Sub-1-Angstrom-Resolution Imaging Reveals Phase Contrast Transition in Ice Ih Caused by Basal Stacking Faults

TL;DR

This study uses sub-1-Angstrom resolution TEM to reveal how basal stacking faults cause phase contrast transitions in ice Ih, clarifying structural relationships among ice phases and demonstrating defect tolerance at atomic resolution.

Contribution

It provides the first sub-1-Angstrom imaging of ice Ih, showing that stacking faults cause phase contrast transitions and clarifying the structural relationships among ice phases.

Findings

Stacking faults produce honeycomb-like TEM contrast in ice Ih.

Imaging at 89 pm resolution reveals defect structures beyond covalent bond length.

Results clarify structural relationships among ice phases.

Abstract

Phase-contrast transmission electron microscopy (TEM) of hexagonal ice (Ih) along [0001] sometimes shows a honeycomb-like pattern, often interpreted as individual oxygen columns in single crystals. Here, we show that this pattern commonly arises from intrinsic basal stacking faults instead. A translational boundary separating domains of comparable thickness, with an in-plane offset of $(\frac{2}{3} a_{1} + \frac{1}{3} a_{2})$, produces this honeycomb-like contrast. Stacking domains translated in nonequivalent directions yields patterns resembling cubic ice (Ic) along [111] but with a 3-fold symmetry. We imaged this structure at a record-breaking line resolution of 89 picometers, finer than the O-H covalent bond length. These findings highlight the defect tolerance of ice's molecular packing and clarify the structural relationships among hexagonal, stacking-disordered, and cubic ice phases. This resolution milestone opens new avenues for characterizing subtle structural perturbations of water in the solid state.