When epitaxial graphene (EG) grows on hexagonal SiC(0001), chemical doping is produced by bonds at the epitaxial interface, or buffer layer. Robust quantum Hall effect (QHE) plateaus are observed at RK/2 = h/2e2, where RK is a constant of electrical resistance honoring Nobel Prize physicist Klaus von Klitzing. This strong quantum effect allows EG devices to serve as fundamental electrical standards, representing a direct basis for electronics calibrations from constants of nature. At the US national metrology institute, or NIST, we are developing improved QHE standards for industrial and scientific measurements, as well as investigating device physics and quantum effects observed in EG for many length and size scales. QHE standards are fabricated at NIST with values other than RK/2 using superconducting NbTiN traces in combination with contact geometries. Our objective is to create large, scalable resistance networks based on multiple Hall bar elements, and to eliminate accumulated internal resistances due to contacts and resistive metallic interconnections. While normally measured at four terminals for high precision, here the precise resistance can be measured at two connection points because superconductivity eliminates spreading resistance and the QHE itself selects preferred current terminals depending on the B-field orientation. The finished devices are functionalized with chromium tricarbonyl [Cr(CO)3], which provides tunable and uniform doping without the need for large-scale electrostatic gates.
Energy Materials Nanotechnology Rome Meeting on Carbon Nanostructures
May 13-17, 2019
epitaxial graphene, quantum Hall effect, superconductivity, electronic calibration