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We describe a technique for making one-dimensional ohmic contacts toindividual graphene layers encapsulated in hexagonal boron nitride (h-BN) usingCF4 and O2 plasmas. The high etch selectivity of h-BN against graphene (>1000)is achieved by increasing the plasma pressure, which enables etching of h-BN,while graphene acts as an etch stop to protect underlying h-BN. A low-pressureO2 plasma anisotropically etches graphene in the vertical direction, whichexposes graphene edges at h-BN sidewalls. Despite the O2 plasma bombardment,the lower h-BN layer functions as an insulating layer. Thus, this method allowsus to pattern metal electrodes on h-BN over a second graphene layer. Subsequentelectron-beam lithography and evaporation fabricate metal contacts at thegraphene edges that are active down to cryogenic temperatures. This fabricationmethod is demonstrated by the preparation of a graphene Hall bar with agraphite back-gate and double bilayer-graphene Hall bar devices. The highflexibility of the device geometries enabled by this method creates access to avariety of experiments on electrostatically coupled graphene layers.

Selective Etching of Hexagonal Boron Nitride by High-Pressure CF4 Plasma for Individual One-dimensional Ohmic Contacts to Graphene Layers