그래핀의 수송현상과 이중 게이트 소자 연구

학위논문 (박사)-- 서울대학교 대학원 : 물리·천문학부(물리학전공), 2014. 2. 박영우.This thesis contains experimental studies on electronic transport properties of graphene with the Aharonov-Bohm (AB) effect, thermopower (TEP) measurements, dual-gated graphene field effect devices, and quantum Hall effect (QHE). First, in an effort to enhance the AB effect in graphene, we place either superconducting-metal (aluminium) or normal-metal (gold) mirrors on the graphene rings. A significant enhancement of the phase coherence effect is conferred from the observation of the third harmonic of the AB oscillations. The superconducting contribution to the AB effect by the aluminium (Al) mirrors is unclear. Instead, we believe that a large mismatch of Fermi velocity between graphene and the mirror materials can account for the enhancement. Second, TEP measurement is performed on wrinkled inhomogeneous graphene grown by chemical vapour deposition (CVD). The gate-dependent TEP shows a large electron-hole asymmetry while resistance is symmetric. In high magnetic field and low temperature, we observe anomalously large TEP fluctuations and an insulating quantum Hall state near the Dirac point. We believe that such behaviors could be ascribed to the inhomogeneity of CVD-graphene. Third, dual-gated graphene field effect devices are made using two gatestop- and back-gates. In particular, the top gate is made of Al deposited directly onto the middle part of the graphene channel. Naturally formed Al2O3 at the interface between Al and graphene can be facilitated for the top-gate dielectric layer. When the Al top-gate is floating, a double-peak structure accompanied by hysteresis appears in the graphene resistance versus back-gate voltage curve. This can be attributed to the finite resistance of top-gate dielectric and the coupling between the two gates. Lastly, we notice that the QHE is very robust in CVD-graphene grown on platinum. The effect is observed not only in high- but also low-mobility inhomogeneous graphene decorated with disordered multilayer patches.Abstract I List of figures VII List of tables XI 1. Introduction 1 1.1 Graphene 2 1.2 Purpose and scope of this thesis 5 2. Concepts 7 2.1 Aharonov-Bohm (AB) effect 7 2.2 Thermopower (TEP) 10 2.3 Graphene p-n-p junctions and graphene-metal contact 14 3. Experimental techniques 17 3.1 Microfabrication of graphene devices 17 3.2 Graphene growth by chemical vapour deposition (CVD) 19 4. The Aharonov-Bohm (AB) effect in graphene rings with metal mirrors 21 4.1 Introduction 21 4.2 AB-ring devices and experimental details 22 4.3 Raman spectrum and Coulomb blockade effect 23 4.4 AB oscillations with Al T- and Al L-mirrors 25 4.5 AB oscillations with Al L-mirrors and without mirrors 29 4.6 AB oscillations with Au T- mirrors, Au L-mirrors and without mirrors 30 4.7 Conclusions 31 5. Unusual thermopower (TEP) of inhomogeneous graphene grown by chemical vapour deposition 33 5.1 Introduction 33 5.2 The thermopower device and experimental details 35 5.3 AFM and Raman mapping 36 5.4 Gate voltage dependence of resistance and thermopower 37 5.5 Simulation of inhomogeneity effect using simple mesh 39 5.6 Quantum Hall effect (QHE) 41 5.7 Magneto thermopower 42 5.8 Conclusions 44 6. Graphene p-n-p junctions made of naturally oxidized thin aluminium films 45 6.1 Introduction 45 6.2 The graphene p-n-p device and experimental details 46 6.3 Al oxidation at the interface with graphene 47 6.5 Double-peak structure in the transfer curve when Al top gate is floating 50 6.6 Circuit model to account for the hysteresis in the double-peak structure 53 6.7 Conclusions 55 7. Quantum Hall effect in graphene decorated with disordered multilayer patches 57 7.1 Introduction 57 7.2 Graphene growth on platinum by CVD 59 7.3 Transfer curves and Raman mapping 60 7.4 Quantum Hall effect (QHE) 63 7.5 Unusual ν = 0 quantum Hall state 66 7.5 Conclusions 67 8. Summary 69 References 71 국문 초록 81Docto

LR법에 기초한 복합 화력 발전기를 포함하는 발전기 기동정지 계획

학위논문(석사)--서울대학교 대학원 :전기공학부,1999.Maste

콜롬비아에 찾아온 평화: 콜롬비아 정부와 무장혁명군이 평화협정안에 서명하다

이 글은 멕시코 일간지 (La Jornada)의 기사(2016년 8월 25일자)를 번역한 것이다지난 8월 24일 콜롬비아 정부와 게릴라단체 무장혁명군(FARC)은 역사적인 최종 평화협정안에 서명하였다. 이로써 반세기 이상 지속된 무장 투쟁에 종지부를 찍기 위하여 거의 4년 동안 계속된 협상이 마무리되고, 그 결과는 10월 2일의 국민투표를 통하여 최종 확정될 예정이다. 이 평화협정안은 정부 측 협상책임자인 움베르토 델 라 카이예와 무장혁명군의 대표자 이반 마르케스가 서명했으며, 이 자리에는 쿠바의 외무장관 브루노 로드리게스가 참석하였다. 그동안 협상 감독국가 대표로 참여한 로돌포 베니테스(쿠바)와 닥 닐렌데르(노르웨이)는 이 날 최종 합의에 대한 공동성명을 발표하고, 콜롬비아에서 무장 충돌의 영구적인 종식 및 안정적이고 지속적인 평화의 정착을 선언하였다. 200페이지가 넘는 최종 평화협정안은 콜롬비아 전 국민이 항구적인 평화 건설에 참여하게 되었으며, 이를 위하여 지금까지 되풀이된 폭력의 역사를 마감하고 평화의 기틀을 마련하였음을 강조하고 있다

(An)Analysis of the effect of market contracts on market power in a transmission constrained electricity market

학위논문(박사)--서울대학교 대학원 :전기·컴퓨터 공학부,2006.Docto

순간 낙하점 변화율 및 실시간 낙하 분산 영역을 고려한 발사체의 비행안전 의사결정 법칙과 디스플레이 설계

학위논문(석사) - 한국과학기술원 : 우주탐사공학학제전공, 2014.2, [ 63 p. ]This study proposes a new flight termination decision rule and a flight safety display related with range safety. The proposed rule and display uses information on both of the time derivatives of instantaneous impact point (IIP) of a launch vehicle and dispersion of the impact point calculated in real time. The time de-rivative of the IIP is defined as the impact point’s movement on the Earth’s surface, and the method makes it possible to know the IIP derivative and the IIP considering time delay of the operation of a fight terminate system can be found at the same time. Furthermore, this paper proposes the impact point dispersion that is calculated in real-time by dividing impacted velocity caused by fragments of a launch vehicle into three or-thogonal directions and defining a sensitive function on each direction. If the proposed analytic method of the time derivative of IIP and the real time impact point dispersion are to be applied in a flight safety infor-mation system (FSIS), a flight safety officer (FSO) would be able to make more accurate and reasonable deci-sions making.한국과학기술원 : 우주탐사공학학제전공