Scanning tunneling microscopy of chain-molecules at solid-fluid-interfaces

Scanning tunneling microscopy has been employed to investigate chain molecules, which have been self-assembled at the interface between their melts or organic solutions, and a solid flat surface of a semimetal or a semiconductor. Also it has been used to observe chain molecules in a precursor wetting layer in the vicinity of the edge of a solidified alkane melt drop. With a resolution in space and time of 10 pm and 10 μs, respectively, it is possible to investigate (i) commensurability between substrate and adsorbate lattices, (ii) the packing of molecules and molecular mixtures with various symmetries on several structurally and chemically different substrates, (iii) temperature and composition induced order-disorder transitions between 2-dimensional crystals and liquid crystals, and (iv) the current through individual molecular segments at different bias voltages. We summarize some of our work in this area, and report on new results on an alkoxylated poly(p-phenylene) on the basal plane of highly oriented pyrolytic graphite (HOPG).