Acetylene adsorption on the Si(001) surface

Abstract

Using a first-principles pseudopotential technique, we have investigated the adsorption of C 2 H 2 on the Si͑001͒ surface. We have found that, at low temperatures, the di-bond configuration is the most stable structure from the energetic point of view. According to our calculations C 2 H 2 adsorbs preferentially on the alternate dimer sites, corresponding to a coverage of 0.5 monolayer. Our calculated surface band structure suggests that the end-bridge configuration, recently pointed out as a more favorable configuration by firstprinciples calculations, presents a metallic character and thus is Peierls unstable. The di-adsorbed system is characterized by symmetric and slightly elongated Si-Si dimers, and by a symmetric CC bond with length close to the double carbon bond length of the ethylene molecule. Our total-energy calculations suggest that other metastable configurations, like the 1,2-hydrogen transfer, the p bridge and the tetra-model are also possible. Available high-resolution electron-energy-loss spectroscopy experimental data are reinterpreted to support the existence of the tetra-model.

CH3CN on Si(001): adsorption geometries and electronic structure

“…Upon the adsorption of CH 3 -CN, the Si-Si dimer gets elongated by approximately 2% and becomes symmetric. This is in agreement with experimental [6] as well as theoretical [7] findings for other small hydrocarbon molecules, like acetylene and ethylene. Structural data for the Si-Si dimers that do not correspond to an adsorption site are not discussed, as they are very similar to the values found for the free surface.…”

“…Structural data for the Si-Si dimers that do not correspond to an adsorption site are not discussed, as they are very similar to the values found for the free surface. For the adsorbed structure, the calculated C-H bond length of ∼1.11Å is in good agreement with early theoretical estimates for other small hydrocarbon molecules [7] and is close to that observed for the free CH 3 -CN molecule. Our calculations also indicate that the C-Si bond length is approximately 1.90Å, which is again comparable to the C-Si bond length observed for other hydrocarbons (see, for example, Ref.…”

“…Our calculations also indicate that the C-Si bond length is approximately 1.90Å, which is again comparable to the C-Si bond length observed for other hydrocarbons (see, for example, Ref. [7]). …”

Theoretical modelling of surface phonons

“…Unfortunately, as can be noted from the table, there is a large spread in C-C vibrational modes from HREELS measurements from different groups [23][24][25]. Although total energy calculations [26] suggest that di-σ -bond structure is the most stable, some of the metastable configurations, such as the tetra-σ model, are also possible. Indeed, Nishijima et al [23] have reinterpreted their HREELS data to support the tetra-σ model.…”

“…More work is required to finalise the reaction of the molecule with the Si(001) surfaces. [26]. [24] 2980 1450 1240 1065 680 HREELS [25] 2980 1450 1240-1065 680…”