Atomic Engineering of Triangular Nanopores in Monolayer hBN for Membrane Applications: A Decoupled Seeding and Growth Approach

Nanopores in two-dimensional (2D) materials are of considerable interest in advanced membrane technologies for the sensing and separation of ions and molecules. These applications necessitate nanopores that are precise in size and shape and abundant in number. However, conventional fabrication techniques struggle to achieve both high precision and high throughput. To address this, we developed a decoupled defect seeding and growth approach for fabricating geometric nanopores in freestanding hexagonal boron nitride. Using dose-controlled light ion showering, we first created vacancy defect seeds. These are then expanded into triangular nanopores under electron irradiation in a transmission electron microscope or via thermal annealing in air. While the electron-induced growth step offers the highest precision, air annealing allows fabrication over much larger areas, concurrently removing hydrocarbon contamination. In an aging study conducted in air at room temperature, subnanometer triangular pores in contamination-free regions are found to be stable. Following the method introduced here, ensembles of stable nanopores with a narrow size distribution and consistent geometry can thus be fabricated, facilitating the development of next-generation porous membrane-based devices.