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 journalArticlepeer-review

17 Scopus citations


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
Issue number3
StatePublished - 24 Jan 2019

Bibliographical note

Publisher Copyright:
© 2018 American Chemical Society.


Dive into the research topics of 'Identification of Lone-Pair Surface States on Indium Oxide'. Together they form a unique fingerprint.

Cite this