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Oh, Semi,Ha, Kab,Kang, Soo-Hyun,Yohn, Gyu-Jae,Lee, Hyo-Ju,Park, Seong-Ju,Kim, Kyoung-Kook IOP 2018 Nanotechnology Vol.29 No.1
<P>Self-standing ZnO nanotube (ZNT) arrays were fabricated on the surface of a GaN-based emitter with an indium tin oxide (ITO) transparent layer using a hydrothermal method and temperature cooling down process. For the greater enhancement of photon extraction efficiency, ZNT/SiO<SUB>2</SUB> core–shell nanostructure arrays were fabricated on the emitter with a 430 nm wavelength. The optical output power of ZNT/SiO<SUB>2</SUB> core–shell arrays on the emitter with ITO electrode was remarkably enhanced by 18.5%, 28.1%, and 55.9%, compared to those of ZNTs, ZNRs on an ITO film on an emitter and ITO film on an emitter as a conventional emitter, respectively. The large enhancement in optical output is attributable to the synergistic effect of efficient photon injection from the ITO/GaN layer to ZNTs because of the well-matched refractive indices and wave-guiding, in addition to the superior photon extraction by the SiO<SUB>2</SUB> coating layer on the ZNTs.</P>
Oh, Semi,Lee, Kwang Jae,Lee, Hyo-Ju,Kim, Sang-Jo,Han, Janghwan,Kang, Nam-Woo,Kwon, Joon-Sung,Kim, Hyunsoo,Kim, Kyoung-Kook,Park, Seong-Ju Elsevier 2018 Scripta materialia Vol.146 No.-
<P><B>Abstract</B></P> <P>We report on the periodic air-nanoplate-embedded omnidirectional reflectors (ODRs) to enhance the efficiency of AlGaN-based ultraviolet (UV) emitters composed of periodic quarter-wavelength-thick air-nanoplates/Al reflective layer and indium tin oxide (ITO) mesh ohmic layer. To enhance the photon extraction efficiency (PEE) of UV emitter by increasing the volume of air in ODRs, the coverage of the air-nanoplates in ODRs could be increased to 70% per chip. The optical output of UV emitter with 70% coverage of air-nanoplate was significantly improved by the Lambertian enhancement of 28.7% at an injection current of 10mA, compared with that of ITO film/Al UV emitter.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Oh, Semi,Shin, Kyung-Sik,Kim, Sang-Woo,Lee, Sangbin,Yu, Hyeongwoo,Cho, Soohaeng,Kim, Kyoung-Kook American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.5
<P>The improvement of the optical output power of GaN-based light emitting diodes (LEDs) was achieved by employing nano-sized flat-top hexagonal ZnO rods. ZnO nanorods (NRs) with the average diameters of 250, 350, and 580 nm were grown on p-GaN top surfaces by a simple wet-chemical method at relatively low temperature (90 degrees C) to investigate the effect of the diameter of ZnO NRs on the light extraction efficiency. Consequently, the enhancement by the factor of as high as 2.63 in the light output intensity at 20 mA for the LED with 350 nm ZnO NRs was demonstrated without the increase in the operation voltage compared to the reference LED.</P>
Oh, Semi,Lee, Sung-Nam,Cho, Soohaeng,Kim, Kyoung-Kook American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.7
<P>The improvement of the optical output power of GaN-based light emitting diodes (LEDs) was achieved by a novel bi-layer transparent top electrode scheme. The proposed bi-layer structure is composed of a Ga-doped ZnO layer with nano-patterns obtained solely by wet etching process and an Indium Tin Oxide p-type transparent conducting electrode layer. We employed various wet-etching conditions to maximize light extraction efficiency and it was observed that the crystal morphologies of nano-patterns and optoelectronic properties are dependent on etching duration. Because of ITO under GZO layer, the current spreading was not affected even after formation of nano-patterned surface on the GZO layer by wet etching. Consequently, an enhancement of as high as 43.1% in optical output power at an injection current of 100 mA for the LED with nano-patterns wet-etched by 0.025% HCl for 30 seconds was realized without significant degradation in electrical property when compared to a reference LED.</P>
오세미 ( Semi Oh ),안준기 ( Junki Ahn ) 한국여성경제학회 2023 여성경제연구 Vol.20 No.3
