| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 96 === In the past decades, thermal conductivities of nanostructures have attracted considerable attention with the increased importance of nanodevices. Experimental results showed that the thermal conductivities of nanostructures are often smaller than those of their corresponding bulk material. The causes of the reduction of thermal conductivity include the micro-structural difference and the boundary and interface effects. There are two groups to model the thermal conductivities in nanostructures. One group is wave models, which assumes that phonons form superlattice bands and calculates the modified phonon dispersion using lattice dynamics. The other group is particle models, which assumes that the major reason for reduction of the thermal conduction is the scattering of phonons at interfaces. This thesis focus on the particle models in one-dimension and two-dimension nanostructures for studying the thermal
conductivities.
As the size becomes smaller, the larger temperature drop at the interfaces occurs which is resulted from the ballistic transport and the effect of interface. There are many theories for treating the reaction of phonons striking onto the interface, such as acoustic mismatch model(AMM), diffuse mismatch model(DMM), and inelastic mismatch model(IDMM). The results of simulation shows that the temperature jump at the interface of acoustic model is larger than diffuse model. The thermal conductivities of all models are decreased as the decreasing of thickness. And as the films thick, the
thermal conductivity approaches the value of bulk.
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