Date: Fri, 17 Nov 2000 10:03:33 -0500

Author: "Hsu-Chang Lu"

Subject: RE: Electron diffraction

Post:

I checked the book. It seemed to be a polycrystalline graphite film
(annealed carbon foil). The nice figure is possible only when you hit a nice
area.

I thought you actually need a single crystal (my impression from previous
posts), not polycrystalline film.

It seems that if the electron beam is fine enough, one could find a single
crystalline area on a polycrystalline film to get the nice patterns, which
is enough for demo purposes.

Lu



-----Original Message-----
From: owner-tap-l@listproc.appstate.edu
[mailto:owner-tap-l@listproc.appstate.edu]On Behalf Of Wolfgang Rueckner
Sent: Friday, November 17, 2000 8:35 AM
To: tap-l@listproc.appstate.edu
Subject: RE: Electron diffraction


>It's much straightforward to deal with keV electrons that goes through. But
>I don't think it's possible to find a single crystal that's so thin (for
keV
>electrons to get through) yet still allow you to handle/position it.

The Welch apparatus has a 2x2 cm mesh in the CRT between the electron gun
and the end of the CRT (which itself is a phosphor screen). It's fully
described (complete with pictures of the diffraction patterns -- fig 38-45
is gorgeous!) in "Physics Demonstration Experiments," edited by H.F.
Meiners, vol II, pp 1196-1198.

Wolfgang

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