Scanning Tunneling Microscopy of Monolayer Hexagonal Boron Nitride Nanoribbons Grown on HOPG*

Van der Waals heterostructures involving 2D materials such as graphene (Gr) and hexagonal boron nitride (hBN) exhibit a variety of interesting physics in prototype devices, but require improvements in large-area growth and control over defect densities for wafer-scale implementation. In this work, we use scanning tunneling microscopy (STM) to characterize monolayer ribbons of hBN grown on highly oriented pyrolytic graphite (HOPG) via high-temperature molecular beam epitaxy. STM images confirm that the hBN ribbons grow outward from Gr edges and the morphology depends on the Gr armchair or zig-zag termination. FFT analysis indicates that the hBN and Gr lattices are aligned across the growth interface. We observe large area single-periodicity moire patterns with a spacing consistent with the intrinsic lattice mismatch between rotationally aligned Gr and hBN. Atomic-resolution imaging reveals three distinct periodicities: in addition to the expected hBN honeycomb lattice, there are hexagonal and superstructure periodicities which may reflect variations in local strain and/or the presence of intercalated species. These studies provide atomic-level insights into the growth of single-domain hBN by high-temperature MBE.