Imaging surface structure and premelting of ice Ih with atomic resolution

Area of Science:

• Surface Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Ice surfaces influence crucial physical and chemical processes, including melting, friction, and atmospheric reactions.
• Despite extensive research, the precise atomic structures of ice interfaces remain poorly understood due to the delicate hydrogen-bonding network and complex premelting phenomena.

Purpose of the Study:

• To achieve atomic-resolution imaging of the basal (0001) surface of hexagonal water ice (ice Ih).
• To elucidate the atomic structure of ice surfaces and understand the molecular mechanisms behind ice premelting.

Main Methods:

• Utilized qPlus-based cryogenic atomic force microscopy (AFM) with a carbon monoxide-functionalized tip for high-resolution imaging.
• Employed density functional theory (DFT) calculations to investigate surface reconstruction and stabilization mechanisms.

Main Results:

• Atomic-resolution imaging revealed the ice-Ih surface comprises mixed Ih- and cubic (Ic)-stacking nanodomains forming periodic superstructures.
• DFT calculations indicated that surface reconstruction, stabilized by minimizing electrostatic repulsion from dangling OH bonds, is energetically favorable over the ideal ice surface.
• Observed surface disordering above 120 Kelvin, signifying the onset of premelting, which initiates at domain boundaries and is influenced by planar local structures.

Conclusions:

• The study provides definitive atomic-scale structural information for the basal ice surface, resolving long-standing debates.
• Identified the molecular origins of ice premelting, highlighting the role of domain boundaries and local structures.
• These findings may necessitate a paradigm shift in understanding ice physics and chemistry, with implications for various surface-dependent phenomena.