Adsorption of Cu and Ag atoms on Si(111) surfaces: Local density functional determination of geometries and electronic structures

Shih Hung Chou, Arthur J Freeman, S. Grigoras, T. M. Gentle, B. Delley, E. Wimmer

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

The electronic structures, adsorption geometries, chemisorption energies, and vibrational frequencies of single Cu and Ag atoms on Si(111) surfaces are determined by self-consistent total energy calculations using first principles, local density functional theory, with a numerical basis for a cluster of 20 Si atoms. The binding energy results reveal that both Cu and Ag adsorb in threefold hollow sites with equilibrium heights of 0.74 Å (Cu) and 1.48 Å (Ag) above the plane of the surface Si atoms. The adsorption energies are found to be 92 kcal/mol for Cu and 72 kcal/mol for Ag. Assuming a rigid substrate, the calculated frequencies of the perpendicular vibrational modes are 58 cm -1 for Cu and 90 cm-1 for Ag. The lateral diffusion barriers, assuming an unreconstructed rigid Si(111) surface, are found to be 12 and 8 kcal/mol for Cu and Ag, respectively. Calculations for Cu and Ag atoms being moved towards the interior of the cluster, including geometric relaxation of the nearest-neighbor Si atoms, demonstrate that Cu has a much lower vertical penetration barrier than Ag (4 vs 53 kcal/ mol). Therefore, at elevated temperatures, Cu can be expected to penetrate through the silicon surface, whereas Ag should remain above the surface Si atoms. Adsorbate-induced electron density differences indicate that Cu weakens the bonds between surface and subsurface silicon atoms, while Ag has a significantly smaller effect. Contour maps of eigenfunctions, which are associated with surface states, show that the dangling bonds of the silicon atoms at the surface interact with the metal s and d orbitals. The Cu 3d orbitals interact stronger than the Ag 4d electrons. The results suggest that the catalytic activity of Cu and the absence of activity of Ag in the syntheses of methylchlorosilanes ("direct process") is possibly due to the ability of Cu to penetrate into the surface thus forming the initial stages of a copper-silicide, whereas Ag stays at the surface and desorbs at higher temperatures.

Original languageEnglish
Pages (from-to)5177-5189
Number of pages13
JournalJournal of Chemical Physics
Volume89
Issue number8
Publication statusPublished - 1988

Fingerprint

Electronic structure
electronic structure
Adsorption
Atoms
adsorption
Geometry
geometry
atoms
Silicon
silicon
Dangling bonds
Diffusion barriers
orbitals
Surface states
Vibrational spectra
Adsorbates
Chemisorption
Binding energy
Eigenvalues and eigenfunctions
guy wires

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Adsorption of Cu and Ag atoms on Si(111) surfaces : Local density functional determination of geometries and electronic structures. / Chou, Shih Hung; Freeman, Arthur J; Grigoras, S.; Gentle, T. M.; Delley, B.; Wimmer, E.

In: Journal of Chemical Physics, Vol. 89, No. 8, 1988, p. 5177-5189.

Research output: Contribution to journalArticle

Chou, Shih Hung ; Freeman, Arthur J ; Grigoras, S. ; Gentle, T. M. ; Delley, B. ; Wimmer, E. / Adsorption of Cu and Ag atoms on Si(111) surfaces : Local density functional determination of geometries and electronic structures. In: Journal of Chemical Physics. 1988 ; Vol. 89, No. 8. pp. 5177-5189.
@article{534f8462290e42599be4f2bb405397b7,
title = "Adsorption of Cu and Ag atoms on Si(111) surfaces: Local density functional determination of geometries and electronic structures",
abstract = "The electronic structures, adsorption geometries, chemisorption energies, and vibrational frequencies of single Cu and Ag atoms on Si(111) surfaces are determined by self-consistent total energy calculations using first principles, local density functional theory, with a numerical basis for a cluster of 20 Si atoms. The binding energy results reveal that both Cu and Ag adsorb in threefold hollow sites with equilibrium heights of 0.74 {\AA} (Cu) and 1.48 {\AA} (Ag) above the plane of the surface Si atoms. The adsorption energies are found to be 92 kcal/mol for Cu and 72 kcal/mol for Ag. Assuming a rigid substrate, the calculated frequencies of the perpendicular vibrational modes are 58 cm -1 for Cu and 90 cm-1 for Ag. The lateral diffusion barriers, assuming an unreconstructed rigid Si(111) surface, are found to be 12 and 8 kcal/mol for Cu and Ag, respectively. Calculations for Cu and Ag atoms being moved towards the interior of the cluster, including geometric relaxation of the nearest-neighbor Si atoms, demonstrate that Cu has a much lower vertical penetration barrier than Ag (4 vs 53 kcal/ mol). Therefore, at elevated temperatures, Cu can be expected to penetrate through the silicon surface, whereas Ag should remain above the surface Si atoms. Adsorbate-induced electron density differences indicate that Cu weakens the bonds between surface and subsurface silicon atoms, while Ag has a significantly smaller effect. Contour maps of eigenfunctions, which are associated with surface states, show that the dangling bonds of the silicon atoms at the surface interact with the metal s and d orbitals. The Cu 3d orbitals interact stronger than the Ag 4d electrons. The results suggest that the catalytic activity of Cu and the absence of activity of Ag in the syntheses of methylchlorosilanes ({"}direct process{"}) is possibly due to the ability of Cu to penetrate into the surface thus forming the initial stages of a copper-silicide, whereas Ag stays at the surface and desorbs at higher temperatures.",
author = "Chou, {Shih Hung} and Freeman, {Arthur J} and S. Grigoras and Gentle, {T. M.} and B. Delley and E. Wimmer",
year = "1988",
language = "English",
volume = "89",
pages = "5177--5189",
journal = "Journal of Chemical Physics",
issn = "0021-9606",
publisher = "American Institute of Physics Publising LLC",
number = "8",

