Although hexagonal boron nitride (h-BN) is a good candidate for gate-insulating materials by minimizing interaction from substrate, further applications to electronic devices with available two-dimensional semiconductors continue to be limited by flake size. While monolayer h-BN has been synthesized on Pt and Cu foil using chemical vapour deposition (CVD), multilayer h-BN is still absent. Here we use Fe foil and synthesize large-area multilayer h-BN film by CVD with a borazine precursor. These films reveal strong cathodoluminescence and high mechanical strength (Young’s modulus: 1.16±0.1 TPa), reminiscent of formation of high-quality h-BN. The CVD-grown graphene on multilayer h-BN film yields a high carrier mobility of ∼24,000 cm² V⁻¹ s⁻¹ at room temperature, higher than that (∼13,000 ² V⁻¹ s⁻¹) with exfoliated h-BN. By placing additional h-BN on a SiO₂/Si substrate for a MoS₂ (WSe₂) field-effect transistor, the doping effect from gate oxide is minimized and furthermore the mobility is improved by four (150) times.

Larger monolayers with gold tapes: Although the exfoliation of monolayers of materials such as transition metal dichalcogenides produces high-quality electronic materials with low defect densities, the size of the monolayers is limited to the micrometer scale. Liu et al. modified this method by creating atomically flat gold layers on polymer supports. The strong van der Waals adhesion of the gold layer allowed monolayers to be exfoliated on the centimeter scale. Multilayers could be reassembled to artificial structures, such as a MoSe ₂ /WSe ₂ single-crystal bilayer with a twist angle chosen to quench intralayer exciton formation. Science , this issue p. 903