Evolution of nanopores in hexagonal boron nitride

The engineering of atomically-precise nanopores in two-dimensional materials presents exciting opportunities for both fundamental science studies as well as applications in energy, DNA sequencing, and quantum information technologies. The exceptional chemical and thermal stability of hexagonal boron nitride (h-BN) suggest that exposed h-BN nanopores will retain their atomic structure even when subjected to extended periods of time in gas or liquid environments. Here we employ transmission electron microscopy to examine the time evolution of h-BN nanopores in vacuum and in air and find, even at room temperature, dramatic geometry changes due to atom motion and edge contamination adsorption, for timescales ranging from one hour to one week. The discovery of nanopore evolution contrasts with general expectations and has profound implications for nanopore applications of two-dimensional materials. Nanopore engineering holds great promise for energy, DNA sequencing, and quantum information technologies, but pore evolution, particularly in presumably stable materials such as boron nitride, is largely unexplored. Here, the authors use high-resolution transmission electron microscopy to show that different nanopores formed in mono- and multi-layer hexagonal boron nitride are stable in vacuum but undergo dramatic changes in air.