The island-to-percolation transition during growth of metal films.

摘要

The formation of percolating Pb films thermally evaporated onto SiO{dollar}sb2{dollar} substrates has been experimentally studied using electron microscopy. Pb does not wet SiO{dollar}sb2{dollar} so that compact, three-dimensional islands are formed during the initial stages of film growth. As these islands grow in size they eventually touch their neighbors and coalesce due to surface diffusion. Islands smaller than a critical radius, R{dollar}rmsb{lcub}c{rcub},{dollar} fully coalesce and form a single island with a compact shape. However, islands larger than this critical radius undergo a partial coalescence to form an elongated island. This crossover to partial coalescence produces a network of connected metal structures which increase in size until the percolation threshold is crossed. The main topics studied in this work are: (1) the film's area coverage at the percolation threshold, {dollar}rm psb{lcub}c{rcub},{dollar} is often quite high (p{dollar}rmsb{lcub}c{rcub}{dollar} {dollar}sbsp{lcub}sim{rcub}{lcub}>{rcub}{dollar} 80%) and (2) the factors controlling the size at which the crossover from full to partial coalescence occurs. The high values of p{dollar}rmsb{lcub}c{rcub}{dollar} result from the combination of wiping during coalescence and the coalescence crossover which cause the larger droplets to effectively repel one another. The coalescence crossover is described by a Kinetic Freezing Model in which the crossover is due to a competition between the time for two touching islands to coalesce and the time for one of the islands to grow in size, due to continuing deposition, and make contact with a neighboring island. The predictions of this model are tested and some of the absent features are discussed.; Computer simulations of the profile decay of a corrugated crystalline surface due to surface diffusion are also investigated. A fast Monte Carlo algorithm is used to solve a (1 {dollar}+{dollar} 1)D system at low temperature. The results are significantly different than those predicted by the high-temperature continuum model.