Molecular Dynamics Simulation of Heat Conduction in Si Thin Films Induced by Ultrafast Laser Heating

Molecular dynamics simulations are carried out to study the thermal and mechanical phenomena of ultra-high heat flux conduction induced by ultrafast laser heating in thin Si films. Nanoscale Si films with various depths in heat flux direction are treated as a semi-infinite model for the study of ultrafast heat conduction. A distribution of internal heat source is applied to simulate the absorption of the laser energy in films and the induced temperature distribution. Stress distribution and the evolution of the displacement are calculated. Thermal waves are observed from the development of temperature distribution in the heat flux direction, though the average temperature of the simulated Si films increases monotonically. The average stress shows periodic oscillations. The time development of strain has the same trend as the average stress, and the net heat flux shows the same trend as the stress at different depths of the Si films in the direction of heat flux. This reveals a close relationship between stress and net heat flux in the Si films in the process of ultrafast laser heating.