Patterning of Si(001) with halogens: Surface structure as a function of the halogen chemical potential - art. no. 041402

Chlorine- and bromine-chemisorbed Si(001) surfaces at various coverages (th eta) are studied using first-principles density functional calculations. Di fferent stable reconstructions are obtained for the two halogen species. At theta =0.5, Br stabilizes a c(4 x 2) reconstruction with adatoms only on n ext-nearest neighbor dimers, whereas Cl stabilizes a p(4 x 2) structure wit h alternating fully chlorinated and empty dimer rows. At theta =1, a 3 x 2 reconstruction consisting of dimer rows separated by missing atom rows is m ost stable for Br, whereas for Cl such a structure is degenerate with the c onventional 2 x I reconstruction. These findings are in agreement with rece nt scanning tunneling microscopy experiments. They can be rationalized on t he basis of a stronger steric hindrance for Br.