▎ 摘　　要

The high dispersion found in the literature for the conductivity of Reduced Graphene Oxide (RGO) layers makes it highly desirable to develop fast and non-invasive methods for their characterization. Here we show that Electrostatic Force Microscopy (EFM) is an in situ, fast, and contactless technique to evaluate the conductivity of chemically derived graphene layers. The dielectric response of RGO flakes is observed to depend on their conductivity in the range of 0-3 S m(-1). Interestingly, we also find that for electrostatic purposes, a graphene layer is equivalent to an extremely thin dielectric layer with an effective permittivity (epsilon(eff)) that depends on the conductivity of the layers and spans from 5 for the insulating layers, to 2000 for the more conductive ones. We discuss how these high values of epsilon(eff) are a consequence of the incomplete screening of electric fields through graphene layers.