LOW-TEMPERATURE GROWTH ON SI(111) SUBSTRATES

Low-temperature (T < 150 K) reflection high-energy electron-diffractio n (RHEED) oscillations during the growth of ultrathin films suggest th e presence of nonzero adatom mobility. In most systems thermal diffusi on cannot account for the observed oscillations, and the origin of the oscillations is still unclear. Experiments on Ag/Si(111) at 150 K dem onstrate the absence of thermal diffusion based on the scaling of the RHEED intensity at different flux rates (i.e., the diffracted intensit y is only a function of the total deposited amount independent of the flux rate). We have performed molecular-dynamics simulations to unders tand possible low-temperature mechanisms responsible for the oscillati ons. Classical two- and three-body Si potentials were used together wi th an adatom mass that is 3.84 times the Si mass to account for the Ag /Si mass ratio. Results indicate that the landing site of the adatom i s important in predicting the subsequent lateral motion of the adatom. A majority (about 75%) of the deposited atoms adsorb within a lattice spacing of the landing site. However, a fraction (25%) of the deposit ed atoms eventually adsorb a few lattice spacings away from the landin g site before equilibration to the substrate, but it is not clear if t his is sufficient to account for the oscillations. The energy transfer to the substrate is much less efficient than in fcc/fcc systems, beca use of the stiffness of the Si-Si potentials.