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Pulsed laser depostion (PLD)법으로 증착된 BaTiO₃ / SrTiO₃ 산화물 초격자의 성장 및 유전특성
김주호(Juho Kim),김이준(Leejun Kim),정동근(Donggeun Jung),김용성(Young Sung Kim),이재찬(Jaichan Lee) 한국진공학회(ASCT) 2002 Applied Science and Convergence Technology Vol.11 No.3
BaTiO₃(BTO)/SrTiO₃(STO) 산화물 인공 초격자가 MgO (100) 단결정 기판위에 Pulsed laser deposition(PLD)법으로 증착되었다. 다층구조에서 BTO/STO 층의 적층 주기는 BTO_(1 unit cell)/STO_(1 unit cell)에서 BTO_(125 unit cell)/STO_(125 unit cell) 두께로 변화시켰고 초격자 전체 두께는 100 ㎚으로 고정시켰다. X-ray 회절 결과는 다양한 주기의 BTO/STO 산화물 박막에서 초격자의 특성을 보였고 투과형 전자 현미경을 통해서 BTO와 STO의 두 층간의 계면에서 상호확산이 일어나지 않고 초격자가 잘 성장된 것을 확인하였다. 초격자의 유전율은 임계 두께 내에서 적층주기가 감소함에 따라 증가하였다. 이러한 초격자의 유전율은 낮은 주기 즉 BTO_(2 unit cell)/STO_(2 unit cell)주기에서 1230으로 높게 나왔으며 이러한 원인은 격자 변형(c/a ratio)에 기여된 것으로 분석되었다. Artificial BaTiO₃(BTO)/SrTiO₃(STO) oxide superlattice have been deposited on MgO (100) single crystal substrate by pulsed laser deposition(PLD) method. The stacking periodicity of BTO/STO superlattice structure was varied from BTO_(1 unit cell)/STO_(1 unit cell) to BTO_(125 unit cell)/STO_(125 unit cell) thickness with the total thickness of 100 ㎚. The result of X-ray diffraction showed the characteristics of superlattice in the BTO/STO multilayer structure. we have also confirmed that there was no interdiffusion at the interface between BTO and STO layers by high resolution transmission electron microscopy(HRTEM). The dielectric constant of superlattice increased with decreasing stacking periodicity of the BTO/STO superlattice within the critical thickness. The dielectric constant of the BTO/STO superlattice reached a maximum i.e., 1230 at a stacking perioicity of BTO_(2 unit cell)/STO_(2 unit cell).
정기덕(Jung, Kideok),정주호(Jung, Juho),김민정(Kim, Minjung),조민효(Cho, Rosa Minhyo) 서울행정학회 2017 한국사회와 행정연구 Vol.28 No.2
본 연구는 김영란법의 정책결정과정을 분석하고 정책적 함의를 제시하기 위하여 다중흐름모형과 정책옹호연합모형의 융합모형을 활용하였다. 이를 통해 단일모형의 한계를 극복하고 정책결정 과정을 보다 더 정밀히 분석하고자 하였다. 분석결과 문제·정치·대안의 세 가지 흐름이 확인되었고, 흐름들이 독립적으로 흘러가는 가운데 추친옹호연합과 저지옹호연합 간 세 번의 갈등이 발생하였다. 세월호 침몰사고가 외부충격으로 작용하며 국회에서 계류 중이던 김영란법이 다시 주목받게 되었다. 또한 이완구 국무총리 후보자의 녹취록 공개사건이 내부충격으로 발생하며 정책의 창이 열렸다. 이때 김영란법은 국회 본회의를 통과하였으나 옹호연합들 간 갈등은 계속 이어졌고, 헌법재판소의 합헌 판결 끝에 갈등이 소강되고 김영란법은 계획대로 시행되었다. 이러한 분석결과는 실제 정책결정이 우연한 사건 등을 포함한 다양한 요인들의 상호작용을 통해 매우 복잡하게 이루어지기 때문에 체계적인 분석을 위해서는 하나의 모형에만 의존하기 보다는 다양한 모형들의 적절한 수정 또는 융합이 유용함을 보여준다. The purpose of this paper is to critically analyze the policymaking process of Improper Solicitation and Graft Act, often referred to as the Kim Young-ran Act, and suggest the policy implications. Authors use a combined model of the Advocacy Coalition Framework and the Multiple Streams Framework to overcome the limitations of the single model and examines policy change more precisely. Results show that three flows of problems, politics, and alternatives were confirmed, and conflicts between the advocacy coalition occurred three times while the flows flowed independently. The tragic sinking of ferry Sewol was an external shock and attracted the attention to Kim Young-ran Act, which had been pending in the National Assembly. In addition, revealing the tape-recording case of Prime Minister Lee Wan-koo was an internal shock which opened a window of policy. At this moment, Kim Young-ran Act passed the National Assembly plenary session, however, the conflict between the advocacy alliances continued. After the constitutional decision by Constitutional Court, the conflict was lulled and Kim Young-ran Act was implemented as planned. These findings suggest that proper modification or convergence of policy making model is useful for comprehensive and systematic analysis, rather than relying solely on single model, since the actual policy decisions are made very complex interaction of various factors including accidental events.
