bring the SEM chamber up to atmosphere with nitrogen and purge it while the glove bag is on prior to opening the SampleSaverTM. Scott Walck
swalck@southbaytech.com Mon Jun 21
www.microscopy-today.com • 2010 September
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