Nanoscale Band Gap Modulation and Dual Moiré Superlattices of Hexagonal Boron Nitride Weakly Coupled to Graphite.

Van der Waals (vdW) materials, such as hexagonal boron nitride (h-BN), are highly promising for applications in optoelectronics and quantum technologies. When assembled into heterostructures, h-BN can form moiré superlattices, enabling the engineering of electronic and optical properties by varying the interlayer twist angle. However, understanding the nanoscale interplay between moiré patterns and electronic properties such as the band gap or work function, particularly in optically active h-BN structures, remains a challenge. Here, we use the atomic-scale precision of scanning tunneling microscopy (STM) to uncover the role of moiré superlattices in the electronic properties of a weakly coupled h-BN/Graphite heterostructure. Our STM study reveals large moiré patterns (14.8-18.3 nm periodicity) on the surface, implying slight local variations in the h-BN/Graphite stacking throughout the sample. Spectroscopic measurements show significant modulations of 330 meV in the local work function and 170 meV in the band gap within a moiré unit cell, which are comparable to h-BN/metallic interfaces. Additionally, we identify dual moiré superlattices in twisted homobilayers of h-BN/Graphite, offering an extra degree of freedom to tune the heterostructure's properties. These findings suggest that moiré engineering in h-BN-based systems could lead to a range of effects, including exciton broadening, twist-tunable defect luminescence, and the theoretically predicted trapping of excitons within the moiré landscape. Furthermore, this tunability may also affect adjacent layered materials, providing a versatile platform for tailoring the electronic and optical properties of h-BN and its van der Waals heterostructures.