Search

Several models have been proposed in the literature for the initial stages of the dissociative chemisorption of silane (SiH 4 ) on the Si(1 1 1)7 × 7 surface. In this paper, geometry optimisation calculations using the extended Brenner empirical potential have been performed to determine which of these models yields the minimum energy structure. The lowest energy configurations are found to correspond to the dissociation of silane into SiH 2 and two hydrogen atoms. The minimum energy structure involves the adsorption of the two hydrogen atoms onto the dangling bonds of an adjacent adatom and rest atom, and the insertion of the remaining SiH 2 fragment into one of the adatom backbonds. These results are discussed in the light of the existing experimental data.

Previous work has shown that the extended Brenner potential provides a good description of the Si(111)7×7 surface and Si–H molecules. In this paper, we employ this empirical potential to study the interaction of atomic hydrogen with the Si(111)7×7 surface. Energy curves for a single hydrogen atom chemisorbed above the adatom and rest atom sites of the Si(111)7×7 surface, and the various equilibrium structures and binding energies of the hydrogen chemisorbed Si(111)7×7 surface, have been determined. These empirical potential calculations have been performed using both small and large clusters of atoms. Comparison of the results with previous ab initio Hartree–Fock/density functional theory calculations shows that the extended Brenner potential provides a good representation of the Si(111)7×7:H system.

Ab initio Hartree-Fock-DFT cluster calculations have been performed of the interaction of hydrogen with the Si(111)7 × 7 surface. These calculations have enabled the determination of the various equilibrium structures which result when up to five hydrogen atoms are allowed to adsorb near the adatom and rest atom sites of the Si(111)7 × 7 surface. As progressively more hydrogen atoms are chemisorbed near an adatom site, each hydrogen-bonded adatom is found to move from its original three-fold (T4) site (one hydrogen atom) to an adjacent bridge site (two and three hydrogen atoms), and then on-top of a neighbouring first layer silicon atom (more than three hydrogen atoms). The lowest calculated adatom desorption energy is found to be 2.40 eV and corresponds to the desorption of SiH2 from above a neighbouring first layer silicon atom. In contrast to an adatom, a hydrogen-bonded rest atom is found to remain close to its original three-fold equilibrium position. The smallest rest atom desorption energy is 2.10 eV and corresponds to an SiH3 surface complex.