Soon Joon Rho

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.

Ion-beam induced liquid crystal alignment on diamond-like carbon and fluorinated diamond-like carbon thin films

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.

Vertical Alignment of Liquid Crystals with Negative Dielectric Anisotropy on an Inorganic Thin Film with a Hydrophilic Surface

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.

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.

Ultrafast switching of randomly-aligned nematic liquid crystals.

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.

The Field Emission Characteristics of a-C:H Thin Films Prepared by Helical Resonator Plasma Enhanced Chemical Vapor Deposition

The field emission characteristics of hydrogenated amorphous carbon (a-C:H) films prepared by helical resonator-plasma enhanced chemical vapor deposition (HR-PECVD) are examined. a-C:H films are deposited with CH4/H2 and CH4/Ar gases under different substrate RF bias conditions. The properties of a-C:H films are investigated by Raman spectroscopy, Fourier transform IR (FT-IR), UV spectroscopy and elastic recoil detection (ERD). Field emission characteristics of a-C:H coated on Si whiskers which are grown by the vapor-liquid-solid (VLS) method are tested under ultrahigh vacuum. Highly efficient field emission characteristics are achieved in the specimen deposited at a substrate RF bias higher rather than in the ground deposition condition regardless of the nature of the reactant gas. As the substrate RF bias is changed from ground to a higher RF substrate bias, the deposited a-C:H films have lower hydrogen contents and higher sp2-bonds. Therefore, the field emission characteristics of a-C:H thin films are affected by the hydrogen contents of the films rather than by the sp3/sp2 ratio.

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.