Density functional studies on the adsorption of acetylene and ethylene molecules on Ge(001) surface

By using the first-principles method based on density functional theory and slab model, we have studied the atomic geometries and electronic structures of adsorptions of ethylene and acetylene on Ge(001) surface. By studying a series of possible adsorption configurations for both the acetylene and ethylene, we found that di-σ configuration is the most stable one at coverage of 0.5 ML (monolayer), while paired end-bridge configuration is the most stable one at the coverage of 1.0 ML. Our study of the electronic band structure show that both the adsorption configuration and coverage are important factors for the band structure near the Fermi level, the reason is that the surface states near the Fermi level are from the Ge atoms of the dimer on the surface, and mainly determined by the coordinate environment of Ge atoms, which are related to the adsorption model and coverage. While for the same adsorption model, the adsorption configuration and electronic structure are similar for both the ethylene and acetylene molecules. Moreover, the adsorption on Ge(001) and Si(001) have been compared for the two molecules.