Identification of Lone-Pair Surface States on Indium Oxide

Daniel W. Davies, Aron Walsh, James J. Mudd, Chris F. McConville, Anna Regoutz, J. Matthias Kahk, David J. Payne, Vin R. Dhanak, David Hesp, Katariina Pussi, Tien Lin Lee, Russell G. Egdell, Kelvin H.L. Zhang

Research output: Contribution to journalArticle

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Abstract

Indium oxide is widely used as a transparent electrode in optoelectronic devices and as a photocatalyst with activity for reduction of CO 2 . However, very little is known about the structural and electronic properties of its surfaces, particularly those prepared under reducing conditions. In this report, directional "lone-pair" surface states associated with filled 5s 2 orbitals have been identified on vacuum-annealed In 2 O 3 (111) through a combination of hard and soft X-ray photoemission spectroscopy and density functional theory calculations. The lone pairs reside on indium ad-atoms in a formal +1 oxidation state, each of which traps two electrons into a localized hybrid orbital protruding away from the surface and lying just above the valence band maximum in photoemission spectra. The third electron associated with the ad-atoms is delocalized into the conduction band, thus producing the surface electron accumulation layer identified previously on vacuum-annealed In 2 O 3 (111) (1 × 1) surfaces. The surface structure is further supported by low-energy electron diffraction, but there is no chemical shift in indium core level X-ray photoelectron spectra between surface In(I) ad-atoms and bulk In(III). The 5s 2 lone pairs confer Lewis basicity on the surface In sites and may have a pronounced impact on the catalytic or photocatalytic activity of reduced In 2 O 3 .

Original languageEnglish
Pages (from-to)1700-1709
Number of pages10
JournalJournal of Physical Chemistry C
Volume123
Issue number3
DOIs
Publication statusPublished - 2019 Jan 24

Fingerprint

Surface states
indium oxides
Indium
Oxides
Atoms
Electrons
Vacuum
indium
photoelectric emission
Core levels
Low energy electron diffraction
Chemical shift
Photoemission
Carbon Monoxide
Photoelectron spectroscopy
Alkalinity
Photocatalysts
Photoelectrons
Valence bands
X ray spectroscopy

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Cite this

Davies, D. W., Walsh, A., Mudd, J. J., McConville, C. F., Regoutz, A., Kahk, J. M., ... Zhang, K. H. L. (2019). Identification of Lone-Pair Surface States on Indium Oxide. Journal of Physical Chemistry C, 123(3), 1700-1709. https://doi.org/10.1021/acs.jpcc.8b08623
Davies, Daniel W. ; Walsh, Aron ; Mudd, James J. ; McConville, Chris F. ; Regoutz, Anna ; Kahk, J. Matthias ; Payne, David J. ; Dhanak, Vin R. ; Hesp, David ; Pussi, Katariina ; Lee, Tien Lin ; Egdell, Russell G. ; Zhang, Kelvin H.L. / Identification of Lone-Pair Surface States on Indium Oxide. In: Journal of Physical Chemistry C. 2019 ; Vol. 123, No. 3. pp. 1700-1709.
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abstract = "Indium oxide is widely used as a transparent electrode in optoelectronic devices and as a photocatalyst with activity for reduction of CO 2 . However, very little is known about the structural and electronic properties of its surfaces, particularly those prepared under reducing conditions. In this report, directional {"}lone-pair{"} surface states associated with filled 5s 2 orbitals have been identified on vacuum-annealed In 2 O 3 (111) through a combination of hard and soft X-ray photoemission spectroscopy and density functional theory calculations. The lone pairs reside on indium ad-atoms in a formal +1 oxidation state, each of which traps two electrons into a localized hybrid orbital protruding away from the surface and lying just above the valence band maximum in photoemission spectra. The third electron associated with the ad-atoms is delocalized into the conduction band, thus producing the surface electron accumulation layer identified previously on vacuum-annealed In 2 O 3 (111) (1 × 1) surfaces. The surface structure is further supported by low-energy electron diffraction, but there is no chemical shift in indium core level X-ray photoelectron spectra between surface In(I) ad-atoms and bulk In(III). The 5s 2 lone pairs confer Lewis basicity on the surface In sites and may have a pronounced impact on the catalytic or photocatalytic activity of reduced In 2 O 3 .",
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Davies, DW, Walsh, A, Mudd, JJ, McConville, CF, Regoutz, A, Kahk, JM, Payne, DJ, Dhanak, VR, Hesp, D, Pussi, K, Lee, TL, Egdell, RG & Zhang, KHL 2019, 'Identification of Lone-Pair Surface States on Indium Oxide', Journal of Physical Chemistry C, vol. 123, no. 3, pp. 1700-1709. https://doi.org/10.1021/acs.jpcc.8b08623

