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Graphene transport and dual-gate devices : 그래핀의 수송현상과 이중 게이트 소자 연구

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Authors

남영우

Advisor
박영우
Major
자연과학대학 물리·천문학부(물리학전공)
Issue Date
2014-02
Publisher
서울대학교 대학원
Keywords
grapheneelectron transportAharonov-Bohm effectthermopowerchemical vapour depositiondual-gated graphene field effect devicesquantum Hall effect
Description
학위논문 (박사)-- 서울대학교 대학원 : 물리·천문학부(물리학전공), 2014. 2. 박영우.
Abstract
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 gates
top- 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.
Language
English
URI
https://hdl.handle.net/10371/121517
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