SLOPE SELECTION AND COARSENING IN MOLECULAR-BEAM EPITAXY

We propose a simple Langevin equation that describes the growth of pyr amidlike structures on a surface under conditions typical of molecular beam epitaxy. The slope of these pyramids is selected by the crystall ine symmetries of the growing film. By analogy with the problem of dom ain growth of systems with a conserved order parameter we show that th e dynamic exponent that controls the growth of the pyramids is z congr uent-to 4. There is no mechanism that limits the size of the growing s tructures. This implies that the roughness exponent is alpha = 1, in a greement with recent experiments.