228 research outputs found
Nature of band-gap states in V-doped TiO2 revealed by resonant photoemission
Band-gap states in V-doped TiO2 have been studied by photoemission spectroscopy over a range of photon energies encompassing the Ti 3p and V 3p core thresholds. The states show resonant enhancement at photon energies significantly higher than found for Ti 3d states introduced into TiO2 by oxygen deficiency or alkalimetal adsorbates. This demonstrates that the gap states relate to electrons trapped on dopant V cations rather than host Ti cations
Galore: Broadening and weighting for simulation of photoelectron spectroscopy
Galore simplifies and automates the process of simulating photoelectron spectra from ab
initio calculations. This replaces the tedious process of extracting and interpolating crosssectional weights from reference data and generates tabulated data or publication-ready
plots as needed. The broadening tools may also be used to obtain realistic simulated
spectra from a theoretical set of discrete lines (e.g. infrared or Raman spectroscopy)
High resolution X-ray photoemission study of nitrogen doped TiO 2 rutile single crystals
Abstract The electronic structure of nitrogen doped TiO 2 prepared by annealing single crystal rutile (1 1 0) substrates in NH 3 at elevated temperatures was investigated using high resolution X-ray photoelectron spectroscopy. NH 3 treatment at 600°C introduced N into the TiO 2 lattice without concomitant surface reduction of the rutile phase. This doping leads to bandgap narrowing associated with the appearance of new N 2p electronic states above the O 2p band in valence region photoemission spectra. Surface modification at the higher temperature of 700°C also produced bandgap narrowing but at the same time led to pronounced surface reduction
Electronic properties of antimony-doped anatase TiO2 thin films prepared by aerosol assisted chemical vapour deposition
The electronic properties of antimony-doped anatase (TiO2) thin films deposited via aerosol assisted chemical vapour deposition were investigated by a range of spectroscopic techniques. The incorporation of Sb(V) into the TiO2 lattice was characterised by X-ray absorption spectroscopy and resulted in n-type conductivity, with a decrease in sheet resistance by four-orders of magnitude compared to that of undoped TiO2 films. The films with the best electrical properties displayed charge carrier concentrations of ca. 1 × 1020 cm−3 and a specific resistivity as low as 6 × 10−2 Ω cm. Doping also resulted in an orange colouration of the films that became progressively stronger with increasing Sb content. X-ray photoelectron spectroscopy showed that substantial segregation of Sb(III) to the surface of the film was associated with the appearance of lone pair surface states lying above the top of the main O 2p valence band. The pronounced visible region absorption in the films is attributed to transitions from the Sb(III) states at surface and grain boundary interfaces into the conduction band. The segregation of Sb leads to p-type surface layers at high doping levels and limits the mobility in this new conducting oxide
Nature of the band gap of In2O3 revealed by first-principles calculations and x-ray spectroscopy
Bulk and surface sensitive x-ray spectroscopic techniques are applied in tandem to show that the valence band edge for In2O3 is found significantly closer to the bottom of the conduction band than expected on the basis of the widely quoted bulk band gap of 3.75 eV. First-principles theory shows that the upper valence bands of In2O3 exhibit a small dispersion and the conduction band minimum is positioned at Gamma. However, direct optical transitions give a minimal dipole intensity until 0.8 eV below the valence band maximum. The results set an upper limit on the fundamental band gap of 2.9 eV
Photoemission study of the metal-insulator transition in VO_2/TiO_2(001) : Evidence for strong electron-electron and electron-phonon interaction
We have made a detailed temperature-dependent photoemission study of
VO_2/TiO_2(001) thin films, which show a metal-insulator transition at \sim 300
K. Clean surfaces were obtained by annealing the films in an oxygen atmosphere.
Spectral weight transfer between the coherent and incoherent parts accompanying
the metal-insulator transition was clearly observed. We also observed a
hysteretic behavior of the spectra for heating-cooling cycles. We have derived
the ``bulk'' spectrum of the metallic phase and found that it has a strong
incoherent part. The width of the coherent part is comparable to that given by
band-structure calculation in spite of its reduced spectral weight, indicating
that the momentum dependence of the self-energy is significant. This is
attributed to by ferromagnetic fluctuation arising from Hund's rule coupling
between different d orbitals as originally proposed by Zylbersztejn and Mott.
In the insulating phase, the width of the V 3d band shows strong temperature
dependence. We attribute this to electron-phonon interaction and have
reproduced it using the independent boson model with a very large coupling
constant.Comment: 7 pages, 7 figures, submitted to Phys. Rev.
Electronic structure of In₂O₃ and Sn-doped In₂O₃ by hard x-ray photoemission spectroscopy
The valence and core levels of In₂O₃ and Sn-doped In₂O₃ have been studied by hard x-ray photoemission spectroscopy (hν=6000 eV) and by conventional Al Kα (hν=1486.6 eV) x-ray photoemission spectroscopy. The experimental spectra are compared with density-functional theory calculations. It is shown that structure deriving from electronic levels with significant In or Sn 5s character is selectively enhanced under 6000 eV excitation. This allows us to infer that conduction band states in Sn-doped samples and states at the bottom of the valence band both contain a pronounced In 5s contribution. The In 3d core line measured at hν=1486.6 eV for both undoped and Sn-doped In₂O₃ display an asymmetric lineshape, and may be fitted with two components associated with screened and unscreened final states. The In 3d core line spectra excited at hν=6000 eV for the Sn-doped samples display pronounced shoulders and demand a fit with two components. The In 3d core line spectrum for the undoped sample can also be fitted with two components, although the relative intensity of the component associated with the screened final state is low, compared to excitation at 1486.6 eV. These results are consistent with a high concentration of carriers confined close to the surface of nominally undoped In₂O₃. This conclusion is in accord with the fact that a conduction band feature observed for undoped In₂O₃ in Al Kα x-ray photoemission is much weaker than expected in hard x-ray photoemission
Insights into the electronic structure of OsO2 using soft and hard x-ray photoelectron spectroscopy in combination with density functional theory
Theory and experiment are combined to gain an understanding of the electronic properties of OsO2, a poorly studied metallic oxide that crystallizes in the rutile structure. Hard and soft valence-band x-ray photoemission spectra of OsO2 single crystals are in broad agreement with the results of density-functional-theory calculations, aside from a feature shifted to high binding energy of the conduction band. The energy shift corresponds to the conduction electron plasmon energy measured by reflection electron energy loss spectroscopy. The plasmon satellite is reproduced by many-body perturbation theory
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