Anchoring Structure of Binary Mixture of Liquid Crystals Studied by Scanning Tunneling Microscopy

Abstract

The anchoring structures of the binary mixture of 4′-n-octyl-4-cyanobiphenyl (8CB) and 4′-n-decyl-4-cyanobiphenyl (12CB) on molybdenum disulfide (MoS2) are directly observed, with molecular resolution, by scanning tunneling microscopy (STM) for the first time. The STM images indicate that the technique not only resolves the individual molecules, but it also makes a clear distinction between the 8CB and 12CB molecules by their different alkyl chain lengths. The binary mixture takes a bilayer (double-row) structure, consisting of an 8CB subunit and a 12CB subunit, while the pure 8CB molecules do not show a bilayer, but a monolayer (single-row) structure on MoS2. The ratio of 8CB and 12CB adsorbed on MoS2 substrate is different from that in the bulk.

Scanning Tunneling Microscopy Investigation of the Ordered Structures of Dialkylamino Hydroxylated Squaraines Adsorbed on Highly Oriented Pyrolytic Graphite

“…This system is best exemplified by liquid crystals. [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] Molecules that form liquid crystalline phases generally contain a polar head group and an aliphatic tail. Within the adsorbate layer the main intermolecular interactions are dipole-dipole and van der Waals.…”

“…The second group shows a relatively balanced influence of intermolecular interactions within the adsorbed layer and between the adsorbed molecules and the substrate. This system is best exemplified by liquid crystals. − Molecules that form liquid crystalline phases generally contain a polar head group and an aliphatic tail. Within the adsorbate layer the main intermolecular interactions are dipole−dipole and van der Waals.…”

Dynamical Exchange Behavior in Organic Monolayers Studied by STM Analysis of Labeled Mixtures

“…Mixed monolayers containing more than one organic compound are also of interest, but they greatly complicate the interpretation of STM images. However, several mixtures have been studied, including alkane/alcohol mixtures, 1 alcohols 2 or acids 3 of different chain lengths, n-alkylcyanobiphenyls, [4][5][6] unsaturated liquid crystals, 7 and others. [8][9][10] In most cases, the mixtures were observed to form separate domains, each composed of a pure component.…”

“…Mixed monolayers containing more than one organic compound are also of interest, but they greatly complicate the interpretation of STM images. However, several mixtures have been studied, including alkane/alcohol mixtures, alcohols or acids of different chain lengths, n -alkylcyanobiphenyls, − unsaturated liquid crystals, and others. − In most cases, the mixtures were observed to form separate domains, each composed of a pure component. The cyanobiphenyls form stoichiometric mixed-crystal domains, with the monolayer containing the two components in a fixed ratio and with a specific ordered structure in each unit cell.…”

Liquid Crystals — as seen by the Scanning Tunnelling and Force Microscopes

“…10) [8]. The binary mixture takes on the double-row structure observed for 8CB on graphite and for 12CB on graphite and on MoS 2 • Close examination of the parallel rows reveals that they are composed of 8CB and 12CB subunits.The ratio of 8CB and 12CB adsorbed on the substrate is different from that in the bulk .…”