Enhanced Photosensitivity in Monolayer MoS₂ with PbS Quantum Dots

Sangeun Cho,Yongcheol Jo,Hyeonseok Woo,Jongmin Kim,Jungwon Kwak,Hyungsang Kim,Hyunsik Im 한국진공학회(ASCT) 2017 Applied Science and Convergence Technology Vol.26 No.3

Enhanced Photosensitivity in Monolayer MoS₂ with PbS Quantum Dots

Cho, Sangeun,Jo, Yongcheol,Woo, Hyeonseok,Kim, Jongmin,Kwak, Jungwon,Kim, Hyungsang,Im, Hyunsik The Korean Vacuum Society 2017 Applied Science and Convergence Technology Vol.26 No.3

Photocurrent enhancement has been investigated in monolayer (1L) $MoS_2$ with PbS quantum dots (QDs). A metal-semiconductor-metal (Au-1L $MoS_2$-Au) junction device is fabricated using a standard photolithography method. Considerably improved photo-electrical properties are obtained by coating PbS QDs on the Au-1L $MoS_2$-Au device. Time dependent photoconductivity and current-voltage characteristics are investigated. For the QDs-coated $MoS_2$ device, it is observed that the photocurrent is considerably enhanced and the decay life time becomes longer. We propose that carriers in QDs are excited and transferred to the $MoS_2$ channel under light illumination, improving the photocurrent of the 1L $MoS_2$ channel. Our experimental findings suggest that two-dimensional layered semiconductor materials combined with QDs could be used as building blocks for highly-sensitive optoelectronic detectors including radiation sensors.

페로브스카이트 CsPbX₃ Quantum dots 을 이용한 방사선 & 광 발광 특성 분석

Sangeun Cho,Sungwoo Kim,Jungwon Kwak,Ilhwan Ryu,Jongmin Kim,Yongcheol Jo,Jiwoo Seo,Samkyu Noh,Jaejoon Lee,Hyungsang Kim,Hyunsik Im 한국진공학회 2018 한국진공학회 학술발표회초록집 Vol.2018 No.8

Optimizing nanosheet nickel cobalt oxide as an anode material for bifunctional electrochemical energy storage and oxygen electrocatalysis

Cho, Sangeun,Lee, Seongwoo,Hou, Bo,Kim, Jongmin,Jo, Yongcheol,Woo, Hyeonseok,Pawar, Sambhaji M.,Inamdar, Akbar I.,Park, Youngsin,Cha, SeungNam,Kim, Hyungsang,Im, Hyunsik Pergamon Press 2018 Electrochimica Acta Vol. No.

<P><B>Abstract</B></P> <P>Mesoporous Ni-Co oxide (NCO) nanosheet electrodes are fabricated on Ni foam via an electrodeposition technique. Their bifunctional activities for electrochemical energy storage and electro-catalysis for water splitting in strong alkaline media are optimized by varying the ratio of concentrations of the Ni and Co precursors. The ratio-based changes vary the pore size of the NCO nanosheets between 92.5 and 200 nm, and structural analyses reveal that the electrode films have a spinel NiCo<SUB>2</SUB>O<SUB>4</SUB> structure. The obtained specific capacitance varies dramatically between 613 and 2704 Fg<SUP>−1</SUP> at 2 mA cm<SUP>−2</SUP>, with good capacity retention (80–90%) after 2000 cycles. The NCO nanosheet electrodes also exhibit a good oxygen evolution reaction at the surface. The lowest overpotential (315 mV at 10 mA cm<SUP>−2</SUP>) is obtained with a Tafel slope of 59 mV dec<SUP>−1</SUP>. The observed bifunctional activities of the new NCO nanosheet electrode are superior to those of nanostructured NCO electrodes prepared via hydrothermal and SILAR methods. The analyses regarding the electrochemically active surface area and electrochemical impedance spectroscopy, together with the observed electrochemical performance, reveal that the most-optimized Ni and Co composition produces the synergetic effects of an electrochemically active surface area and great stability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mesoporous Ni-Co oxide (NCO) nanosheet electrodes are fabricated on Ni foam via an electrodeposition technique. </LI> <LI> Excellent specific capacitance and electrochemical stability are obtained. </LI> <LI> The overpotential of 315 mV at 10 mA cm<SUP>−2</SUP> is obtained with a Tafel slope of 59 mV dec<SUP>−1</SUP>. </LI> </UL> </P>

