Water Structures Reveal Local Hydrophobicity on the In2O3(111) Surface

TL;DR

This study combines experiments and DFT calculations to reveal how the In2O3(111) surface exhibits local hydrophobicity, with water forming ordered clusters and pockets due to surface heterogeneity.

Contribution

It demonstrates the chemical heterogeneity of In2O3(111) and shows how water molecules organize into nanoscopic clusters with hydrophobic regions, advancing understanding of oxide-water interfaces.

Findings

Water dissociates at specific surface sites and desorbs above room temperature.

Ordered water clusters form with hydrophobic pockets on the surface.

Surface heterogeneity influences water adsorption and clustering behavior.

Abstract

Clean oxide surfaces are generally hydrophilic. Water molecules anchor at undercoordinated surface metal atoms that act as Lewis-acid sites, and they are stabilized by H bonds to undercoordinated surface oxygens. The large unit cell of In2O3(111) provides surface atoms in various configurations, which leads to chemical heterogeneity and a local deviation from this general rule. Experiments (TPD, XPS, ncAFM) agree quantitatively with DFT calculations and show a series of distinct phases. The first three water molecules dissociate at one specific area of the unit cell and desorb above room temperature. The next three adsorb as molecules in the adjacent region. Three more water molecules rearrange this structure and an additional nine pile up above the OH groups. Despite offering undercoordinated In and O sites, the rest of the unit cell is unfavorable for adsorption and remains water-free. The first water layer thus shows ordering into nanoscopic 3D water clusters separated by hydrophobic pockets.