• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.541-544
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• 1999

We synthesised a novel photo-alignment material of PCEMA (poly(cinnamolyethyl methacrylate)) on photo-dimerization reaction. Next we investigated the electro-optical (EO) characteristics of photo-aligned twisted nematic (TN)-liquid crystal display (LCD) with linearly polarized ultraviolet (UV) light irradiation on PCEHA surface. The excellent voltage-transmittance characteristics of photo-aligned TN-LCD on PCEMA surface were obtained. The threshold voltage of photo-aligned TN-LCD decreases with increasing the UV light irradiation time on PCEMA surface. Also, the response time of photo-aligned TN-LCD on PCEMA surface is almost the same as rubbing-aligned TN-LCD.

• Journal of the Optical Society of Korea
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• v.5 no.1
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• pp.16-19
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• 2001

A photopolymer, copoly (M4Ch-ChMA), copoly ((4-methacryloyloxy) chalcone-cholesteryl methacrylate), was synthesized in this study. The electro-optical (EO) characteristics for the photo-aligned vertical-alignment (VA)-liquid crystal display (LCD) were investigated. Excellent voltage-transmittance curves for the VA-LCD photo-aligned by polarized UV exposure on the copoly (M4Ch-ChMA) surface were observed. The response time for the photo-aligned VA-LCD decrease with increasing UV exposure time. consequently, the photo-dimerized chalcone moiety increased with increasing UV exposure time, which then contributed to a low response time for the VA-LCD photo-aligned.

• Nano
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• v.13 no.10
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• pp.1850122.1-1850122.6
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• 2018

Vertically aligned $WO_3$-CuO core-shell nanorod arrays for $NH_3$ sensing are prepared. The sensor is fabricated by preparing $WO_3$-CuO nanorod arrays directly on silicon wafer with interdigital Pt electrodes. The $WO_3$-CuO nanorod arrays are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The sensor based on the vertically aligned $WO_3$-CuO nanorod arrays exhibits ultrasensitive $NH_3$ detection, indicating p-type behavior. The optimum sensing temperature is found to be about $150^{\circ}C$. Both response and recovery time to $NH_3$ ranging from 50 ppm to 500 ppm are around 10-15 s. A possible $NH_3$ sensing mechanism of the vertically aligned hybrid nanorod arrays is proposed.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1765-1767
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• 1999

We synthesised a photo-alignment material of PM4Ch (poly(4-methacryloylloxychalcone)). The electro-optical (EO) characteristics of photo-aligned twisted nematic (TN)-liquid crystal display (LCD) with linearly polarized ultraviolet (UV) light irradiation on PM4Ch surface were investigated. The uniform alignment of NLC with polarized UV light irradiation on PM4Ch surface was measured. Also, We had The excellent voltage-transmittance characteristics of photo-aligned TN-LCD. The low threshold voltage of photo-aligned TN-LCD was measured. Moreover, the fast response time of photo-aligned TN-LCD on PM4Ch was successfully achieved. Finally The reduction DC voltage of photo-aligned TN-LCD decreases with increasing the UV light irradiation time on photo-dimerized PM4Ch surface.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.275-278
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• 1999

We have grown vertically aligned carbon nanotubes in a large area of Co-Ni codeposited Si substrates by the thermal CVD using $C_2$H$_2$gas. Since the discovery of carbon nanotubes, Synthesis of carbon nanotubes for mass production has been achieved by several methods such as laser vaporization, arc discharge, and pyrolysis. In particular, growth of vertically aligned nanotubes is of technological importance for applications to FED. Recently, vertically aligned carbon nanotubes have been grown on glass by PECVD. Aligned carbon nanotubes can be also grown on mesoporous silica and Fe patterned porous silicon using CVD. Despite such breakthroughs in the growth, the growth mechanism of the alignment are still far from being clearly understood. Furthermore, FED has not been clearly demonstrated yet at a practical level. Here, we demonstrate that carbon nanotubes can be vertically aligned on catalyzed Si substrate when the domain density reaches a certain value. We suggest that steric hindrance between nanotubes at an initial stage of the growth forces nanotubes to align vertically and then nanotubes are further grown by the cap growth mechanism.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.8
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• pp.451-454
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• 2000

We have grown vertically aligned carbon nanotubes in a large area of Co-Ni codeposited Si substrates by the thermal CVD usign $C_2H_2$ gas. Since the discovery of carbon nanotubes, growth of carbon nanotubes has been achieved by several methods such as laser vaporization, arc discharge, and pyrolysis. In particular, growth of vertically aligned nanotubes is important to flat panel display applications. Recently, vertically aligned carbon nanotubes have been grown on glass by PECVD. Aligned carbon nanotubes can be also grown on mesoporous silica and Fe patterned porous silicon using CVD. In this paper, we demonstrate that carbon nanotubes can be vertically aligned on catalyzed Si substrate when the domain density of catalytic particles reaches a certain value. We suggest that steric hindrance between nanotubes at an initial stage of the growth forces nanotubes to align vertically and each nonotubes are grown in bundle.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.278-279
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• 2006

