Thin films of LiF and NaCl were prepared by evaporation in a vacuum and studied by means of electron diffraction, electron microscopy, x‐ray diffraction, and optical methods. It was found that on amorphous substrates the films possessed a crystal orientation which varied with the film thickness. For both LiF and NaCl deposits thinner than a hundred angstroms showed almost completely random structure but with a small amount of [100] preferred orientation. As the thickness was increased there was a change, first to completely random, and then to a very definite and strong preferred orientation which was [111] for LiF and [110] for NaCl. The extent of these orientations both on the surface and in the interior of the film was studied in relation to crystal growth. The films are composed of loosely packed crystals set together so as to give the characteristic orientation and with appreciable spaces where the crystals do not make contact. A less extensive study of five other substances showed the following orientations: CaF2, [111]; KCl, [110]; MgF2, [302]; NaBr and KBr, random or a vague [211]. MgF2was amorphous for deposits under 1000A but became crystalline for greater thicknesses. Detailed consideration is given to the comparison and interpretation of results obtained by different experimental methods.
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