SELF-ASSEMBLY OF ORGANOPOLYSILANES ON GRAPHITE - A SCANNING-TUNNELING-MICROSCOPY STUDY

In this study the observation of self-assembled monolayers of poly(dimethylsilanes) and poly(di-n-hexylsilanes) on the basal plane of highly oriented pyrolytic graphite (HOPG) is reported. The layers were characterized by scanning tunneling microscopy (STM). Individual polysilane molecules, the polysilane backbone and the hydrocarbon side chains within an individual molecule could be identified. Measured atomic distances were found to correspond to the expected values. The polysilanes formed regular molecular patterns, such that the polysilane backbone chains were stretched out straight, aligned parallel to each other separated by the alkyl side groups. The molecules were found in the all-trans zigzag conformation, the dihedral angle of the silicon backbone chain atoms is proposed to be perpendicular to the graphite substrate. The relative orientation of the polysilane molecules on graphite and the relative orientation of the molecules to each other is different for each of the investigated polysilanes. The structural behaviour of polysilanes is of interest, since it may allow future investigations on the conductivity of sigma-bonded polysilanes on the molecular scale.