The transition from 2D to 3D growth of Ge on Si(001) has been investigated with scanning tunneling microscopy. A metastable 3D cluster phase with well-defined structure and shape is found. The clusters have a {105} facet structure. Results suggest that these clusters define the kinetic path for formation of ‘‘macroscopic’’ Ge islands.

Scanning tunneling microscopy observations of several forms of disorder on Si surfaces are presented. These include dimer vacancies on Si(001), step bunches associated with a morphological phase transition on vicinal Si(111), and step structure on vicinal Si(001). A recipe for cleaning of Si surfaces to produce a minimum amount of disorder is presented.

The diffusion of Si dimers on the Si(001) surface at temperatures between room temperature and 128 °C is measured using a novel atom-tracking technique that can resolve every diffusion event. The atom tracker employs lateral-positioning feedback to lock the scanning tunneling microscope (STM) probe tip into position above selected atoms with subangstrom precision. Once locked the STM tracks the position of the atoms as they migrate over the crystal surface. By tracking individual atoms directly, the ability of the instrument to measure dynamic events is increased by a factor of $\sim 1000$ over conventional STM imaging techniques.

Scanning-tunneling-microscopy images of vicinal Si(001) with an equilibrium distribution of steps and kinks have been analyzed to determine the distribution of kink separations and kink lengths. From these distributions, step and kink energies have been directly determined.

Scanning-tunneling-microscopy measurements of submonolayer growth of Si on Si(001) show anisotropic island shapes. From coarsening experiments it is determined that these shapes are a consequence of the growth kinetics. They can be explained by a lateral accommodation coefficient for atoms arriving at the edge of islands that differs by an order of magnitude at the ends and at the sides of dimer rows.