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Design and Simulation of Spin Transport in Graphene Based Nanostructures

Chaghazardi, Zahra | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50324 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Faez, Rahim; Pourfath, Mahdi
  7. Abstract:
  8. Graphene -a two-dimensional monolayer of graphite- was realized for the first time in 2004.Owing to its physical extra ordinary properties, graphene has attracted growing interest in research from fundamental physics to electronics, spintronics, and thermoelectrics. Importantly, it is an attractive material for electronics and spintronics due to its specific physical properties such as high electron mobility and gate tunable carrier concentration. Furthermore,achievement of room-temperature spin transport with relatively long spin relaxation time makes graphene nanoribbons the best candidate for spintronics. Based on the theoretical predictions, the weak spin-orbit interaction in graphene due to low atomic number of carbon results in spin relaxation times in the order of microseconds. However, much shorter relaxation times in the range of pico- to few nanoseconds have been experimentally reported. The discrepancy between theory and experiment is not yet well understood and the origin of spin relaxation in graphene is under debate. Since then, experimental and theoretical studies have been done to find the causes of the spin-relaxation time degradation in graphene.On the other hand, The surface roughness of the graphene has been proved experimentally both on free-standing graphene and on graphene supported by a substrate. Substrate surface roughness can affect spin transport in graphene. In this thesis the spin transport in armchair graphene nanoribbon in presence of surface roughness is studied. In an ideal graphene sheet, spin-orbit interaction between nearest neighbors vanishes, whereas next nearest neighbors have negligible effects on spin flipping. Substrate surface roughness enhances mixing between σ and π orbitals by hopping between neighboring atoms, and therefore increases spin-orbit interaction. Accordingly, it is predicted that the ultra-smooth substrate surface will enhances spin-relaxation time and make experimental results close to theoretical predictions.However, a relatively weak intrinsic spin-orbit coupling (SOC) is the big advantage for spin transport in room temperature, it imparts the bad spin controllability in graphene. In this thesis we study the spin controllability of the Spin FET by applying an external electric field and in the presence of surface roughness
  9. Keywords:
  10. Graphene ; Spin-Orbit Coupling ; Surface Roughness ; Field Effect Transistors ; Lyapunov-Krasovskii Function ; Time Delay ; Attitude Control ; Attitude Estimation ; Spintronic Devices ; Armchair Graphene Nanoribbon ; Stark Effect

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