In this study, we report the synthesis of single-crystalline h-BN on Ni(111) under ultrahigh vacuum (UHV) conditions using hexamethylborazine (HMB) as a nonclassical precursor. The novel use of HMB facilitates the diffusion of methyl groups into the bulk of Ni(111), playing a critical role in the achievement of high-quality crystalline h-BN layers. The synthesis is performed on a 2 mm-thick Ni(111) single crystal and on a 2-μm-thick Ni(111) thin film on sapphire to evaluate the feasibility of synthesizing h-BN on industrially relevant substrates. Advanced microscopic and spectroscopic techniques confirm the successful synthesis of h-BN. The growth of h-BN was investigated by scanning tunneling microscopy and low-energy electron microscopy. Low-energy electron diffraction confirms the single crystallinity of the grown 2-dimensional layer. X-ray photoelectron spectroscopy confirms the presence of boron and nitrogen bonds at the same binding energies reported in the literature for h-BN. In contrast, photoemission electron microscopy allows identification of the presence of h-BN throughout the Ni(111) surface. This work advances the understanding of h-BN growth mechanisms on metal substrates and provides a foundation for improving synthesis methods to meet the demands of next-generation materials and devices.

The high flexibility, impermeability and strength of graphene membranes are key properties that can enable the next generation of nanomechanical sensors. However, for capacitive pressure sensors, the sensitivity offered by a single suspended graphene membrane is too small to compete with commercial sensors. Here, we realize highly sensitive capacitive pressure sensors consisting of arrays of nearly ten thousand small, freestanding double-layer graphene membranes. We fabricate large arrays of small-diameter membranes using a procedure that maintains the superior material and mechanical properties of graphene, even after high-temperature annealing. These sensors are readout using a low-cost battery-powered circuit board, with a responsivity of up to 47.8 aF Pa⁻¹ mm⁻², thereby outperforming the commercial sensors.