AGGREGATION AT EARLY STAGE OF GROWTH IN THIN-FILMS

A growth model is presented to simulate the diffusion-limited aggregation pattern appearing in the formation process of thin films deposited by sputtering or evaporation. In the submonolayer range of deposits, aggregates are controlled by the sticking probability of sputtered (or vaporing) particles, the ballistic motion of particles and Brownian motion of particles on the deposition plate. By using computer simulation it is found that the deposit at early stage of growth becomes a quasi-two dimensional structure extending on the deposition plate at a typical height of a few particles. The pattern obtained by the computer simulation is similar to that found in experiments. A top view of the structure of clusters deposited on the plate shows the DLA fractal at low particle numbers. The cluster-size distribution n(s)(t) obeys the dynamic scaling: n(s)(t) almost-equal-to t(w)s(-tau)f(s/t(z)) (tau=0.92+/-0.03, z=0.34+/-0.01, and w=0.58+/-0.03) where the cutoff function f(x) is a constant for x much less than 1. The scaling structure of the deposit shows a characteristic property definitely different from those of the diffusion-limited cluster-cluster aggregation (CCA).