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산소와 수소 플라즈마로 처리한 사파이어 기판 위에 성장된 ZnO 박막의 구조적.광학적 특성
이선균,김지영,곽호상,권봉준,고항주,조용훈,Lee, S.K.,Kim, J.Y.,Kwack, H.S.,Kwon, B.J.,Ko, H.J.,Yao, Takafumi,Cho, Y.H. 한국진공학회 2007 Applied Science and Convergence Technology Vol.16 No.6
[ $Al_2O_3$ ]기판을 산소 plasma 또는 수소 plasma로 표면 처리한 후 그 위에 plasma-assisted molecular beam epitaxy 방법으로 성장된 ZnO 박막의 구조적 특성과 광학적 발광 특성을 체계적으로 조사하였다. 제작된 ZnO 박막은 high resolution X-ray diffraction 측정과 atomic force microscope를 사용하여 구조적 특성과 표면 특성을 관찰하였으며, photoluminescence (PL) 측정을 통하여 엑시톤과 관련된 광학적 전이특성을 온도에 따라 조사하였다. free exciton, bound exciton, 그리고 이들의 phonon replica들의 특성을 온도에 따라 분석하였으며, 산소 plasma로 표면 처리한 시료의 PL 세기가 수소 plasma 표면 처리한 시료의 PL 세기보다 상당히 커짐을 관찰하였다. 산소 plasma로 처리된 기판 위에 성장된 ZnO 시료가 수소 plasma로 처리된 경우보다 우수한 구조적 특성과 광학적 특성을 보였는데, 이는 산소 plasma로 표면 처리함으로써 산소 공공(oxygen vacancy)과 같은 결함 구조가 적게 생성되고 좋은 격자 상수 일치를 보여주므로 구조적 특징과 발광 특징이 향상되는 것으로 해석되었다. Structure and optical properties of ZnO epilayers grown on oxygen- and hydrogen-plasma treated sapphire substrates by plasma-assisted molecular beam epitaxy (denoted as samples A and B, respectively) have been investigated by various techniques. The crystal quality and structural properties of the surface for the ZnO epilayers were investigated by high-resolution X-ray diffraction and atomic force microscope. For investigating the optical properties of excitonic transition of ZnO, we carried out photoluminescence experiments as a function of temperature. The free exciton, bound exciton emission and their phonon replicas were investigated as a function of temperature from 10 to 300 K, and the intensity of excitonic PL peak emission from the sample A is found to be higher than that of sample B. From the results, we found that sample A has better crystal structure quality and optical properties as compared to sample B. The number of oxygen vacancies may be decreased in sample A, resulting in an enhancement of the crystal quality and a higher intensity of excitonic emission band as compared to sample B.
Solvent effect on hydrogen bonded Tyr...Asp...Arg triads: Enzymatic catalyzed model system
Yan, S.,Yao, L.,Kang, B.,Lee, J.Y. Pergamon 2016 Computational biology and chemistry Vol.65 No.-
The hydrogen bond plays a vital role in structural arrangement, intermediate state stabilization, materials function, and biological activity of certain enzymatic reactions. The solvent and electronic effects on hydrogen bonds are illustrated employing the polarizable contimuum model at B3LYP/6-311++G(d,p) level. Geometry optimizations reflect the significant solvent and electronic effect. The proton departs spontaneously upon oxidation from the hydroxyl group of tyrosyl in hydrogen bonded Tyr...Asp...Arg triads in both gas phase and solvents. The electron transfer isomers are observed for anionic triads, no matter what the solvent is. The difference of distance between two hydrogen bonds is enlarged in solvent as compared to that in gas phase. The electronic effect on IR spectra is distinctive. The tyrosyl fragment tends to be oxidized and the arginine moiety is easier to bind an excess electron. The variations of chemical shift and spin-spin coupling constant are more significant upon electron transfer than upon solvent dielectric constant. The augmentation of solvent dielectric constant stabilizes the system, enhances the difference of isomers, and increases the vertical ionization potential and vertical electron affinity values.
