A Model Study of CO−CO Adsorbate Interaction on Si(100)-2×1

Abstract

The CO-CO adsorbate interaction on Si(100)-2×1 has been investigated with ab initio molecular orbital and hybrid density functional theory calculations using cluster models of the surface. Different adsorption combinations for one and two CO molecules on single-and double-dimer cluster models, Si 9 H 12 and Si 15 H 16 , respectively, are described. Our calculations indicate that the second CO molecule is physisorbed on the same surface Si dimer where the first CO molecule is chemisorbed. The chemisorption of the first CO molecule induces a change in the charge of the surface Si dimer atoms which inhibits further adsorbate-surface interaction. The dissociation energy of the physisorbed second CO molecule is less than 1 kcal/mol. Adsorption of the second CO molecule on the second Si dimer is energetically preferred over coadsorption of CO on the same Si dimer. The 2OC-normal.d14 structure is the most stable configuration, with the two CO molecules adsorbed diagonally across the two Si dimers. The dissociation energy of the chemisorbed second CO molecule in the 2OC-normal.d14 structure is 13.8 kcal/mol, about 4 kcal/mol less stable than the first adsorbed CO. Adsorption of two CO molecules in a bridge configuration indicates a weak surface-adsorbate and/or adsorbate-adsorbate interaction. The dissociation energy of the single chemisorbed CO in the bridged state is 5.0 kcal/mol while that of the second CO is 1.7 kcal/mol. A mixed configuration, i.e., OC-normal with OC-bridge, was found to be unstable based on the Si 15 H 16 surface model.

Adsorption, Isomerization, and Decomposition of HCN on Si(100)2 × 1: A Computational Study with a Double-Dimer Cluster Model

“…Recently, we have carried out a series of quantum-chemical studies on the adsorption mechanisms of CO, , NH 3 , , HN 3 , C 2 H 2 , CH 3 OH, CH 2 O, and HCOOH 12 with the reconstructed Si(100)-2 × 1 surface using the density functional theory and the cluster models of the surface. − We have also extended our theoretical study to the adsorption, isomerization, and decomposition of the HCN molecule on the Si(100)-2 × 1 surface. The preliminary result of this work using a single-dimer Si 9 H 12 surface model has been published previously .…”

Adsorption of CO Molecules on Si(001) at Room Temperature

“…Early theoretical studies reported that both T-CO and B-CO were stable, , which is in contrast to a recent theoretical result that the B-CO is unstable . A model of CO–CO adsorbate interaction on the Si(001)-(2 × 1) surface was also calculated by using cluster models of the surface …”

“…8 A model of CO−CO adsorbate interaction on the Si(001)-(2 × 1) surface was also calculated by using cluster models of the surface. 9 Thus, previous studies on the CO adsorption on Si(001) suggest scattered adsorption behaviors lacking a consensus. Some reported a unique adsorption configuration, while others reported two different configurations.…”

Molecular Motion Induced by Multivibronic Excitation on Semiconductor Surface

“…The Si(001)- c (4 × 2) surface adsorbs CO molecules below ∼100 K with an adsorption probability close to unity without decomposition. , There are two stable adsorption sites, − where CO either (i) terminates a dangling bond at the down-Si of a dimer (T-CO), or (ii) sits on the metastable bridge site of two Si atoms of the dimer (B-CO). On a clean surface, T-CO is the ground-state configuration, and the formation of B-CO requires an activation energy of 1.1 eV, which can be achieved, for example, by an accelerated CO molecular beam .…”