Changing thin-film growth by modulating the incident flux

Thin films are usually obtained by depositing atoms with a continuous flux. We show that using a chopped flux leads to different morphologies or growth regimes. For example, growth cannot be simply understood by replacing the chopped flux by its average (or instantaneous) value and using the usual growth theories: different regimes appear, and in one of them the diffusion constant has no effect on the saturation island density, contrary to what is observed in all theories with continuous fluxes. We present a simple scaling analysis to predict how the island densities change as a function of the frequency of the chopped flux in several growth regimes: irreversible aggregation with mobile islands, reversible aggregation (critical island size greater than 1). These predictions are confirmed by computer simulations. The model is useful to study growth over a larger range of growth conditions, especially for the growth of thin films prepared by pulsed sources.