title: Near-field microwave scanning probe imaging of conductivity inhomogeneities in CVD graphene.
abstract: We have performed near-field scanning microwave microscopy (SMM) of graphene grown by chemical vapor deposition. Due to the use of probe-sample capacitive coupling and a relatively high ac frequency of a few GHz, this scanning probe method allows mapping of local conductivity without a dedicated counter electrode, with a spatial resolution of about 50 nm. Here, the coupling was enabled by atomic layer deposition of alumina on top of graphene, which in turn enabled imaging both large-area films, as well as micron-sized islands, with a dynamic range covering a low sheet resistance of a metal film and a high resistance of highly disordered graphene. The structures of graphene grown on Ni films and Cu foils are explored, and the effects of growth conditions are elucidated. We present a simple general scheme for interpretation of the contrast in the SMM images of our graphene samples and other two-dimensional conductors, which is supported by extensive numerical finite-element modeling. We further demonstrate that combination of the SMM and numerical modeling allows quantitative information about the sheet resistance of graphene to be obtained, paving the pathway for characterization of graphene conductivity with a sub-100 nm special resolution.
authors.affiliation: The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. tseleva@ornl.gov
authors.forename: Alexander
authors.initials: A
authors.lastname: Tselev
authors.forename: Nickolay V
authors.initials: NV
authors.lastname: Lavrik
authors.forename: Ivan
authors.initials: I
authors.lastname: Vlassiouk
authors.forename: Dayrl P
authors.initials: DP
authors.lastname: Briggs
authors.forename: Maarten
authors.initials: M
authors.lastname: Rutgers
authors.forename: Roger
authors.initials: R
authors.lastname: Proksch
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Kalinin
mesh_terms: D006108:Graphite / Q000737:chemistry*; D008422:Materials Testing; D020527:Microscopy, Scanning Probe / Q000379:methods*; D008872:Microwaves; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D013499:Surface Properties
chemical_list: D006108:Graphite