HWE(Hot Wall Epitaxy)에 의한 CuGaSe₂/GaAs epilayer 성장과 광전기적 특성

홍광준,정준우,백형원,정경아,방진주,진윤미,김소형 조선대학교 기초과학연구소 2001 自然科學硏究 Vol.24 No.-

수평 전기로에서 CuGaSe₂ 다결정을 합성하여 HWE(Hot Wall Epitaxy) 방법으로 CuGaSe₂/GaAs epilayer를 반절연성 GaAs(100)기판 위에 성장하였다. CuGaSe₂/GaAs epilayer는 증발원의 온도를 610℃, 기판의 온도를 450℃로 하였다. CuGaSe₂/GaAs epilayer의 결정성의 조사에서 20K에서 광발광(photoluminescence) 스펙트럼이 672.6nm(1.8432eV)에서 엑시톤 방출 스펙트럼이 가장 강하게 나타났으며, 이중결정 X-선 요동곡선(DCRC)의 반폭치(FWHM)도 138 arcsec로 가장 작아 최적 성장 조건임을 알 수 있었다. Hall 효과는 van der Pauw 방법에 의해 측정되었으며, 온도에 의존하는 운반자 농도와 이동도는 293K에서 각각 4.87×10^(23) electron/m³, 1.29×10² m²/v-s 였다. CuGaSe₂/GaAs epilayer의 광전류 단파장대 봉우리들로부터 20K에서 측정된 ΔCr(Crystal field splitting)은 약 0.09 eV ΔSo(spin orbit coupling)는 0.2498 eV였다. 20K의 광발광 측정으로부터 고품질의 결정에서 볼 수 있는 자유 엑시톤 (free exciton)과 매우 강한 세기의 중성 받개(acceptor) 구속 엑시톤 (bound exciton)등의 피크가 관찰되었다. 이때 받개 구속 엑시톤 (bound exciton)의 반치폭과 결합에너지는 각각 8meV와 93.2meV 였다. 또한 Haynes rule에 의해 구한 불순물의 활성화 에너지는 466meV였다. The stochiometric mixture of evaporating materials for the CuGaSe₂/GaAs epilayer was prepared from horizontal furnace. Using extrapolation method of X-ray diffraction patterns for the polycrystal CuGaSe₂, it was found tetragonal structure whose lattice constant a_(0) and c_(0) were 5.615 Å and 11.025 Å, respectively. To obtain the CuGaSe₂/GaAs epilayer, CuGaSe₂ mixed crystal was deposited on throughly etched GaAs(100) by the Hot Wall Epitaxy(HWE) system. The source and substrate temperature were 610 ℃ and 450 ℃ respectively. The crystalline structure of CuGaSe₂/GaAs epilayer was investigated by the double crystal X-ray diffraction(DCXD). Hall effect on this sample was measured by the method of van der pauw and studied on carrier density and mobility depending on temperature. From Hall data, the mobility was likely to be decreased by pizoelectric scattering in the temperature range 30 K to 150 K and by polar optical scattering in the temperature range 150 K to 293 K. From the photocurrent spectra by illumination of polarized light of the CuGaSe₂/GaAs epilaye. We have found that values of spin orbit coupling ΔSo and crystal field splitting ΔCr was 0.0900 eV and 0.2498 eV, respectively. From the photoluminescence measurement of CuGaSe₂/GaAs epilayer, we observed free excition(Ex) observable only in high quality crystal and neutral acceptor-bound exciton (A^(0); X) having very strong peak intensity. And, the full width at half maximum and binding energy of neutral donor bound excition were 8 meV and 93.2 meV, respectively. By Haynes rule, an activation energy of impurity was 466 meV.

