Graphene/α-RuCl₃ Lateral p-n Junctions

Nanoscale lateral p-n junctions in graphene provide a powerful platform for investigating fundamental quantum interfacial phenomena. In this work, we study graphene/α-RuCl3 intrinsic nanobubbles as a testbed for probing sharp p-n interfaces at the boundaries. In order to elucidate this, we deployed scanning tunneling microscopy (STM) and spectroscopy (STS), and scattering-type scanning nearfield optical microscopy (s-SNOM) as multi-messenger local probes to study both the electronic and plasmonic properties. Our differential conductivity (dI/dV) results indicate a substantial band offset of more than 0.6 eV due to work function mediated charge transfer between α-RuCl3 and graphene. Further, our findings show an abrupt junction along nanobubble boundaries separated by a lateral distance of ~ 3 nm and vertically by ~ 0.5 nm, giving rise to internal fields on the order of 10⁸ V/m. The lateral length scale is one order of magnitude smaller than previously reported junctions by lithographically defined gated devices. The rapid change in the graphene conductivity is also captured well in s- SNOM measurements validating these nano-junctions in plasmonically-active media. Our results are in agreement with density functional theory (DFT) calculations shedding light on the in-plane and out-of-plane charge transfer process. Our study provides insight for nano-scale device engineering using interfacial charge transfer in graphene.