Epitaxial van der Waals Contacts between Transition-Metal Dichalcogenide Monolayer Polymorphs
Lee, Chang-Soo,Oh, Seung Jae,Heo, Hoseok,Seo, Seung-Young,Kim, Juho,Kim, Yong Hyeon,Kim, Donghwi,Ngome Okello, Odongo Francis,Shin, Hocheol,Sung, Ji Ho,Choi, Si-Young,Kim, Jun Sung,Kim, Jong Kyu,Jo, M American Chemical Society 2019 Nano letters Vol.19 No.3
<P>We have achieved heteroepitaxial stacking of a van der Waals (<I>vdW</I>) monolayer metal, 1T’-WTe<SUB>2</SUB>, and a semiconductor, 2H-WSe<SUB>2</SUB>, in which a distinctively low contact barrier was established across a clean epitaxial <I>vdW</I> gap. Our epitaxial 1T’-WTe<SUB>2</SUB> films were identified as a semimetal by low temperature transport and showed the robust breakdown current density of 5.0 × 10<SUP>7</SUP> A/cm<SUP>2</SUP>. In comparison with a series of planar metal contacts, our epitaxial <I>vdW</I> contact was identified to possess intrinsic Schottky barrier heights below 100 meV for both electron and hole injections, contributing to superior ambipolar field-effect transistor (FET) characteristics, i.e., higher FET mobilities and higher on-off current ratios at smaller threshold gate voltages. We discuss our observations around the critical roles of the epitaxial <I>vdW</I> heterointerfaces, such as incommensurate stacking sequences and absence of extrinsic interfacial defects that are inaccessible by other contact methods.</P> [FIG OMISSION]</BR>
Convex Optimization-based Entry Guidance for Spaceplane
Juho Bae,Sang-Don Lee,Young-Won Kim,Chang-Hun Lee,Sung-Yug Kim 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.5
This paper aims to propose convex-optimization-based entry guidance for a spaceplane, which has potential in online implementation with less sensitivity to initial guess accuracy while mitigating a high-frequency jittering issue in the entry trajectory optimization problem. To this end, a highly nonlinear, constrained, and nonconvex entry guidance problem is converted into sequential convex sub-problems in the second-order cone programming (SOCP) form by an appropriate combination of successive linearization and convexification techniques. From the investigation on the potential sub-problem infeasibility due to a rough initial guess for radial distance, a linear penalized term associated with a virtual control for an inequality constraint is used to relieve the sub-problem infeasibility while preserving the standardized SOCP form. An adjustable trust-region bound is also adopted in the proposed approach to improve the convergence property further. Additionally, a change of control variables and a relaxation technique are utilized to relieve the high-frequency jittering issue. It is proven that the Lossless convexification property is preserved for the relaxed problem even in the presence of the penalty terms. The feasibility of the proposed method is investigated through numerical simulations.