Papers by Author: Hyoun Woo Kim

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Authors: Chong Mu Lee, Seung Mo Kang, Keun Bin Yim, Sook Joo Kim, Hyoun Woo Kim
Abstract: Epoxy molding compounds (EMC) with higher thermal stabilities are urgently needed as the light emitting diode (LED) becomes brighter and the wavelength of the its light becomes shorter. This paper proposes a simple reliable method of evaluating the thermal stabilities of commercial EMCs. The transmittances of most commercial EMC samples for high power short wavelength LED packages were decreased by heat treatment at 150oC for 200hr. Also the thermal stabilities of the samples were confirmed by measuring the weight losses through TGA. The experimental results suggest that employing a good heatsink is indispensable in highly bright short wavelength LED packages.
Authors: Hyoun Woo Kim, Ju Hyun Myung, S.H. Shim
Abstract: We have synthesized gallium oxide (Ga2O3) nanomaterials at two different growth temperatures on iridium (Ir)-coated substrates by thermal evaporation of GaN powders. The products consist mainly of nanobelts, with some additional nanosheets. The nanobelts were of a single-crystalline monoclinic Ga2O3 structure. The broad emission photoluminescence band of 900°C-products had a different peak position from that of the 970°C-products.
Authors: Hyoun Woo Kim, S.H. Shim, C. Lee
Abstract: This study shows the effect of thermal annealing on GaN/ZnO/Si structures prepared by rf magnetron sputtering. Thermal annealing tended to induce a different crystalline orientation from the c-axis orientation observed with as-deposited films. The sample annealed at 900 oC under excitation at 325 nm showed two emission bands centered at approximately 380 and 550 nm.
Authors: Kyung Chul Lee, Nam Ho Kim, B.H. O, Hyoun Woo Kim
Abstract: We have investigated the effect of annealing temperature on the structural property of Au thin films deposited on Si(100) substrate using the radio frequency (RF) magnetron sputtering technique. X-ray diffraction revealed that the relative intensities and FWHM of (111), (200), and (311) peaks increased and decreased, respectively, after thermal annealing at 600°C. Scanning electron microscopy indicated that after annealing at 600-700°C, Au structures agglomerated on Si(100) surfaces. Energy dispersive x-ray spectrometry (EDX) revealed that the agglomerated structure was composed of pure Au.
Authors: Ju Hyun Myung, Hyoun Woo Kim, S.H. Shim
Abstract: We report on the first synthesis of nanosized In2O3 rods using the TEI as a precursor in the presence of oxygen. The samples were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy. XRD analysis revealed that the products are In2O3 phase with a tetragonal cubic structure. SEM analysis indicated that the obtained nanorods have a circular cross section and a diameter in the range of 50-150 nm.
Authors: S.H. Shim, Hyoun Woo Kim, C. Lee, D.J. Chung, S.G. Park, S.G. Lee, B.H. O, J. Kim, S.P. Chang, S.H. Lee
Abstract: We have obtained one-dimensional (1D) nanomaterials of tin oxide (SnO2) on silicon nitride (Si3N4)-coated Si substrates by carrying out the thermal evaporation of solid Sn powders and varying the substrate temperature in an Ar/O2 ambient gas. We analyzed the samples with scanning electron microscopy, X-ray diffraction, transmission electron microscopy and photoluminescence (PL). Reactions at a lower substrate temperature gave rise to thinner 1D structures. The obtained 1D nanomaterials were single crystalline with a tetragonal rutile structure. We proposed a vapor-solid process as the growth mechanism for SnO2 nanorods. The PL spectrum exhibited visible light emission.
Authors: Hyoun Woo Kim, S.H. Shim
Abstract: We have synthesized the high-density Ga2O3 nanowires on gold (Au)-coated silicon substrates using metalorganic chemical vapor deposition. The nanowires exhibited one-dimensional structures having circular cross sections with diameters in the range of 30-200 nm. The energy dispersive x-ray spectroscopy revealed that the nanowires contained elements of Ga and O, without Au-related impurities. X-ray diffraction analysis and high-resolution transmission electron microscopy showed that the Ga2O3 nanowires were crystalline.
Authors: Hyoun Woo Kim, Ju Hyun Myung, S.H. Shim, Woon Suk Hwang
Abstract: In2O3 materials consisting of dense arrays of vertically aligned rod-like structures were deposited on sapphire substrates by thermal chemical vapor deposition (CVD) using triethylindium (TEI) and oxygen as precursors at a substrate temperature of 350 oC. The rod-like structure with a triangular cross section had a cubic structure, exhibiting preferred crystallographic orientation in the [111] direction. The photoluminescence spectra of In2O3 structures under excitation at 325 nm revealed a visible emission.
Authors: Hyoun Woo Kim, S.H. Shim, Ju Hyun Myung
Abstract: One-dimensional structures of tin oxide (SnO2) on TiN-coated substrates were obtained by simple heating of Sn powders. X-ray diffraction, high-resolution transmission electron microscopy, and the selected area electron diffraction showed that 1D structures are composed of SnO2 with rutile structure. The photoluminescence of the structures in the visible region suggests possible applications in nanoscaled optoelectronic devices.
Authors: Chong Mu Lee, Anna Park, Young Joon Cho, Hyoun Woo Kim, Jae Gab Lee
Abstract: It is very desirable to grow ZnO epitaxial films on Si substrates since Si wafers with a high quality is available and their prices are quite low. Nevertheless, it is not easy to grow ZnO films epitaxially on Si substrates directly because of formation of an amorphous SiO2 layer at the interface of ZnO and Si. A Zn film and an undoped ZnO film were deposited sequentially on an (100) Si substrate by rf magnetron sputtering. The sample was annealed at 700°C in a nitrogen atmosphere. X-ray diffraction (XRD), photoluminescence (PL) and atomic force microscopy (AFM) analyses were performed to investigate the cristallinity and surface morphology of the ZnO film. According to the analysis results the crystallinity of a ZnO thin film deposited by rf magnetron sputtering is substantially improved by using a Zn buffer layer. The highest ZnO film quality is obtained with a 110nm thick Zn buffer layer. The surface roughness of the ZnO thin film increases as the Zn buffer layer thickness increases.
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