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Your search keyword '"Egdell, R. G"' showing total 190 results
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190 results on '"Egdell, R. G"'

1. Revisiting the origin of satellites in core level photoemission of transparent conducting oxides: the case of $n$-doped SnO$_2$

Author

Borgatti, F., Berger, J. A., Céolin, D., Zhou, J. S., Kas, J. J., Guzzo, M., McConville, C. F., Offi, F., Panaccione, G., Regoutz, A., Payne, D. J., Rueff, J. -P., Bierwagen, O., White, M. E., Speck, J. S., Gatti, M., and Egdell, R. G.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

The longstanding problem of interpretation of satellite structures in core level photoemission spectra of metallic systems with a low density of conduction electrons is addressed using the specific example of Sb-doped SnO$_2$. Comparison of {\it ab initio} many-body calculations with experimental hard X-ray photoemission spectra of the Sn 4$d$ states shows that strong satellites are produced by coupling of the Sn core hole to the plasma oscillations of the free electrons introduced by doping. Within the same theoretical framework, spectral changes of the valence band spectra are also related to dynamical screening effects. These results demonstrate that, for the interpretation of electron correlation features in the core level photoelectron spectra of such narrow-band materials, going beyond the homogeneous electron gas electron-plasmon coupling model is essential., Comment: 6 PAGES, 4 FIGURES

Published
2017
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3. Nature of the Band Gap of In₂O₃ Revealed by First-Principles Calculations and X-Ray Spectroscopy

Author

Walsh, Aron, Silva, Juarez L. F. Da, Wei, Su-Huai, Körber, C., Klein, Andreas, Piper, L. F. J., DeMasi, Alex, Smith, Kevin E., Panaccione, G., Torelli, P., Payne, D. J., Bourlange, A., and Egdell, R. G.

Abstract

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 Γ. 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.

Published
2022

4. Electronic structure of In₂O₃ and Sn-doped In₂O₃ by hard x-ray photoemission spectroscopy

Author

Körber, C., Krishnakumar, V., Klein, Andreas, Panaccione, G., Torelli, P., Walsh, A., Silva, J. L. F. Da, Wei, S.-H., Egdell, R. G., and Payne, D. J.

Abstract

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.

Published
2022

8. Theoretical and Experimental Study of the Electronic Structures of MoO3and MoO2

Author

Scanlon, David O., Watson, Graeme W., Payne, D. J., Atkinson, G. R., Egdell, R. G., and Law, D. S. L.

Abstract

The geometric and electronic structures of MoO3and MoO2have been calculated using the generalized gradient approximation to density functional theory. The calculated cross-section weighted densities of states are compared with high-resolution X-ray photoemission spectra. There is very good agreement between the calculated structures and those determined previously by X-ray diffraction and between the computed densities of states and the present photoemission measurements. MoO2is shown to be a metallic material, as is found experimentally, but the Fermi level sits in a distinct trough in the density of states. Satellite peaks found in core photoemission spectra of MoO2are shown to derive from final state screening effects in this narrow band metallic material.

Published
2024
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9. Identification of the Mechanism of Electrocatalytic Ozone Generation on Ni/Sb-SnO2

Author

Christensen, P. A., Attidekou, P. S., Egdell, R. G., Maneelok, S., Manning, D. A. C., and Palgrave, R.

Abstract

This paper reports a systematic study of the codoping of SnO2with Sb and Ni to identify the mechanism responsible for the electrocatalytic generation of ozone on Ni/Sb-SnO2. On the basis of interpretation of a combination of X-ray diffraction, BET surface area measurements (N2), and thermal analysis, the formation of ozone appears to take place on particle surfaces of composite Sb-SnO2grains and is controlled by diffusion of OH along internal crystallite surfaces within the grain. Sb-doped SnO2is inactive with respect to ozone evolution in the absence of Ni, demonstrating a synergic interaction between nickel and antimony. From X-ray photoelectron spectroscopy (XPS) investigations, Sb(V) ions substitute for Sn(IV) in the lattice with a preference for centrosymmetric coordination sites, while the Sb(III) ions occur at grain surfaces or boundaries. Ni was not detected by XPS, being located in the subsurface region at concentrations below the detection limit of the instrument. In addition to identification of a possible mechanism for ozone formation, the study resulted in the production of active nanopowders which will allow the fabrication of high-surface-area anodes with the potential to exceed the space-time yields of β-PbO2anodes, permitting the application the Ni/Sb-SnO2anodes in the treatment of real waters.

Published
2024
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10. Surface composition and electronic structure of the In4+xSn3-2xSbxO12 (0⩽x⩽1) solid solution.

Author

O'Neil, D. H., Egdell, R. G., and Edwards, P. P.

