Adsorption and reaction processes of physisorbed molecular oxygen on Si(111)-$(7\ifmmode\times\else\texttimes\fi{}7)$

Adsorption and reaction processes of physisorbed molecular oxygen on Si(111)- $(7 \times 7)$

Kazuyuki Sakamoto, H. M. Zhang, and R. I. G. Uhrberg

Phys. Rev. B 72, 075346 – Published 18 August 2005

Abstract

The adsorption and reaction processes of physisorbed oxygen molecules on a Si(111)- $(7 \times 7)$ surface have been investigated using time-resolved O $1 s$ core-level photoemission measurements at 45 K. Physisorbed oxygen molecules are only observed at 45 K and lower temperatures on a Si(111)- $(7 \times 7)$ surface. At the dosage when the dangling bonds are saturated by chemisorbed oxygen, the coverage of the physisorbed species increases drastically. This result indicates that oxygen species, which are chemisorbed on top of adatoms, modifies the potential energy curve for an oxygen molecule approaching the surface such that physisorbed oxygen molecules are stabilized. Further, the longer lifetime at a higher dosage indicates that an intermolecular force plays a role for the stabilization of this species. Taking these results into account, an oxidation stage-dependent gas-surface interaction for an oxygen molecule approaching the Si(111) surface is suggested.

Received 16 November 2004

DOI:https://doi.org/10.1103/PhysRevB.72.075346

Authors & Affiliations

Kazuyuki Sakamoto^1,*, H. M. Zhang², and R. I. G. Uhrberg²

¹Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
²Department of Physics and Measurement Technology, Linköping University, S-581 83 Linköping, Sweden

^*Electronic address: sakamoto@surface.phys.tohoku.ac.jp

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Vol. 72, Iss. 7 — 15 August 2005

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Figure 1
(Color online) (a) One-dimensional potential energy diagrams illustrating the gas-surface interaction that a diatomic oxygen molecule approaching a surface feels. $Z$ corresponds to the distance from the surface. (b) Schematic illustrations of the bonding configurations of chemisorbed oxygen species discussed in the text. The notations “paul” and “grif” indicate $O_{2}$ molecules adsorbed on top of adatoms of a Si(111)- $(7 \times 7)$ surface, and “ad” and “ins” correspond to an O atom bonding on top of a Si adatom and to an O atom inserted into its back bond.Reuse & Permissions
Figure 2
(Color online) O $1 s$ core-level spectrum of a 10 L $O_{2}$ exposed Si(111)- $(7 \times 7)$ surface at 45 K, recorded 45 min after the exposure. The open circles are the experimental data, and the solid line overlapping the circles is the fitting result that is obtained using the components shown below the spectrum.Reuse & Permissions
Figure 3
(Color online) (a) Normalized dosage-dependent intensities of the 528.7-, 533.1-, 534.6-, and 537.6-eV O $1 s$ components. The intensity of each component is normalized with its maximum intensity in (a). (b) Dosage-dependent intensities of the 528.7-, 533.1-, 534.6-, and 537.6-eV O $1 s$ component up to 4 L. The crosses in (b) are the sum of the intensities of the 528.7- and 534.6-eV components, which are multiplied by 3. The intensities in (a) and (b) are obtained by continuously measuring photoemission spectra of the Si(111) surface exposed to ambient $O_{2}$ pressures of $1 \times 10^{- 9} Torr$ at dosages up to 3 L and of $5 \times 10^{- 9}$ Torr at dosages above 3 L. The difference in time between one data point and the next is approximately 30 s.Reuse & Permissions
Figure 4
(Color online) Time dependences of the O $1 s$ core-level intensities for the physisorbed oxygen molecules (the sum of the intensities of the 537.6- and 538.8-eV components) of 1, 2, 5, and 10 L oxygen exposed surfaces (open symbols), and the 533.1- and 533.7-eV components of a 10 L oxygen exposed surface (filled symbols). The inset shows the time-dependent intensities of the O $1 s$ core-level of the physisorbed oxygen of a 10 L exposed surface obtained under continuous photon irradiation (solid line), and by turning off the photon irradiation for a period (photon irradiation was turned off between measuring the open circles).Reuse & Permissions
Figure 5
(Color online) One-dimensional potential energy diagrams illustrating the gas-surface interaction that an oxygen molecule approaching a Si(111)- $(7 \times 7)$ surface feels on the time scale of the present study. (a)–(d) show the potential energy diagrams at different stages of oxidation.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Adsorption and reaction processes of physisorbed molecular oxygen on Si(111)- $(7 \times 7)$

Kazuyuki Sakamoto, H. M. Zhang, and R. I. G. Uhrberg

Phys. Rev. B 72, 075346 – Published 18 August 2005

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Physical Review B

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Adsorption and reaction processes of physisorbed molecular oxygen on Si(111)-(7×7)

Kazuyuki Sakamoto, H. M. Zhang, and R. I. G. Uhrberg

Phys. Rev. B 72, 075346 – Published 18 August 2005

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Adsorption and reaction processes of physisorbed molecular oxygen on Si(111)- $(7 \times 7)$