Abstract: Monolayer hexagonal boron nitride (hBN) has been widely considered as a fundamental building block for two–dimensional (2D) heterostructures and devices. However, the controlled and scalable synthesis of hBN and its 2D heterostructures has remained a daunting challenge. Here, we propose and further demonstrate a hBN/graphene (hBN/G) interface–mediated growth process for the controlled synthesis of high–quality monolayer hBN. We discover that the in–plane hBN/G interface can be precisely controlled, enabling the scalable epitaxy of unidirectional monolayer hBN on graphene, which exhibits a uniform moiré superlattice consistent with single–domain hBN, aligned to the underlying graphene lattice. Furthermore, we identify that the deep–ultraviolet emission at 6.12 eV stems from the 1s–exciton state of monolayer hBN with a giant renormalized direct bandgap on graphene. This work provides a viable path for the controlled synthesis of ultraclean, wafer–scale, atomically ordered 2D quantum materials, as well as the fabrication of 2D quantum electronic and optoelectronic devices.
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