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

In this study the observation of self-assembled monolayers of poly(dim ethylsilanes) and poly(di-n-hexylsilanes) on the basal plane of highly oriented pyrolytic graphite (HOPG) is reported. The layers were chara cterized by scanning tunneling microscopy (STM). Individual polysilane molecules, the polysilane backbone and the hydrocarbon side chains wi thin an individual molecule could be identified. Measured atomic dista nces were found to correspond to the expected values. The polysilanes formed regular molecular patterns, such that the polysilane backbone c hains were stretched out straight, aligned parallel to each other sepa rated by the alkyl side groups. The molecules were found in the all-tr ans zigzag conformation, the dihedral angle of the silicon backbone ch ain atoms is proposed to be perpendicular to the graphite substrate. T he relative orientation of the polysilane molecules on graphite and th e relative orientation of the molecules to each other is different for each of the investigated polysilanes. The structural behaviour of pol ysilanes is of interest, since it may allow future investigations on t he conductivity of sigma-bonded polysilanes on the molecular scale.