Subjects
*ENERGY bands, *ATOMIC structure, *ELECTRICAL properties of condensed matter, *SOLID solutions, *CRYSTALLIZATION
Abstract

The electronic structures of In4Sn3O12, In5 SnSbO12 and the intermediate solid solution In4+xSn3-2xSbxO12 have been studied by x-ray photoemission spectroscopy. The surfaces were found be consistently rich in indium and deficient in tin, with the extent of the deviation from bulk stoichiometry decreasing with increasing cosubstitution of In and Sb for Sn.We find that the valence band structure of the In4+xSn3-2xSbxO12 solid solution evolves with the degree of cosubstitution and shows well-defined features that arise from the hybridization of O 2p states with In 5s, Sn 5s, and Sb 5s states. We determine the fundamental electronic gaps of In4Sn3O12 and In5SnSbO12 as 2.66 eV and 2.79 eV, respectively. [ABSTRACT FROM AUTHOR]

Published
2010
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11. The influence of Sn doping on the growth of In2O3 on Y-stabilized ZrO2(100) by oxygen plasma assisted molecular beam epitaxy.

Author

Bourlange, A., Payne, D. J., Palgrave, R. G., Zhang, H., Foord, J. S., Egdell, R. G., Jacobs, R. M. J., Veal, T. D., King, P. D. C., and McConville, C. F.

Subjects
MOLECULAR beam epitaxy, TIN, PLASMA gases, CONDUCTION bands, HIGH temperatures, PHOTOEMISSION
Abstract

The influence of Sn doping on the growth of In2O3 on Y-stabilized ZrO2(100) by oxygen plasma assisted molecular beam epitaxy has been investigated over a range of substrate temperatures between 650 and 900 °C. The extent of dopant incorporation under a constant Sn flux decreases monotonically with increasing substrate temperature, although the n-type carrier concentration in “overdoped” films grown at 650 °C is lower than in films with a lower Sn concentration grown at 750 °C. The small increase in lattice parameter associated with Sn doping leads to improved matching with the substrate and suppresses breakup of the films into square islands observed in high temperature growth of undoped In2O3 on Y-stabilized ZrO2(100). Plasmon energies derived from infrared reflection spectra of Sn-doped films are found to be close to satellite energies in core level photoemission spectroscopy, but for a nominally undoped reference sample there is evidence for carrier accumulation at the surface. This influences both the In 3d core line shape and the intensity of a peak close to the Fermi energy associated with photoemission from the conduction band. [ABSTRACT FROM AUTHOR]

Published
2009
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12. A study of the metal to nonmetal transition in Bi-doped β-PbO2 by high resolution x-ray photoemission.

Author

Rothenberg, S., Payne, D. J., Bourlange, A., and Egdell, R. G.

Subjects
ELECTRON emission, SOLUTION (Chemistry), INTERMEDIATES (Chemistry), CONDUCTION electrons, ELECTRONIC structure
Abstract

The influence of Bi doping on the electronic structure of β-PbO2 has been studied by high resolution x-ray photoemission spectroscopy. Doped films were prepared on Pt substrates by electrochemical deposition from solutions of Pb(NO3)2 and Bi(NO3)3 in HNO3. Bi doping was found to lead to a lowering of the density of states at the Fermi energy in valence region x-ray photoemission and to suppression of final state screening by mobile conduction electrons in Pb 4f core level photoemission. A metal to nonmetal transition was found to occur for bulk doping levels around 5 at. % Bi. There is evidence of pronounced surface segregation of Bi. In contrast to host Pb ions, core holes on surface Bi ions do not couple to the mobile conduction electrons in the metallic state. It is concluded that Bi acts as a p-type acceptor in β-PbO2 and traps charge carriers introduced by oxygen deficiency in PbO2-x. [ABSTRACT FROM AUTHOR]

Published
2007
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13. High resolution x-ray photoemission study of plasma oxidation of indium-tin-oxide thin film surfaces.

Author

Christou, V., Etchells, M., Renault, O., Dobson, P. J., Salata, O. V., Beamson, G., and Egdell, R. G.

Subjects
PHOTOEMISSION, PLASMA gases, INDIUM, THIN films
Abstract

Reports on findings of a high resolution x-ray photoemission study of plasma oxidation of indium-tin-oxide thin films surfaces. Plasma oxidation n-type doping in the near surface region; Shift to low binding energy for both core and valence band photoemission features; Fixed conduction band of the indium-tin-oxide.

Published
2000
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16. Determination of the Poisson ratio of (001) and (111) oriented thin films of In2O3 by synchrotron-based x-ray diffraction

Author

Zhang, K H L, Regoutz, A, Palgrave, R G, Payne, D J, Egdell, R G, Walsh, Aron, Collins, S P, Wermeille, D, and Cowley, R A

Subjects
Condensed Matter::Materials Science
Abstract

The Poisson ratio ν of In 2O 3 has been determined by measurement of the covariation of in-plane and out-of-plane lattice parameters of strained thin films grown epitaxially on (111) and (001) oriented cubic Y-stabilized ZrO 2 substrates. The experimental results are in good agreement with values for ν calculated using atomistic simulation procedures. © 2011 American Physical Society.

