Transport Properties Of Graphene Nanoribbon

Carbon is the most common element in nature. In recent years,the discover of C60 and successful preparation of carbon nanotubes exploited the new configuration of carbon, and the findings of magnetism and superconductivity for carbon compound have attracted much interests for this common element and even some people give so-called"carbon electronics". Scientists are still investigating the new configuration of carbon, so that much more new phenomena can be found. However, conventional configuration of carbon is often ignored. Graphene, which is one of carbon configurations and belongs to carbon electronics field, is layer structure and each carbon atom of interlayer is sp2 hybridized orbital with neighboring three carbon atoms form three equivalent distanceσbond, therefore conform carbon atomic infinite planar layer, and also, every carbon atom is vertical with this pz orbital of planar and they overlapped each other to form delocalizationπbond. Electron presents metallic conductivity property in inner planar, whereas, high resistance when it is vertical with the planar. Thus, graphene is considered planar conductor and belongs to conventional semi-metallic materials whose transportation character is intervenient of metal and semiconductor.Nano graphene layer may be a new generation electrics basal materials based on design and preparation of graphene nanoribbons. These basic functional apparatus consists of rectifier, PN junctions, field effect transistor and so on. We must make a systemic study for each kind of grapheme in order to observe most valuable physical phenomena, which could make the application of graphene on nano-apparatus to be realized. The theoretic investigation which is not restricted by laboratorial techniques, provided some instructional information for experimental study. It can afford credible physical law for establishing and enriching principle of relativity condensed matter physics basal theory system. It provided valuable theoretic information for apparatus design of orgin from granpene nano-electrics. Graphene open a wide filed for future application of electrical apparatus, such as ballistic transistor. Planar graphene material could become basal material of nano-electrics since electron of graphene keep high mobility even at room temperature and high carrier concentration and it could be cut into diversified nanostructures.Different from other semiconductor system, description of graphene should adopt Dirac equation which was used to describe relativistic particles, not Schrodinger equation which was used to describe non- relativism. Equations in this system consists of two kinds of non- equivalent A atom and B atom, form two energy band and intersect in Brillouin zone boundary neighborhood and come into being conical type energy spectroscopy. Thus the quasiparticle of graphene existed a linear dispersive connection. It is just this linear spectrum that we may think that quasiparticle character of graphene is different from our familiar particle properties of metallic and semiconductor.Transport properties of electrons are usually calculated by density functional theory (DFT) and nonequilibrium Green function. We simulate nanostructure system and electrical perproties of nano-apparatus and transport properties of quanta. Based on electronic calculations such as pseudopotential method and linear combination of atomic orbital, electronic transport properties of nano-device under external voltage and graphene under external magnetic field were disposed by using nonequilibrium Green's function method and transport theory method. We will discuss the effect of size of boundary and device zone on conductivity.In this thesis, electronic transport properties of graphene ribbons were calculated through tight-banding calculation and Landau-Buttiker formula. Exoteric factors such as voltage, magnetic field and their corporate influence on graphene ribbons conductivity were investigated. Wave function of nanoribbons was processed through Dirac equation.First of all, we settled graphene planar infinity system, energy and wave function of armchair and zigzag bondary infinity nanoribbons. The merit and limitation of two kinds of methods were compared through the results of the two approximate calculations.Secondary, electronic transport under voltage and vertical magnetic field was investigated through transport theory. Interestingly, energy band of graphene ribbons can move up and down, however, the tunnel integral among carbon atoms hasn't changed under voltage influence. Under vertical magnetic field influence, energy band and tunnel integral are also changed and tunnel integral varied as exponential.In the end, we discussed the conductivity spectrum change under the influence of graphene ribbons different bondary under the voltage and magnetic field through above theory. Through theory and numerical value calculation, we have a more clear understanding. More important result is that our theory studying will provide directive information for application of graphene on nano-device.