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

From far-IR Drude absorption measurement we determine carrier density (N) and carrier scatter ing rate ( Γ ) of graphene deposited on buffer-layer / SiO 2 composite substrate. Two types of buffer-layers, (1) polar dielectric oxide ZnO and SrTiO 3 (2) organic thin film hexamethyl disilazane and polymethyl methacrylate (PMMA) were studied. N varies widely over 0.12 - 11.8 ( × 10 12 cm − 2 ) range depending on the buffer-layer. In contrast Γ remains almost constant, ∼ 100 cm − 1 , irrespective of the buffer-layers. This indicates that carrier mobility ( μ ) of graphene depends on substrate through N, but not by Γ as commonly believed.