Si adsorption on SiC(0001) surfaces

Activation energies and atomic geometries associated with Si adsorption and desorption processes on the Si face of SiC(0001) have been obtained from in situ reflection high-energy electron diffraction measurements and ab initio pseudopotential calculations. During the initial stage of Si deposition, the SiC(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 energy E-a is 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 (root3 x root3-)R30degrees to (3 x 3). These observations are interpreted with the help of ab initio pseudopotential calculations. It is concluded that E-aroot3 = 4.5 eV measured on (root3 x root3) R30degrees corresponds to adsorption at adatom vacancy while E-a3 = 1.6 eV measured on (3 x 3) corresponds to adsorption on top of a capping adatom. Finally, the development of surface structures from the (root3 x root3)R30degrees surface to silicon-rich and carbon-rich extremes is discussed.