title: Direct imaging of charged impurity density in common graphene substrates.
abstract: Kelvin probe microscopy in ultrahigh vacuum is used to image the local electrostatic potential fluctuations above hexagonal boron nitride (h-BN) and SiO2, common substrates for graphene. Results are compared to a model of randomly distributed charges in a two-dimensional (2D) plane. For SiO2, the results are well modeled by 2D charge densities ranging from 0.24 to 2.7 × 10(11) cm(-2), while h-BN displays potential fluctuations 1-2 orders of magnitude lower than SiO2, consistent with the improvement in charge carrier mobility for graphene on h-BN compared to SiO2. Electron beam exposure of SiO2 increases the charge density fluctuations, creating long-lived metastable charge populations of ~2 × 10(11) cm(-2) at room temperature, which can be reversed by heating.
authors.affiliation: Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742-4111, United States.
authors.forename: Kristen M
authors.initials: KM
authors.lastname: Burson
authors.forename: William G
authors.initials: WG
authors.lastname: Cullen
authors.forename: Shaffique
authors.initials: S
authors.lastname: Adam
authors.forename: Cory R
authors.initials: CR
authors.lastname: Dean
authors.forename: K
authors.initials: K
authors.lastname: Watanabe
authors.forename: T
authors.initials: T
authors.lastname: Taniguchi
authors.forename: Philip
authors.initials: P
authors.lastname: Kim
authors.forename: Michael S
authors.initials: MS
authors.lastname: Fuhrer