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Influence of Mg Flux on the Photoelectrochemical Properties of p-Type GaN for Hydrogen Production
Bae, Hyojung,Kim, Eunsook,Park, Jun-Beom,Fujii, Katsushi,Lee, Sanghyun,Lee, Hyo-Jong,Ryu, Sang-Wan,Lee, June Key,Ha, Jun-Seok American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10
<P>This study investigates the effects of the doping flux of magnesium (Mg) on the photoelectrochemical (PEC) properties of p-type GaN. The Mg-doped GaN samples were deposited directly on c-plane Al2O3 substrates by metalorganic chemical vapor deposition (MOCVD). The Mg flux during growth was controlled by a mass flow controller at flows of 50, 100, 200, and 500 sccm. Optical property analysis revealed band-gaps for the films between 3.2 eV and 3.4 eV. The PEC properties of the films were examined by potentiostat with a three-electrode configuration. The photocurrent density of the 200 sccm sample was the highest, which would be attributed to vacancies or other intrinsic defects, such as interstitials and antisites, giving n-type conductivity.</P>
Hydrothermal Synthesis of CaMn2O4·xH2O Nanorods as Co-Catalysts on GaN Nanowire Photoanode
Bae Hyojung,Kim Hyunggu,Burungale Vishal,Min Jung‐Wook,Cha An‐na,Rho Hokyun,Ryu Sang‐Wan,Kang Soon Hyung,Ha Jun‐Seok 대한화학회 2021 Bulletin of the Korean Chemical Society Vol.42 No.6
Co-catalysts play a crucial role in photoelectrochemical (PEC) water splitting reactions by improving slow kinetics and reducing surface recombination, thereby enhancing PEC performance. However, achieving a well-defined interface between low-dimensional semiconductors and co-catalysts is challenging due to difficulties in depositing a uniform co-catalyst layer and attaining mixed and disordered states. CaMn2O4 xH2O has been extensively studied for the purpose of decreasing the overpotential in the oxygen evolution reaction. In this study, CaMn2O4xH2O was synthesized via a hydrothermal method, and loaded onto a GaN nanowire (NW) photoanode. Optimized CaMn2O4xH2O layers were decorated on GaN NWs to create CaMn2O4@GaN, which delivered a maximum photocurrent of 0.4 mA/cm2 at 0 V vs. the Ag/AgCl reference electrode under an AM 1.5 G solar simulator, 1.6-fold higher than that (0.25 mA/cm2) of bare GaN NWs. Thus, highly efficient and stable PEC water splitting was achieved on the GaN NW photoanode.
Bae, Hyojung,Rho, Hokyun,Min, Jung-Wook,Lee, Yong-Tak,Lee, Sang Hyun,Fujii, Katsushi,Lee, Hyo-Jong,Ha, Jun-Seok Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.422 No.-
<P><B>Abstract</B></P> <P>Gallium nitride (GaN) nanowires are one of the most promising photoelectrode materials due to their high stability in acidic and basic electrolytes, and tunable band edge potentials. In this study, GaN nanowire arrays (GaN NWs) were prepared by molecular beam epitaxy (MBE); their large surface area enhanced the solar to hydrogen conversion efficiency. More significantly, graphene was grown by chemical vapor deposition (CVD), which enhanced the electron transfer between NWs for water splitting and protected the GaN NW surface. Structural characterizations of the prepared composite were performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocurrent density of Gr/GaN NWs exhibited a two-fold increase over pristine GaN NWs and sustained water splitting up to 70min. These improvements may accelerate possible applications for hydrogen generation with high solar to hydrogen conversion efficiency.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Pristine GaN NWs were grown on n-type Si (111) substrates using radio-frequency plasma-assisted MBE. </LI> <LI> The graphene grown by CVD was coated on surface of GaN nanowires (Gr/GaN NWs). </LI> <LI> The photoelectrochemical properties of these structures were investigated. </LI> <LI> The saturated photocurrent density increased in Gr/GaN NWs than ref GaN NWs. </LI> <LI> We reported the reason for this difference. </LI> </UL> </P>
