Tunable Electronic Transport Properties In Graphene Nanoribbons

In recent years, graphene has attracted great interest in materials science and condensed matter physics. Through cutting graphene, one-dimensional carbon nanomaterial—graphene nanoribbons can be obtained. Due to the intriguing hexagonal lattice structure, graphene nanoribbons exhibit excellent electronic transport properties, which lead to their widespread potential applications in nanoelectronic devices. However, different devices require different transport properties. Modulation of the electronic transport properties in graphene nanoribbons is interesting and importtant. In this thesis, using Green's function method we mainly investigate the electronic transport properties by stacking graphene flakes(GFs) and applying strain . This thesis is divided into the following several parts:In chapter one, the basic electrical properties of graphene and armchair-edged graphene nanoribbons (AGNRs) and zigzag-edged graphene nanoribbons(AGNRs) are described.In chapter two, the Green's function method is introduced. Firstly, we introduce the definition of Green's function, and then introduce two methods for solving double-electrode system: whole Green's function and recursive Green's method.In chapter three, the effect of stacked GFs on the electronic transport properties of ZGNRs is investigated. By using the Green's function method, we calculate the conductance of ZGNRs with two different stacked-types GFs. It is found that the coupling effect between ZGNRs and GFs can induce dips at the conductance profiles in two different stacking types. For both stacking types, the dips far away from the Fermi level are nearly overlapped. However, the position of conductance dips near the Fermi level depends on the stacking type. In addition, we discuss the effect of geometric size of GFs on the electronic transport properties. Our results indicate that the stacked GFs can effectively tune the electronic transport of ZGNRs.In chapter four, we study the electronic transport properties of AGNRs under uniaxial strain by using the Green's function methods. The results show that, square dips emerge in the conductance spectrum of AGNRs when considering the edge effect. Through adjusting the uniaxial strain, the square dips move into the high-energy region with increase of the compression stress and their widths decrease accordingly. On the contrary, they move into the low-energy region with the increase of the tensile stress and their widths will increase. In addition, the conductance gap of the AGNRs changes with the stain in a Z pattern. It indicates that the strain can effectively tune the electronic transport properties of AGNRs.In the fifth chapter, we make a summary and describe the problems for future investigations.