(a) Supercooled water (blue) at 230 K within the 45° wedge (green). The spontaneous formation of an ordered structure (highlighted) near the wedge contact line eventually leads to ice crystallization. Side view of ice is shown in b. (c–e) Nucleation pathway of ice within the 45° wedge. As a comparison, the nucleation pathway within the 70° wedge is shown in g–i. (f,j) Side views of the defect complex (e) and cubic ice complex (i), respectively.