Theoretical studies on the adsorption of Si and C chains onto unfaulted and faulted Si(111) surfaces

Density functional theory and ab initio elongation-method-based calculations have been performed on the adsorptions of Si and C chains on unfaulted and faulted Si(111) surfaces and of Si chains on the Si(111)-OH surface. The C-chain adsorptions on the faulted and unfaulted Si(111) surfaces have almost the same geometries but different reaction energies. The C chain adsorbs more easily on the faulted Si(111) surface than on the unfaulted surface. The Si linkage atom is stabilized upon adsorption of a C chain on the unfaulted and faulted Si(111) surfaces. The band gap of a Si(111)-OH surface with an adsorbed Si chain and a Si-O linkage becomes narrower with respect to that of a clean Si(111)-OH surface. The local density of states of the Si substrate atom in the Si-O linkage shows that the electron peaks become more localized and stronger near the conduction band after the adsorption of the Si chain. Because of the replacement of the H atom bonded to the O atom by the adsorption of the Si chain, the energy range of the occupied molecular orbitals of the O linkage atom becomes broader near the band gap. The reaction energy of a C chain on the faulted Si(111) surface remains constant with C-chain length.