Carrier concentration adjustment in graphene QHR devices for metrology applications

We report on the reversible tuning of the carrier concentration n of molecular-doped epigraphene designed for application as a quantum Hall resistance standard. Fine tuning of the carrier concentration required for optimal realization of the Hall resistance quantization is achieved by annealing, to increase n, or by pulsed application of ions created by an electrostatic discharge above the surface of the graphene device to decrease n. We also report on a rapid reduction in n when a device is exposed to air. These observations are part of a growing body of information on the long-term stability of epigraphene primary resistance standards.