}

TY - JOUR

T1 - Adsorption of Cu and Ag atoms on Si(111) surfaces

T2 - Local density functional determination of geometries and electronic structures

AU - Chou, Shih Hung

AU - Freeman, Arthur J

AU - Grigoras, S.

AU - Gentle, T. M.

AU - Delley, B.

AU - Wimmer, E.

PY - 1988

Y1 - 1988

N2 - The electronic structures, adsorption geometries, chemisorption energies, and vibrational frequencies of single Cu and Ag atoms on Si(111) surfaces are determined by self-consistent total energy calculations using first principles, local density functional theory, with a numerical basis for a cluster of 20 Si atoms. The binding energy results reveal that both Cu and Ag adsorb in threefold hollow sites with equilibrium heights of 0.74 Å (Cu) and 1.48 Å (Ag) above the plane of the surface Si atoms. The adsorption energies are found to be 92 kcal/mol for Cu and 72 kcal/mol for Ag. Assuming a rigid substrate, the calculated frequencies of the perpendicular vibrational modes are 58 cm -1 for Cu and 90 cm-1 for Ag. The lateral diffusion barriers, assuming an unreconstructed rigid Si(111) surface, are found to be 12 and 8 kcal/mol for Cu and Ag, respectively. Calculations for Cu and Ag atoms being moved towards the interior of the cluster, including geometric relaxation of the nearest-neighbor Si atoms, demonstrate that Cu has a much lower vertical penetration barrier than Ag (4 vs 53 kcal/ mol). Therefore, at elevated temperatures, Cu can be expected to penetrate through the silicon surface, whereas Ag should remain above the surface Si atoms. Adsorbate-induced electron density differences indicate that Cu weakens the bonds between surface and subsurface silicon atoms, while Ag has a significantly smaller effect. Contour maps of eigenfunctions, which are associated with surface states, show that the dangling bonds of the silicon atoms at the surface interact with the metal s and d orbitals. The Cu 3d orbitals interact stronger than the Ag 4d electrons. The results suggest that the catalytic activity of Cu and the absence of activity of Ag in the syntheses of methylchlorosilanes ("direct process") is possibly due to the ability of Cu to penetrate into the surface thus forming the initial stages of a copper-silicide, whereas Ag stays at the surface and desorbs at higher temperatures.

AB - The electronic structures, adsorption geometries, chemisorption energies, and vibrational frequencies of single Cu and Ag atoms on Si(111) surfaces are determined by self-consistent total energy calculations using first principles, local density functional theory, with a numerical basis for a cluster of 20 Si atoms. The binding energy results reveal that both Cu and Ag adsorb in threefold hollow sites with equilibrium heights of 0.74 Å (Cu) and 1.48 Å (Ag) above the plane of the surface Si atoms. The adsorption energies are found to be 92 kcal/mol for Cu and 72 kcal/mol for Ag. Assuming a rigid substrate, the calculated frequencies of the perpendicular vibrational modes are 58 cm -1 for Cu and 90 cm-1 for Ag. The lateral diffusion barriers, assuming an unreconstructed rigid Si(111) surface, are found to be 12 and 8 kcal/mol for Cu and Ag, respectively. Calculations for Cu and Ag atoms being moved towards the interior of the cluster, including geometric relaxation of the nearest-neighbor Si atoms, demonstrate that Cu has a much lower vertical penetration barrier than Ag (4 vs 53 kcal/ mol). Therefore, at elevated temperatures, Cu can be expected to penetrate through the silicon surface, whereas Ag should remain above the surface Si atoms. Adsorbate-induced electron density differences indicate that Cu weakens the bonds between surface and subsurface silicon atoms, while Ag has a significantly smaller effect. Contour maps of eigenfunctions, which are associated with surface states, show that the dangling bonds of the silicon atoms at the surface interact with the metal s and d orbitals. The Cu 3d orbitals interact stronger than the Ag 4d electrons. The results suggest that the catalytic activity of Cu and the absence of activity of Ag in the syntheses of methylchlorosilanes ("direct process") is possibly due to the ability of Cu to penetrate into the surface thus forming the initial stages of a copper-silicide, whereas Ag stays at the surface and desorbs at higher temperatures.

UR - http://www.scopus.com/inward/record.url?scp=36549099163&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=36549099163&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:36549099163

VL - 89

SP - 5177

EP - 5189

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 8

ER -