The Effects Of Gradient Disorder And Contact Scattering On Electronic Transport In Quasi-one-dimensional Nanosystems

The investigation on electronic transport properties of quasi-one-dimensional structure is one of hot topic of condensed matter physics. In these systems there show a large number of novel and marvelous physics properties and prospective potential applications. Experimentally, there is disorder in quasi-one-dimensional structure due to the doping, vacancies, adsorption, and so on. It is proved that the disorder plays a crucial role in the electron transport of quasi-one-dimensional structure. By developing Green's function method, we study the effects of disorder on the conductance of quasi-one-dimensional structure. The new physical mechanism of these systems is revealed, and these results are helpful for the design and application of nano-devices. The present thesis is organized as follows:The first chapter is the introduction, a brief review of basic theoretical about the quasi-one dimensional disordered system and the theoretical background. In chapter two, the theoretical basis and a brief description of Green's function method is given.In chapter three, considering both the gradient decay of the real disorder and contact scattering, we investigate the electronic transport in quasi-one-dimensional nanowires by developing a decomposition elimination method for Green's function matrix. In the presence the contact scattering, the conductance oscillates with energy. In some energies, an abnormal enhancement of the average conductance is obtained, at much low disorder. There is a new conductance peak appearance. For such energies, the introduction of disorder destroys the coherence. In the absence of disorder gradient, the average conductance firstly decreases and then increases with disorder strength, indicating a localization-delocalization transition exists there. In the presence of linearly decaying disorder, the average conductance increases slightly in the strong disorder region. In the case of the Gaussian-type decaying disorder, the average conductance decreases exponentially, the localization-delocalization transition disappearing, which is different from previous theory. The results are helpful for design and applications of quasi-one-dimensional nanowires device.In chapter four, based on tight-binding theory, we explore electron transport properties of armchair graphene with the different disorder models and contact scattering. We are simulating long-range disorder with Gaussian form and the edge of disorder, respectively. It is found that zigzag graphene's electronic transport is intimately related to the different effect of disorder and the contact scattering. The results are useful for understanding the electronic transport properties of zigzag grapheme and its potential applications.Lastly, we present a conclusion of this thesis, and discussed some prospects for further investigation.