Molecular dynamics simulation of heat conduction in Si nano-films induced by ultrafast laser heating

a r t i c l e i n f o Molecular dynamics simulations are carried out to study the thermal and mechanical phenomena of heat conduction induced by ultrafast laser heating of nanoscale Si films. A distribution of internal heat source obeying Beer–Lambda law is applied to model the laser energy deposition in the film and to calculate the induced temperature and stress distributions. Thermal waves are observed from the local temperature temporal variations and spatial distributions. The developments of averaged static pressure and local displacement in the film show a consistent periodicity. The time evolutions of both the local pressure and net heat flux fluctuate strongly, but show similar trends between these two local physical quantities, demonstrating a close relationship between the stress and the net heat flow. Ultrafast lasers have been widely applied to thin film surface modifications and diagnostics related to medical science and engineering [1,2], micro/nano machining [3,4], high-density information storage [5], to name a few. Understanding basic thermodynamic phenomenon of interaction between ultrafast lasers and materials is critical. The mechanism of energy conversion and transport process is one important problem in basic research of many fields like energy, information technology , material processing, micro/nano fabrication, etc. It manifests the interaction of energetic-particles with material at the nano/pico level, whereas the time and space scales of these interactions are in the range of femtosecond–picosecond and nanometer, respectively. Ultrafast laser pump-probe technology provides an avenue to investigate and observe such interactions [6–8]. An early study on micro heat transport induced by ultrafast laser exciting in metal films was carried out in 1980s [6]. The ensuing series of meticulous and in-depth work last until today, mainly focusing on metal materials [3,6–13] with some extension to semiconductors [14], dielectric materials [1,2], and polymers [4]. Some theoretical models on micro/nano non-equilibrium heat transport include heat wave Cattaneo and Vernotte (CV) model [15] that is also known as non-Fourier phenomenon, Anisimov's [16] semi-classical two-temperature model (TTM) that describes a non-equilibrium state between electrons and the lattice, Tzou's [17] dual-phase-lagging model, and models based on plasma formation rate equation [14,18]. Specially, TTM model could effectively describe heat transport in metal films under ultrafast laser irradiation. With the mutual verification and promotion of experiments and theories, research on micro/nano non-equilibrium heat transport in metals has become quite mature today. Nevertheless, theoretical research on nanoscale heat transport in semiconductors and super-lattices, a large …