Semiparametric mixture: Continuous scale mixture approach
Xiang, S.,Yao, W.,Seo, B. North-Holland Pub. Co ; Elsevier Science Ltd 2016 Computational statistics & data analysis Vol.103 No.-
<P>In this article, we propose a new estimation procedure for a class of semiparametric mixture models that is a mixture of unknown location-shifted symmetric distributions. The proposed method assumes that the nonparametric symmetric distribution falls in a rich class of continuous normal scale mixture distributions. With this new modeling approach, we can suitably avoid the misspecification problem in traditional parametric mixture models. In addition, unlike some existing semiparametric methods, the proposed method does not require any modification or smoothing of the likelihood as it can directly estimate parametric and nonparametric components simultaneously in the model. Furthermore, the proposed parameter estimates are robust against outliers. The estimation algorithms are introduced and numerical studies are conducted to examine the finite sample performance of the proposed procedure and to compare it with other existing methods. (C) 2016 Elsevier B.V. All rights reserved.</P>
Fabrication of p-Type Nitrogen-Doped MgZnO by Depressing N-Related Donors
B. Yao,Z. P. Wei,Y. F. Li,D. Z. Shen,Y. M. Lu,Z. Z. Zhang,B. H. Li,C. J. Zheng,X. H. Wang,J. Y. Zhang,D. X. Zhao,X. W. Fan,Z. K. Tang 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
Wurtzite nitrogen-doped MgZnO (MgZnO:N) films were grown on c-plane sapphire by using plasma-assisted molecular beam epitaxy with radical NO as the oxygen source and nitrogen dopant. P-type conduction of MgZnO:N was obtained by decreasing the donor defects ((N2)O, VO, etc.) through annealing, revealing a hole concentration of 6.1 × 1017 cm−3 and a mobility of 6.42 cm2/Vs. Furthermore, as-grown p-type films with a hole concentration of 1 × 1017 cm−3 and a mobility of 3 cm2/Vs were obtained by decreasing the (N2)O double donor defect through control of the plasma conditions. ZnMgO:N/ZnO p-n junctions were obtained by using these p-type films. ode-like, rectifying I-V characteristics with a threshold voltage of about 5 V and a different reverse leakage current were observed at room temperature.
Hydrochlorofluorocarbon and hydrofluorocarbon emissions in East Asia determined by inverse modeling
Stohl, A.,Kim, J.,Li, S.,O&,apos,Doherty, S.,Mü,hle, J.,Salameh, P. K.,Saito, T.,Vollmer, M. K.,Wan, D.,Weiss, R. F.,Yao, B.,Yokouchi, Y.,Zhou, L. X. Copernicus GmbH 2010 Atmospheric Chemistry and Physics Vol.10 No.8
<P>Abstract. The emissions of three hydrochlorofluorocarbons, HCFC-22 (CHClF2), HCFC-141b (CH3CCl2F) and HCFC-142b (CH3CClF2) and three hydrofluorocarbons, HFC-23 (CHF3), HFC-134a (CH2FCF3) and HFC-152a (CH3CHF2) from four East Asian countries and the Taiwan region for the year 2008 are determined by inverse modeling. The inverse modeling is based on in-situ measurements of these halocarbons at the Japanese stations Cape Ochi-ishi and Hateruma, the Chinese station Shangdianzi and the South Korean station Gosan. For every station and every 3 h, 20-day backward calculations were made with the Lagrangian particle dispersion model FLEXPART. The model output, the measurement data, bottom-up emission information and corresponding uncertainties were fed into an inversion algorithm to determine the regional emission fluxes. The model captures the observed variation of halocarbon mixing ratios very well for the two Japanese stations but has difficulties explaining the large observed variability at Shangdianzi, which is partly caused by small-scale transport from Beijing that is not adequately captured by the model. Based on HFC-23 measurements, the inversion algorithm could successfully identify the locations of factories known to produce HCFC-22 and emit HFC-23 as an unintentional byproduct. This lends substantial credibility to the inversion method. We report national emissions for China, North Korea, South Korea and Japan, as well as emissions for the Taiwan region. Halocarbon emissions in China are much larger than the emissions in the other countries together and contribute a substantial fraction to the global emissions. Our estimates of Chinese emissions for the year 2008 are 65.3±6.6 kt/yr for HCFC-22 (17% of global emissions extrapolated from Montzka et al., 2009), 12.1±1.6 kt/yr for HCFC-141b (22%), 7.3±0.7 kt/yr for HCFC-142b (17%), 6.2±0.7 kt/yr for HFC-23 (>50%), 12.9±1.7 kt/yr for HFC-134a (9% of global emissions estimated from Velders et al., 2009) and 3.4±0.5 kt/yr for HFC-152a (7%). </P>
