Hyun-Jae Na

Low-power operation of vertically aligned liquid-crystal system via anatase-TiO 2 nanoparticle dispersion

Electro-optic performance of a liquid-crystal (LC) system is enhanced by TiO(2) nanoparticle dispersed in nematic liquid crystal (NLC). The 2.5 V threshold voltage of LC for device operation is lowered to 0.5 V through TiO(2) nanoparticle mixing up to 2 wt.%. To characterize the shape and size distribution of the nanoparticles, high-resolution transmission electron microscopy is employed. Transmittance spectra for the TiO(2) dispersed LC structure and nondispersed LC structure showed that transparency of the TiO(2) dispersed LC is similar to that of pure liquid LC.

Vertical alignment of liquid crystals on a fully oxidized HfO2 surface by ion bombardment

High-performance liquid crystals (LCs) driven at a 0.9 V threshold were demonstrated on very thin HfO2 films with vertical (homeotropic) alignment by ion bombardment. Atomic layer deposition was used to obtain LC orientation on ultrathin high-quality films of double-layer HfO2/Al2O3. X-ray photoelectron spectroscopy indicated that full oxidization of HfO2 film surfaces was induced by ion bombardment, shifting the Hf 4f spectra to lower binding energies. The increased intensities of the Hf 4f peaks after ion bombardment confirmed that nonstoichiometric HfOx was converted to the fully oxidized HfO2 surfaces.

Interdiffusion problems at CdTe/InSb heterointerfaces grown by temperature gradient vapor transport deposition

CdTe epitaxial films were grown by a simple method of temperature gradient vapor transport deposition on p‐InSb (111) orientation substrates in the growth temperature range between 200 and 280 °C. Raman spectroscopy showed the optical phonon modes of the CdTe thin films and the formation of an indium telluride interfacial layer in the CdTe/InSb heterostructures. The stoichiometry of the CdTe/InSb heterostructures was observed by the Auger electron spectroscopy, and Auger depth profiles also demonstrated that the CdTe/InSb heterointerface was not abrupt. The results indicated that the films grown at about 265 °C posed a significant problem due to interdiffusion from the InSb substrates during the growth.

Selective liquid crystal molecule orientation on ion beam irradiated tantalum oxide ultrathin films

We recently achieved the homogeneous alignment of liquid crystal (LC) on amorphous Ta2O5 layers. This study demonstrates that LC layers could be aligned either homogeneously or vertically by increasing the growth temperature of rf magnetron sputtering device and the irradiation time of the DuoPIGatron type Ar ion beam device causing uniform and dense plasma. We attained two LC orientations by observing Ta 4f and O 1s peak shifts with x-ray photoelectron spectroscopy. Moreover, the decreased thickness of layers with high-k dielectric constants helped to decrease driving LC voltages and in turn to achieve low power consumption.

Titanium dioxide surface modification via ion-beam bombardment for vertical alignment of nematic liquid crystal

We introduce the characteristics of the titanium dioxide (TiO(2)) inorganic film deposited by rf magnetron sputtering for liquid crystal display applications. The TiO(2) films demonstrated vertical alignment (VA) of the liquid crystals (LCs) obtained by using ion-beam (IB) bombardment. As observed by using x-ray photoelectron spectroscopy, the chemical structure of the TiO(2) was changed by IB bombardment, altering the Ti-O bonding of the Ti 2p spectra to lower intensity levels. Breaking Ti-O bonding by IB bombardment created pretilt angles between the TiO(2) film and LC molecules. The better voltage-transmittance characteristics of the VA LCDs based on TiO(2) film were measured and compared with the same characteristics of polyimide film.

Alignment Characteristics of Liquid Crystal Molecules on Titanium Dioxide Thin Film

We present the characteristics of titanium dioxide (TiO2) inorganic film deposited by RF magnetron sputtering for liquid crystal display applications in this paper. TiO2 films supported vertically aligned liquid crystal (LC) molecules based on ion-beam (IB) irradiation time dependence. Uniform alignment was obtained only when the incident time was two minutes with 1.8 keV of incident energy and an incident angle of 45°. Energy from uniform high-density plasma by IB irradiation affected the interaction between the TiO2 layer and LC molecules to produce vertical alignment of the LC molecules.

Vertically Aligned Liquid Crystal Molecules on TiO2 Film Treated by Ion-Beam Irradiation

In this paper, we describe the formation of vertically aligned liquid crystal molecules on TiO2 films treated by ion-beam (IB) irradiation. Regular or irregular pretilt angles were achieved as a function of IB incident angle. Uniform alignment was obtained only at an incident angle of 45°. The contact angle, which is related to the surface energy, was measured to confirm the tendency of variation in the pretilt angle. In addition, the weak anchoring energy of LC molecules on IB-irradiated TiO2 was ascertained by the thermal stability at low temperature.

Directional behaviour of liquid crystals on homogeneous polyimide surfaces induced by polarised ultraviolet exposure and rubbing

We studied liquid crystal (LCs) alignment effects on homogeneous polyimide (PI) surfaces induced by polarised UV (PUV) exposure and rubbing in different directions. We found that the LC orientation is not affected by PUV exposure times of less than 90 min after rubbing, and that PUV exposure times over 90 min after rubbing resulted in LC orientations that were more closely aligned with the direction of PUV exposure than the direction of rubbing. Short-term PUV exposure affects the variation of the pretilt angle of the PI and LC. In addition, as PUV exposure time increases, it can convert the LC alignment direction from the rubbing direction to the PUV direction.

Pretilt Angles Transition via Mixture Liquid Crystal System

We studied the state of the dual liquid crystal (LC) alignment which displays both homeotropic and homogeneous alignment on blended polyimide (PI) layer. The research was conducted using rubbing method at different imidizing temperatures and the blended PI was made using homeotropic PI having an alkyl side chain and homogeneous PI without the side chain. The uniform LC alignments were achieved, and have thermal stability. The results of contact angles were similar to that of pretilt angles.

Low-Voltage Driving of Liquid Crystals Vertically Aligned by Ion-Beam Bombardment on High-k HfO2 Surface

Ion-beam irradiation (IB) on HfO2 surface induced high-performance liquid crystal (LC) driving at a 1-V threshold with vertical alignment of liquid crystals (LC). The high-k materials Atomic layer deposition was used to obtain LC orientation on ultrathin and high-quality films of HfO2 layers. To analyze surface morphological transition of HfO2 which can act as physical alignment effect of LC, atomic force microscopy images are employed with various IB intensities. The contact angle was measured to elucidate the mechanism of vertical alignment of LC on HfO2 with IB irradiation. Contact angle measurements show the surface energy changes via IB intensity increasing.