CRYSTAL-GROWTH AND MOLECULAR-ORIENTATION OF VANADYLNAPHTHALOCYANINE IN THIN-FILMS

Vanadyl-2,3-naphthalocyanine (VONc) was vacuum-evaporated onto a KCl (001) surface. The crystal structure and molecular arrangement were determined by high-resolution electron microscopy (HREM) and electron diffraction. The crystal growth depended on the substrate temperature. The thin film deposited on KCl kept at 30°C was composed of amorphous and microcrystalline structure. At the substrate temperature range of 100-200°C the deposited VONc formed tentacle-like crystals, the column axes of which lay on the substrate surface. The epitaxial film grew on KCl kept at temperatures higher than 300°C. The high-resolution structure image elucidated that the planar VONc molecules tilt and stack in parallel along the b axis which stood perpendicular to the substrate surface. The origin of the molecular stacking was attributed to the V-O bonds which stick out of the molecular plane. The epitaxial nucleation was explained in terms of interaction between the electronegative oxygen atoms in the VONc molecule and the positive potassium ions in the KCl surface. The relative orientation between the deposit and the substrate cyrstals originated in the close lattice match of both crystals. Absorption and reflection spectra showed that the optical properties were significantly changed according to the differences in the orientation growth. Deposition of VONc at 300°C results in an intensive absorption at 872 nm. © 1990 American Chemical Society.