Cluster model study of the chemisorption of atomic carbon on Si(100) surfaces (original) (raw)
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The interaction of carbon with Si(1 1 1):As and Si(1 1 1):H surfaces, a theoretical study
Surface Science, 2009
Density functional theory calculations have been performed to determine the adsorption site of carbon at the Si(1 1 1):As and Si(1 1 1):H surfaces at different coverages. The As-and H-passivated surfaces were simulated by replacing the topmost Si layer by As or by saturating the Si dangling bonds with hydrogen atoms, respectively. Different high symmetry sites were considered. Carbon was placed successively in the fourfold (T 4 ) or threefold coordinated (H 3 ), the ontop (T 1 ) sites or substituted for a Si atom in the S 5 position located underneath the Si adatom in the T 4 site. We found that the preferred carbon adsorption site depends on the coverage of the passivated surfaces. At low coverages i.e. at 1/16 ML and 1/3 ML, it prefers a distorted T 4 position whereas at 1 ML, it occupies an H 3 site. This contrasts with the clean surface where the most energetically favored site is the S 5 at all coverages. Carbon adsorption induces a significant change in the structural geometry of the surface atoms, leading to a charge re-arrangement in the surface layers.
Cluster model study of the chemisorption of atomic hydrogen on the basal plane of graphite
Surface Science, 1987
Structural parameters for chemisorption of atomic carbon above a Si(100) surface have been obtained through a Si35H 32 cluster model and a MINDO/3 hamiltonian. The most stable position has been found to be the bridge one when considering the unrelaxed surface. The stability increases about 14 kcal/mol when relaxation of the surface is allowed. Further research has been carried out using a reduced cluster model (SigH i2) at the ab initio Hartree-Fock level of calculation. Results confirm the increase of stability of the relaxed system. At this level, the binding energy is 90 kcal/mol for the unrelaxed surface and the stabilization when the surface is relaxed is of about 20% with respect to the non-relaxed surface.
Surface Science, 1996
The chemisorption of fluorine on atomic clusters modelling an adatom and a rest-atom site of the Si(111)7 × 7 surface is studied using the first principles all-electron Hartree-Fock and Density Functional method embodied in the Gaussian92/DFT package. A number of equilibrium geometries corresponding to n fluorine atoms chemisorbing onto an adatom (n _< 5) or rest-atom (n < 6) cluster are discussed. Our results show that, as progressively more fluorine is chemisorbed onto an adatom site, the fluorine bonded silicon adatom moves from its original 3-fold (T 4) site (one fluorine atom), to an adjacent bridge site (2 fluorine atoms) and then on top of a neighbouring first layer atom (3 fluorine atoms). For a fluorine bonded silicon rest-atom, a series of strained surface configurations are found as a result of the displacement of the rest-atom from its 3-fold equilibrium position. The lowest calculated resorption energy is 0.11 eV and corresponds to SiF 4 bonded to a rest-atom site. The smallest resorption energy for the adatom site is found to be 1.09 eV for the case of SiF 2. Extrapolating these results to the fluorinated Si(111)7 × 7 surface suggests that a low fluence of fluorine should produce a stable fluorosilyl layer which consists mainly of SiF and SiF 3 species, and corresponds to a fluorine coverage of 1.35 ML. The presented results may be of great importance for the understanding and modelling of the etching of silicon surfaces by fluorine.
Theoretical Studies of CO Adsorption on Si(100)-2 × 1 Surface
The Journal of Physical Chemistry B, 1998
Ab initio molecular orbital and density functional calculations have been carried out to investigate the adsorption of CO on the Si(100)-2 × 1 surface using the Si 9 H 12 and Si 13 H 20 cluster models of the surface. It was found that B3LYP/6-31G(d) is a reasonable level of theory for calculation of the geometries of the clusters and adsorbates, as well as energetics of the adsorbates of the CO/Si(100)-2 × 1 surface. The addition of a doubly contracted polarizarion d-function for the non-hydrogen atoms changes the calculated CO desorption energy by 1 kcal/mol. Increasing the size of the cluster from Si 9 H 12 to Si 13 H 20 , in general, increases the CO desorption energy by 1-2 kcal/mol, while it does not change the Si d-Si d , Si d-Si sub , and Si sub-Si sub bond distances, which suggests that the Si 9 H 12 cluster is a good model for the single-dimer cluster. Interaction of the CO molecule with the surface dramatically changes the Si d-Si d and Si d-Si sub bond distances corresponding to the silicon dimer on the surface and that between the first-and second-layer atoms, respectively. These results suggest that the geometry relaxation of the cluster upon interaction with gas molecules should be taken into account. Different adsorption geometries of CO on the silicon surface dimer have been studied. The adsorbed CO is most stable when bonded perpendicularly to the surface dimer with the C atom attached to one of the Si atoms. The calculated CO desorption energy at the B3LYP/6-311G(2d) level, 10.5 kcal/mol, is in good agreement with the experimental value, 11.4 kcal/mol. Vibrational frequencies of the different CO adsorption isomers have been analyzed. For the OC-normal adsorption process, an extensive search for its transition state failed to locate it; this suggests that the adsorption reaction is a nonactivated process with zero barrier.
