Quantum Transport Research On Nano-device Based On Graphene

Since Novoselov et al. successfully prepared the single-layer graphite(Graphene) in 2004. Graphene has arosed scientists'wide attention due to the unique electrical properties, such as Klein tunneling, Zitterbewegung and half an integer hall effect. In the rapid development of technology today, graphene become a new kind of carbon nano materials, and make out many nanometer sized graphene devices by it, such as quantum junction, double layer graphene structure, graphene nanoribbons(GNRs) etc, which has great application prospect. Graphene as a kind of quasi-one-dimensional nanomaterials, geometric structure is the main factors to determine its electronic structure, and it has strong boundary effect and complex electrical properties in practical application,therfore, the research on the device based on graphene has the vital significance.Through the introduction of various disorder (including defect and doping and other ways) to study the electronics and transport properties of graphene nanoribbons become the hot topic in the current research. This paper mainly ues material simulation software ATK which based on the non-balance green function combined with density functional theory to study the singular charge transport properties of nitrogen/boron doped heterojunction, and combined with spin density functional theory to study full carbon's tunneling of magnetic resistance device, and to study on a new type of no spin-orbital coupling two-way pure spin flow switch controled by voltage.The research on the charge transport properties of nitrogen/boron doped heterojunctions show that the doped armchair heterojunctio which connect directly or have the separate region not only in positive and negative bias possess 1 negative differential resistance which have larger peak to valley value, and the two heterojunction also appeared diode-like phenomenon that rectifier coefficient is very large. Our analysis shows that the resonance peak chang a lot with external bias's change, which have very important influence on the nonlinear behavior for heterojunction A and B, and we also see MPSH gap also play a very important role for the singular transport properties of the system of A. we studied the giant magnetoresistance effect on the all carbon tunneling of magnetic resistance device which composed by partially open carbon nanotubes (graphene) and metal carbon nanotubes. In this partilly open carbon nanotubes structure which edge carbon atoms asymmetric saturated, its tunneling of magnetic resistance (TMR) as presents irregular oscillation with the change of external bias and gradually attenuation to 0,during oscillation process we found positive and negative TMR even appeared TMR reversal phenomenon. Our analysis shows that this bizarre tunneling reluctance phenomenon has the close relations with the asymmetric saturated structure of the partially open carbon nanotubes. And we find that the electronic states of this device are deeply influenced by the external voltage.Finally we make a pure spin flow two-way switch which have no spin-orbital coupling and controled by voltage based on a new type of doped zigzag spin gapless graphene nanoribbons(GNRs) -- through change voltage direction, we can get 100% spin polarization direction opposite pure spin flow. We analyzes the mechanism of the phenomenon through energy bands, molecular projected self-consistent Hamiltonian (MPSH) eigenvalues. Due 100% spin polarization of the excited electrons near the Feimi level, an don't need the energy of the excite, also the carriers of this spin gapless semiconductor can travel quickly, so this kind of pure spin flow switch have important application in spintronics, quantum information storage, quantum computing.