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M. Wagner, P. Lackner, S. Seiler, A. Bunsch, R. Bliem, S. Gerhold, Z. Wang, J. Osiecki, K. Schulte, L. Boatner, M. Schmid, B. Meyer, U. Diebold:
"Resolving the Structure of a Well-Ordered Hydroxyl Overlayer on In₂O₃(111): Nanomanipulation and Theory";
ACS Nano, 11 (2017), 11531 - 11541.

Changes in chemical and physical properties resulting from
water adsorption play an important role in the characterization and
performance of device-relevant materials. Studies of model oxides with wellcharacterized
surfaces can provide detailed information that is vital for a
general understanding of water−oxide interactions. In this work, we study
single crystals of indium oxide, the prototypical transparent contact
material that is heavily used in a wide range of applications and most
prominently in optoelectronic technologies. Water adsorbs dissociatively
already at temperatures as low as 100 K, as confirmed by scanning tunneling
microscopy (STM), photoelectron spectroscopy, and density functional
theory. This dissociation takes place on lattice sites of the defect-free surface. While the In2O3(111)-(1 × 1) surface offers
four types of surface oxygen atoms (12 atoms per unit cell in total), water dissociation happens exclusively at one of them
together with a neighboring pair of 5-fold coordinated In atoms. These O−In groups are symmetrically arranged around
the 6-fold coordinated In atoms at the surface. At room temperature, the In2O3(111) surface thus saturates at three
dissociated water molecules per unit cell, leading to a well-ordered hydroxylated surface with (1 × 1) symmetry, where the
three water OWH groups plus the surface OSH groups are imaged together as one bright triangle in STM. Manipulations
with the STM tip by means of voltage pulses preferentially remove the H atom of one surface OSH group per triangle. The
change in contrast due to strong local band bending provides insights into the internal structure of these bright triangles.
The experimental results are further confirmed by quantitative simulations of the STM image corrugation.

indium oxide, water dissociation, hydroxylation, scanning tunneling microscopy, density functional theory