First-principles study of the adsorption ofC2H2and

Abstract

The adsorption of acetylene and ethylene on the Si͑100͒ surface is studied by first-principles densityfunctional calculations within the generalized gradient approximation. Both molecules are found to adsorb identically on the top of Si dimers, forming two bonds between C and Si atoms. This result does not support a recent photoelectron imaging observation where the adsorption sites of the two molecules differ from each other. Controversial issues, such as the intactness of the Si dimer bond and the saturation coverages of both adsorbed molecules, are discussed.

Acetylene adsorption on the Si(001) surface

“…4͒. Furthermore, our findings are also in agreement with the recent first-principles theoretical calculation by Cho and co-workers, 31 where coverage of 0.5 ML was found to correspond to the most stable configuration, but without the exclusion of a possible 1.0-ML coverage, but are in contrast with the theoretical estimation of 1-ML coverage by Tanida and Tsukada. 26 However, for the end-bridge configuration, the small difference between the adsorption energies for the 0.5-and 1-ML coverages ͓0.03 eV per (2ϫ2) unit cell͔ indicates that both coverages can coexist, which is inconsistent with the experimental observations, as in this case the sticking coefficient should not decrease smoothly, as observed by Cheng et al 4 Considering the phenomenological approach in the form of the Arrhenius equation, with the choice for the A factor between 10 13 Ϫ10 15 s Ϫ1 , 43 we have estimated that complete desorption of the C 2 H 2 molecule is unlikely, as it will occur only at very high temperatures ͑around 1600 K͒.…”

Acetylene adsorption on Si(100): A study of the role of surface steps

“…The C-C and Si-C distances therein reported are similar to the values reported in the literature for adsorption on the flat surface [9,15,17,18] and this also applies to the Mulliken charges transferred from silicon to the carbon atoms [10]. All these features are in agreement with the similarity of the adsorbed configurations on the flat surface and on steps, mentioned above.…”

“…However further experiments (see [3][4][5][6] and references therein) suggested the existence of different adsorption sites, though the assignment of the observed configurations to those sites is still hotly contended. Furthermore the dependence on temperature and coverage of the population of those sites indicates that the early stages of adsorption are kinematically, rather than thermodynamically, driven so that the motions of the molecule have to be carefully considered (earlier and recent references are [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], respectively. These studies offer a representative list of theoretical and experimental works up to date).…”

Chemical and electronic characterization of methyl-terminated Si(111) surfaces by high-resolution synchrotron photoelectron spectroscopy

“…2 For example, cycloaddition of the simplest and smallest alkene, ethylene, has been studied extensively by photoelectron spectroscopy. [6][7][8][9][10][11][12] The unreconstructed Si͑111͒-1 ϫ 1 surface, which can be made atomically flat on the scale of hundreds of Å through simple solution etching procedures that produce hydrogen termination of the silicon, provides another model substrate for the study of surface modification chemistry. 13 Recent studies of the ambient pressure modification of Si͑111͒ surfaces have focused on the preparation of straight-chain alkyl overlayers by wet chemical methods such as exposing the hydrogen-or halide-terminated Si surface to alkylmagnesium or alkyllithium reagents, [14][15][16] or by the free radical activation of a terminal alkene.…”