Bendable RuO₂/graphene thin film for fully flexible supercapacitor electrodes with superior stability

Cho, Sangeun,Kim, Jongmin,Jo, Yongcheol,Ahmed, Abu Talha Aqueel,Chavan, H.S.,Woo, Hyeonseok,Inamdar, A.I.,Gunjakar, J.L.,Pawar, S.M.,Park, Youngsin,Kim, Hyungsang,Im, Hyunsik ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.725 No.-

<P><B>Abstract</B></P> <P>Ruthenium oxide (RuO<SUB>2</SUB>) is fabricated on graphene (Gr)-coated Copper (Cu) foil by using a cathodic electroplating technique for flexible supercapacitor electrode applications. The electrochemical properties of the RuO<SUB>2</SUB>/Gr/Cu electrode are investigated with a conventional three electrode configuration in 0.5 M H<SUB>2</SUB>SO<SUB>4</SUB> electrolyte. The graphene insertion layer plays a key role in improving the structural and electrochemical properties of the RuO<SUB>2</SUB> electrode film under the bent condition. The electrode exhibits a specific capacitance of 1561 F g<SUP>−1</SUP> (0.015 F cm<SUP>−1</SUP>) at a scan rate of 5 mV s<SUP>−1</SUP> and a significantly improved retention of 98% under the bent condition. The flexible RuO<SUB>2</SUB>/Gr/Cu electrode exhibits a high energy density of ∼13 Wh kg<SUP>−1</SUP> at a power density of ∼21 kW kg<SUP>−1</SUP>. The excellent capacitance retention and electrochemical stability of the flexible RuO<SUB>2</SUB>/Gr/Cu electrode are due to the improved mechanical adhesion between the RuO<SUB>2</SUB> and the current collector. This flexible RuO<SUB>2</SUB>/Gr/Cu film could be used as a supercapacitor electrode with a high capacity and long-cycle life for the next-generation flexible electronic applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A binder-free Bendable RuO<SUB>2</SUB> thin film is fabricated on a graphene/Cu substrate using an electroplating method. </LI> <LI> Electrochemical energy storage properties of RuO<SUB>2</SUB> are investigated for supercapacitor applications. </LI> <LI> Excellent capacitance retention and electrochemical stability are obtained. </LI> </UL> </P>

Photosensitivity of bulk and monolayer MoS2-based two-terminal devices

Cho Sangeun,Park Wooyoung,Im Hyunsik,김형상 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.5

Transition metal dichalcogenides (TMDCs), such as MoS2, MoSe2, WS2, and WSe2, have attracted enormous attention owing to their unique electrical and optical properties. A type of material known as TMDC has the MX2 formula with a direct bandgap in ultra-thin layers and indirect bandgap properties in the bulk. TMDCs have attracted significant research interest due to their use in nano-devices, opto-electronics, and next-generation electronics. In the study, two different MoS2 devices, Au–bulk MoS2–Au and Au–monolayer MoS2–Au, were fabricated, and their photon-induced current–voltage characteristics at different wavelengths (red ≈ 650 nm, green ≈ 532 nm and blue ≈ 450 nm) and values were compared. Additionally, the time-dependent photoresponses of these devices under red light irradiation (wavelength, λex = 650 nm) were analyzed. The Au–monolayer MoS2–Au device had a higher current response compared with the Au–bulk MoS2–Au device. These results suggest that single-layer MoS2 devices could be more efficient and responsive than bulk MoS2 devices for a variety of applications.

Distinctive Spectroscopic Characteristics Observed in Colloidal Perovskite CsPbBr₃ Quantum Dot

Sangeun Cho,Sam Kyu Noh,Hyungsang Kim,Hyunsik Im 한국진공학회(ASCT) 2021 Applied Science and Convergence Technology Vol.30 No.4

Distinctive spectroscopic characteristics are observed in colloidal perovskite CsPbBr₃ quantum dot (QD) dispersed in octane doped with PPO. As the content of CsPbBr₃-QD increases, the emission and the absorption energies decrease due to QD-cluster formed in case of the inter-QD distance smaller than diameter of QD. Spectroscopic evidences supporting QD-cluster are found in the Urbach energy and the carrier lifetime. Unusual absorption lines showing explicit QD dependence are observed in Fourier-transform infrared spectra, which is explained by vibrational modes of bound PPO hybridized with CsPbBr₃-QD.

