Research On Carrier Transport Property In Low-dimension Nano-system

Low dimensional nano-scale systems have become one of the forefront researchtopics in condensed matter physics in recent years. In this thesis, we present somedetailed theoretical investigations on the ballistic phonon transport and thermalconductance in multiple channels nanostructure, and the electronic transmissionproperties in nano-scale moelcular device. The achievements made in this thesis aresummarized as follows:Based on the elastic continue model and the scattering matrix method, we studiedthe properties of the ballistic acoustic phonon transmission and the thermalconductance of the H-type four-channel nano-structure. For H-type four-channelnano-structure, when the incident phonon frequency closes to0, the transmissionprobability of the zero mode is independent of the structural parameters, but that ofthe high-frequency is sensitive to the structural parameters. The transmissionprobability in the channel III is bigger than that in other channels. When thetemperature approaches0K, the thermal conductance in each channel is closed to be aquarter of the quantum of thermal conductanceπ2k2BT/(3h). With the increase of thetemperature, the total thermal conductance in each channel is different from eachother, and the changes of channel III is more obvious than that in other channels. It issuggested that the acoustic phonon transmission and thermal conductance can beeffectively adjusted by changing the structural parameters of the H-type four-channelnano-structure.By applying the first principle of density functional theory and nonequilibriumGreen function method, we study the transport properties of a single phenalenylmolecular device which constructed by single phenalenyl molecule and graphenenanoribbon electrode. We mainly discussed the effect of contact sites on electronictransport properties, and then we compared the electronic transport properties ofgraphene nanoribbon electrode with metal electrode. The results show that theelectronic transport properties are strongly dependent on these contact sites and theelectrode materials are also an important factor for electronic transport. These resultsmay be helpful for the design of molecular device.