Comparative scanning tunneling microscopy observation of a homologous series of n-alkyloxy-cyanobiphenyles

Abstract
In scanning tunneling microscopy (STM) experiments liquid crystals (LC) do often serve as model substances for organic adsorbates on solid substrates. Especially, the group of alkyl-cyanobiphenyle (nCB, n=number of carbon atoms in the alkyl chain) liquid crystals has been in the center of interest for a long time. In this work we present STM results of adsorbate studies of the closely related molecules of the alkyloxy-cyanobiphenyle type (nOCB, with n=5,7,8). Under the influence of the electric field at the STM tip apex these LC molecules form well-ordered structures, which are determined by the atomic structure of the substrate surface. This molecular ordering of a thin adsorbate layer above the substrate is investigated by STM. The results on OCBs are compared with data from x-ray diffraction studies and with results of STM measurements of the closely related 8 CB. Both highly oriented pyrolytic graphite and molybdenum disulfide have been used as substrates.

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