DISLOCATION-MEDIATED HEALING OF IDEAL AND ADSORBED MONOLAYERS WITH VACANCY DAMAGE

A spontaneous self-healing mechanism, called dislocation-mediated heal ing (DMH), is demonstrated by molecular-dynamics simulation in ideal ( i.e., constrained in two dimensions) and adsorbed monolayers. The self -healing involves a rapid condensation of the vacancies into dislocati on dipoles. It is complete at temperatures above the self-diffusion te mperature. An associated collapse of the shear modulus similar to the Kosterlitz-Thouless dipole dissociation is observed for high vacancy c oncentrations. The phenomenon is observed in monolayers with a long-ra nge interparticle interaction and is more effective as the mobility of the vacancies increases. In Lennard-Jones monolayers (LJM's) a small compressive pressure is required to observe the effect. In a system wi th a longer-range potential it has been observed even with the monolay er under expansion. It also occurs in monolayers with nearest-neighbor piecewise-linear force interactions (PLFM's) under pressure provided that a third degree of freedom is present. But in general, in PLFM's v acancies agglomerate into clusters (voids). The same applies to LJM's below a critical pressure which decreases with temperature and vacancy concentration. The annealing of the vacancies by the formation of voi ds is a slower process than DMH, usually by at least an order of magni tude.