Electric-field control of hydrogen-bond ordering in monolayer ice on graphite

Hydrogen-bond (HB) networks govern molecular structure and function across chemistry, biology and materials science, yet their deterministic control at the atomic scale remains a central challenge. Here, we directly visualize and control HB ordering in monolayer ice on graphite by an external electric field and how this control arises from interfacial charge redistribution. Low-temperature scanning tunnelling microscopy reveals a field-driven two-dimensional (2D) liquid-to-solid transition from a mobile, non-wetting water adlayer to an ordered hexagonal monolayer ice. Systematic field variation is accompanied by a continuous change in apparent lattice spacing, while bias-resolved imaging reveals discrete conductance states set by the 2D-ice band edge, exposing coupled structural and electronic responses. At higher fields, we observed a 2D solid-solid phase transition between hexagonal and square ice. First-principles computation and biasdependent imaging support that the 2D transitions and physical effects arise from fieldinduced interfacial charge redistribution, thereby providing a field-tunable parameter for electrically programming HB networks and electronic properties at interfaces.