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.

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The authors report the vertical alignment of liquid crystal (LC) through the ion beam exposure on amorphous oxygen-doped SiC (SiOC) film surfaces deposited at room temperature. The optical transmittance of these films was similar to that of polyimide layers, but much higher than that of SiOx films. The light leakage of a LC cell aligned vertically on SiOC films was much lower than those of a LC cell aligned on polyimide layers or other inorganic films. They found that LC molecules align vertically on ion beam treated SiOC film when the roughness of the electrostatic force microscopy (EFM) data is high on the SiOC film surface, while they align homogeneously when the roughness of the EFM data is low.

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We investigated the liquid crystal (LC) alignment on SiO x film surfaces as a function of ion beam exposure time using scanning probe microscopy and X-ray photoemission spectroscopy. It was concluded that the LC alignment with high or low pretilt angles did not contribute to the morphological roughness but depended on the roughness in the electric potential of the SiO x surfaces. We also found that SiO x films with vertical LC alignment show relatively low values of stoichiometry parameters (1.42 < x < 1.57), whereas those with homogeneous LC alignment show relatively high values of stoichiometry parameters (1.58 < x < 1.77). All the experimental results showed that the electric dipole-dipole interactions between the LC molecules and the SiO x surfaces played a dominant role in aligning LC molecules on ion-beam-treated inorganic surfaces.