Motorized & Steromicroscope z-stack of Oberonia flower

[RosieC]

Originally Posted by tropterrarium

Thanks.

SEM can easily be used for low mag shots. I attach an image of a different species done by SEM. Sorry for the ugly writing, but I still want to publish this image. The problem is, that the specimen needs to be in pretty high vacuum, so all water has to be removed without the specimen shriveling. That is done by Critical Point Drying, where the specimen is first preserved in 100% ethanol, then transferred to liquid carbon dioxide. The carbon dioxide is under pressure raised to above 31 deg C, where upon it goes "supercritical": the fluid has zero viscosity, and it is in a gas-fluid hybrid state. Then the gas is slowly released. So this procedure requires specific equipment.

I sputter coat the flowers with gold, then put them into a variable pressure SEM (Zeiss EVO 40XVP). Chamber pressure is relatively high for SEM, I like 30 Pa. The air helps with reducing charging on those highly branched structures, and produces more even illumination on the specimen. The column and the gun are isolated from the chamber by a lower 100 micron aperture, at which differential pumping is going on. The column is still under 10-4 to 10-5 Pa pressure, just with turbomolecular pump, not with ion gate.

I can do higher mag shots, too, say of pollinia, or details of cell surface structures on various parts of the flowers. Very interesting results.

Atomic resolution is very difficult to get with SEM. Our scope can't do that at all (I think specs are 4-5 nm resolution). In general, you would rather go to TEM or STEM, or atomic force microscopy. In silicates you can resolve crystals no problem, but not atoms or molecules.

Hope that feeds your curiosity.

Thanks yes it does feed my curiosity. I used TEM as well in the same university project so I'm perhaps confusing which one gave us atomic level images. Really interesting about how you remove the water, of course I didn't have that problem with silicon structures, though I did have problems getting them clean enough to scan. TEM initially gave lots of pictures of the invisible to the eye debris because my supervisor thought you could just wash them in pure water in a fume cupboard (I wasn't convinced of that from the start). Ultra low vacuum techniques helped there though

Really interesting to see