Coarsening Dynamics of Crystalline Thin Films

The formation of pyramidlike structures in thin-film growth on substrates with a quadratic symmetry, e.g., ${001}$ surfaces, is shown to exhibit anisotropic scaling as there exist two length scales with different time dependences. Numerical results indicate that for most realizations coarsening of mounds is described by an exponent $n\ensuremath{\simeq}1/4$. However, depending on material parameters it is shown that $n$ may lie between 0 (logarithmic coarsening) and 1/3. In contrast, growth on substrates with triangular symmetries $({111}$ surfaces $)$ is dominated by a single length $\ensuremath{\sim}{t}^{1/3}$.