Scanning tunnelling microscopy on ultrathin organic layers of phthalocyanine and naphthalocyanines on highly oriented pyrolytic graphite (0001)

The adsorption geometry of the monolayers of planar palladium phthalocyanine (PdPc), naphthalocyanine (Nc), and non-planar tin-naphthalocyanine (SnNc) on the basal plane (0001) of graphite have been studied. Monolayers were prepared using organic molecular beam epitaxy (OMBE) under ultrahigh vacuum (UHV) conditions at room temperature. Planar PdPc and Ne molecules form large areas of ordered monolayers with their molecular plane parallel to the substrate. PdPc forms quadratic and Nc forms distorted quadratic superstructures, however the superstructure is non-commensurate with the substrate lattice. Non-planar SnNc shows a commensurism with graphite and forms a hexagonal superstructure, which indicates a stronger molecule-substrate interaction compared to the planar derivatives revealing the influence of geometry on the adlayer structure.