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Identification of lone pair surface states on indium oxide

DOI: 10.1021/acs.jpcc.8b08623 DOI Help

Authors: Daniel W. Davies (University of Bath) , Aron Walsh (Imperial College London) , James J. Mudd (University of Warwick; Diamond Light Source) , Chris F. Mcconville (University of Warwick; RMIT University) , Anna Regoutz (Imperial College London) , J. Matthias Kahk (Imperial College London) , David J. Payne (Imperial College London) , Vin R. Dhanak (University of Liverpool) , David Hesp (University of Liverpool) , Katariina Pussi (Lappeenranta University of Technology) , Tien-lin Lee (Diamond Light Source) , Russell G. Egdell (University of Oxford) , Kelvin H. L. Zhang (Xiamen University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: The Journal Of Physical Chemistry C

State: Published (Approved)
Published: December 2018
Diamond Proposal Number(s): 8441

Abstract: Indium oxide is widely used as transparent electrode in optoelectronic devices and as a photocatalyst with activity for reduction of CO2. 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 5s2 orbitals have been identified on vacuum-annealed In2O3(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 localised 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 delocalised into the conduction band, thus producing the surface electron accumulation layer identified previously on vacuum-annealed In2O3(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 5s2 lone pairs confer Lewis basicity on the surface In sites and may have a pronounced impact on the catalytic or photo-catalytic activity of reduced In2O3.

Subject Areas: Chemistry


Instruments: I09-Surface and Interface Structural Analysis