Theoretical study of the induced attachment of benzene to Si(111) 7 x 7

The structure of benzene adsorbed on Si(1 1 1) has been studied by AM1 and DFT calculations on large and small Si clusters, respectively. Four stable structures have been calculated, corresponding to local energy-minima of the potential-energy hypersurface. Pathways were calculated for the conversion from a strained di-sigma-bound state (S), proposed by previous authors, to a more strongly bound state (B) consisting of a phenyl perpendicular to the surface plus an H-atom bound to the surface. The present calculations give a phenyl-surface binding energy for structure B of D-c (C-Si) = 3.6 eV, compared to similar to1.0 eV total binding energy for the two strained C-Si bonds of structure S, with a barrier to S --> B conversion of 2.6 eV. These findings are consistent with the recent experimental observations of the radiation-induced attachment of benzene and chlorobenzene to Si(1 1 1) 7 x 7, thought to involve conversion of two strained sigma bonds (structure S; SiC6H6-Si) into a single strong sigma bond (structure B; C6H5-Si). (C) 2003 Elsevier B.V. All rights reserved.