Melting-assisted assembly of twisted graphene/h-BN superlattices with clean interfaces

Twisted van der Waals heterostructures (vdWHs) designed with atomic-scale precision have interesting properties and are important for modern electronics. However, fabricating large-area, two-dimensional (2D) vdWHs with clean interfaces and controllable twist angles remains challenging. Here we successfully fabricated twisted graphene (Gr)/hexagonal boron nitride (h-BN) heterojunctions under vacuum by developing a quasi-melting transfer technique for Gr/Ge (110) and h-BN/Ge (210) substrates. By precisely aligning the Gr/Ge and h-BN/Ge stacks with specific in-plane lattices, we achieved ultraclean transfer of Gr/h-BN superlattices with adjustable stacking orders and precise angles through the sequential transfer of Gr and h-BN monolayers. Transmission electron microscopy, atomic force microscopy, nano angle-resolved photoemission spectroscopy and second-harmonic generation measurement confirmed that the Gr/h-BN superlattices fabricated exhibit atomic-level precision, are of high quality, are free of wrinkles and have controllable twist angles. Theoretical calculations demonstrated that breaking the Ge–Ge bonds in the melted substrate greatly weakens the binding strength of Gr and h-BN to the surface, thereby facilitating the clean transfer of the 2D materials. This study provides a viable pathway for the precise fabrication of large-scale 2D vdWHs and lays a solid material foundation for their application in next-generation electronic devices. (Figure presented.)