Molecular Alignment in Monolayer of $n$-Alkyloxy-Cyanobiphenyl and Clear Evidence of the Odd–Even Effect

概要

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Systematic observations are carried out to determine molecular alignments of monolayers of homologous series in $n$-alkyloxy-cyanobiphenyl ($n$OCB) liquid crystals in the range of $n=7$ to 10 on both molybdenum disulfide (MoS2) and highly oriented pyroritic graphite (HOPG) substrates using a scanning tunneling microscope. Our observations determined the following. For odd $n$ of carbon atoms in alkylchains such as 7OCB and 9OCB, the molecular alignments on both substrates (MoS2 and HOPG) are mainly due to the interaction between alkylchains and substrates. For even $n$, on the other hand, the alignments are basically due to the dipole-dipole interaction between liquid crystal molecules on the substrates. These differences occur due to the situation of the end-carbon in an alkylchain. However, 10OCB on HOPG shows an exceptional alignment resulting from the alkylchain-length effect. Excluding this case, all other seven combinations clearly indicate the odd–even effect. The validity of our previous model for molecular alignments of $n$CB monolayers has been confirmed for $n$OCB.
Publication Office, Japanese Journal of Applied Physics, Faculty of Science, University of Tokyoの論文
2001-06-15