국제기능장애건강분류틀(ICF)에 기반한 노년기 건강과 다차원적 장애: 지지환경의 조절효과를 중심으로

조상은(Cho, Sangeun) 한국웰니스학회 2020 한국웰니스학회지 Vol.15 No.1

본 연구에서는 2014년도 노인실태조사를 활용하여 65세 이상 노인 10,451명을 대상으로 만성질환이 심리 · 정서기능, 일상활동수행능력, 사회참여빈도의 세 영역으로 구성된 다차원적 장애에 미치는 영향, 공식 · 비공식 지지환경이 다차원적 장애에 미치는 영향, 공식 · 비공식 지지환경의 조절효과를 살펴보고자 하였다. 위의 관계를 확인하기 위해 구조방정식 모델(Structural equation modeling; SEM)을 활용했고 상호작용항을 생성하여 조절효과를 확인하였다. 연구결과는 첫째, 노인이 보유한 만성질환 수가 증가할수록 노인의 심리 · 정서기능, 일상활동 수행능력, 사회참여빈도는 낮아졌다. 둘째, 공식적 지지환경이 긍정적일수록 노인의 심리 · 정서기능과 사회참여빈도는 증가하였고, 긍정적인 비공식적 지지환경은 심리 · 정서기능과 일상활동 수행능력, 사회참여빈도에 긍정적인 영향을 미쳤다. 셋째, 공식적 지지환경은 만성질환과 심리 · 정서기능 간 관계를 완화하는 것으로 나타난 반면, 비공식적 지지환경의 조절효과는 유의미한 완충효과를 보이지 않았다. 연구결과를 근거로 노인의 건강수준을 향상시키고 장애수준을 낮출 수 있는 방안과 공식적 · 비공식적 지지환경의 중요성에 관한 실천적 · 정책적 함의를 제시하였다. The purposes of this study are to investigate a) the association between chronic illnesses and multidimensional disability (i.e., psychological/emotional functions (PF), activity capacity for daily movements (A), and participation frequency (P)), b) the association between formal/informal supporting environments and multidimensional disability, and c) the moderating effects of formal/informal supporting environments among older adults in South Korea. A total number of 10,451 older adults aged 65 years or older were selected for the study sample. The 2014 Survey of Living Conditions and Welfare Needs of Korean Older Persons, the nationally representative data, was used for analysis. The results of the study showed that older adults’ chronic illnesses had negative influences on PF, A, and P. Older adults with better formal supporting environment showed better level of PF and P. Better informal supporting environment the older adults had led to higher PF, A, and P. Regarding the moderating effects of the supporting environments, only the formal supporting environment buffered the association between the chronic illnesses and PF. Implications for theory, practice, and policy regarding health, multidimensional disability, and supporting environments among older adults were further addressed.

