We carried out molecular dynamics simulations (MD) of heat conduction in Si thin film and Si films with a nano-hole to represent the nano-structure, in order to investigate the mechanism of the thermal conductivity reduction of nano-structured materials. The Stillinger-Weber potential is used in this study. Different temperatures are applied at the both sides of boundaries of the calculation domain in the z-direction, and periodic boundary conditions are applied in the x and y directions. The calculated temperature profile of a Si thin film of 10.86nm thickness is compared to that calculated by using the phonon Boltzmann transport equation (BTE). These agreed reasonably well with each other, and the phonon mean free path of Si is estimated to be several tens of nanometers. Molecular dynamics simulation of Si at the uniform temperature of 800K is also carried out. Phonon dispersion curves are calculated by using the time-space 2D Fourier transform. The phonon modes at high frequency are not present in nano-structures of Si. We discuss the mechanism of the reduction of the thermal conductivity of nano-structured material on the atomic scale.

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