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Thermal transport in nanoscale and nanostructured materials
In recent years, nanoscale synthesis and processing of materials are developing rapidly. The scientific understanding of the thermal transport in nanoscale and nanostructured materials is of great importance in terms of understanding and optimizing these processes. In this dissertation, three aspects of the thermal transport at nanoscale length are studied. ^ First, the phonon thermal transport in three types of nanoscale materials is studied. The thermal conductivities of nanofilms, nanowires, and nanoparticles are studied using equilibrium molecular dynamics simulation. It is found that their thermal conductivity depends significantly on the characteristic size until it reaches a large value. Comparison with the results of Lattice Boltzmann method reflects strong effects of surface structure especially when the characteristic size of nanomaterials is comparable to the mean free path of phonons. Study of the phonon thermal transport in nanowires and nanoparticles reveals much stronger boundary scattering effect on thermal transport than that in nanofilms, which is attributed to the more confined phonon movements in these nanomaterials. ^ Second, thermal transport in nanocrystalline materials is studied using large-scale equilibrium molecular dynamics simulation. Nanocrystalline materials with different grain sizes are studied to explore how and to what extent the size of nanograins affects the thermal conductivity and specific heat. Substantial thermal conductivity reduction is observed and the reduction is stronger for nanocrystalline materials with smaller grains. On the other hand, the specific heat of nanocrystalline materials shows little change with the grain size. ^ Finally, a novel photothermal experiment is designed and conducted to characterize the thermal transport in carbon nanotubes along the axial direction exclusively. Experimental value of the thermal conductivity is much smaller than the theoretical prediction, which is due to the structure difference and imperfection of the carbon nanotubes. The thermal contact resistance between the nanotubes and chromium layer is very small. On the other hand, the thermal contact resistance between the chromium layer and silicon substrate is large. ^
Engineering, Mechanical|Engineering, Materials Science
Zhong, Zhanrong, "Thermal transport in nanoscale and nanostructured materials" (2005). ETD collection for University of Nebraska - Lincoln. AAI3186891.