Nanometer-scale lateral junctions in graphene/α-RuCl₃ heterostructures

Accessing nano-scale and high-quality lateral p-n junctions in graphene is crucial for studying numerous emergent quantum interfacial phenomena. Here we investigate graphene/α-RuCl₃ heterostructures that are revealed to host sharp p-n interfaces at the boundaries of intrinsic nanobubbles. We utilized scanning tunneling microscopy (STM) and spectroscopy (STS) and scattering-type scanning nearfield optical microscopy (s-SNOM) as multi-messenger local probes to explore both the electronic and plasmonic properties of nanobubble p-n junctions. Both STS and s-SNOM results demonstrate a substantial shift in Dirac point (~0.6 eV) as a result of work function mediated charge transfer between α-RuCl₃ and graphene. Further, we observe the formation of an abrupt junction along nanobubble boundaries with an exceptionally sharp lateral width (<3 nm). This is one order of magnitude smaller than junctions produced via state-of-the-art lithographically defined gated devices. Our results are supported by density functional theory (DFT) calculations which help to elucidate the origins of both in-plane and out-of-plane charge transfer behavior. Our work opens up routes toward device engineering via interfacial charge transfer in graphene and other low-density 2D materials.