▎ 摘　　要

We investigate electron transport properties in large-area, single-layer graphene embedded in dielectric media, using free-space terahertz (THz) imaging and time-domain spectroscopy. Sandwiched between a thin polymethyl methacrylate (PMMA) layer and a Si substrate, graphene layers of different growth recipes exhibit distinctive spatial inhomogeneity of sheet conductivity. The non-contacting, non-destructive THz probe reveals that the PMMA layer induces a small, yet noticeable reduction in conductivity. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4749280]