Extended Data Figure 3: Dynamics of 2D ice crystallites and formation of defects.

a–f, High-resolution snapshots from the Supplementary Video illustrate continuous reorganization of ice crystallites. Red lines highlight some of the changes: the bilayer crystal in a thins down to a monolayer in b, then splits into two crystals separated by a grain boundary in c, and a trilayer is formed in the same area in d. In e, a new crystallite, outlined in blue, appears in the top right corner, growing and propagating towards the centre in f. Other crystallites also change from panel to panel. g–j, Examples of an edge dislocation (g) and tilt grain boundaries (i) in 2D ice. h and j are the same images as g and i, respectively, but with reduced contrast; atomic rows are overlaid with red and blue lines to highlight the defects. Red lines mark existing atomic rows; blue lines mark extra rows originating from dislocations; green shapes outline defects without discernible atomic structures. k, l, Monolayer ice found in MD simulations also shows dislocations, indicating that they are intrinsic to the formation of 2D ice at room temperature.