• Applied Science and Convergence Technology
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• 제26권4호
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• pp.79-85
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• 2017

The crack-free AlGaN template has been successfully grown by using selective area growth with triangular GaN facet. The triangular GaN stripe structure was obtained by vertical growth rate enhanced mode with low growth temperature of $950^{\circ}C$ and high growth pressure of 500 torr. The lateral growth rate enhanced mode of AlGaN for crack-free and flat surface was also investigated. Low pressure of 30 torr and high V/III ratio of 4400 were favorable for lateral growth of AlGaN. It was confirmed that the $4{\mu}m$ -thick $Al_{0.2}Ga_{0.8}N$ was crack-free over entire 2-inch wafer. The dislocation density of $Al_{0.2}Ga_{0.8}N$ was as low as ${\sim}7.6{\times}10^8/cm^2$ measured by cathodoluminescence. Based on the high quality AlGaN with low dislocation density, the ultraviolet laser diode epitaxy with cladding, waveguide and GaN/AlGaN multiple quantum well (MQW) was grown by metalorganic chemical vapor deposition. The stimulated emission at 349 nm with full width at half maximum of 1.8 nm from the MQW was observed through optical pumping experiment with 193 nm KrF laser. We also have fabricated the deep ridge type ultraviolet laser diode (UV-LD) with $5{\mu}m-wide$ and $700{\mu}m-long$ cavity for electrical properties. The turn on voltage was below 5 V and the resistance was ${\sim}55{\Omega}$ at applied voltage of 10 V. The amplified spontaneous emission spectrum of UV-LD was also observed from pulsed current injection.

• 한국전기전자재료학회논문지
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• 제19권8호
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• pp.707-711
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• 2006

ZnO was doped up to 0.3 wt% for improving the electrical properties of lead-free $[Li_{0.04}(Na_{0.44}Ko_{0.52})-(Nb_{0.86}\;Ta_{0.10}\;Sb_{0.04})]O_3$ piezoelectric ceramics. The ceramics were fabricated with the conventional sintering processes. Crystal structure of the samples was tetragonal phase regardless of ZnO amount. However, the piezoelectric properties were varied with the ZnO amount. The electro-mechanical coupling factor $(k_p)$ was with the ZnO amount up to 0.2 wt% but decreased with the further addition. the maximum value of $k_p$ was 0.475. Density, piezoelectric charge constant and relative dielectric constant was also showed maximum value at 0.2 wt%. The maximum values are $4.75g/cm^3$, 275 pC/N, 1403, respectively. In contrast, the mechanical quality factor $(Q_m)$ was not varied with increasing the ZnO addition up to 0.2 wt% but rapidly increased at 0.3 wt%.

• Journal of Electrochemical Science and Technology
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• 제1권1호
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• pp.25-30
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• 2010

This study demonstrated the synthesis of high-surface-area metal-free carbonaceous electrodes (CE) from anodic aluminum oxide (AAO) templates, and their application as supercapacitors. Multi-walled Carbon nanotubes (MWCNTs) were interwoven into a porous network sheet that was attached to one side of AAO template through a vacuum filtration of the homogeneously dispersed MWCNT toluene solution. Subsequently, the conducting polymer was electrochemically grown into the porous MWCNT network and nanochannels of AAO, leading to the formation of a carbonaceous metal-free film electrode with a high surface area in the given geometrical surface area. Typical conducting polymers such as polypyrrole (PPY) and poly(3,4-ethylenedioxythiophene) (PEDOT) were examined as model systems, and the resulting electrodes were investigated as supercapacitors (SCs). These SCs exhibited stable, high capacitances, with values as high as 554 F/g, 1.08 F/$cm^2$ for PPY and 237 F/g, 0.98 F/$cm^2$ for PEDOT, that were normalized by both the mass and geometric area.

• 한국정보과학회 언어공학연구회:학술대회논문집(한글 및 한국어 정보처리)
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• 한국정보과학회언어공학연구회 2012년도 제24회 한글 및 한국어 정보처리 학술대회
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• pp.138-141
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• 2012

한국어 서답형 문항의 자동채점 프로그램을 개발하기 위해서는 모범답안, 오답, 부분점수 부여를 위한 세부적인 내용을 채점 기준표로 기술해야 한다. 자동채점에 필요한 구체적인 사항들을 기술하기 위하여 XML 형식으로 정답 템플릿을 정의하였다. 채점에 필요한 내용을 단위 개념으로 정의하고 이를 컴퓨터가 엑세스 가능한 형태의 정답 템플릿을 설계하였다. 정답 템플릿 형식에 맞게 편리하게 템플릿을 작성할 수 있는 작성 도구를 이용하여 학업 성취도평가 각 문항에 대한 채점 기준표를 정답 템플릿으로 작성하여 채점기준표를 작성하는 실험을 수행하였다.

