CRITICAL OPTIMIZATION OF THIN FILM PROPERTIES: A STRUCTURAL EXPLANATION.

A wide range of vacuum-deposited materials (both organic and inorganic) show sharply optimized properties (including carrier mobility, smoothness, epitaxial order, electrophotographic performance and photo-emf) when the condensation (substrate) temperatures are held in a very narrow range near 0. 33 of the respective normal boiling points. A proposed model invoked some kind of bulk structural singularity common to the various films; however, little structural data has been available to support or elaborate on this concept. Moreover, the previous work made few correlations between different properties for any one material. A detailed study of this ″critical optimization″ effect in 0. 1 mu m phthalocyanine films on glass substrates, an organic being chosen as the model material principally because of its lack of stoichiometric complications. From a detailed analysis of the data, it is concluded that films deposited at T(o) possess crystallites having substantially different orientations with respect to the substrate, compared with the other samples.