Properties Of Acoustic Phonon Heat Transport In Low-Dimensional Nanostructures

The nanoscale quantum structures and devices have already become a research hotspot of the condensed matter physics due to their novel physical properties and prospective and potential applications in recent years. For nanoscale devices, size effects on thermal conductivity have become particularly important. In this thesis, we mainly investigate the influence of geometrical shapes and structure parameters on ballistic phonon transport and thermal conductance in low-dimensional quantum structure.By using the transfer-matrix method, we study the phonon transport properties in two-dimensional (2D) quantum structures at low temperature. Our work primarily focuses on the effects of the structural parameters on properties of the phonon transport. Six distinct vibrational modes (four acoustic modes: Dilatational mode, torsional mode, two flexural modes and two low-lying optical modes: two shear modes) are considered in calculation of the phonon transport in the structure. The results show that the behavior of the phonon transport is qualitatively different for different vibrational modes. Moreover, we also find that the transmission coefficient is sensitive to the variation of the structural parameters. It is expected that the phonon transport can be artificially controlled by adjusting the parameters of the proposed micro-structures. This will be very useful for the design of thermal quantum devices.By using the scattering matrix method, we study the thermal transport by ballistic phonon in a semiconductor rectangular quantum wire modulated with quantum dot at low temperatures with finite thickness is investigated with the use of the scattering matrix method. The calculated results show that the total transmission coefficient versus the reduced phonon frequency exhibits interesting characteristics such as inhomogeneous quantum transport steps. Quantized thermal conductance plateau can be observed at low temperatures, and the thermal conductance is not increased monotonically with increasing temperature. The results also show that the phonon transport probability and thermal conductance can be controlled to a certain degree by adjusting the parameters of the proposed quantum structure.