Bae, Hyojung,Park, Seung Hwan,Nakamura, Akihiro,Koike, Kayo,Fujii, Katsushi,Park, Hyung-Jo,Lee, Hyo-Jong,Oh, Tae-Sung,Ha, Jun-Seok The Electrochemical Society 2013 Journal of the Electrochemical Society Vol.160 No.11
<P>The effects of annealing with H<SUB>2</SUB> and N<SUB>2</SUB> on the photoelectrochemical (PEC) properties of annealed Nb-doped TiO<SUB>2</SUB> (ann-TNO) film were investigated. The photocurrent density of the ann-TNO film was 2 to 3 orders of magnitude higher than that of u-TiO<SUB>2</SUB> film. To understand this phenomenon, ann-TNO film was investigated by comparing u-TiO<SUB>2</SUB> and Nb-doped TiO<SUB>2</SUB> (TNO) films. An investigation was conducted using Hall effect estimation, photoluminescence (PL) analysis, and band-gap calculation.</P>
Bae, Hyojung,Kim, Haseong,Ju, Jin-Woo,Jeon, Dae-Woo,Ryu, Sang-Wan,Moon, Youngboo,Ha, Jun-Seok The Electrochemical Society 2019 Journal of the Electrochemical Society Vol.166 No.4
<P>Photoelectrochemical (PEC) characteristics of GaN grown by hydride vapor-phase epitaxy (HVPE) with different polarizations were studied and compared. The polar GaN used a (0001)-oriented plane and the semipolar GaN used a (20-21)-oriented plane. The photocurrent density of polar GaN exhibited a two-fold increase over that of semipolar GaN. Bulk GaN sustained water splitting up to 400 h at 0 V versus the reference electrode. To the best of our knowledge, this is the highest value reported for PEC water-splitting stability. This demonstrates the potential of GaN thin films grown by HVPE for application in large-scale solar-fuel conversion.</P>
YAG:Ce<SUP>3+</SUP>@ beta-SiALON 형광체를 이용한 InGaN 광전극의 효과적인 물분해
배효정(Hyojung Bae),이대장(Daejang Lee),차안나(An-Na Cha),주진우(Jin-Woo Ju),문영부(Youngboo Moon),하준석(Jun-Seok Ha) 한국태양광발전학회 2020 Current Photovoltaic Research Vol.8 No.2
GaN based photoelectrode has shown good potential owing to its better chemical stability and tunable bandgap with materials such as InN and AlN. Tunable bandgap allows GaN to make the maximum utilization of solar spectrum, which could improve photoelectrode performance. However, the problems about low photoelectrode performance and photo-corrosion still remain. In this study, we attempt to investigate the photoelectrochemical (PEC) properties of phosphor application to InGaN photoelectrode. Experimental result shows YAG:Ce<SUP>3+</SUP> and beta-SiALON phosphor result in the highest photoelectrode performance of InGaN.
복합환승센터 주변 가로의 보행·자전거 중심 정비에 따른 접근성 변화 분석에 관한 연구
배효정(BAE, Hyojung),엄홍민(EOM, Hongmin),서민호(SEO, Minho) 한국도시설계학회 2014 도시설계 : 한국도시설계학회지 Vol.15 No.5
복합환승센터는 교통수단간 환승연계시설과 상업·업무·문화시설을 복합하는 계획개념으로 역세권 정비를 촉진할 수 있는 새로운 대안이다. 그러나 대형 상업시설 입점과 승용차 중심 주변 가로 정비에 따른 상권 빨대효과와 이용자 접근성 저하가 우려되고 있다. 본 연구에서는 복합환승센터 주변의 보행?자전거 중심 가로 정비가 이용자 접근성에 어떤 변화를 가져올 수 있는지 분석하여 정책 개선대안을 모색하고자 하였다. 동대구역을 대상으로 보행·자전거 중심의 네트워크와 가로 정비 대안을 상정하고 통행수단별 이동경로 및 시간, 직접 연결도 등 접근수준, 이용자 분포가 어떻게 변화하는지 GIS를 통해 분석하였다. 분석 결과, 10분 이동권역 내 보행 접근성은 33.6%, 자전거 접근성은 29%, 가로 직결도는 15.7% 증가하였으며, 보행 및 자전거 이용자는 11~91% 증가할 수 있는 것으로 추정되었다. 