Surface Polar Ordering in a Liquid Crystal Observed by Optical Second-Harmonic Generation

Abstract

Using optical second-harmonic generation as a probe, we have observed polar ordering of $4^{\prime }-n-\mathrm{octyl}-4-\mathrm{cyanobiphenyl}$ (8CB) molecules in a monolayer at an 8CB-glass interface, but nonpolar ordering at the free surface of 8CB as well as in the bulk with the molecules forming quadrupole-type pairs. The surface polar ordering was independent of temperature and unaffected by the phase transitions in the bulk 8CB.