SiADSORPTION ONSiC(0001)SURFACES

Activation energies and atomic geometries associated with Si adsorption and desorption processes on the Si face ofSiC(0001)have been obtained fromin situreflection high-energy electron diffraction measurements andab initiopseudopotential calculations. During the initial stage of Si deposition, theSiC(0001)surface develops a series of superstructures, depending on temperature and Si coverage. A kinetic diagram of the structural transformations during Si exposure or annealing is outlined and the adsorption energyEais determined. The latter is found to be strongly affected by the surface structure and coverage, changing from 4.5 eV to 1.6 eV as the geometry of the Si adlayer changes from$(\sqrt{3}\times\sqrt{3}){\rm R}30^{\circ}$to (3×3). These observations are interpreted with the help ofab initiopseudopotential calculations. It is concluded that$E_{a\sqrt{3}}=4.5 {\rm eV}$measured on$(\sqrt{3}\times\sqrt{3}){\rm R}30^\circ$corresponds to adsorption at adatom vacancy whileEa3=1.6eVmeasured on (3×3) corresponds to adsorption on top of a capping adatom. Finally, the development of surface structures from the$(\sqrt{3}\times\sqrt{3}){\rm R}30^\circ$surface to silicon-rich and carbon-rich extremes is discussed.