Homogeneous and homeotropic orientations of nematic liquid crystal (NLC) are investigated on various inorganic thin films which are exposed to Ar ion-beam. It is the novel investigations which results in a completely dry processing technique for both the thin film deposition and alignment steps. In the case of homogenous alignment on diamond-like carbon (DLC) layer, optical band gap and the polar surface energy are investigated in order to elucidate the alignment mechanism by ion beam (IB) irradiation. We elucidate the role of surface polarity in DLC films with respect to the LC orientation. On the other hand, FDLC thin films are selected by homeotropic alignment layer with regard to the relationship between surface tension and LC orientation. Selected pretilt angles in the range of 71.1–89.8° can be easily obtained with ion beam irradiation. It is sensitively changed by thin films composition and the angle of ion beam irradiation.

We propose an ultrafast nematic liquid crystal (LC) device without alignment layers, where both the dark and bright states can be realized by applying an electric field. A vertical electric field is applied to vertically align the LCs for the dark state, whereas an in-plane electric field is applied to homogeneously align the LCs for the bright state. We achieved a total response time of less than 3 ms in the proposed device. This device may contribute, not only to a significant improvement of the switching speed in liquid crystal devices, but also to the simplification of the device fabrication by the omission of the alignment layer coating and the rubbing process.

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.

No abstract

The vertical alignment of liquid crystals having negative dielectric anisotropy on an amorphous silicon oxide (a-SiO(x)) thin film is the consequence of the anisotropic interaction between liquid crystals and a-SiO(x) thin films. To investigate the mechanism of the vertical alignment, we changed the physicochemical characteristics of alignment layers by controlling the composition, since the anisotropic interaction depends on the nature of both liquid crystals and an alignment layer. The variation of composition gives rise to a change in the polarizability, which is a simple measure of induced-dipole strength at the surface of the alignment layer. There is a critical transition point from planar to vertical alignment of liquid crystals, and it is the long-range van der Waals interaction that is responsible for the vertical alignment. The competition between long-range van der Waals interaction and short-range dipolar interaction were investigated and analyzed in terms of the interfacial energy between liquid crystals and an alignment layer.