Nanostructure initiation during the early stages of thin film growth

It is shown how the combination of atomic deposition and nonlinear diffusion may lead, below a critical temperature, to the growth of nonuniform layers on a substrate. The dynamics of such a system is of the Cahn–Hilliard type, supplemented by reaction terms representing adsorption–desorption processes. The instability of uniform layers leads to the formation of nanostructures which correspond to regular spatial variations of substrate coverage. Patterns wavelengths and symmetries are selected by the dynamics and not by variational arguments. For increasing coverage, one should observe a succession of structures going from hexagonal arrays of high coverage dots, to stripes and finally to hexagonal arrays of low coverage dots. At low deposition rates instability may occur for certain time intervals only, and induce transient structures which may provide templates for further structure development.