Metal films grown on nonwetting substrates evolve from an early stage
of isolated compact islands to a later stage of elongated islands and
percolation. Results are presented of a scanning electron microscopy s
tudy of Pb on SiO2 showing that the critical island radius R(c) at whi
ch this crossover occurs is strongly dependent on temperature and weak
ly dependent on deposition rate. The experimental results are semiquan
titatively described by a kinetic freezing model, in which the rate of
island coalescence due to surface diffusion competes with the rate of
island growth due to deposition.