Won-Kyu Lee

Vertically aligned liquid crystals on a γ-Al2O3 alignment film using ion-beam irradiation

Using ion-beam (IB) irradiation, liquid crystals (LCs) were vertically aligned (VA) on a γ-Al2O3 alignment film. Atomic-layer deposition was used to orient the LCs on high-quality γ-Al2O3 alignment films. The LC molecule orientation indicates the vertical direction of the atomic-layer-deposited γ-Al2O3 alignment films. X-ray photoelectron spectroscopy showed that IB irradiation changed the chemical structure, shifting the Al–O binding energy and altering the Al–O bonding intensity. The low-voltage transmittance characteristics of the VA LC displays on the γ-Al2O3 alignment films were also measured, showing reduced voltage and power requirements.

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.

Transmission electron microscopy study on ferromagnetic (Ga,Mn)N epitaxial films

We report on the crystal structure of epitaxial (Ga,Mn)N films with Mn=0.2% grown by plasma-enhanced molecular beam epitaxy, exhibiting n-type conductivity and room temperature ferromagnetism (Ms=0.76u2009emu/cm3, Hc=90u2009Oe). The additional diffraction spots are found in the zone axis of B=[1100] for the (Ga,Mn)N epilayer due to a single twin orientation in the closed packed hexagonal matrix. High-order Laue zone measurements reveal the expansion of lattice parameter a (3.1851–3.1865 A) by doping Mn, demonstrating that Mn ions substitute for Ga ions in the (Ga,Mn)N.

Zinc oxide nanolevel surface transformation for liquid crystal orientation by ion bombardment

This paper introduces the characteristics of the zinc oxide (ZnO) inorganic film deposited by radio-frequency magnetron sputtering as an alternative alignment layer for liquid crystal display (LCD) applications. The crystalline structure related to the texture formation of ZnO (101¯3) was observed with a tilt angle of approximately 28.1° to the ZnO (0001) plane, leading to a smooth surface and high-density structure. Ion beam (IB) bombardment at various incident angles was used to induce liquid crystal (LC) alignment and cause the measured pretilt angle on ZnO films to assume a triangular contour. The orientation order of liquid crystal molecules was due to the van der Waals force for the vertical alignment of LCs with selective breaking of O–Zn bonds by IB bombardment. The contact angle contour as a function of the IB incident angle resembled the behavior of the pretilt angle. The pretilt angle is controllable by adjusting the surface features on ZnO films with IB bombardment. The electro-optic character...

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.

Enriching a motion database by analogous combination of partial human motions

We have synthesized new human body motions from existing motion data, by dividing the body of an animated character into several parts, such as upper and lower body, and partitioning the motion of the character into corresponding partial motions. By combining different partial motions, we can generate new motion sequences. We select the most natural-looking combinations by analyzing the similarity of partial motions, using techniques such as motion segmentation, dimensionality reduction, and clustering. These new combinations can dramatically increase the size of a motion database, allowing more score in selecting motions to meet constraints, such as collision avoidance. We verify the naturalness and physical plausibility of the new motions using an SVM learning model and by analysis of static and dynamic balance.

Microstructure and magnetoresistance of sputtered bismuth thin films upon annealing

We investigated the microstructure and magnetotransport properties of sputtered Bi upon annealing. The grain size and the orientation of polycrystalline Bi thin films can be manipulated through a proper annealing treatment. Weak-oriented fine grains, of which size is about 0.1μm, were found in as-sputtered Bi films. Careful annealing at 270°C results not only in a grain growth of up to 1.1μm but also in a [001]-preferred orientation structure. The grain size increases exponentially with annealing time in the temperature range of 266–270°C. The grain-growth exponent (n) and the activation energy (Q) were evaluated to be 0.32±0.05 and 70.7kJ∕mol, respectively. The magnetoresistance (MR) of Bi films is strongly dependent on the microstructure and thickness of the film, and on the measured temperature. A very high MR of 30,000% can be observed in the annealed 7-μm-thick Bi films when measured at low temperature (4K). The drastic increase in MR after annealing is largely attributed to the trigonal-axis-oriente...

Ion bombardment-induced transformation process on SiN x surfaces to achieve vertical alignment of liquid crystal molecules

The vertical alignment (VA) of liquid crystal display (LCD) devices with upgraded performance is achieved on ion-bombarded SiN x surfaces. We used a plasma-enhanced chemical vapour deposition method to deposit SiN x thin films with high reliability. X-ray photoelectron spectroscopy revealed that change of orientation of LC molecules occurs on the SiO2 surface, which is directionally transformed by ion-bombarded SiN x thin film. The low-voltage transmittance characteristics and reduced response times indicate that the SiN x -based VA-LCDs have potential for low-power operating and high-speed LCD applications.

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.