Published
2016

17. Hard x-ray photoelectron spectroscopy as a probe of the intrinsic electronic properties of CdO

Author

Mudd, James J., Lee, Tien-Lin, Muñoz-Sanjosé, V., Zúñiga-Pérez, J., Hesp, D., Kahk, J. M., Payne, D. J., Egdell, R. G., and McConville, C. F. (Chris F.)

Subjects
QC
Abstract

Hard x-ray photoelectron spectroscopy (HAXPES) is used to investigate the intrinsic electronic properties of single crystal epitaxial CdO(100) thin films grown by metal organic vapor phase epitaxy (MOVPE). The reduced surface sensitivity of the HAXPES technique relaxes stringent surface preparation requirements, thereby allowing the measurement of as-grown samples with intrinsically higher carrier concentration (n=2.4×1020cm-3). High-resolution HAXPES spectra of the valence band and core levels measured at photon energy of 6054 eV are presented. The effects of conduction band filling and band gap renormalization are discussed to explain the observed binding energy shifts. The measured bandwidth of the partially occupied conduction band feature indicates that a plasmon contribution may be present at higher carrier concentrations. The Cd 3d5/2 and O 1s core-level line shapes are found to exhibit an increased asymmetry with increased carrier concentration, interpreted as evidence for final state screening effects from the carriers in the conduction band. Alternatively the core-level line shape is interpreted as arising from strong conduction electron plasmon satellites. The nature of these two competing models to describe core-level line shapes in metallic oxides is explored. © 2014 American Physical Society.

Published
2016

22. Nature of the Band Gap of In 2 O 3 Revealed by First-Principles Calculations and X-Ray Spectroscopy

Author

Walsh, Aron, Da Silva, Juarez L. F., Wei, Su-Huai, Körber, C., Klein, A., Piper, L. F. J., DeMasi, Alex, Smith, Kevin E., Panaccione, G., Torelli, P., Payne, D. J., Bourlange, A., and Egdell, R. G.

Abstract

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.

Published
2008

23. Nature of electronic states at the Fermi level of metallic b-PbO2 revealed by hard x-ray photoemission spectroscopy

Author

Payne, D. J., Egdell, R. G., Paolicelli, G., Offi, F., Panaccione, G., Lacovig, Paolo, Monaco, G., Vanko, G., Walsh, A., Watson, G. W., Guo, J., Beamson, G., Glans, P. A., Learmonth, T., Smith, K. E., D. J., Payne, R. G., Egdell, G., Paolicelli, F., Offi, G., Panaccione, Lacovig, Paolo, G., Monaco, G., Vanko, A., Walsh, G. W., Watson, J., Guo, G., Beamson, P. A., Glan, T., Learmonth, and K. E., Smith

Published
2007

28. Understanding the Electronic Structure ofIrO2Using Hard-X-ray Photoelectron Spectroscopy and Density-Functional Theory

Author

Kahk, J. M., primary, Poll, C. G., additional, Oropeza, F. E., additional, Ablett, J. M., additional, Céolin, D., additional, Rueff, J-P., additional, Agrestini, S., additional, Utsumi, Y., additional, Tsuei, K. D., additional, Liao, Y. F., additional, Borgatti, F., additional, Panaccione, G., additional, Regoutz, A., additional, Egdell, R. G., additional, Morgan, B. J., additional, Scanlon, D. O., additional, and Payne, D. J., additional

Published
2014
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34. An in situ FTIR spectroscopic and thermogravimetric analysis study of the dehydration and dihydroxylation of SnO2: the contribution of the (100), (110) and (111) facets.

Author

Christensen, P. A., Attidekou, P. S., Egdell, R. G., Maneelok, S., and Manning, D. A. C.

Abstract

Nanoparticulate SnO2 produced by a hydrothermal method was characterised by BET, XRD, TGA-MS and in situ variable temperature diffuse reflectance infra red spectroscopy (DRIFTS) to determine the surface behaviour of water. For the (100) facets, hydrogen bonding does not occur, and water adsorption is less strong than for the (111) and (110) facets where hydrogen bonding does occur. Reversible uptake of oxygen was observed. These findings have implications for other surface-gas reactions in which Ni and Sb co-doped SnO2 (NATO) anodes are used for ozone generation. BET showed the relatively high surface area and nanometer scale of the SnO2 particles, whilst XRD confirmed the nano dimension of the crystallites and showed only the cassiterite phase. TGA analysis indicated four temperature regions over which mass loss was observed. These and the in situ DRIFTS studies revealed the existence of various forms of water associated with specific crystal facets of the SnO2, as well as the existence of isolated O–H groups and adsorbed oxygen species. Electronic absorptions were also observed and the data rationalised in terms of the existence of both free electron absorptions, and absorptions from oxygen vacancy states. The role of adsorbed molecular oxygen in electrochemical ozone generation at Ni and Sb co-doped SnO2 (NATO) anodes was strongly suggested by this work. [ABSTRACT FROM AUTHOR]

Published
2016
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