Chul-Ho Ok

Liquid Crystal Alignment Effects on SiNx Thin Film Layers Treated by Ion-Beam Irradiation

Nematic liquid crystal (NLC) alignment effects on SiNx thin film layers treated by ion-beam irradiation for three types of N ratio were successfully studied for the first time. The SiNx thin film was deposited by plasma-enhanced chemical vapor deposition using three types of N ratio. To characterize the film, atomic force microscopy was performed. Good LC aligning capabilities on the SiNx thin film treated by ion-beam irradiation for all N ratios can be achieved. The low pretilt angle for an NLC on the SiNx thin film treated by ion-beam irradiation was observed and could be adopted in planar alignment liquid crystal display applications as in-plane switching and fringe-field switching modes.

Electro optical performance characteristic of in-plane switching cell treated on nitrogen-doped diamond-like carbon thin film surfaces by ion beam alignment

The nematic liquid crystal (NLC) alignment capability achieved by ion beam alignment on a nitrogen-doped diamond-like carbon (NDLC) thin film was investigated. To characterize the NDLC thin film, we analyzed the obtained atomic force microscopy (AFM) images and pretilt angle. Moreover, we investigated the electro optical (EO) performance characteristics of ion-beam-aligned in-plane switching (IPS) cell with the NDLC thin film. The EO performance characteristics of the ion-beam-aligned IPS cell were observed by ion beam exposure on the NDLC thin film and compared with those of a rubbing aligned polyimide (PI) thin film. Finally, similarly prominent capacitance–voltage (C–V) characteristics were achieved in the ion-beam-aligned NDLC thin film compared with the rubbing-aligned PI thin film.

Novel Encapsulation Method for Flexible Organic Light-Emitting Diodes using Poly(dimethylsiloxane)

We have developed a novel encapsulation method for flexible organic light-emitting diodes (OLEDs) using poly(dimethylsiloxane) (PDMS). The new method, which uses polycarbonate film, silicon dioxide, and PDMS, was found to enhance the lifetime of OLEDs in air. Optical measurements of the preservation of calcium films encapsulated with PDMS showed that the water and oxygen permeation rates of the PDMS encapsulation were reduced from a level of 0.57 g m-2 d-1 (bare substrate) to 1×10-7 g m-2 d-1. These results indicate that the PDMS barrier coatings have a good potential for flexible OLED applications.

A chemically modulated polystyrene surface for homogeneously aligned liquid crystals using various ion beam exposure angles

In this study, transparent polystyrene (PS) was replaced with conventional polyimide material. As a non-contact process, an ion beam (IB) bombardment process was applied to align the homogeneous liquid crystal (LC) material on the PS surfaces. Confirming the atomic force microscopy and X-ray photoelectron spectroscopy analysis, the chemical compositional changes of the IB-irradiated PS surfaces were determined as a function of the IB exposure angle although there was no effect of modulation of the physical geographic characteristics on IB-irradiated PS surfaces. Using this analysis, the optimal IB bombardment condition was determined at the IB exposure angle of 45°. Finally, the electro-optical properties of an LC cell suggest the use of PS in conventional LC alignment materials.

IPS mode investigation of liquid crystal alignment on organic hybrid overcoat layer via ion beam irradiation

The nematic liquid crystal alignment capability and electro‐optical (EO) performance characteristics of in‐plane switching (IPS) cells were first demonstrated on organic hybrid overcoat layers via ion beam irradiation. Usually the organic hybrid overcoat is used as the material for making a plate alignment layer in a colour filter process. To characterise the organic hybrid overcoat layer, we analysed the surface composition of the organic hybrid overcoat by X‐ray photoelectron spectroscopy. The results show that the intensity of C = O and C–O bonding undergoes a change corresponding to the changes in energy of the ion beam exposure. Moreover, EO performance characteristics of IPS cells on the organic hybrid overcoat layer via ion beam irradiation were observed to have similar characteristics to the polyimide.

