Adsorbate Induced Change of Equilibrium Surface during Crystal Growth: Si on Si(111)/H

Surface termination of Si(111) with atomic hydrogen changes the homoepitaxial growth from a layer-by-layer mode (bare surface) to a faceting of the whole surface. This decomposition of the planar surface into a ``hill-and-valley'' structure is explained by a change of the surface free energy during Si deposition and H termination. This favors the growth of facets, which are stable as long as the surface is covered with H. The effect is reversible, with the growth mode returning to layer by layer after H desorption.