본 연구는 청년층의 성별 임금 격차를 확인하기 위해 기존의 연구 방법에 비해 엄밀한 통제 방법을 활용하였다. 먼저 성별 임금 격차를 확인하기 위해 횡단 분석이 아닌 패널자료를 이용한 코호트(Cohort) 비교 분석법을 이용하였다. 또한 성향점수매칭 방법을 활용하여 성별 외에 생산성과 관련된 요소들은 노동시장 진입 단계에서부터 유사하게 통제한 상태에서 장기간의 성별 임금 변화를 추적하였다. 분석 결과 임금 영향요인들의 초기 상태를 통제했음에도 노동시장 진입 후 시간이 지날수록 성별 임금 격차는 증가하였다. 이러한 격차가 생산성 차이 때문인지 차별과 같은 설명 불가능한 요인에 의한 것인지 Oaxaca-Blinder 분해법을 통해 살펴본 결과, 설명가능한 요인 외에 설명 불가능한 요인이 큰 비중을 차지하여 사회구조적 차별 같은 문제들이 존재할 가능성을 보여주었다. 이를 토대로 시사점과 향후 연구과제를 제안하였다. This study sought to analyze the gender wage gap using a distinctive approach compared to existing studies. First, panel data, instead of cross-sectional data, was utilized to consider both observable and unobservable characteristics that may contribute to structural differences in wages. Furthermore, the study aimed to measure the gender wage gap more accurately by controlling for the initial labor market entry status and tracking long-term wage changes. The analytical methods employed included propensity score matching and Oaxaca-Blinder decomposition. The research findings showed that, even after controlling for potential wage-affecting factors, the gender wage gap widened over time. Decomposition of the wage gap indicated that beyond the factors that can be explained, significant unexplainable factors contribute to the wage gap. This points to potential societal structural issues, such as discrimination. Based on these results, policy implications and suggestions for future research were drawn.
A Study on 3D Locomotion of Intravascular Therapeutic Microrobot using EMA System
Semi Jeong,Hyunchul Choi,Cheong Lee,Kiduk Kwon,Gwangjun Go,Doo Sun Sim,Kyung Seob Lim,Myung Ho Jeong,Seong Young Ko,Jong-oh Park,Sukho Park 제어로봇시스템학회 2013 제어로봇시스템학회 국제학술대회 논문집 Vol.2013 No.10
In this paper, we proposed an intravascular microrobot using an EMA system with bi-plane X-ray fluoroscopy. The proposed EMA system consists of a pair of stationary Helmholtz-Maxwell coils in x-axis and a pair of rotational uniform-gradient saddle coils on x-axis. The microrobot using the EMA system can be aligned to the desired direction by the uniform magnetic field from the Helmholtz-uniform saddle coil pairs and can be propelled to the aligned direction by the uniform gradient magnetic field from the Maxwell-gradient saddle coil pairs. Based on this actuating principle, we developed the microrobot which can move and have a treatment function in blood vessel. For the position recognition of the microrobot, a bi-plane X-ray fluoroscopy was installed in the EMA system. The bi-plane X-ray fluoroscopy can provide frontal and lateral views of mini-pig and the image of the microrobot. In addition, the bi-plane X-ray fluoroscopy can be rotated together with the pair of rotational uniform-gradient saddle coils on x-axis. Through various in-vitro and in-vivo experiments, we could verify the feasibility of the proposed intravascular therapeutic microrobot.
수용성 희생층을 활용한 태양전지용 다결정 실리콘 멤브레인 제조
강세미(Semi Kang),권정규(Jungkyu Kwon),정창훈(Changhoon Jeong),모성인(Sung-In Mo),오준호(Joon-Ho Oh),유상우(Sangwoo Ryu) 한국세라믹학회 2022 세라미스트 Vol.25 No.1
During the fabrication of crystalline silicon solar cells, kerf-loss caused by the wire-sawing of silicon ingots to produce thin wafers inevitably limits the reduction of electricity production cost. To avoid the kerf- loss, direct growth of crystalline silicon wafers of 50-150 μm with a porous separation layer that can be mechanically broken during the exfoliation process, has been widely investigated. However, several issues including flattening of the surface after the exfoliation remain unsolved. In this work an alternative method that utilizes a water-soluble Sr3Al2O6 (SAO) sacrificial layer inserted between the mother substrate and the grown crystalline silicon layers is introduced. Polycrystalline silicon layers were grown on SAO/Si by plasma- enhanced CVD process and silicon membranes could be successfully obtained after the dissolution of SAO in the water. Same process could be applied to obtain flexible amorphous silicon membranes. Further research is being conducted to increase the size of the exfoliated wafer, which expects to reduce the production cost of crystalline silicon solar cells effectively.