A new strategy to model the Si(100) surface
Comptes Rendus Chimie, 2005
We have built a large, reliable model of a Si(100) surface, which is appropriate for the study of surface adsorption processes of large molecules. We have performed QM/QM hybrid calculations in this study, and the results have been successfully compared with experimental values. The clusters studied with this methodology allow for the concentration of the computational effort in the most important parts of the cluster, using DFT, while treating the outer parts with the semi-empirical method AM1. Several problems were found and solutions were investigated to mitigate their effect or simply resolve them. From the comparison of our large cluster with ab initio only smaller clusters, it was found that the methodology used here presents an opportunity to work with much larger clusters than the present ones without incurring in large computational expenses. The largest investigated cluster that presented excellent results was Si 252 H 100. To cite this article:
Solid State Communications, 2002
Energetics and structural relaxations related to the surface complexes formed by mixed Si±Ge and C±C dimer adsorption on prede®ned adsorption sites on a (2 £ 1) reconstructed Si (001) surface are investigated. Monte Carlo simulated annealing procedure is used in conjugation with Tersoff's semi-empirical potentials. The reliability check of the method is performed by comparing our results for the case of Si±Ge dimer adsorption with the results reported by using ab initio pseudo-potential calculations. The agreement is found to be good. For carbon dimer adsorption, the nucleation centers are found to be different from those for Si and Ge. It is seen that carbon has a tendency to get adsorbed at the dangling bond site, or to form a Si±C±C±Si chain like structure under speci®c conditions.
Solid State Communications, 1988
The interaction of atomic F and CI with C4H9 cluster model has been studied by using nonempirical Hartree-Fock computations with basis sets of increasing flexibility. Although the inclusion of polarization functions is mandatory for a quantitative investigation even computations at the minimal basis set or semiempirical MNDO level are able to provide general trends both for chemisorption energies and equilibrium geometries of different absorbates. As in the case of silicon surfaces the charge transfer and the chemisorption energy decrease with the atomic number of the absorbate and the equilibrium bond length increases in the same sense. The local nature of the chemisorption bond is confirmed by computations employing the C10Hls cluster both at STO-3G and MNDO levels.
Journal of Molecular Structure-theochem, 1993
The configuration interaction (CI) approach to the study of chemisorption on metal and semiconductor surfaces is described through the use of some selected examples as atop and four-fold H on Cu(lOO), four-fold interaction of 0 on Cu(100) and Al on Si(ll1) at three different sites. Electronic correlation effects on structural parameters and on the description of the surface chemical bond are analyzed by comparing Hartree-Fock and CI wavefunctions. The analysis of dipole moment curves and of the electrical field effects induced by a uniform external field permits the importance of electronic correlation to be quantified in the description of the chemical interaction between an adsorbate and a surface.
First principles calculations of the Sc adsorption on Si(001)-c(2×4)
Surface Science, 2012
We have investigated the energetics and the atomic structure of the adsorption of Sc on the Si(001)-c(2 × 4) surface using first principles total energy calculations, within the periodic density functional. The Sc adsorption has been studied at high symmetry sites considering different concentrations. We have first explored the one atom case and then increased the coverage up to a 0.25 of a monolayer of Sc. For the adsorption of one Sc atom we have obtained that the most stable configuration corresponds to the adsorption in the trench between two Si dimers, at the C1 (cave) site. The interaction of the adsorbed Sc with the Si dimers induces a decrease of the dimers buckling amplitude. On the other hand Si dimers without interaction with the adsorbate have buckling amplitudes similar to those of the clean Si surface. When the Sc coverage is increased to two Sc atoms, the most stable structure corresponds to the adsorption at two consecutive V (valley-bridge) sites along the trench between Si dimers, resulting in the weakening of some of the Si dimers bonds. This result indicates that the formation of one dimensional Sc chains on the silicon surface is energetically and kinetically favorable.