Evolution of nanopores in hexagonal boron nitride

Facile Growth of h-BN Films by Using Surface-Activated h-BN Powders as Precursors

Atomically thick hexagonal boron nitride (h-BN) films have gained increasing interest, such as nanoelectronics and protection coatings. Chemical vapor deposition (CVD) has been proven to be an efficient method for synthesizing h-BN thin films, but its precursors are still limited. Here, it is reported that a novel and easily available precursor, surface-activated h-BN (As-hBN), with NH3/N2 as an additional nitrogen source is used for CVD growth of monolayer h-BN films on the Cu foils. The as-grown h-BN films can significantly enhance the anti-oxidation ability of copper. Molecular dynamics simulations reveal that the reactivity of the As-hBN precursors is attributed to the decomposition of unstable BO3 and O-terminal edges on the surface under H2 atmosphere. This method provides a more reliable approach for fabricating h-BN films.

Correlated Structural and Optical Characterization of Hexagonal Boron Nitride

Hexagonal boron nitride (hBN) plays a central role in nanoelectronics and nanophotonics. Moreover, hBN hosts room-temperature quantum emitters and optically addressable spins, making the material promising for quantum sensing and photonics. Despite significant investigation of the optical and structural properties of hBN, the role of contamination at surfaces and interfaces remains unexplored. We prepare hBN samples that are compatible with confocal photoluminescence (PL) microscopy, transmission electron microscopy (TEM), and atomic-force microscopy (AFM), and we use those techniques to quantitatively investigate correlations between fluorescent emission, flake morphology, and surface residue. We find that the microscopy techniques themselves induce changes in hBN's optical activity and residue morphology: PL measurements induce photobleaching, whereas TEM measurements alter surface residue and emission characteristics. We also study the effects of common treatments─annealing and oxygen plasma cleaning─on the structure and optical activity of hBN. The methods can be broadly applied to study two-dimensional materials, and the results illustrate the importance of correlative studies to elucidate factors that influence hBN's structural and optical properties.

The Impact of Pore Geometry on Frictional Properties of hBN and MoS2 Nanomaterials

Two-dimensional (2D) nanomaterials hold significant promise for reducing energy consumption in water desalination. This study investigates the influence of pore size and shape on the slip behavior of saline water at the interface of two promising 2D nanomaterials: hexagonal boron nitride (hBN) and molybdenum disulfide (MoS2). Slip length, a key parameter governing fluid flow at the nanoscale, is highly dependent on interfacial properties. Here, we explore how the pore characteristics in these 2D nanomaterials can impact slip length, aiming to gain a fundamental understanding of the role of pore size and shape in optimizing desalination efficiency. We performed quantum mechanical calculations to compute the partial atomic charges on atoms in hBN and MoS2 containing pores. Our DFT calculations reveal a spatially varying charge distribution on these 2D nanomaterials with pores, which we then incorporate into molecular dynamic simulations to elucidate their influence on the 2D nanomaterial-water interface. Our results reveal a significant impact of pore size on friction for nanomaterials containing hexagonal pores, while pore size had no effect on nanomaterials containing triangular pores. Moreover, friction increases with pores in both materials. This research contributes to the development of efficient and energy-saving desalination technologies through the manipulation of interfacial properties in 2D nanomaterials.

Ab Initio Molecular Dynamics Investigation on the Permeation of Sodium and Chloride Ions Through Nanopores in Graphene and Hexagonal Boron Nitride Membranes

Nanoporous membranes promise energy-efficient water desalination. Hexagonal boron nitride (h-BN), like graphene, exhibits outstanding physical and chemical properties, making it a promising candidate for water treatment. We employed Car-Parrinello molecular dynamics simulations to establish an accurate modeling of Na+ and Cl- permeation through hydrogen passivated nanopores in graphene and h-BN membranes. We demonstrate that ion separation works well for the h-BN system by imposing a barrier of 0.13 eV and 0.24 eV for Na+ and Cl- permeation, respectively. In contrast, for permeation of the graphene nanopore, the Cl- ion faces a minimum of energy of 0.68 eV in the nanopore plane and is prone toward blockade of the nanopore, while the Na+ ion experiences a slight minimum of 0.03 eV. Overall, the desalination performance of h-BN nanopores surpasses that of their graphene counterparts.

Probing Defectivity Beneath the Hydrocarbon Blanket in 2D hBN Using TEM-EELS

The controlled creation and manipulation of defects in 2D materials has become increasingly popular as a means to design and tune new material functionalities. However, defect characterization by direct atomic-scale imaging is often severely limited by surface contamination due to a blanket of hydrocarbons. Thus, analysis techniques that can characterize atomic-scale defects despite the contamination layer are advantageous. In this work, we take inspiration from X-ray absorption spectroscopy and use broad-beam electron energy loss spectroscopy (EELS) to characterize defect structures in 2D hexagonal boron nitride (hBN) based on averaged fine structure in the boron K-edge. Since EELS is performed in a transmission electron microscope (TEM), imaging can be performed in-situ to assess contamination levels and other factors such as tears in the fragile 2D sheets, which can affect the spectroscopic analysis. We demonstrate the TEM-EELS technique for 2D hBN samples irradiated with different ion types and doses, finding spectral signatures indicative of boron-oxygen bonding that can be used as a measure of sample defectiveness depending on the ion beam treatment. We propose that even in cases where surface contamination has been mitigated, the averaging-based TEM-EELS technique can be useful for efficient sample surveys to support atomically resolved EELS experiments.

Label-Free Imaging of DNA Interactions with 2D Materials

Two-dimensional (2D) materials offer potential as substrates for biosensing devices, as their properties can be engineered to tune interactions between the surface and biomolecules. Yet, not many methods can measure these interactions in a liquid environment without introducing labeling agents such as fluorophores. In this work, we harness interferometric scattering (iSCAT) microscopy, a label-free imaging technique, to investigate the interactions of single molecules of long dsDNA with 2D materials. The millisecond temporal resolution of iSCAT allows us to capture the transient interactions and to observe the dynamics of unlabeled DNA binding to a hexagonal boron nitride (hBN) surface in solution for extended periods (including a fraction of 10%, of trajectories lasting longer than 110 ms). Using a focused ion beam technique to engineer defects, we find that DNA binding affinity is enhanced at defects; when exposed to long lanes, DNA binds preferentially at the lane edges. Overall, we demonstrate that iSCAT imaging is a useful tool to study how biomolecules interact with 2D materials, a key component in engineering future biosensors.