Scanning tunneling microscopy of liquid crystals, perylene‐tetracarboxylic‐dianhydride, and phthalocyanine

Abstract

Scanning tunneling microscopy measurements conducted on pure liquid crystals and liquid crystals in combination with the dyes perylene‐tetracarboxylic‐dianhydride (PTCDA) and phthalocyanine (Pc), all adsorbed on highly oriented pyrolytic graphite (HOPG), are being reported on. The liquid crystal octylcyanobiphenyl (8CB) was used as a solvent for the dyes, allowing the preparation of ordered dye layers in a very simple way. A combination of vapor deposition of PTCDA and liquid deposition of 8CB provided films, where 8CB and PTCDA are embedded in each other on a small length scale. The samples were prepared in two different ways yielding either 8CB islands within a PTCDA monolayer or PTCDA islands surrounded by 8CB. The Pc films on HOPG exhibit a hexagonal molecular lattice that could be related to the lattice of the graphite substrate and for which a structural model is proposed. For dodekylcyanobiphenyl (12CB) on HOPG the ordering in unit cells containing 10 rather than 8 molecules is reported for the first time.