따라서 복합환승센터 구축 시 주변 가로를 보행·자전거 중심으로 동시에 정비하는 패키지형 정책을 추진하여 복합환승센터의 보행·자전거 접근성 제고와 이용자 증대는 물론, 주변 상권 활성화를 도모하는 노력이 필요할 것으로 판단된다. Transit centers, transport hubs that gather transit facilities and commercial, business, and cultural facilities, are a new TOD development alternative. However, large commercial complexes and car-dominated streets are threatening user accessibility and bringing the straw effect to local commerce. This research aims to propose a street refurbishment plan for the transit center development near East Daegu Station to promote walking and cycling, and to measure its impact on accessibility levels. Pedestrian and bicycle networks are built and a street refurbishment plan is postulated. GIS is used for analyzing networks, travel time, and accessibility levels, such as directiveness and number of users. Under the refurbishment plan, pedestrian accessibility increases by 33.6% for 10-minute travel, bicycle accessibility by 29%, and route directiveness by 15.7%. The number of pedestrians and bicycle users increases by 11-91%. In order to improve accessibility, we argue that it is necessary to establish a transit center development plan, including a street refurbishment plan for walking and cycling.
Minjeong Lee(Minjeong Lee),Hyojung Bae(Hyojung Bae),Hokyun Rho(Hokyun Rho),Vishal Burungale(Vishal Burungale ),Pratik Mane(Pratik Mane ),Chaewon Seong(Chaewon Seong),Jun-Seok Ha(Jun-Seok Ha) 한국마이크로전자및패키징학회 2020 마이크로전자 및 패키징학회지 Vol.27 No.4
The Cu/Cu2O/CuO photoelectrode has been successfully fabricated by Rapid Thermal Annealing technique. The structural characterization of fabricated photoelectrode was performed using X-Ray diffraction, while elemental composition of the prepared material has been checked with X-Ray Photoelectron Spectroscopy. The synthesis parameters are optimized on the basis of photoelectrochemical performance. The best photoelectrochemical performance has been observed for the Cu/Cu2O/CuO photoelectrode fabricated at 550 ℃ oxidation temperature and oxidation time of 50 seconds with highest photocurrent density of -3 mA/㎠ at -0.13 V vs. RHE.
HyoJung Kim,SooYeop Kim,Hongjae Lee,Michael Cardinale,SeungJoo Choi,Yongtae Shin,Jong-Bae Kim 보안공학연구지원센터 2016 International Journal of Software Engineering and Vol.10 No.10
This plan explores the marketing potential for the use of Big Data along with visual analytics in neonatal intensive care units. The goal of this technology is to provide more efficient and streamlined data collection and display methods for an extremely vulnerable segment of the population. The applicability of this technology is explored through various business models which address the short, medium, and long term marketing goals, such as SWOT, TOWS, and a Strategic Road Map. The results provide strong support for potential market application in Korea as well as abroad.
정치적 이념에 따른 트위터 공간에서의 집단 간 의견차이 분석
정효정(Hyojung Jung),배정환(Junghwan Bae),홍수린(Sulyn Hong),박찬웅(Chanung Park),송민(Min Song) 한국언론학회 2016 한국언론학보 Vol.60 No.2
In this study, we examine the differences in public opinion posts of Twitter users including a mention on “Sewol ferry accident” in various political stances. We assume the selective exposure theory which states that a connection in Twitter is built between two users who shares similar political stance and the aggregation of all connections constructs a homogeneous network. Besides, twitter users may use the same term in different meaning and context according to their political stances. We apply social network analysis to identify user communities according to political stances and to evaluate the impact of the main players in each community by examining the frequent terms used in the communities. This results in not only structural implications but also semantic implications induced from the different opinions shown across homogeneous networks. Our results show the usefulness of the differences between online groups using network analysis method considering both structural and semantic perspectives. This study is expected to detect different political communities and to become a foundation of semantic network analysis.