Hartree-Fock-DFT cluster calculations 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.