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Jeong, Jaehun,Choi, Yoon-Ho,Jeong, Kwangsik,Park, Hanbum,Kim, Dasol,Cho, Mann-Ho American Physical Society 2018 Physical Review B Vol.97 No.7
<P>The dependence of the optical and electrical properties of two-dimensional transition metal dichalcogenides on the number of layers has garnered significant interest. In particular, the indirect-to-direct band gap transition and the resulting changes, such as improved quantum yield, have been widely studied. However, an experimental investigation of the dependence of the optical transition for a wide range of photon energies is still lacking. Here, we report the broadband optical response of large-area MoSe2 grown from monolayer to pentalayer thicknesses by molecular beam epitaxy, for photon energies in the 0.9-5.5 eV range. We observed a dramatic evolution of the absorption spectrum that depends on the number of layers. Using the density functional theory, we show that this feature is related to a change in the energy and geometric shape of the band structure at the. point in the Brillouin zone. The dependence of these optical properties on the number of layers yields insights into the underlying physics and is promising for photonic and optoelectronic applications.</P>
정광식(Jeong, Kwangsik),민성훈(Min, Seonghun) 도시정책학회 2017 도시정책학회 학술대회 Vol.2017 No.3
This study is about real-estate crowdfunding what recently becomes a magnet for both investors and the company in need of funding support. In terms of a life cycle of company, it could be classified with a few stages from its beginning to extinction. It is surprise to know that less than 15 percent of the company could move on to the growth phase within 3 years. What is the reason that 85 percent of the company go broke? For those reasons, despite its short existence, Crowdfunding has been issued in domestic and abroad in comparison with existing financial system in Korea. This research aims to study quality of crowdfunding, and seek applicability and look for improvement point when crowdfunding a Lending and crowdfunding a Equity applying for real estate, and the consequential research on consumer protection.
Kim, Tae-Hyeon,Jeong, KwangSik,Park, Byung Cheol,Choi, Hyejin,Park, Sang Han,Jung, Seonghoon,Park, Jaehun,Jeong, Kwang-Ho,Kim, Jeong Won,Kim, Jae Hoon,Cho, Mann-Ho The Royal Society of Chemistry 2016 Nanoscale Vol.8 No.2
<P>In a three-dimensional topological insulator Bi2Se3, a stress control for band gap manipulation was predicted but no systematic investigation has been performed yet due to the requirement of large external stress. We report herein on the strain-dependent results for Bi2Se3 films of various thicknesses that are grown via a self-organized ordering process. Using small angle X-ray scattering and Raman spectroscopy, the changes of d-spacings in the crystal structure and phonon vibration shifts resulted from stress are clearly observed when the film thickness is below ten quintuple layers. From the UV photoemission/inverse photoemission spectroscopy (UPS/IPES) results and ab initio calculations, significant changes of the Fermi level and band gap were observed. The deformed band structure also exhibits a Van Hove singularity at specific energies in the UV absorption experiment and ab initio calculations. Our results, including the synthesis of a strained ultrathin topological insulator, suggest a new direction for electronic and spintronic applications for the future.</P>
Effect of the Thermal Conductivity on Resistive Switching in GeTe and Ge2Sb2Te5 Nanowires.
Park, Sungjin,Park, Dambi,Jeong, Kwangsik,Kim, Taeok,Park, SeungJong,Ahn, Min,Yang, Won Jun,Han, Jeong Hwa,Jeong, Hong Sik,Jeon, Seong Gi,Song, Jae Yong,Cho, Mann-Ho American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.39
<P>The thermal conduction characteristics of GeTe and Ge2Sb2Te5(GST) nanowires were investigated using an optical method to determine the local temperature by Raman spectroscopy. Since the localization of surface charge in a single-crystalline nanostructure can enhance charge-phonon scattering, the thermal conductivity value (관) of single crystalline GeTe and GST nanowires was decreased significantly to 1.44 Wm(-1) K(-1) for GeTe and 1.13 Wm(-1) K(-1) for GST, compared to reported values for polycrystalline structures. The SET-to-RESET state in single-crystalline GeTe and GST nanowires are characteristic of a memory device. Unlike previous reports using GeTe and GST nanowires, the SET-to-RESET characteristics showed a bipolar switching shape and no unipolar switching. In addition, after multiple cycles of operation, a significant change in morphology and composition was observed without any structural phase transition, indicating that atoms migrate toward the cathode or anode, depending on their electronegativities. This change caused by a field effect indicates that the structural phase transition does not occur in the case of GeTe and GST nanowires with a significantly lowered thermal conductivity and stable crystalline structure. Finally, the formation of voids and hillocks as the result of the electromigration critically degrades device reliability.</P>
정종덕(Jongduck Jeong),류연경(YeonKyung Ryoo),김재현(Jaehyun Kim),김성석(Sungsuk Kim),정광식(Kwangsik Chung) 한국정보기술학회 2021 Proceedings of KIIT Conference Vol.2021 No.11
미세먼지에 대한 관심이 커지면서, 어린이나 청소년이 오래 머무르는 학교 내외의 미세먼지 예측 시스템 개발이 진행되고 있다. 본 논문에서는 여러 학교에서 수집한 다양한 빅데이터의 특성을 파악하여, 추후 분석 시스템 개발과정에서 중요한 고려요소를 얻고자 하였다. 모든 학교를 대상으로 데이터를 수집하는 것이 곤란하므로, 공공 데이터인 AirKorea와의 비교를 통해 학교 미세먼지의 특성을 분석해보았다. As interests in find dust grows, the development of a fine dust prediction system indoor/outdoor the school where children and adolescents stay for a long time is underway. In this paper, we identify the characteristics of various big data collected from various schools and want to get important considerations in analysis system development process. Since it is difficult to collect data for all schools, the characteristics of school fine dust were analyzed through comparison with AirKorea, a public data.
농업용 저수지의 하한 저수율에 따른 홍수기 무효방류량 저감 방안 고찰
정지연 ( Jiyeon Jeong ),정민혁 ( Minhyuk Jeung ),범진아 ( Jina Beom ),박민경 ( Minkyeong Park ),윤광식 ( Kwangsik Yoon ) 한국농공학회 2022 한국농공학회 학술대회초록집 Vol.2022 No.-
우리나라 대규모 농업용 저수지는 홍수기에 대비한 상한 저수율을 규정되어 있지만, 하한 저수율에 관한 규정은 부재한 상태로 운영되고 있다. 영산강유역 내 최대 유효저수량을 보유하고 있는 나주호는 장마철 홍수기인 6월 21일부터 9월 20일까지 총 92일 동안 제한 수위를 초과하는 수량은 여수로를 통해 무효방류하도록 규정되어 있다. 수자원을 효율적으로 활용하기 위해서는 저수지의 운영을 저해하지 않는 범위 내에서 무효방류량을 최소화하는 방안이 필요하다. 본 연구에서는 2008년부터 2020년의 기간 동안 나주호의 물수지 분석을 수행하고, 나주호의 하한 저수율 설정 시나리오(30%, 35%, 40%)에 따른 무효방류량 변화를 평가하고자 한다. 영농기 초기저수율에 따른 하한 저수율 설정을 통해 농업용수 공급을 모의하였으며, 홍수기 관리규정에 따라 무효방류 모의를 진행하였다. 시나리오별 공급량과 무효방류량 분석 결과, 영농기 초기저수율이 60% 이상일 때 하한저수율을 30%로 관리하는 것이 연구기간 동안 농업용수 공급량은 증가하고 무효방류량은 감소하는 결과를 보였다.