Adsorption and dissociation of disilane on Si(001) studied by STM

Abstract

The surface-adsorbed fragments resulting from the room-temperature adsorption and dissociation of disilane (Si 2H 6) on Si(001) are observed and identified using scanning tunneling microscopy (STM). The predominant fragments are H and SiH 2, 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 SiH 2 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 SiH 2 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 SiH 2 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.