MOLECULAR-DYNAMICS STUDY OF DIFFUSION IN A MOLTEN SURFACE

Using molecular dynamics simulations, we have studied atomic diffusion in a molten Lennard-Jones fcc (110) surface, at temperatures where the thickness of the quasi-liquid layer (QLL) is small. Both short-time (displacement) and long-time (diffusion) dynamics have been found to have anisotropy effects in the plane (between the [11BAR0] and [001] directions) due to the underlying anisotropy of the crystalline periodic potential. The dynamics in the [001] direction is found to be faster in the short-time regime, but slower in the long-time regime. The amount of anisotropy, and the cross-over time are found to decrease as the temperature is increased. Atoms in the QLL are found to diffuse via both single and double jumps along [11BAR0], and mainly via single jumps along [001]. Another, more obvious, anisotropy between the in-plane and vertical motions is found to be very strong when the QLL is thin, and to vanish gradually in the centre of the QLL when the QLL becomes thick. This kind of anisotropy persists up to the triple point close to both the solid-QLL and the QLL-vapour interface.