HWE(Hot Wall Epitaxy)에 의한 ZnIn_2S_4 박막 성장과 광전도 특성

홍광준,이관교,정준우,정경아,방진주,장현규,문종대,김혜숙 조선대학교 기초과학연구소 1999 自然科學硏究 Vol.22 No.1

HWE 방법에 의해 ZnIn_2S_4 박막을 Si(00) 기판 위에 성장시켰다. 증발원과 기판의 온도를 각각 610℃, 450℃로 하여 성장시킨 ZnIn_2S_4 박막의 이중 결정 X-선 요동곡선(DCRC)의 반폭치(FWHM)값이 245 arcsec로 가장 작았다. Van der Pauw 방법으로 Hall 효과를 측정하여 운반자농도의 1n n 대 1/T에서 구한 활성화에너지는 0.17eV로 측정되었다. Hall 이동도의 온도 의존성은 30K에서 100K까지는 불순물산란에 기인하고, 100K에서 293K까지는 격자산란에 기인한것으로 고찰되었다. 광전도셀의 특성으로 spectral response, 최대 허용소비전력(MAPD), 광전류와 암전류(pc/dc)의 비 및 응답시간을 측정하였다. S 증기분위기에서 열처리한 광전도 셀의 경우, 감도(??)는 0.99, pc/dc은 1.37x10^7, 그리고 최대 허용소비전력(MAPD)은 336mW, 오름시간(rise time)은 9ms, 내림시간(decay time)은 9.8ms로 가장 좋은 광전도 특성을 얻었다. The ZnIn_2S_4 thin films were grown on the Si(100) wafers by a hot wall epitaxy method(HWE). The source and substrate temperature are 610℃ and 450℃ respectively. The crystalline structure of epilayers was investigated by double crystal X-ray diffraction(DCXD). Hall effect on the sample was measured by the van der Pauw method and studied on the carrier density and mobility dependence on temperature. From Hall data, the mobility was increased in the temperature range 30K to 100K by impurity scattering and decreased in the temperature range 100K to 293K by the lattice scattering. In order to explore the applicability as a photoconductive cell, we measured the sensitivity(??), the ratio of photocurrent to darkcurrent(pc/dc), maximum allowable power dissipation(MAPD), spectral response and response time. The results indicated that the photoconductive characteristic were the best for the samples annealed in S vapor compare with in Zn, In, air and vacuum vapour. Then we obtained the sensitivity of 0.99, the value of pc/dc of 1.37x10^7, the MAPD of 336mW, and the rise and decay time of 9ms and 9.8ms, respectively.

Castellated tungsten plasma-facing components exposed to H-mode plasma in KSTAR

Hong, S.H.,Lee, H.H.,Kim, K.M.,Kim, H.T.,Bang, E.N.,Son, S.H.,Kim, H.K. North-Holland 2016 Fusion engineering and design Vol.109 No.1

Heat load on the misaligned leading edges of tungsten castellated blocks based on tungsten (W), oxygen-free high conductive copper (OFHC-Cu), and copper-chrome-zirconium (CuCrZr) alloy are studied by COMSOL analysis and infrared (IR) measurements in KSTAR. IR measurements show that 1-3MW/m<SUP>2</SUP> of heat flux has been deposited on the blocks during the inter-ELM (edge localized mode) phase in H-mode plasmas. COMSOL analysis indicates that the temperature of 1mm leading edge in KSTAR under 3MW/m<SUP>2</SUP> would reach the recrystallization temperature within 2s and will be melted within 30s during a long pulse H-mode shot. Rounded and double chamfered blocks show much better thermal response meaning that shaping of divertor block enhances the heat load handling capability. It seems that a simple COMSOL analysis describes heat load patterns on the tungsten blocks of different shapes qualitatively well. Therefore, simple analysis would be useful to make a quick prediction on heat load patterns of blocks with arbitrary shapes.

Molecular characterization of an aldo-keto reductase from Marivirga tractuosa that converts retinal to retinol

Hong, S.H.,Nam, H.K.,Kim, K.R.,Kim, S.W.,Oh, D.K. Elsevier Science Publishers 2014 Journal of biotechnology Vol.169 No.-