Alignment Capabilities and EO Performances of VA-LCD Using Transparent Conductive Al-doped ZnO Films

Transparent electrodes are indispensable for most of the flat panel display as liquid crystal display (LCD). We investigated liquid crystal (LC) aligning capabilities and electro-optical (EO) characteristics of transparent electrodes as Al-doped ZnO (ZnO:Al) substituting indium tin oxide (ITO). The experiment results show that a uniform vertical LC alignment on ZnO:Al electrodes based on a rubbed polyimide (PI) surface were achieved. A high pretilt angle of about 88° was obtained. EO performances of the VA-LCD on rubbed PI surfaces with ZnO:Al is almost the same as that of the VA-LCD with ITO electrodes. These results appeared that ZnO:Al electrodes as transparent electrodes of LCDs could substitute ITO electrodes.

Continuous Pretilt Angle Controlled No-Bias-Bend Pi Cell via Blended Polyimide Liquid Crystal System

The controllable pre-tilt angle of liquid crystals was investigated using a blend of horizontal and vertical polyimide prepared using a rubbing method. Various pretilt angles ranging from 0° to 90° were achieved as a function of the vertical polyimide content. We observed uniform liquid crystal alignment on the rubbing-treated blended polyimide layer. A no-bias-bend (NBB) pi cell with an intermediate pretilt angle of 47.8° was manufactured. This cell had no initial bias voltage and a low threshold voltage, which indicates that it has low power consumption. In addition, the response time of the NBB pi cell was rapid.

Surface oxidation and charge transfer inducing dipole–dipole interactions for homogeneous liquid crystal orientation

Generally, liquid crystal (LC) orientation on rubbed polystyrene (PS) surfaces runs in the direction orthogonal to the rubbing process. In this study, homogeneous LC orientations were produced in the direction parallel to the ion beam (IB) process on PS surfaces using various IB exposure energies. Through x-ray photoelectron spectroscopy it was shown that IB irradiation resulted in the reformation of O=C bonds resulting from surface oxidation or charge transfer, reversely tracing out the produced pretilt angles of the homogeneous LC. Moreover, thermal tests on IB-irradiated PS surfaces were carried out which showed that a relatively high IB exposure energy induced a thermally stable LC alignment property. Finally, we determined the mechanism by which homogeneous LCs are aligned on IB-irradiated PS surfaces with electro-optical properties of twisted-nematic LC cells.

Thermal Stability of Liquid Crystals on Blended Polyimide Layers Treated by Ion Beam Irradiation

We demonstrated the annealing effects displayed by liquid crystal antiparallel cells made from ion beam-irradiated blended polyimide layers. The pretilt angles of the liquid crystals after annealing at 90 °C for 10 min were similar to those before annealing, which demonstrates good thermal stability for liquid crystal antiparallel cells. Contact angle increases as vertical polyimide concentration increases, a trend that corresponds closely to the variation in pretilt angle. Uniform liquid crystal alignment was observed from a photomicrograph. Strong anchoring energies allowed the liquid crystal to maintain homeostasis and withstand thermal stress.

High Pretilt Angle Effects on Electro-Optical Property of Ion-Beam Irradiated Liquid Crystal Cells on a Blended Polyimide Surface

We investigated the high pretilt angle effects on electro-optical properties of ion beam (IB)-irradiated liquid crystal cells on a blended polyimide surface. High pretilt angle of liquid crystals IB-irradiated on a blended polyimide surface including such as 5% and 10% of homeotropic polymer contents can be achieved. The threshold voltages of IB-irradiated twisted nematic (TN) cells on a blended polyimide surface decrease with increasing the pretilt angle. Also, the rising time of IB-irradiated TN cells decreases with increasing the pretilt angle. However the decay time of IB-irradiated TN cells increases with increasing the pretilt angle. Consequently, the electro-optical properties of IB-irradiated TN cells depend strongly on the pretilt angle in a blended polyimide surface.