Two-photon photoemission spectroscopy of TiO2(110) surfaces modified by defects and O2 or H2O adsorbates

Ken Onda, Bin Li, Hrvoje Petek

Research output: Contribution to journalArticle

155 Citations (Scopus)

Abstract

Two-photon photoemission (2PP) spectra of TiO2(110) surfaces are measured for the nearly perfect surface, and surfaces modified by introduction of defects and adsorbed molecules. Defects are generated on nearly perfect surfaces by three methods: electron irradiation, annealing in vacuum, and Ar+ sputtering. Nearly perfect or damaged surfaces can be further modified by adsorption of O2 or H2O molecules. 2PP spectroscopy is used to systematically investigate the work function change due to the presence of defects or adsorbates. 2PP spectroscopy detects both surface and bulk oxygen vacancy defects. We find from the results on oxygen adsorption that oxygen vacancies created by electron irradiation, are localized on the surface and may be removed by O2 adsorption at 100 K. The surface defects are substantially different from those created by annealing or by ion sputtering where vacancies in the subsurface region are proposed. We find that O2 acts as an acceptor molecule on surface defect states whereas H2O acts as a donor molecule. From simulation of the work function change as a function of dosage, the dipole moment of H2O adsorbed on TiO2 surface is derived to be 0.5 D positive outward. We also find an unoccupied electronic state 2.45 eV above the Fermi level that appears at submonolayer coverage of H2O, which we tentatively assign to charge transfer from surface titanium ions to the surface-adsorbed H2O molecules or OH ligands.

Original languageEnglish
Article number045415
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume70
Issue number4
DOIs
Publication statusPublished - Jul 1 2004

Fingerprint

Adsorbates
Photoelectron spectroscopy
photoelectric emission
Photons
Defects
defects
photons
spectroscopy
Molecules
Electron irradiation
Surface defects
molecules
Oxygen vacancies
electron irradiation
surface defects
Adsorption
adsorption
Sputtering
oxygen
sputtering

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Cite this

Two-photon photoemission spectroscopy of TiO2(110) surfaces modified by defects and O2 or H2O adsorbates. / Onda, Ken; Li, Bin; Petek, Hrvoje.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 70, No. 4, 045415, 01.07.2004.

Research output: Contribution to journalArticle

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