A recombinant aldo-keto reductase (AKR) from Marivirga tractuosa was purified with a specific activity of 0.32unitml<SUP>-1</SUP> for all-trans-retinal with a 72kDa dimer. The enzyme had substrate specificity for aldehydes but not for alcohols, carbonyls, or monosaccharides. The enzyme turnover was the highest for benzaldehyde (k<SUB>cat</SUB>=446min<SUP>-1</SUP>), whereas the affinity and catalytic efficiency were the highest for all-trans-retinal (K<SUB>m</SUB>=48μM, k<SUB>cat</SUB>/K<SUB>m</SUB>=427mM<SUP>-1</SUP>min<SUP>-1</SUP>) among the tested substrates. The optimal reaction conditions for the production of all-trans-retinol from all-trans-retinal by M. tractuosa AKR were pH 7.5, 30<SUP>o</SUP>C, 5% (v/v) methanol, 1% (w/v) hydroquinone, 10mM NADPH, 1710mgl<SUP>-1</SUP> all-trans-retinal, and 3unitml<SUP>-1</SUP> enzyme. Under these optimized conditions, the enzyme produced 1090mgml<SUP>-1</SUP> all-trans-retinol, with a conversion yield of 64% (w/w) and a volumetric productivity of 818mgl<SUP>-1</SUP>h<SUP>-1</SUP>. AKR from M. tractuosa showed no activity for all-trans-retinol using NADP<SUP>+</SUP> as a cofactor, whereas human AKR exhibited activity. When the cofactor-binding residues (Ala158, Lys212, and Gln270) of M. tractuosa AKR were changed to the corresponding residues of human AKR (Ser160, Pro212, and Glu272), the A158S and Q270E variants exhibited activity for all-trans-retinol. Thus, amino acids at positions 158 and 270 of M. tractuosa AKR are determinant residues of the activity for all-trans-retinol.

Chemical Bath Deposition 방법으로 제작한 CdSe 박막의 특성

홍광준,이상열,유상하,서상석,문종대,신영진,정태수,신현길,김택성,송정훈,유기수 全北大學校 基礎科學硏究所 1994 基礎科學 Vol.16 No.-

Chemical bath deposition 방법으로 다결정 CdSe 박막을 세라믹 기판 위에 성장시킨 다음 온도를 변화시켜 열처리하고 X-선 회절무늬를 측정하여 결정구조를 밝혔다. 450℃로 열처리한 시료가 X-선 회절무늬로 부터 외삽법에 의해 a_o와 c_o 는 각각 4.302 Å과 7.014 Å인 육방정계임을 알았다. 이 때 낱알크기는 약 0.3㎛이었다. Van der Pauw 방법으로 Hall 효과를 측정하여 운반자 농도와 이동도의 온도의존성을 연구하였다. 이동도는 33 K 에서 200 K 까지는 압전산란에 의하여, 200 k 에서 293 K 까지는 극성광학산란에 의하여 감소하는 경향이 나타냈다. 광전도 셀의 특성으로 스텍트럼 응답, 감도(γ), 최대허용소비전력 및 응답 시간을 측정하였다. Polycrystalline CdSe thin films were grown on creamic substrate using a chemical bath deposition (CBD) method. They were annealed at various temperature and X-ray diffraction patterns were measured by X-ray diffractometer in order to study CdSe polycrystal structure. Using extrapolation method of X-ray diffraction patterns for the CdSe samples annealed in N_2 gas at 450℃ it was found hexagonal structure whose lattice parameters a_o and c_o were 4.302 Å and 7.014 Å, respectively. It grain size was about 0.3 ㎛. Hall effect on this sample was measured by Van der Pauw method and studied on carrier density and mobility depending on temperature. From Hall data, the mobility was likely to be decreased by piezo electric scattering at temperature range of 33 K and 200 K, and by polar optical potical scattering at temperature range of 200 K and 293 K. We measured also spectral response, sensitivily (γ), maximum allowable power dissipation and response time on these samples.

Optical Properties and Glass-forming Region of the K2O-Sm2O3-TeO2 Glass System

K. S. Hong,Y. J. Cha,M. G. Ha,최세용,J. P. Kim,B. S. Lee,정의덕,김현규,P. H. Borse 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.9

The optical properties and the glass-forming region of the K2O-Sm2O3-TeO2 glass system arestudied. In the K2O-Sm2O3-TeO2 system, only the 5K2O-5Sm2O3-90TeO2 composition gives atransparent glass. The refractive index, n, and the optical band-gap energy, Eg, of the 5K2O-5Sm2O3-90TeO2 glass are n = 2.04 ± 0.003 and Eg = 3.2 eV, respectively. A single Sm2Te6O15phase is found to be formed by a two-step thermal treatment process at 370 C for 5 h and 390 Cfor 5 h. This is the first report on the crystallization and the preparation of the K2O-Sm2O3-TeO2glass system.