A strategy to overcome the limits of carbon-based materials as lithium-ion battery anodes
Yao, F.,Li, B.,So, K.,Chang, J.,Ly, T.H.,Vu, A.Q.,Mun, H.,Cojocaru, C.S.,Yue, H.,Xie, S.,Lee, Y.H. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.79 No.-
The free-standing Si-coated carbon nanofiber (Si/CNF) mat was fabricated for the anode of lithium ion battery through combining electrospun CNF mat with electrodeposited Si layer. Spaghetti or granule-like Si was obtained by varying the deposition conditions. This Si/CNF mat was directly used as an active material and a current collector as well, which involves neither binders nor additional metal substrate. The best performance was achieved in spaghetti-like Si due to its highly porous nature which can accommodate volume expansion and large surface area which benefit the efficient charge transfer both at Si/CNF interface and at the electrode/electrolyte interface. The optimized Si/CNF mat after annealing at 1000<SUP>o</SUP>C delivered a capacity of 870mAhg<SUP>-1</SUP> at 1st discharge and 730mAhg<SUP>-1</SUP> at 50th discharge with a capacity retention of 84%, improving the capacity of pure CNF (280mAhg<SUP>-1</SUP> at the 50th discharge) by almost three times. In addition, corrosion of the current collector no longer exists in our approach. Our X-ray photoemission spectroscopy and electrochemical analysis revealed that the formation of Si-C bond through high temperature annealing can enhance the adhesion between silicon and carbon at the interface which benefits the cyclic performance of anode ultimately.
B. H. KOO,C. G. LEE,D. SHINDO,H. MAKINO,J. H. CHANG,T. YAO,T. HANADA,Y.-G. PARK 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
The effect of growth interruption (GI) on the structural and optical properties of InAs nanostructures was investigated by transmission electron microscopy (TEM) and photoluminescence (PL). By introducing the GI, a single PL peak changed to a distinctive multiple-peak feature with average full width at half maximum 30 meV, which shows the state lling of the several low energy peaks. In conjunction with the TEM results, the changes in the PL spectra due to GI are most probably correlated with the formation of different-height islands isolated from neighbor islands due to a 2D-3D transition of the InAs layer during the GI.
Development of the 3.7 GHz LHCD System on HL-2A
B. Lu,M. Huang,H. Zeng,X. Y. Bai,X. H. Mao,Z. H. Lu,J. Liang,Z. H. Kang,M. W. Wang,K. Feng,H. Wang,C. Wang,J. Q. Wang,S. Wei,T. Yao,Y. N. Bu,J. Feng,G. Y. Cheng,S. D. Song,D. H. Xia,J. Rao 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.8
A 2 MW-3.7 GHz lower hybrid current drive (LHCD) system is under development for physicsexperiments on the HL-2A device. The RF Power is generated by four TH2103A klystron amplifiersand propagates in the TE10 mode through WR284 waveguides. The transmission lines with a lengthof 20 m to 30 m are pressurized with 2 bars of nitrogen to decrease the possibility of arcing. Thelauncher, based on the passive-active multi-junction (PAM) concept, has been developed and iscurrently being realized. It was designed for a power spectrum peaked at Nk = 2.75 with goodcoupling properties over a wide range of plasma parameters. The four klystrons are fed by ahigh-voltage power supply (HVPS) based on the pulse step modulation (PSM) concept with a fastswitch-off time of less than ten μs. This system is expected to be in operation within 1 years and willexplore many international thermonuclear experimental reactor (ITER) related LH experiments inthe following years.