Chemical structure and orientation of ethylene on Si(114)-(2 x 1)/c(2 x 2).

The basic chemical structure and orientation of ethylene chemisorbed on Si(114)-(2 x 1) at submonolayer coverage is characterized in ultrahigh vacuum using transmission Fourier transform infrared (FTIR) spectroscopy. The spectra are consistent with di-sigma bonding of ethylene to the surface with a preferential molecular orientation over macroscopic lengths. These results are supported by density functional theory (DFT) calculations of vibrational frequencies for optimized ethylene-Si(114) structures occupying the dimer and rebonded atom surface sites. A detailed analysis of the strong angular and polarization dependence of the C-H stretching mode intensities is also consistent with the adsorption structures identified by DFT, indicating that ethylene chemisorbs with the C-C bond axis parallel to the structural rows oriented along the [10] direction on the Si(114)-(2 x 1) surface. The results indicate that the unique structure of this surface makes it an excellent template for elucidating relationships between surface structure and organic reaction mechanisms on silicon.