Scalable back-diffusion growth of multilayer hBN on Ni–Cu gradient alloy substrates

Abstract Multilayer hexagonal boron nitride (hBN) is a critical dielectric component for high-performance two-dimensional electronics, yet its large-scale synthesis is hindered by the self-terminating nature of growth on standard transition metal catalysts. Here, we report the design of a nickel-copper (Ni–Cu) gradient alloy substrate that enables scalable growth of highly crystalline multilayer hBN films via a back-diffusion mechanism. By engineering a concentration gradient of Ni through the Cu foil, we create a catalytic asymmetry that drives the diffusion of active boron and nitrogen species from the foil backside to the growth interface. We validate this mechanism through regrowth experiments, where removing the passivating layer on the backside re-initiates growth on the front side, doubling the film thickness. Leveraging this back-diffusion-governed mechanism, we employ electropolishing to shorten the diffusion path length, achieving tunable film thicknesses from 3 nm up to 20 nm. Graphene field-effect transistors integrated with these hBN films exhibit a room-temperature hole carrier mobility of ∼7260 cm ⁻² V·s ⁻¹ , which is nearly three times higher than control samples on SiO ₂ . Our approach provides a pathway for scalable production of high-quality dielectric layers for van der Waals heterostructures.