Vertical alignment of liquid crystal on a-SiOx thin film using the ion beam exposure

Abstract

In this letter we demonstrate the vertical alignment of liquid crystal on inorganic thin film surfaces using the ion beam exposure. Nematic liquid crystal can be aligned vertically by the rotational oblique evaporation of a-SiOx thin films. However, the electro-optic switching behavior of liquid crystal along random directions results in disclination lines. By using the ion beam exposure, we can achieve highly uniform alignment without disclination lines. We found from x-ray diffraction and x-ray photoemission spectroscopy data that the vertical alignment can be achieved when x approaches 1.5 at the a-SiOx film surface. We have shown that the pretilt angle can be controlled by changing ion beam parameters, such as the ion beam energy, the angle of incidence, and the exposure time. We also have shown that a liquid crystal cell aligned vertically by the ion beam exposure exhibits the voltage-transmittance curve similar to that of a rubbed polyimide cell.