Orientation Overgrowth of Condensed Polycyclic Aromatic Compounds Vacuum-Evaporated onto Cleaved Face of Mica

Abstract

When Pt‐, Cu‐, and Zn‐phthalocyanines are vacuum‐evaporated onto cleavage faces of muscovite, single‐directional orientation occurs at lower substrate temperature. At higher temperature ranges, Zn‐phthalocyanine has a double‐directional orientation while Pt‐ and Cu‐phthalocyanines show triple‐directional ones. High‐resolution electron diffraction patterns, which were well‐defined fiber diagrams, revealed that all three compounds showed conspicuous isomorphism with one another, and Zn‐ and Cu‐phthalocyanines occurred in the metastable forms of their dimorphs. General crystal structures of metastable forms are discussed on the basis of the found isomorphism with Pt‐derivative. Evaporated films were composed of lamellar crystal strips, and the fiber diagrams showed that at least two kinds of lattice orientations were assumed by all three compounds, while the longitudinal crystal axis of individual strips always ran parallel to their b axes. As to relative orientation of the evaporated films to the substrate, the b axis of the former was parallel to either of the two directions which made ±60° with the a axis of muscovite in the case of the single‐directional orientation. When the evaporated films had double‐ or triple‐directional orientations, the electron diffraction pattern showed twofold symmetries in spite of the apparent triangular configuration. It turned out that this axis of twofold symmetry also coincides with the same axis of muscovite as above. It is presumed that the unique orientation axis of the evaporated films coincides with the staggering direction of the two oxygen tetrahedron sheets in the top subcell of muscovite. Plausible origin of these orientations are also discussed in terms of lattice vibration near the surface. Lattice imperfections of the evaporated films were directly observed in the lattice image obtained by the high‐resolution electron microscopy. The dislocation density seems rather high when compared with other similar lamellar crystal strips of the same compounds formed by colloid chemical methods. This was ascribed to the crystal formation controlled by the epitaxial effect.