Simulations of nanoscale thermal conduction

Abstract

In nanoscale, thermal conduction is affected by system size. Reasons are increased phonon scattering and changes in phonon group velocity. Computational modeling tools for thermal analysis have evolved in the past two decades. A brief overview of the state of the art is given. Nanoscale models can supply microscale computations with important parameters including relaxation times and group velocity. This work concentrates on group velocity and thermal conduction in thin silicon films. Changes in group velocity are addressed by calculating the dispersion relation with the molecular dynamics method, and for comparison, the conductivity is also directly computed. In all cases, the thermal resistivity increases as the film becomes thinner. Thermal conductivity is affected both by surface scattering and decreased group velocity. The group velocity changes both due to band folding and phonon confinement. The results indicate that in very thin films, the conductivity becomes highly anisotropic due to differences in surface scattering. In two low-index surfaces, the role of dispersion is only minor as compared to the role of surface scattering, while in one case, evidence of almost specular scattering was seen.