Laser Ablation of Nanoparticles: A Molecular Dynamics Study

Abstract

We study laser ablation of nanoparticles (NPs). The interaction of a high-intensity laser pulse with NPs brings the NP into a highly non-equilibrium state. Depending on the energy input from the laser, it will melt and may fragment and evaporate off atoms and clusters. We employ molecular dynamics simulation to study this interaction since thermodynamic properties can be extracted from output data of this simulation. The interatomic interaction is modeled by a Lennard-Jones (LJ) potential. The intensity of the laser is above the ablation threshold. The NP has been chosen to have a spherical shape with diameter 50 s in LJ units. The laser energy is given to the NP instantaneously at the beginning of the simulation and homogenously to all atoms; it corresponds to an energy input of 5.4 e per atom. The simulation is continued up to a time 200 t in LJ units. Temperature-density phase-space trajectories show that the nanoparticle density and temperature strongly decrease after the irradiation. The pressure in the sphere becomes strongly tensile after irradiation. The ablation proceeds by spallation of the irradiated cluster. We provide an analysis of the fragments produced by the ablation of the spherical NP. Our results are contrasted to the case of laser ablation of a thin-film target.