Determination of the Surface Tilt Angle by Attenuated Total Reflection

Abstract

Thin SiO₂ layers prepared by oxidizing an organo-silane in an Ar/O₂ rf plasma discharge produce parallel alignment for nematic liquid crystals with essentially zero tilt. In addition, if the rf plasma system is arranged to produce an Ar/O₂ beam, uniform parallel alignment can now be obtained with the director in the substrate plane at an angle perpendicular to the plane of incidence of the rf plasma beam. We have studied the aligning properties of such films using the evanescent wave generated by attenuated total reflection (ATR) on a thin gold film when a surface electromagnetic wave is excited. Liquid crystal cells were constructed on a high index glass prism with a 500 Å gold film and a 200 Å aligning layer. By following the ATR minimum as a function of applied electric field, the tilt at the interface of the liquid crystal and the aligning layer was calculated.