Fig. 2: Evolution of nanopores in monolayer h-BN after being stored in vacuum or air for 1 h.

a–c are for vacuum and d–i are for air. a, d, g The schematics are generic representations of the geometries of the nanopores (and do not necessarily represent a scaled atomic mapping to the TEM images below). The green triangles represent the original geometry of the nanopores. d, g The red arrows show the merging direction of the nanopores, and the gray areas show the newly extended pore regime. a Schematics and b, c TEM images showing the defects b before and c after being stored in a vacuum for 1 h. b Initially, the sample supports suspended zigzag edges around large nanopores and smaller triangular nanopores (highlighted by the red circles). c The separate or adjacent distinct triangular nanopores are stable in a vacuum and preserve their original form. d–i Schematics and TEM images showing the deformation processes of d–f adjacent nanopores and g–i separate nanopores after being stored in air for 1 h. e TEM image of the two adjacent triangular nanopores (highlighted by the red circle). f The adjacent triangular nanopores are unstable in the air and merge into a larger triangular nanopore. h TEM image highlights three groups of nanopores (indicated by the red circles) with a separation from 1 to 5 nm. i The two separated nanopores have, upon exposure to air for 1 h, merged into a single nanopore, as shown schematically in (g). Orange arrows depict the flow of time.