Cleavage in High Vacuums of Alkali Halide Single Crystals—Secondary Electron Emission

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Abstract
Alkali halide single crystals were cleaved along the (100) plane in a high vacuum so that the monolayer adsorption time following cleavage was many hours. Secondary electron emission measurements were made on surfaces clean to within less than 1/100 of a monolayer. Single pulse measurement techniques minimized charging and electron bombardment damage of the surface. Maximum secondary electron emission yields for the cleaved crystals were generally very high, and include NaBr(23), KBr(14), KI(11), KCl(13), NaCl(14), and LiF(7). The maximum yield of a BaF2 single crystal with the surface scraped in the vacuum (but not cleaved) was 6. The most probable energy of the secondary electrons emitted from KCl was close to 1 eV. The yield of these crystals did not deteriorate rapidly with adsorption of gases in the vacuum system, lending support to the conclusion that only certain gases with a small partial pressure (or low accommodation coefficient) degrade their yield. Some reasons for the high yields of these materials are presented.

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