CBD 방법에 의한 CdS 박막의 성장과 광전도 특성

황광준,이상열,유상하,서상석,문종대,신영진,정태수,신현길,김택성,송정훈,유기수 全北大學校 基礎科學硏究所 1994 基礎科學 Vol.16 No.-

Chemical bath deposition 방법으로 다결정 CdS 박막을 세라믹 기판 위에 성장시킨 다음 온도를 변화시켜 열처리하고 X-선 회절무늬를 측정하여 결정구조를 밝혔다. 550℃로 열처리한 시료의 경우 X-선 회절무늬로 부터 외삽법에 의해 a_。와 c_。는 각각 4.1364 Å과 6.7129 Å인 육방정계임을 알았다. 이 때 낱알크기는 약 0.35㎛이었다. Van der Pauw 방법으로 Hall 효과를 측정하여 운반자 농도와 이동도의 온도의존성을 연구하였다. 이동도는 33 K 에서 150 K 까지는 압전산란에 의하여, 150 K 에서 293 K 까지는 극성광학산란에 의하여 감소하는 경향이 나타냈다. 광전도 셀의 특성으로 스텍트럼 응답, 감도(γ), 최대허용소비전력 및 응답 시간을 측정하였다. Polycrystalline CdS thin films were grown on creamic substrate using a chemical bath deposition method. They were annealed at various temperature and X-ray diffraction patterns were measured by X-ray diffractometer in order to study CdS polycrystal structure. Using extrapolation method of X-ray diffraction patterns for the CdS samples annealed in N_2 gas at 550℃ it was found hexagonal structure whose lattice constants a_o and c_o were 4.1364 Å and 6.7120Å, respectively. Its grain size was about 0.35 ㎛. Hall effect on this sample was measured by Van der Pauw method and studied on carrier density and mobility depending on temperature. From Hall data, the mobility was likely to be decreased by piezo electric scattering at temperature range of 33K and 150K and by polar optical scattering at temperature range of 150K and 293K. We measured also spectral response, sensitivity (γ), maximum allowable power dissipation and response time on these samples.

Comparison of 90‐day case‐fatality after ischemic stroke between two different stroke outcome registries using propensity score matching analysis

Yu, K‐,H.,Hong, K‐,S.,Lee, B‐,C.,Oh, M‐,S.,Cho, Y‐,J.,Koo, J‐,S.,Park, J‐,M.,Bae, H‐,J.,Han, M‐,K.,Ju, Y‐,S.,Kang, D‐,W.,Appelros, P. Blackwell Publishing Ltd 2011 Acta neurologica Scandinavica Vol.123 No.5

<P>Yu K‐H, Hong K‐S, Lee B‐C, Oh M‐S, Cho Y‐J, Koo J‐S, Park J‐M, Bae H‐J, Han M‐K, Ju Y‐S, Kang D‐W, Appelros P, Norrving B, Terent A. Comparison of 90‐day case‐fatality after ischemic stroke between two different stroke outcome registries using propensity score matching analysis. 
Acta Neurol Scand: 2011: 123: 325–331. 
© 2010 John Wiley & Sons A/S.</P><P><B>Background – </B> It has not been clarified whether the disparity in ischemic stroke outcome between populations is caused by ethnic and geographic differences or by variations in case mix. Propensity score matching (PSM) analysis can overcome some analytical problems but is rarely used in stroke outcome research. This study was to compare the ischemic stroke case‐fatality between two PSM cohorts of Sweden and Korea.</P><P><B>Methods – </B> Prognostic variables related to baseline characteristics and stroke care were included in our PSM model. Then, we selected 7675 Swedish and 1220 Korean patients with ischemic stroke from each stroke registers and performed one‐to‐one matching based on propensity scores of each patient.</P><P><B>Results – </B> After PSM, all measured variables were well balanced in 1163 matched subjects, and the 90‐day case‐fatality was identical 6.2% (HR 0.997, 95%CI 0.905–1.099) in Sweden and Korea.</P><P><B>Conclusions – </B> No difference is found in the 90‐day case‐fatality in propensity score‐matched Swedish and Korean patients with ischemic stroke.</P>

Role of conserved Met112 residue in the catalytic activity and stability of ketosteroid isomerase

Cha, H.J.,Jang, D.S.,Jeong, J.H.,Hong, B.H.,Yun, Y.S.,Shin, E.J.,Choi, K.Y. Elsevier Science 2016 Biochimica et biophysica acta. Proteins and proteo Vol.1864 No.10

