Epitaxial Ferroelectric Hexagonal Boron Nitride Grown on Graphene.

Ferroelectricity realized in van der Waals (vdW) materials with non-centrosymmetric stacking configurations holds promise for future 2D devices with nonvolatile and reconfigurable functionalities. However, the epitaxial growth of ferroelectric vdW materials often struggles to achieve an energetically unfavorable stacking configuration that enables electric polarization. This challenge is particularly evident when performing heteroepitaxy on another vdW substrate to create versatile and scalable ferroelectric building blocks designed for large-area, atomic-scale thicknesses. Here, epitaxial hexagonal boron nitride (h-BN) multilayer films are successfully grew on single-crystal graphene synthesized on a miscut SiC (0001) substrate. Theoretical calculations illustrate that the moiré-patterned h-BN/graphene hetero-interface intrinsically exhibits polarization, leading to a polarized AB stacking in multilayer h-BN films to minimize the total formation energy, which is validated experimentally by the layer-dependent band dispersions. The as-grown multilayer h-BN layers demonstrated robust, homogeneous ferroelectricity with switchable out-of-plane polarization via interlayer sliding. This study establishes an effective route for stacking-controlled heteroepitaxy, enabling the large-scale integration of vdW materials with ferroelectricity and versatile functionalities, offering a promising platform for next-generation 2D ferroelectric devices.