UC Berkeley

Abstract: Forming heavily‐doped regions in 2D materials, like graphene, is a steppingstone to the design of emergent devices and heterostructures. Here, a selective‐area approach is presented to tune the work‐function and carrier density in monolayer graphene by spatially synthesizing sub‐monolayer gallium beneath the 2D‐solid. The localized metallic gallium is formed via precipitation from an underlying diamond‐like carbon (DLC) film that is spatially implanted with gallium‐ions. By controlling the interfacial precipitation process with annealing temperature, spatially precise ambipolar tuning of the graphene work‐function is achieved, and the tunning effect preserved upon cooling to ambient conditions. Consequently, charge carrier densities from ≈1.8 × 1010 cm−2 (hole‐doped) to ≈7 × 1013 cm−2 (electron‐doped) are realized, confirmed by in situ and ex situ measurements. The theoretical studies corroborated the role of gallium at the heterointerface on charge transfer and electrostatic doping of the graphene overlayer. Specifically, sub‐monolayer gallium facilitates heavy n‐doping in graphene. Extending this doping strategy to other implantable elements in DLC provides a new means of exploring the physics and chemistry of highly‐doped 2D materials.