Far-infrared study of substrate-effect on large scale graphene

From far-IR Drude absorption measurement we determine carrier density (N) and carrier scattering rate (Gamma) of graphene deposited on buffer-layer/SiO2 composite substrate. Two types of buffer-layers, (1) polar dielectric oxide ZnO and SrTiO3 (2) organic thin film hexamethyldisilazane and polymethyl methacrylate (PMMA) were studied. N varies widely over 0.12-11.8 (X10(12) cm(-2)) range depending on the buffer-layer. In contrast Gamma remains almost constant, similar to 100 cm(-1), irrespective of the buffer-layers. This indicates that carrier mobility (mu) of graphene depends on substrate through N, but not by Gamma as commonly believed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3590773]