SCANNING-TUNNELING-MICROSCOPY OF LIQUID-CRYSTALS, PERYLENE-TETRACARBOXYLIC-DIANHYDRIDE AND PHTHALOCYANINE

Scanning tunneling microscopy measurements conducted on pure liquid cr ystals and liquid crystals in combination with the dyes perylene-tetra carboxylic-dianhydride (PTCDA) and phthalocyanine (Pc), all adsorbed o n highly oriented pyrolytic graphite (HOPG), are being reported on. Th e liquid crystal octylcyanobiphenyl (8CB) was used as a solvent for th e dyes, allowing the preparation of ordered dye layers in a very simpl e war. A combination of vapor deposition of PTCDA and liquid depositio n of 8CB provided films, where 8CB and PTCDA are embedded in each othe r on a small length scale. The samples were prepared in two different ways yielding either 8CB islands within a PTCDA monolayer or PTCDA isl ands surrounded by 8CB. The Pc films on HOPG exhibit a hexagonal molec ular lattice that could be related to the lattice of the graphite subs trate and for which a structural model is proposed. For dodekylcyanobi phenyl (12CB) on HOPG the ordering in unit cells containing 10 rather than 8 molecules is reported for the first time.