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Yang, Wooseok,Lee, Seungmin,Kwon, Hyeok-Chan,Tan, Jeiwan,Lee, Hyungsoo,Park, Jaemin,Oh, Yunjung,Choi, Hyunyong,Moon, Jooho American Chemical Society 2018 ACS NANO Vol.12 No.11
<P>Solar-energy conversion by photoelectrochemical (PEC) devices is driven by the separation and transfer of photogenerated charge carriers. Thus, understanding carrier dynamics in a PEC device is essential to realizing efficient solar-energy conversion. Here, we investigate time-resolved carrier dynamics in emerging low-cost Sb<SUB>2</SUB>Se<SUB>3</SUB> nanostructure photocathodes for PEC water splitting. Using terahertz spectroscopy, we observed an initial mobility loss within tens of picoseconds due to carrier localization and attributed the origin of carrier localization to the rich surface of Sb<SUB>2</SUB>Se<SUB>3</SUB> nanostructures. In addition, a possible recombination at the interface between Sb<SUB>2</SUB>Se<SUB>3</SUB> and the back contact is elucidated by time-resolved photoluminescence analysis. We also demonstrated the dual role of the RuO<SUB><I>x</I></SUB> co-catalyst in reducing surface recombination and enhancing charge transfer in full devices using intensity-modulated spectroscopy. The relatively low onset potential of the Sb<SUB>2</SUB>Se<SUB>3</SUB> photocathode is attributed to the sluggish charge transfer at a low applied bias rather than to fast surface recombination. We believe that our insights on carrier dynamics would be an important step toward achieving highly efficient Sb<SUB>2</SUB>Se<SUB>3</SUB> photocathodes.</P> [FIG OMISSION]</BR>
Rapid advances in antimony triselenide photocathodes for solar hydrogen generation
Yang, Wooseok,Moon, Jooho The Royal Society of Chemistry 2019 Journal of materials chemistry. A, Materials for e Vol.7 No.36
<P>One of the paramount challenges for realizing practical solar hydrogen production is the development of a low-cost semiconductor that is suitable for large-area and high-performance photoelectrochemical devices. Antimony triselenide (Sb2Se3) has emerged as a nearly ideal semiconductor material that satisfies nearly all requirements for effectively generating hydrogen using solar energy. In this report, we highlight the extraordinary characteristics of Sb2Se3 relative to the myriad of other emerging semiconductors, in terms of cost, band gap, optoelectronic properties, photocorrosion stability, and processability. Additionally, we discuss recent studies on Sb2Se3 photocathodes with a focus on their intrinsic properties, use of co-catalysts, and top and bottom interface engineering for enhanced performance. Unresolved issues and future research directions will also be discussed briefly. We believe that the rapid advances in Sb2Se3-photocathode water splitting over the past three years suggest a positive outlook for the cost-effective production of solar hydrogen.</P>
Yang, Wooseok,Oh, Yunjung,Kim, Jimin,Kim, Hyunchul,Shin, Hyunjung,Moon, Jooho American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.1
<P>Although copper-based chalcopyrite materials such as CuInS2 have been considered promising photocathodes for solar water splitting, the fabrication route for a nanostructure with vertical orientation has not yet been developed. Here, a fabrication route for vertically aligned CuInS2 nanorod arrays from an aqueous solution using anodic aluminum oxide template-assisted growth and transfer is presented. The nanorods exhibit a phase-pure CuInS2 chalcopyrite structure and cathodic photocurrent response without co-catalyst loading. Small particles of CdS and ZnS were conformally decorated onto CuInS2 nanorods using a successive ion layer adsorption and reaction method. With surface modification of CdS/ZnS, the photoelectrochemical properties of CuInS2 nanorod arrays are enhanced via flat-band potential shift, as determined by analyses of onset potential and Mott-Schottky plots.</P>
GaN-HEMT를 이용한 X-대역 이단 전력증폭기 설계
이우석(Wooseok Lee),이휘섭(Hwiseob Lee),박승국(Seungkuk Park),임원섭(Wonseob Lim),한재경(Jaekyoung Han),박광근(Kwanggun Park),양영구(Youngoo Yang) 한국전자파학회 2016 한국전자파학회논문지 Vol.27 No.1
본 논문에서는 GaN-HEMT를 이용하여 X-대역에서 동작하는 이단으로 구성된 전력증폭기를 설계 및 제작하였다. 높은 전력 이득을 얻기 위해 간단한 구조의 중간 단 정합 네트워크를 통해 이단으로 구성하였다. 3D EM 시뮬레이션을 통하여 본드와이어 인덕턴스와 기생 캐패시턴스를 예측하였다. 본드와이어 인덕턴스를 줄임으로써 정합 네트워크의 Q(quality-factor)를 최소화하여 대역 특성을 향상시켰다. 제작된 전력증폭기는 40 V의 동작 전압을 인가하였으며, 8.1~8.5GHz에서 16 dB 이상의 전력 이득, 42.5 dBm 이상의 출력 전력, 35 % 이상의 효율 특성을 나타냈다. This paper presents an X-band two-stage power amplifier using GaN-HEMT. Two-stage structure was adopted to take its high gain and simple inter-stage matching network. Based on a 3D EM simulation, the bond-wire inductance and the parasitic capacitance were predicted. By reducing bond-wire inductance, Q of the matching network is decreased and the bandwidth is improved. The implemented two-stage PA shows a power gain of more than 16 dB, saturated output power of more than 42.5 dBm, and a efficiency of more than 35 % in frequency range of 8.1~8.5 GHz with an operating voltage of 40 V.
음향산란이론모델을 이용한 살오징어(Todarodes pacifica)의 음향후방산란강도 측정
양희승(HeeSeung YANG),김민수(MinSoo KIM),오우석(WooSeok OH),이경훈(KyoungHoon LEE) 전남대학교 어업기술연구소 2021 어업기술연구소보고지 Vol.14 No.1
Recently, Japenese common squid, an important fisheries resource, has been decreased in the coastal waters of Korea. The purpose of this study is to estimate the TS of Japanese common squid and to use it as basic data to figure out the exact amount of resources of Japanese common squid. In order to estimate the TS, the total length and mantle length of 26 common squids were measured and photographed. The samples photographed were digitized and applied to the DWBA theoretical model. In the shortest mantle length No. 10 sample, the range of acoustic backscattering target strength for each frequency was measured –101.4 dB∼–55.9 dB at 38 kHz, –91.9 dB∼–57.1 dB at 70 kHz, –99.8 dB∼–56.2 dB at 120 kHz. The acoustic scattering strength range of No. 21 sample with the longest mantle length was measured –98.44 dB∼–55.3 dB at 38 kHz, –84.9 dB∼–53.8 dB at 70 kHz, and –89.5 dB ∼–51.5 dB at 120 kHz. The TS regression equations for common squid at each frequency was as follows; 38kHzMax = 20log10(ML) - 71.5, 38 kHzAvg = 20log10(ML) – 81.5, 70kHzMax = 210log10(ML) – 76.9, 70kHzAvg. 20log10(ML) - 82.8, 120kHzMax = 20log10(ML) – 75.6, 120kHzAvg = 20log10(ML) – 83.0