We demonstrate the fabrication of individual nanopores in hexagonal boron nitride (hBN) with atomically precise control of the pore size. Previous methods of pore production in other 2D materials create pores of irregular geometry with imprecise diameters. By taking advantage of the preferential growth of boron vacancies in hBN under electron beam irradiation, we are able to observe the pore growth via transmission electron microscopy, and terminate the process when the pore has reached its desired size. Careful control of beam conditions allows us to nucleate and grow individual triangular and hexagonal pores with diameters ranging from subnanometer to 6nm over a large area of suspended hBN using a conventional TEM. These nanopores could find application in molecular sensing, DNA sequencing, water desalination, and molecular separation. Furthermore, the chemical edge-groups along the hBN pores can be made entirely nitrogen terminated or faceted with boron-terminated edges, opening avenues for tailored functionalization and extending the applications of these hBN nanopores.

Controlling the size and shape of nanopores in two-dimensional materials is a key challenge in applications such as DNA sequencing, sieving, and quantum emission in artificial atoms. We here experimentally and theoretically investigate triangular vacancies in (unconventional) Bernal-stacked AB-h-BN formed using a high-energy electron beam. Due to the geometric configuration of AB-h-BN, triangular pores in different layers are aligned, and their sizes are controlled by the duration of the electron irradiation. Interlayer covalent bonding at the vacancy edge is not favored, as opposed to what occurs in the more common AA′-stacked BN. A variety of monolayer, concentric, and bilayer pores in the bilayer AB-h-BN are observed in high-resolution transmission electron microscopy and characterized using ab initio simulations. Bilayer pores in AB-h-BN are commonly formed and grow without breaking the bilayer character. Nanopores in AB-h-BN exhibit a wide range of electronic properties, ranging from half-metallic to non-magnetic and magnetic semiconductors. Therefore, because of the controllability of the pore size, the electronic structure is also highly controllable in these systems and can potentially be tuned for particular applications.

This corrects the article DOI: 10.1038/nmat4795.

We demonstrate the fabrication of individual nanopores in hexagonal boron nitride (h-BN) with atomically precise control of the pore shape and size. Previous methods of pore production in other 2D materials typically create pores with irregular geometry and imprecise diameters. In contrast, other studies have shown that with careful control of electron irradiation, defects in h-BN grow with pristine zig-zag edges at quantized triangular sizes, but they have failed to demonstrate production and control of isolated defects. In this work, we combine these techniques to yield a method in which we can create individual size-quantized triangular nanopores through an h-BN sheet. The pores are created using the electron beam of a conventional transmission electron microscope; which can strip away multiple layers of h-BN exposing single-layer regions, introduce single vacancies, and preferentially grow vacancies only in the single-layer region. We further demonstrate how the geometry of these pores can be altered beyond triangular by changing beam conditions. Precisely size- and geometry-tuned nanopores could find application in molecular sensing, DNA sequencing, water desalination, and molecular separation.

One dimensional boron nitride (BN) nanomaterials with a high aspect ratio are of great interest due to their unique properties and potential applications. However, BN nanomaterials are generally difficult to synthesize. Here, we describe the creation of arrays of vertically aligned pure BN nanofibers and BN coated carbon nanofibers, fabricated on-chip via a straightforward template-assisted chemical conversion reaction. The template, a glassy carbon nanofiber array, is produced by plasma processing of conventional photoresists. The method is highly controllable, patternable, and scalable, and the final arrays can be fabricated over large areas with a controlled fiber length. We characterize the electron field emission properties of the BN-coated carbon nanofiber array and find a large field enhancement factor, low turn-on voltage, and good stability. The outstanding field emission performance results from the small tip size and high aspect ratio of the nanofiber as well as the high chemical stability and high thermal conductivity of the BN coating.

The relative orientation of successive sheets, i.e. the stacking sequence, in layered 2D materials is central to the electronic, thermal, and mechanical properties of the material. Often different stacking sequences have comparable cohesive energy, leading to alternative stable crystal structures. Here we theoretically and experimentally explore different stacking sequences in the van der Waals bonded material hexagonal boron nitride (h-BN). We examine the total energy, electronic bandgap, and dielectric response tensor for five distinct high symmetry stacking sequences for both bulk and bilayer forms of h-BN. Two sequences, the generally assumed AA′ sequence and the relatively unknown (for h-BN) AB (Bernal) sequence, are predicted to have comparably low energy. We present a scalable modified chemical vapor deposition method that produces large flakes of virtually pure AB stacked h-BN; this new material complements the generally available AA′ stacked h-BN.

Light emitters in wide-band-gap semiconductors are of great fundamental interest and have potential as optically addressable qubits. Here we describe a unique color center in high-quality hexagonal boron nitride (h-BN) with a sharp emission line at 435 nm. The emitters are activated and deactivated by electron beam irradiation and have spectral and temporal characteristics consistent with atomic color centers weakly coupled to lattice vibrations. The emitters are conspicuously absent from commercially available h-BN and are present in only ultrahigh-quality h-BN grown using a high-pressure, high-temperature Ba-B-N flux/solvent, suggesting that these emitters originate from impurities or related defects specific to this unique synthetic route. Our results imply that the light emission is activated and deactivated by electron beam manipulation of the charge state of an impurity-defect complex.

The low mass density and high mechanical strength of graphene make it an attractive candidate for suspended-membrane energy transducers. Typically, the membrane size dictates the operational frequency and bandwidth. However, in many cases it would be desirable to both lower the resonance frequency and increase the bandwidth, while maintaining overall membrane size. We employ focused ion beam milling or laser ablation to create kirigami-like modification of suspended pure-graphene membranes ranging in size from microns to millimeters. Kirigami engineering successfully reduces the resonant frequency, increases the displacement amplitude, and broadens the effective bandwidth of the transducer. Our results present a promising route to miniaturized wide-band energy transducers with enhanced operational parameter range and efficiency.