ADSORPTION AND DISSOCIATION OF DISILANE ON SI(001) STUDIED BY STM

The surface-adsorbed fragments resulting from the room-temperature adsorption and dissociation of disilane (Si2H6) on Si(001) are observed and identified using scanning tunneling microscopy (STM). The predominant fragments are H and SiH2, which are identified by the symmetries of their binding sites on the surface. H atoms often bind near single or double dimer vacancy defects. We find that adsorbed H atoms induce buckling of the dimer rows on the Si(001) surface, while SiH2 groups do not. This difference is ascribed to differences in the electronic structure of the two surface-bound species. No systematic correlation between the positions of the SiH2 groups is evident, which indicates that the fragments of a single disilane molecule are not localized in a small region. This fact suggests that at least some of the molecular fragments from disilane dissociation are mobile on the Si(001) surface at room temperature. Further decomposition of the SiH2 fragments can be induced by annealing, which produces surface structures similar to those seen in molecular-beam epitaxial growth of silicon: small asymmetric islands form with low disilane coverages, whereas higher coverages give multilayer island growth.