Valence-band structure ofTiO2along the Γ-Δ-Xand Γ-Σ-Mdirections

Abstract

Angle-resolved photoemission spectra of the (100) and (110) faces of Ti02 have been recorded in the photon-energy range from 18 to 47 eV. These normal emission data have been analyzed on the basis of direct transitions into free-electron-like final states, yielding valence-band dispersion relations, E(k), along the high-symmetry 5 and X lines of the bulk Brillouin zone. Polarization selection rules are derived for the appropriate nonsymmorphic space group, which are used to identify the symmetries of the valence bands. Empirical dispersion relations are compared with the results of a band-structure calculation, which employed an ab initio atomic orbital-based method. While there is reasonable agreement overall, for a 6-line empirical band at about 1.2 eV below the valence-band maximum (E"& ) there is no counterpart in the calculated bulk band structure. This discrepancy may be related to a Ti02(100) surface resonance predicted to lie 1.5 eV below E"& .

First-principles study of potassium adsorption onTiO2surfaces

“…4. The band gap of TiO 2 has been measured recently to be 4 eV, 15 which is somewhat larger than the value of 3 eV quoted previously. 54 Here the band gap is computed to be 12 eV.…”

“…The location of this state was determined, using band-mapping photoemission experiments, to be about 3 eV above the O 2p band maximum. 15 Theoretical calculations on the reduced ͑110͒ surface have reported similar states at 1-2 eV above the O 2p band 16,17 with the reduced Ti ions inducing local distortions of the lattice at the surface. 16 A more controlled reduction of the surfaces can be achieved by adsorbing species which readily donate electrons to the substrate.…”

Self-energy and excitonic effects in the electronic and optical properties ofTiO2crystalline phases

“…33,50 Assuming that the bulk electronic gap determination is not strongly affected by the surface states, we can adopt a value in the range of 3.3− 3.6 eV as a reference for rutile in the following discussion. Keeping also in mind an older measurement of 4.0 eV, 50 quite large degree of uncertainty exists in the experimental electronic gap of the rutile phase. To our knowledge, there are no reported measurements of the electronic band gap for anatase from combined UPS and IPES measurements.…”

“…32-45͒ and have been reinvestigated more recently. [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65] From the photoemission data on rutile 42,44,47,50,53,63 the electronic band gap, corresponding to the difference between the valence-band maximum ͑VBM͒ and the conduction-band minimum ͑CBM͒, has reported values of 3.3Ϯ 0.5 eV ͑Ref. 53͒ ͓ultraviolet photoemission spectroscopy ͑UPS͒ and inverse photoemission spectroscopy ͑IPES͔͒, 3.6Ϯ 0.2 eV ͑Ref.…”

Pre-edge structure analysis of Ti K-edge polarized X-ray absorption spectra in TiO2 by full-potential XANES calculations

“…This paper deals with the rutile phase of Tit2 which became an excellent case for testing new developments in bandstructure methods (Hamann et al, 1997). Although its electronic structure is now assumed to be well-known (Hardman et al, 1994;Sorantin & Schwarz, 1992;Glassford & Chelikowsky, 1992;Khan et al, 1991;Poumellec et al, 1991b), there is still a doubt about the interpretation of its x-ray absorption pre-edge structure at the Ti A'-edge, which is composed of three well defined features (usually labelled Al, A2 and A3). Indeed the pre-edge region is the subject of a large debate not closed yet: in section V-E, Farges et al (1997) recall the recent studies of the pre-edge structure.…”