STRUCTURAL-ANALYSIS OF LEAD PHTHALOCYANINE ULTRATHIN FILMS GROWN ON CLEAVED FACES OF ALKALI-HALIDES BY REFLECTION HIGH-ENERGY ELECTRON-DIFFRACTION

Growth of lead phthalocyanine (PbPc) ultrathin films has been examined on cleaved (001) faces of KBr, KCl and NaCl by molecular beam epitaxy. Molecular arrangements on the surface were determined by reflection high-energy electron diffraction. PbPc molecules are found to form commensurate square lattices in the initial grown layer. They form two equivalent square lattices (square-root 10 x square-root 10-R +/- 18.4-degrees) on Kcl and NaCl, while they form a single domain square lattice (3 x 3) on KBr. The arrangements seem to be determined by two factors. One is the electrostatic interaction between a center metal atom of the molecule and a halogen anion of the surface, and another is the van der Waals interaction between each molecule. These considerations lead to the guiding principles for epitaxial growth of metal phthalocyanines which have pyramidal molecular structure on the (001) surface of rocksalt-type alkali halides.