Phonon Dynamics at an Oxide Layer in Silicon: Heat Flow and Kapitza Resistance

The interactions between heat flow and an oxide layer in Si are studied within two temperature windows using non-equilibrium ab initio molecular-dynamics (MD). The model system is a H-saturated Si nanowire containing an amorphous SiOx layer. The nanowire is in a large 1-D periodic box which prevents thermal contamination between image nanowires. The results show that the oxide acts as barrier to heat flow and substantially increases the time required for the system to reach thermal equilibrium. This effect is caused by the higher-frequency vibrational modes in the oxide relative to Si, and is unrelated to the low thermal conductivity of SiOx. A new first-principles method to calculate the Kapitza resistance of the interface directly from the MD data is proposed.