Effects Of The Positions Of Defects And Electrodes In Graphene Nanoribbons Of The Electronic Transport Properties

Graphene nano-material is one of most active fields in the study of the condensed matter physics at present. The two-dimensional system with an atomic thickness presents many unusual properties and shows many potential applications. The thesis mainly uses ATK software to simulate and calculate, and studies the electronic transport properties of several kinds of Graphene nano-materials. By simulating its electronic transport properties, we put forward some devices design and some proposals on constructing graphene nano-materials devices.Firstly, we review the crystal structure of the graphene, and the dispersion relations of graphene obtained by the band theory. Furthermore, we derive the band structure of two kinds of graphene nanoribbons and discuss its properties.Secondly, we study the effects of a vacancy and an adatom defect on the electronic transport properties of graphene nanoribbon respectively. It is found that various defects dramatically impact the energy band structure and electrical conductivity. The physical origin is that the defect destroys the symmetry of the geometric structure. Further study shows that from the point of energy view, it is more stable for the case that the defects are located on the edge of the graphene nanoribbon, which is agreement with the experiment results.Thirdly, we investigate the spin polarization property of Au electrodes coupled to graphene nanoribbon. It is found that when the electrodes partially coupled to the graphene sheet, we can obtain two kind of spin-polarized currents by changing the contact locations of the electrodes to the graphene sheet.Finally, we study the negative differential resistance (NDR) phenomena of the atomic carbon chain graphene junctions. It is found that the electronic transport properties of the atomic carbon chain graphene junctions are closely related to the contact geometry of carbon chain and the negative differential resistance (NDR) phenomena is discovered in such junctions. The qualitative results obtained by theoretical research in this thesis provide a theoretical guidance for the applications of nano-devices of the graphene material.