Evaluation of the Alignment of Liquid Crystal Molecules on SiO₂ Alignment Layer by Attenuated Total Reflection Method Utilizing Surface Plasmon and Guided Wave Excitation Modes

Abstract

In this study, we report on the evaluation of tilt angles of liquid crystal (LC) molecules near the surface of SiO₂ alignment layers and in the whole cell when constant voltages are applied. A LC molecule, 4-cyano-4'n-pentylbiphenyl, was used in this study. The LC cell consisted of Au (50nm) / SiO₂ (30nm) /LC (3 μm)/ SiO₂ (30nm) / Au (100nm) system. SiO₂ alignment layers were obliquely evaporated on both Au surfaces. Surface plasmon resonance and guided waveguide excitation modes in attenuated total reflection configuration were used to monitor the alignment property of LC molecules adjacent to the surface and the bulk in the LC cell. In the ATR angular scan properties, the theoretical fittings agreed well with the experimental data on the assumption of simplified 5 LC layers model. The profile of the tilt angles from the surface to inside the cells was obtained by the theoretical fitting. In comparison with the internal bulk region, LC molecules near the surface required higher voltages to change their tilt angles toward vertical direction. As demonstrated in this report, this technique should provide the useful information to understand the interfacial phenomena for LC displays.