Water aggregation and dissociation on the ZnO(101[combining macron]0) surface

Area of Science:

• Surface Science
• Computational Materials Science
• Physical Chemistry

Background:

• Understanding water adsorption on metal oxide surfaces is crucial for catalysis and environmental science.
• The ZnO(101[combining macron]0) surface, a well-studied non-polar surface, presents unique adsorption properties.
• Previous studies have primarily focused on low water coverages.

Purpose of the Study:

• To investigate stable water structures and aggregation states on the ZnO(101[combining macron]0) surface at low (0-1 ML) and higher coverages (2-3 ML).
• To analyze the driving forces behind water aggregation and dissociation on this surface.
• To explore novel water structures beyond the monolayer regime.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to search for stable water structures.
• Analysis of binding and adsorption energies to determine structural stability.
• Application of a Born-Haber cycle decomposition scheme to understand energetic contributions.

Main Results:

• Identified ladder-like structures of half-dissociated water dimers as the most stable aggregates at low coverages (≤1 ML).
• Discovered a novel honeycomb-like 2D network of hydrogen bonds at 2 ML, forming a stable double-monolayer.
• Observed restructuring at 3 ML into a contact layer of half-dissociated dimers and a liquid-like overlayer.

Conclusions:

• Water aggregation on ZnO is favored by direct water-water interactions (H-bonds, dipole-dipole) and enhanced water-surface interactions.
• Partial or full water dissociation becomes favorable within aggregates, driven by a balance between surface interactions and geometric energy costs.
• The discovered honeycomb structure at 2 ML acts as a stable termination layer, hindering further water film growth.