• 산업기술연구
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• 제28권B호
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• pp.143-148
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• 2008

A real-time face detection is to find human faces robustly under the cluttered background free from the effect of occlusion by other objects or various lightening conditions. We propose a face detection system for real-time applications using wavelet decomposition method based on Gabor features. Firstly, skin candidate regions are extracted from the given image by skin color filtering and projection method. Then Gabor-feature based template matching is performed to choose face cadidate from the skin candidate regions. The chosen face candidate region is transformed into 2-level wavelet decomposition images, from which feature vectors are extracted for classification. Based on the extracted feature vectors, the face candidate region is finally classified into either face or nonface class by the Levenberg-Marguardt back-propagation neural network.

• Journal of Electrochemical Science and Technology
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• 제3권2호
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• pp.68-71
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• 2012

The electrospinning technique is a revolutionary template-catalyst-free method that can generate 1D nanostructure with the tunability and the potential for the mass production. This approach received a great deal of attention due to its ability to give direct pathways for electrical current and has been utilized in various electronic applications. However, the delamination of inorganic electrospun film has prevented the intense utilization due to the thermal expansion/contraction during the calcination. In this study, we propose an electrical grounding method for transparent conducting oxide and electrospun nanowires to enhance the adhesion after the calcination. Then, we examined the potential of the technique on ZnO based dye-sensitized solar cells.

• 공업화학
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• 제21권3호
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• pp.353-355
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• 2010

양이온성의 2,2'-azobis(2-methylpropionamidine) (AIBA) 개시제를 이용한 methylmethacrylate (MMA)의 무유화제 에멀전 중합을 통해 polymethylmethacrylate (PMMA) 입자를 합성하였다. 스퇴버 방법을 이용하여 양이온성의 PMMA 입자 표면에 실리카를 코팅하였다. 음전하의 실리카 전구체는 양이온성의 PMMA 입자 표면과의 정전기적 인력에 의해 코팅된다. 실리카 코팅 과정 중에 PMMA 입자가 용해되어 후처리 없이 실리카 중공체를 얻을 수 있었다.

• Carbon letters
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• 제22권
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• pp.1-13
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• 2017

Porous materials play a vital role in science and technology. The ability to control their pore structures at the atomic, molecular, and nanometer scales enable interactions with atoms, ions and molecules to occur throughout the bulk of the material, for practical applications. Three-dimensional (3D) porous carbon-based materials (e.g., graphene aerogels/hydrogels, sponges and foams) made of graphene or graphene oxide-based networks have attracted considerable attention because they offer low density, high porosity, large surface area, excellent electrical conductivity and stable mechanical properties. Water pollution and associated environmental issues have become a hot topic in recent years. Rapid industrialization has led to a massive increase in the amount of wastewater that industries discharge into the environment. Water pollution is caused by oil spills, heavy metals, dyes, and organic compounds released by industry, as well as via unpredictable accidents. In addition, water pollution is also caused by radionuclides released by nuclear disasters or leakage. This review presents an overview of the state-of-the-art synthesis methodologies of 3D porous graphene materials and highlights their synthesis for environmental applications. The various synthetic methods used to prepare these 3D materials are discussed, particularly template-free self-assembly methods, and template-directed methods. Some key results are summarized, where 3D graphene materials have been used for the adsorption of dyes, heavy metals, and radioactive materials from polluted environments.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.414-414
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• 2008

Vertically well-aligned Ga-doped ZnO nanorods with different Ga contents were grown by thermal evaporation on a ZnO template. The Ga-doped ZnO nanorods synthesized with 50 wt % Ga with respect to the Zn content showed maximum compressive stress relative to the ZnO template, which led to a rapid growth rate along the c-axis due to the rapid release of stored strain energy. A further increase in the Ga content improved the conductivity of the nanorods due to the substitutional incorporation of Ga atoms in the Zn sites based on a decrease in lattice spacing. The p-n diode structure with Ga-doped ZnO nanorods, as a n-type, displayed a distinct white light luminescence from the side-view of the device, showing weak ultraviolet and various deep-level emissions.

• 한국전기전자재료학회논문지
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• 제31권6호
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• pp.357-361
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• 2018

We demonstrated a crack-free ${\alpha}-Ga_2O_3$ on sapphire substrate by horizontal halide vapor phase epitaxy (HVPE). Oxygen-and gallium chloride-synthesized Ga metal and HCl were used as the precursors, and $N_2$ was used as the carrier gas. The HCl flow and growth temperature were controlled in the ranges of 10~30 sccm and $450{\sim}490^{\circ}C$, respectively. The surface of ${\alpha}-Ga_2O_3$ template grown at $470^{\circ}C$ was flat and the root-mean-square (RMS) roughness was ~2 nm. The full width at half maximum (FWHM) values for the symmetric-plane diffractions, were as small as 50 arcsec and those for the asymmetric-plane diffractions were as high as 1,800 arcsec. The crystal quality of ${\alpha}-Ga_2O_3$ on sapphire can be controlled by varying the HCl flow rate and growth temperature.