Phil Kook Son

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

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.

Vertical alignment of liquid crystal through ion beam exposure on oxygen-doped SiC films deposited at room temperature

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.

Ion Beam Alignment of Liquid Crystal on Amorphous SiOx Film

Liquid crystal alignment on a-SiOx film surfaces through the ion beam exposure is studied. The pre-tilt angle of liquid crystals on a-SiOx film surfaces can be controlled from about 8° to about 89° by changing the ion beam incident angle from 25° to 80°. Vertical alignment of liquid crystal can be ascribed to high contact angles on ion-beam exposed inorganic film surfaces.

Control of Liquid Crystal Alignment on SiOx Film Surfaces by Low-Energy Ion Beam

In this paper, liquid crystal alignment on SiOx film surfaces irradiated by a low-energy ion beam is systematically examined experimentally. As a consequence of low-energy ion beam exposure, LCs can be aligned vertically when a high rms of electric potential is present on SiOx film surfaces on the basis of electric force microscopy data, while they can be aligned homogeneously when a low rms of electric potential is present on those surfaces. It is also found by X-ray photoemission spectroscopy and the contact angle method that, for the vertical alignment, the absorption curve shifts to a lower binding energy and a higher contact angle, respectively. All experimental results consistently show that the Coulomb interaction between LC molecules and inorganic film surfaces has a dominant effect on LC alignment on films irradiated by a low-energy ion beam.

Multi Domain Alignment of Liquid Crystals on Silicon Oxide Film Surfaces through Ion Beam Exposure

We propose a method for the multi domain alignment of liquid crystals (LCs) through ion beam exposure. We have demonstrated the multi domain ion-beam vertical alignment (IVA) of LC on SiOx film surfaces using a stainless steel mask. We found that IVA cells require a polar anchoring energy higher than 2×10-4 J/m2. The disclination linewidth of an IVA cell decreased from 45 to 13 µm with an increase in polar anchoring energy from 2 to 5.8×10-4 J/m2. The turn-on time of an IVA cell was 35% faster than that of a patterned vertical alignment cell.

Direct Control of Liquid Crystal Pretilt Angle by Deposition of Oxygen-Doped SiC Alignment Layers

In this paper, we propose a technique for the alignment of liquid crystals (LCs) on SiOxCy (x + y ≈2) films, where the pretilt angle can be directly controlled by adjusting the carbon content, y, of the films deposited at room temperature by oblique evaporation. LC cells with an arbitrary pretilt angle can be obtained simply by controlling the y value between 0.05 and 0.2 at the film surfaces. LCs can be aligned vertically or homogeneously by making use of the hydrophilic or hydrophobic properties of the film surfaces, respectively. We found that the LCs aligned by the proposed technique exhibit electro-optic characteristics similar to those of LCs aligned on rubbed polyimides.

P-161: Multi-domain Vertical Alignment of Liquid Crystal by the Ion Beam Exposure on Inorganic Film Surfaces

We propose a method for the multi-domain vertical alignment of liquid crystal through the ion beam exposure. We demonstrated 4-domain twisted vertical alignment of liquid crystal on SiOx film surfaces at intervals of 100 μm by using a stainless steel mask. We have shown that multi-domain liquid crystal alignment can be formed (anchoring energy > 2× 10−4 J/m2) at SiOx film surfaces through the irradiation of the ion beam. We found that the disclination width of the multi-domain are related with the polar anchoring energy that can be controlled by changing ion beam parameters, such as the ion beam energy and the beam flux density.

Influences of Target-to-Substrate Distance and Deposition Temperature on a-SiOx/Indium Doped Tin Oxide Substrate as a Liquid Crystal Alignment Layer

We present the structural, optical, and electrical properties of amorphous silicon suboxide (a-SiO ) films grown on indium tin oxide glass substrates with a radio frequency magnetron technique from a polycrystalline silicon oxide target using ambient Ar. For different substrate-target distances (d = 8 cm and 10 cm), the deposition temperature effects were systematically studied. For d = 8cm, oxygen content in a-SiO decreased with dissociation of oxygen onto the silicon oxide matrix; temperature increased due to enlargement of kinetic energy. For d = 10 cm, however, the oxygen content had a minimum between 150 C and 200 C. Using simple optical measurements, we can predict a preferred orientation of liquid crystal molecules on a- SiO thin film. At higher oxygen content (x > 1.6), liquid crystal molecules on an inorganic liquid crystal alignment layer of a-SiO showed homogeneous alignment; however, in the lower case (x < 1.6), liquid crystals showed homeotropic alignment.

Ion Beam Alignment of Liquid Crystal on SiOC Films

We investigated vertical alignment of liquid crystal (LC) on SiOC films deposited at the room temperature. We found from the electrostatic force microscopy (EFM) data that Coulomb interaction between LC and the ionized film surface has a dominant effect upon LC alignment on inorganic film surfaces by the ion beam exposure.