▎ 摘　　要

We report on strong interference effects on the ratio of the integrated intensities of the Raman 2D- and G-mode features (herein denoted I-2D/I-G) in suspended graphene monolayers. Free from substrate-induced doping and residual charge inhomogeneity, suspended samples are an ideal platform to study the intrinsic properties of graphene. Here, we demonstrate that I-2D/I-G, measured on a pressurized suspended graphene blister, depends very sensitively on the distance between the bulged graphene membrane and the underlying substrate. The data obtained on three different samples are fit to theoretically predicted Raman enhancement factors and allow to extract an intrinsic, i.e., doping-and interference-free, value of (I-2D/I-G) intr = 5 +/- 1 for undoped, unscreened graphene at a laser photon energy of 2.33 eV. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim