First-Principles Studies of Functionalized Si(111) in Air and in Water

We have investigated structural, electronic and vibrational properties of hydrogen and methyl-terminated Si(111) surfaces both in air and in contact with water, by combining density functional theory and many-body perturbation theory within the GW approximations. The computed surface dipole moments for both H-Si(111) and CH3-Si(111) surfaces were found to be consistent with measured electron affinities (EAs), and can be explain by simple electronegative trends. While GW self-energy corrections greatly improve the absolute values of EAs, the EA difference of the two surfaces remains overestimated by about 0.3 eV. The variations in CH3 frequencies, e.g. the umbrella mode and CH stretching mode, for the surface in air and water are also well reproduced by our calculations. The influence exerted by the adsorption of water molecules on the hydrophobic H-Si(111) and CH3-(111) surfaces, in particular, on the EAs and the surface vibrational frequencies will be discussed and compared with recent experiments.\\[4pt] [1] A. Aliano, Y. Li, G. Cicero and G. Galli, J. Phys. Chem. C 114, 11898 (2010).\\[0pt] [2] Y. Li and G. Galli, Phys. Rev. B 82, 045321 (2010).