Sublayer Si atoms as reactive centers in the chemisorption on Si(100): Adsorption of C2 H2 and C2 H4

The chemisorption of C2 H2 and C2 H4 on Si(100) is re-examined by first-principles calculations to sort out the relative importance of the intradimer di- σ and interdimer end-bridge structures. Based on reactive trajectories calculated by ab initio molecular dynamics, we identify a reaction channel by the nudged elastic band method, in which a sublayer Si atom is attacked. In the case of C2 H2 adsorption, this channel is barrierless and plays an important role as an intermediate that leads to the relative abundance of the interdimer end-bridge structure. In the case of C2 H4, the channel is not as important due to bond-angle distortions. The formation of intradimer di- σ structures is preferred, but interdimer end-bridge structures should be a minor product. Scanning tunnel microscope images and vibrational frequencies are also calculated for the identification of these structures in future experiments.