Abstract
Electron microscopy replica techniques and photo-optical microscopy were applied in an investigation of the surface morphological changes occurring on the cleaved (111) CaF2 face when the crystals were heated in ultrahigh vacuum and technical vacuum. A characteristic macromorphology consisting of ridges, hills, and valleys was observed. The micromorphology consisted initially of crystallographic micropits and steps which gave way to a crystallographically terraced surface containing terraced hillocks in its final stage. Micropits were rarely observed in ultrahigh vacuum, and then only when air-cleaved crystals were used. The density of the terraced hillocks also was much less in ultrahigh vacuum than in technical vacuum. The results are interpreted and discussed in terms of impurity effects and the theories of thermal vaporization.
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