Controlling Fermi level in single layer graphene QHE device for resistance standard

NMIJ/AIST and NIST are collaborating on the development of graphene-based quantized Hall resistance (QHR) devices. We formed graphene films on SiC(0001) substrates and processed the samples into Hall bar devices using the NIST clean room facility. The electronic transport properties have been observed at the NIST and NMIJ/AIST. We used two methods to control the Fermi level in the samples. One is hydrogen intercalation and the other is photochemical gating. Using the former technique, the Fermi level moved across the Dirac point. For the latter technique, it moved closer to the Dirac point.