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Re: [Phys-L] electron microscope rehab



Note: writ before JD to --------------



What!


This instrument is so simple I can’t believe you’ll give up. That is if the magnets are still gud. Even replacing the HV P/S is likely easy.

Come on fellows!

bc would like to have it and “get it” running.

The HV is 50kV and does require a vacuum, as the e-beam path length is v. ~ a foot. I suspect even significant scattering in just a mm at 50 kV.

Whatever, this article likely gives the answer:
To cite this article: D A Moncrieff et al 1979 J. Phys. D: Appl. Phys. 12 481

Beam profiles at 25 keV w/ various pressure of N2. Curiously SEM tolerates p. as great as 100 Pa w/ a working distance of 15 mm

Fig. 4 shows ~ 90% scattering out of a beam w/ 100 Pa and working distance of 40 mm. (25 keV) (less scattering w/ a 10 keV beam) Initial beam is, evidently, < 0.1 micron. Another experimenter found a “… 50 nm beam after a 20 mm flight path, changes little up to a p of ~ 10 Pa."

------------------------------------------

bc is a dolt as he forgot the oxidation of the filament pointed out by JD. and knew the MFP was much! shorter than a mm, and uses the “excuse” he's 80+ w/ incipient Alzheimer’s.
Re: sample prep. My job was simple, as it involved coating a plastic object w/, IIRC, carbon (vacuum deposition) and dissolving the plastic, then placing the film on a screen. Also, IIRC, one must coat insulator objects w/ a conductive coating (TEM & SEM), otherwise the deposited charge will deflect the beam and thus defocus.

My PhD research involved vacuum deposition in UHV using a Varian Vacion pumping system and sorption pump roughing. (no grease or oil ever! … over night degassing w/ an internal heater (1966=>69)

Ted Pella sells a primer for TEMicroscopists.

And, all this is unnecessary w/, as JD wrote, an STM. AJP archive describes one using the quartz tuning fork from a clock. Wrong, memory?

Here’s one tho: Citation: American Journal of Physics 59, 38 (1991)




On 2017/Nov/17, at 04:47, Peter Schoch <pschoch@fandm.edu> wrote:

Brian Whatcott asked if
https://www.smecc.org/rca_emt_tabletop.htm <https://www.smecc.org/rca_emt_tabletop.htm>

was the instrument in question. In fact, it is.

Amazingly there's no vacuum pump as the distant from electron gun to sample
holder is <1mm. The resolution is not great compared to modern machines.

After examining the link John D. sent along, I think we may, indeed, be
better off trying to just build one from scratch.

Thanks everyone for your collective wisdom,
Peter