Molecular dynamics simulations and potential energy calculations have been performed to investigate the dissociative chemisorption of disilane (Si 2 H 6 ) on the Si(001)2ϫ1 surface. These calculations have been carried out using the extended Brenner ͑XB͒ empirical potential. The minimum energy atomic configurations for SiH 3 , SiH 2 , and H-Si-Si-H ͑Si 2 H 2 ͒ species chemisorbed on the Si(001)2ϫ1 surface have been determined. The chemisorption of SiH 3 radicals has been observed to occur predominantly at the dangling bond sites of the Si͑001͒ surface. The most stable SiH 2 configurations are found to be the on-dimer and intrarow structures. Seven different Si 2 H 2 chemisorption structures have been investigated and the on-dimer-B structure found to be the most energetically favorable. These theoretically predicted structures are discussed in the light of recent experimental studies. Comparison of the results of these XB potential energy calculations with all-electron ab initio cluster calculations has also been made for a number of these different chemisorption structures. ͓S0163-1829͑99͒13135-7͔ PHYSICAL REVIEW B 15 SEPTEMBER 1999-II VOLUME 60, NUMBER 12 PRB 60 0163-1829/99/60͑12͒/8686͑9͒/$15.00 8686
The various equilibrium structures of the hydrogen chemisorbed surface are investigated using the semiempirical molecular orbital Austin 1 calculational method (AM1). Up to five hydrogen atoms are allowed to adsorb near the corner adatom, centre adatom and restatom adsorption sites of the surface. The results obtained from minimizing the energy of the system show very little difference between the chemisorption processes occurring at the two different adatom sites. In both cases, as progressively more hydrogen atoms are chemisorbed, the hydrogen bonded adatom is found to move from its original threefold (T4) site (one hydrogen atom), to an adjacent bridge site (two or three hydrogen atoms) and then on top of a neighbouring first-layer silicon atom (more than three hydrogen atoms). The lowest calculated adatom desorption energies are 1.59 and 1.62 eV, and correspond to the desorption of at a corner adatom and centre adatom site, respectively. In contrast to an adatom, a hydrogen bonded restatom is found to remain close to its original threefold equilibrium position. The smallest desorption energy for this site is 0.75 eV and also corresponds to an surface complex.
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