Identification of Lone-Pair Surface States on Indium Oxide. / Davies, Daniel W.; Walsh, Aron; Mudd, James J.; McConville, Chris F.; Regoutz, Anna; Kahk, J. Matthias; Payne, David J.; Dhanak, Vin R.; Hesp, David; Pussi, Katariina; Lee, Tien Lin; Egdell, Russell G.; Zhang, Kelvin H.L.

In: Journal of Physical Chemistry C, Vol. 123, No. 3, 24.01.2019, p. 1700-1709.

Research output: Contribution to journalArticle

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T1 - Identification of Lone-Pair Surface States on Indium Oxide

AU - Davies, Daniel W.

AU - Walsh, Aron

AU - Mudd, James J.

AU - McConville, Chris F.

AU - Regoutz, Anna

AU - Kahk, J. Matthias

AU - Payne, David J.

AU - Dhanak, Vin R.

AU - Hesp, David

AU - Pussi, Katariina

AU - Lee, Tien Lin

AU - Egdell, Russell G.

AU - Zhang, Kelvin H.L.

PY - 2019/1/24

Y1 - 2019/1/24

N2 - Indium oxide is widely used as a transparent electrode in optoelectronic devices and as a photocatalyst with activity for reduction of CO 2 . However, very little is known about the structural and electronic properties of its surfaces, particularly those prepared under reducing conditions. In this report, directional "lone-pair" surface states associated with filled 5s 2 orbitals have been identified on vacuum-annealed In 2 O 3 (111) through a combination of hard and soft X-ray photoemission spectroscopy and density functional theory calculations. The lone pairs reside on indium ad-atoms in a formal +1 oxidation state, each of which traps two electrons into a localized hybrid orbital protruding away from the surface and lying just above the valence band maximum in photoemission spectra. The third electron associated with the ad-atoms is delocalized into the conduction band, thus producing the surface electron accumulation layer identified previously on vacuum-annealed In 2 O 3 (111) (1 × 1) surfaces. The surface structure is further supported by low-energy electron diffraction, but there is no chemical shift in indium core level X-ray photoelectron spectra between surface In(I) ad-atoms and bulk In(III). The 5s 2 lone pairs confer Lewis basicity on the surface In sites and may have a pronounced impact on the catalytic or photocatalytic activity of reduced In 2 O 3 .

AB - Indium oxide is widely used as a transparent electrode in optoelectronic devices and as a photocatalyst with activity for reduction of CO 2 . However, very little is known about the structural and electronic properties of its surfaces, particularly those prepared under reducing conditions. In this report, directional "lone-pair" surface states associated with filled 5s 2 orbitals have been identified on vacuum-annealed In 2 O 3 (111) through a combination of hard and soft X-ray photoemission spectroscopy and density functional theory calculations. The lone pairs reside on indium ad-atoms in a formal +1 oxidation state, each of which traps two electrons into a localized hybrid orbital protruding away from the surface and lying just above the valence band maximum in photoemission spectra. The third electron associated with the ad-atoms is delocalized into the conduction band, thus producing the surface electron accumulation layer identified previously on vacuum-annealed In 2 O 3 (111) (1 × 1) surfaces. The surface structure is further supported by low-energy electron diffraction, but there is no chemical shift in indium core level X-ray photoelectron spectra between surface In(I) ad-atoms and bulk In(III). The 5s 2 lone pairs confer Lewis basicity on the surface In sites and may have a pronounced impact on the catalytic or photocatalytic activity of reduced In 2 O 3 .

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Davies DW, Walsh A, Mudd JJ, McConville CF, Regoutz A, Kahk JM et al. Identification of Lone-Pair Surface States on Indium Oxide. Journal of Physical Chemistry C. 2019 Jan 24;123(3):1700-1709. https://doi.org/10.1021/acs.jpcc.8b08623