▎ 摘　　要

We demonstrate ultrasharp (less than or similar to 10 nm) lateral p-n junctions in graphene using electronic transport, scanningtunneling microscopy, andfirst-principles calculations. The p-n junction lies at the boundary between differentially doped regionsof a graphene sheet, where one side is intrinsic and the other ischarge-doped by proximity to aflake of alpha-RuCl3across a thininsulating barrier. We extract the p-n junction contribution to thedevice resistance to place bounds on the junction width. Weachieve an ultrasharp junction when the boundary between theintrinsic and doped regions is defined by a cleaved crystalline edgeof alpha-RuCl3located 2 nm from the graphene. Scanning tunnelingspectroscopy in heterostructures of graphene, hexagonal boronnitride, and alpha-RuCl3shows potential variations on a sub 10 nmlength scale. First-principles calculations reveal that the charge-doping of graphene decays sharply over just nanometers from theedge of the alpha-RuCl3flake