<P>Ketosteroid isomerase (3-oxosteroid Delta(5)-Delta(4)-isomerase, KSI) from Pseudomonas putida catalyzes allylic rearrangement of the 5,6-double bond of Delta(5)-3-ketosteroid to 4,5-position by stereospecific intramolecular transfer of a proton. The active site of KSI is formed by several hydrophobic residues and three catalytic residues (Tyr14, Asp38, and Asp99). In this study, we investigated the role of a hydrophobic Met112 residue near the active site in the catalysis, steroid binding, and stability of KSI. Replacing Met112 with alanine (yields M112A) or leucine (M112L) decreased the k(cat) by 20- and 4-fold, respectively. Compared with the wild type (WT), M112A and M112L KSIs showed increased K-D values for equilenin, an intermediate analogue; these changes suggest that loss of packing at position 112 might lead to unfavorable steroid binding, thereby resulting in decreased catalytic activity. Furthermore, M112A and M112L mutations reduced melting temperature (T-m) by 6.4 degrees C and 2.5 degrees C, respectively. These changes suggest that favorable packing in the core is important for the maintenance of stability in KSI. The M112K mutation decreased k(cat) by 2000-fold, compared with the WT. In M112K KSI structure, a new salt bridge was formed between Asp38 and Lys112. This bridge could change the electrostatic potential of Asp38, and thereby contribute to the decreased catalytic activity. The M112K mutation also decreased the stability by reducing T-m by 4.1 degrees C. Our data suggest that the Met112 residue may contribute to the catalytic activity and stability of KSI by providing favorable hydrophobic environments and compact packing in the catalytic core. (C) 2016 Published by Elsevier B.V.</P>

Overview of KSTAR research progress and future plans toward ITER and K-DEMO

Park, H.K.,Choi, M.J.,Hong, S.H.,In, Y.,Jeon, Y.M.,Ko, J.S.,Ko, W.H.,Kwak, J.G.,Kwon, J.M.,Lee, J.,Lee, J.H.,Lee, W.,Nam, Y.B.,Oh, Y.K.,Park, B.H.,Park, J.K.,Park, Y.S.,Wang, S.J.,Yoo, M.,Yoon, S.W.,B IOP 2019 Nuclear fusion Vol.59 No.11

<P>A decade-long operation of the Korean Superconducting Tokamak Advanced Research (KSTAR) has contributed significantly to the operation of superconducting tokamak devices and the advancement of tokamak physics which will be beneficial for the ITER and K-DEMO programs. Even with limited heating capability, various conventional as well as new operating regimes have been explored and have achieved improved performance. As examples, a long pulse high-confinement mode operation with and without an edge-localized mode (ELM) crash was well over 70 and 30 s, respectively. The unique capabilities of KSTAR allowed it to improve the capability of controlling harmful instabilities, and they have been instrumental in uncovering much new physics. The highlights are that the L/H transition threshold power is sensitive to the resonant magnetic perturbation (RMP) and insensitive to non-resonant magnetic perturbation. Co-<I>I</I> <SUB>p</SUB> offset rotation dominated by an electron channel predicted by general neoclassical toroidal viscosity theory was confirmed. Improved heat dispersal in a divertor system using three rows of rotating RMP was demonstrated and predictive control of the ELM-crash with <I>a priori</I> modeling was successfully tested. In magnetohydrodynamic physics, validation of the full reconnection model (i.e. <I>q</I> <SUB>0</SUB>  >  1 right after the sawtooth crash) and self-consistent validation of the anisotropic distribution of turbulence amplitude and flow in the presence of the 2/1 island with theoretical models were achieved. The turbulence amplitude induced by RMP was linearly increased with the slow RMP coil current ramp-up time (i.e. the magnetic diffusion time scale). The <I>D</I> <SUB> <I>α</I> </SUB> spikes (i.e. ELM-crash amplitude) was linearly decreased with the turbulence amplitude and not correlated with the perpendicular electron flow. In the turbulence area, a non-diffusive ‘avalanche’ transport event and the role of a quiescent coherent mode in confinement were studied. To accommodate the anticipation of a higher performance of the KSTAR plasmas with the increased heating powers, a new divertor/internal interface with a full active cooling system will be implemented after a full test of the new heating (neutral beam injection II and electron cyclotron heating) and current drive (CD) (Helicon and lower hybrid CD) systems. An upgrade plan for the internal hardware, heating systems and efficient CD system may allow for a long pulse operation of higher performance plasmas at <I>β</I> <SUB>N</SUB>  >  3.0 with <I>f</I> <SUB>bs</SUB> ~ 0.5 and <I>T</I> <SUB>i</SUB>  >  10 keV.</P>