Molecular-dynamics simulations of nucleation and crystallization in supercooled liquid silicon: Temperature-gradient effects

We have investigated atomistic processes of nucleation and crystallization in supercooled liquid silicon (Si) based on molecular-dynamics (MD) simulations using the Tersoff potential. MD cells composed of up to 8192 Si atoms were heated to produce melted Si, and then melted Si was quenched under various supercooled conditions with or without a temperature gradient and the corresponding nucleation processes were visualized. The critical nucleation radius was determined as a function of the amount of supercooling ΔT and it was found to be inversely proportional to ΔT. It was also found, in the case of supercooling under a linear temperature gradient, that nucleation first occurred at the lower-temperature region and then crystallization proceeded toward the high-temperature region with the (111) surface mostly parallel to the temperature gradient.