Using the first-principle method with the density functional theory and the slab model, the geometries and electronic structures of the adsorptions of acetylene and ethylene molecules on Si(100) surface have been investigated. Our results indicate that the dimerized model is the most stable configuration for both ethylene and acetylene when the converge is 0.5 ML, while the end-bridge configuration becomes the most favorable structure when the converge increases to 1.0 ML. The analyses of the band structures show that the variations of the band gap could be explained by considering the coordination environment of Si atoms of the dimer, and for the same adsorption model, nearly identical band gap was observed for both ethylene and acetylene. The configuration of adsorption and the converge have obvious effects on the value of the band gap, as well as the origin of the smallest band gap. Moreover, our results demonstrate that the hybrid density functional method is suitable to describe the electronic structure of Si(100) surface, especially for the end-bridge model.

Key words: density functional theory, Si(100) surface, ethylene, acetylene, band structure