장애인에 대한 돌봄부담이 가족의 경제활동에 미치는 영향

조상은 ( Cho Sangeun ),오욱찬 ( Oh Ukchan ) 한국사회복지연구회 2021 사회복지연구 Vol.52 No.4

이 논문에서는 장애인에 대한 돌봄부담이 가족의 고용과 노동시간에 영향을 미치는지 확인하고, 돌봄부담과 고용 여부 간 관계와 돌봄부담과 노동시간 간 관계에서 성별에 따른 차이가 있는지 확인하였다. 기존 국외 문헌들을 통해 장애인에 대한 돌봄이 가족돌봄제공자의 고용 여부, 노동시간 등 경제활동에 부정적인 영향을 미치는 것을 확인했으나 이러한 돌봄부담과 가족의 경제활동에 관한 국내 연구는 부족하다. 따라서 이 연구에서는 장애인 부가조사가 실시된 한국복지패널 5개 차수 자료를 활용하여 18∼64세의 근로연령대 비장애인을 대상으로 장애인에 대한 돌봄부담 정도가 경제활동에 미치는 영향을 분석하였다. 연구대상은 최대 13,336명(남성 6,424명, 여성 6,912명)이고 5개 차수의 개인-연도 사례수로는 최대 37,419명이었다. 자료 분석에서는 패널 회귀분석에 하이브리드 방법(hybrid method)을 적용했다. 주요 연구결과를 살펴보면, 첫째, 장애인에 대한 돌봄부담은 남성에 비해 여성이 더 높게 나타났고, 둘째, 기술통계에서 여성은 장애인에 대한 돌봄부담이 높은 경우 돌봄부담이 없는 경우에 비해 고용률과 연간 노동시간이 상당히 낮아 매우 큰 악영향을 받는데, 남성의 경우에는 다소 낮을 뿐 큰 차이를 보이지 않았다. 셋째, 패널 회귀분석 결과 남성은 장애인에 대한 돌봄부담 수준에 따라 고용과 노동시간에 영향을 받지 않는 것으로 나타난 반면, 여성은 장애인에 대한 돌봄부담이 높은 경우 돌봄부담이 없는 경우에 비해 고용률은 6.5%포인트, 연간 노동시간은 364.8시간 적은 것으로 나타났다. 이러한 연구결과를 바탕으로 실천적·정책적 제언을 제시하였다. This study investigated whether care burden of persons with disabilities affected a family’s employment and work hours, and whether the association between care burden and employment and the association between care burden and work hours differed by gender. Existing foreign literature revealed that caring for persons with disabilities negatively affected labor force participation such as employment status and work hours of family caregivers. However, domestic studies on the caregiver’s burden family’s labor force participation were scant. People without a disability aged 18 to 64 participated as a study sample and five waves of the supplementary data for a person with a disability from the Korea Welfare Panel Study were used. The subjects were a maximum of 13,336 people (6,424 male and 6,912 female); in terms of the number of individual-year cases in five waves, they were 37,419 at a maximum size. We applied a hybrid method in conducting panel regression analysis. The findings showed, first, female had a higher burden in caring a person with a disability than male; second, in the descriptive statistics, female had a significantly lower employment rate and annual work hours than those without care burden; however, male did not show much difference. Third, the panel regression analysis showed that the level of care burden for a person with a disability did not affect employment and work hours among male; whereas female with higher care burden had a 6.5% point less employment rate and 364.8 hours less annual work hours than those without any care burden. Based on these results, practical and policy suggestions were presented.

아동특성, 부모특성, 가족특성이 아동의 사회성 발달에 미치는 영향

조상은 ( Sangeun Cho ) 사단법인 아시아문화학술원 2021 인문사회 21 Vol.12 No.4

만 3세에서 8세 기간은 사회성이 발달하고 사회적 행동이 현저히 증가하는 시기이다. 하지만 최근에는 따돌림, 부적응, 은둔형 외톨이 등 낮은 사회성과 관련된 문제들이 낮은 연령대에서도 발생되고 있어 주목이 필요하다. 이에 본 연구에서는 아동의 사회성에 미치는 요인을 아동, 부모, 가족환경 특성으로 구분하고 각 차원이 아동의 사회성에 미치는 영향과 각 차원의 설명력을 실증적으로 확인해보고자 하였다. 전국데이터인 2018 아동종합실태조사 자료를 활용하여 만 3-8세 아동(부모가 대리응답) 1,094명을 대상으로 위계적 회귀분석(hierarchical regression analysis)을 실시하였다. 연구결과를 살펴보면, 아동의 사회성에 아동 특성인 아동의 또래관계가 가장 큰 영향을 미쳤고 부모효능감, 양육스트레스, 가족건강성이 통계적으로 유의미한 영향을 미치는 것으로 나타났다. 연구결과를 토대로 본 연구에서는 아동의 긍정적인 사회성 발달을 위해 아동의 또래관계 증진, 부모효능감 강화, 양육스트레스 해소 지원, 가족건강성 제고를 위한 실천적ㆍ정책적 함의를 제언하였다. Age three to eight is a period where sociability develops and social activities increase. However, recently low sociability-related issues such as bullying, maladaptation, and social withdrawal are happening in lower age. Thus, the present study attempted to investigate the effects of child, parent and home environment factors on sociability and their explanatory power. 2018 National Survey on Child with 1,094 children aged three to eight (parent proxies) and hierarchical regression analysis were used. The findings showed children’s peer relationship was most influential in their sociability; parenting efficacy, parenting stress, and family strengths were statistically associated with children’s sociability. This study recommended practical and policy implications for enhancement of peer relationship, parenting efficacy and family strengths, and alleviation of parenting stress were discussed.