Structure and properties of vacuum-deposited thin films: A new basic relationship

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Abstract
We show that a wide range of vacuum‐deposited materials exhibits sharply optimized properties and, in some cases, unusual crystal structures when the temperatures at which the materials are condensed (the substrate temperatures) are in a narrow range near 0.33 of their respective normal boiling points. This generalization applies to essentially all the really sharp optima we can find (for nonmetals) in the recent literature. The materials include organics (our own data on anthracene, phthalocyanine, and pyrene) and inorganics (Se, ZnO, SnTe, and most of the sulphides, selenides, and tellurides of lead, cadmium, and zinc). Both polycrystalline and epitaxial films are involved. The properties optimized include charge‐carrier mobility, smoothness, epitaxial order, electrophotographic performance, and photo‐emf. We propose a possible explanation for these effects which gives good numerical agreement the experiment; our main postulate is that the optimum properties occur when the rate of reevaporation from well‐defined, but disordered, regions of the growing films (probably glassy areas) is just sufficient to exceed the deposition rate.

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