In this study, we investigated the electro-optical (EO) characteristic of fringe-field switching (FFS) mode cell by the two kinds of ultraviolet (UV) alignment method on the organic thin film (polyimide Pl). The suitable organic layers for FFS cell and the aligning capabilities of nematic liquid crystal (NLC) using the in-situ photo-alignment method were studied. An unstable V-T curve of UV-aligned FFS-LCD with conventional photo-alignment method can be achieved. However, a stable V-T curve of UV-aligned FFS-LCD with in-situ photo-alignment method (1h), and V-T curve of UV-aligned FFS-LCD with in-situ photo-alignment method was much stable comparing with that of other UV-aligned FFS-LCD's, As a result, more stable EO performance of UV-aligned FFS-LCD with in-Situ photo-alignment method is obtained than that of the other UV-aligned FFS-LCD's.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.47-56
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• 2019

Crossing (X-type) flaws are commonly encountered in rock mass. However, the crack coalescence and failure mechanisms of rock mass with X-type flaws remain unclear. In this study, we investigate the compressive failure process of rock-like specimens containing two X-type flaws aligned in the loading direction. For comparison purposes, compressive failure behavior of specimens containing two aligned single flaws is also studied. By examining the crack coalescence behavior, two characteristics for the aligned X-type flaws under uniaxial compression are revealed. The flaws tend to coalesce by cracks emanating from flaw tips along a potential path that is parallel to the maximum compressive stress direction. The flaws are more likely to coalesce along the coalescence path linked by flaw tips with greater maximum circumferential stress if there are several potential coalescence paths almost parallel to the maximum compressive stress direction. In addition, we find that some of the specimens containing two aligned X-type flaws exhibit higher strengths than that of the specimens containing two single parallel flaws. The two underlying reasons that may influence the strengths of specimens containing two aligned X-type flaws are the values of flaw tips maximum circumferential stresses and maximum shear stresses, as well as the shear crack propagation tendencies of some secondary flaws. The research reported here provides increased understanding of the fundamental nature of rock/rock-like material failure in uniaxial compression.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1759-1761
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• 1999

The generation of pretilt in nematic liquid crystal(NLC)and electro-optical(EO) characteristics of photo-aligned twisted nematic (TN)-LCD with oblique p-polarized ultraviolet (UV) light irradiation on the two kinds of the soluble polyimide (PI) surfaces containing trifluoromethyl moieties were investigated. The generated pretilt angle of NLC is about $2.5^{\circ}$ with p-polarized UV light irradiation of $20^{\circ}$ on PI-3 surface at 20 min.; However pretilt angle of about $0.5^{\circ}$ are observed on PI-1 and PI-2 surfaces. The generated pretilt angle of NLC on PI-3 surface may be attributed to the trifluoromethyl moieties attached to the lateral benzene rings. The voltage-transmittance and response time characteristics of photo-aligned TN-LCD with p-polarized UV light irradiation of $20^{\circ}$ on PI-1 surfaceat at 20 min were almost same in comparison with the rubbing-aligned TN-LCD. However, the high threshold voltage and slow response are observed on PI-3 surface. Also, the decay time $\tau_d$ of photo-aligned TN-LCD is attributed to the anchoring energy of NLC.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.343-346
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• 1998

The generation of pretilt angle in nematic liquid crystal (NLC) and electro-optical (EO) characteristics of photo-aligned twisted nematic (TN)-LCD with oblique P-polarized ultraviolet (UV) light irradiation on the two kinds of the soluble polyimide (PI) surfaces containing trifluoromethyl moieties were investigated. The generated pretilt angle of NLC is about 2.5$^{\circ}$with P-polarized UV light irradiation of 20$^{\circ}$on PI-3 surface at 20 min.; However pretilt angle of about 0.5$^{\circ}$are observed on PI-1 and PI-2 surfaces. The generated pretilt angle of NLC on PI-3 surface may be attributed to the trifluoromethyl moieties attached to the lateral benzene rings. The voltage-transmittance and response time characteristics of photo-aligned TN-LCD with P-polarized UV light irradiation of 20$^{\circ}$on PI-1 surface at 20 min were almost same in comparison with the rubbing-aligned TN-LCD. However, the high threshold voltage and slow response are observed on PI-3 surface. Also, the decay time $\tau$$\sub$d/ of photo-aligned TN-LCD is attributed to the anchoring energy of NLC.