| Summary: | 博士 === 國立清華大學 === 工程與系統科學系 === 101 === The low-dimensional materials exhibit a lot of innovative behaviors different from the bulk materials. The interactions of phonon-electron, phonon-interface, and phonon-grain boundary in low dimension materials attracted a lot of attentions in the research society. This initiated my motivation to investigate the electrical and thermodynamic properties in low dimensional systems for understanding their fundamental physics. One important measuring technique is the 3ω method, which can be applied to evaluate the thermal conductivity for low dimensional systems. In this work, the techniques have been developed to measure the cross-plane and in-plane thermal conductivity of a thin film and the longitudinal direction thermal conductivity of an individual nanowire. By comparison with other methods, the techniques yield more information, which is very helpful for understanding the behavior of phonon and electron in low dimension materials. For two-dimensional system, we have measured the cross-plane thermal conductivity of CuFeSe2 thin film which is considered to be the photoelectric material. The results indicate thermal conductivity of the films is strongly dependent on film crystallization, the better crystallization the higher thermal conductivity. In the meantime, the interfacial thermal resistance between film and substrate should also be taken into account for obtaining accurate total thermal conductivity. For one-dimensional system, a series of single crystalline Bi2-xSbxTe3-y nanowires (150 - 890 nm) were fabricated for the thermoelectric properties measurement. The phonon thermal conductivity decreases as the wire diameter reduces at low temperatures, indicating the enhancement of boundary scattering in one-dimensional system. The Seebeck coefficient and electrical resistivity were also measured for the same nanowire subsequently. The results show the Seebeck coefficient and electrical resistivity are greatly dependent on the composition of the nanowires.
|
|---|
