Interfacial structures of graphene/diamond heterojunctions investigated by scanning transmission electron microscopy

Graphene/diamond (sp2–sp3) heterojunctions have gained considerable attention as promising platforms for photomemristive devices; however, the detailed interfacial structure crucial for understanding the origin of resistance switching remains unclear. In this study, we analyzed the interfacial structure and electronic states of graphene/diamond junctions using transmission electron microscopy (TEM), wide-area four-dimensional scanning transmission electron microscopy (4D-STEM), and electron energy-loss spectroscopy (EELS). The samples were fabricated on boron-doped diamond by microwave plasma-assisted chemical vapor deposition (CVD) and copper (Cu) annealing.In the CVD-grown samples, (111)-faceted diamond twins form during graphene growth, and their domain size increases with increased substrate temperature, leading to a larger interfacial area. STEM–EELS analysis also reveals the presence of sp3-rich diamond regions within the graphene layer on the diamond surface. In contrast, no diamond twins are observed in the Cu-annealed samples. Graphene forms multilayer domains whose size and coherency with the diamond substrate strongly depend on the fabrication method. CVD-grown graphene aligns parallel to the diamond (111) planes owing to high interfacial coherency, with an increased interlayer spacing near the interface. In contrast, Cu-annealed graphene grows predominantly perpendicular to the interface and exhibits a larger interlayer spacing that decreases toward the interface. These structural features are considered key factors to governing the observed material properties.