The neck growth mechanisms in low energy laser sintering of gold nanoparticles - A Molecular Dynamics simulation study

Molecular Dynamics simulations were employed to investigate the mechanism and kinetics of the sintering of two crystalline gold nanoparticles (4.4-10.0nm) induced by low energy laser heating. At low temperature (300K), sintering can occur between two bare nanoparticles by elastic and plastic deformations driven by strong local potential gradients. This initial neck growth occur very fast (< 150ps), therefore they are essentially insensitive to laser irradiation. This paper focuses on the subsequent longer time scale intermediate neck growth process induced by laser heating. The classical diffusion based neck growth model is modified to predict the time resolved neck growth during continuous heating with the diffusion coefficients and surface tension extracted from MD simulation. The diffusion model underestimates the neck growth rate for smaller particles (5.4nm) while satisfactory agreement is obtained for larger ones (10nm). The deviation is due to the ultra-fine size effect of below 10nm particles. Possible mechanisms were discussed.