Non-centrosymmetric stacking in boron nitride (BN) enables out-of-plane polarization, offering a route toward 2D dielectrics with embedded nonvolatile functionality. However, achieving uniform, wafer-scale growth of metastable Bernal-stacked BN (bBN) remains challenging, as it requires breaking interlayer inversion symmetry. Here, we demonstrate the wafer-scale epitaxial growth of single-crystal bBN bilayers on Ni(111)/sapphire substrates using metal-organic chemical vapor deposition. By employing a flow-modulation epitaxy approach, we enhanced surface reaction kinetics while suppressing secondary nucleation, thereby enabling self-limiting growth of uniform bilayer bBN films. Monoatomic Ni step edges deterministically enforced the AB stacking order, energetically stabilizing the bilayer configuration by lifting the degeneracy of competing stacking orientations, as confirmed by atomic-resolution imaging and density functional theory calculations. The resulting bBN films served as atomically thin dielectric interlayers in top-gated molybdenum disulfide (MoS2) transistor arrays, yielding spatially uniform device performance across the wafer and enabling nonvolatile ferroelectric switching of the MoS2 channels via polarization reversal in the bBN interlayer. These results expand the understanding of step-edge-guided growth mechanisms for controlling stacking order and layer number in metastable 2D materials, and demonstrate a reliable wafer-scale approach to phase-controlled synthesis of single-crystal bBN bilayers with their integration as functional 2D dielectrics for practical electronic applications.
Wang et al. (Sun,) studied this question.