Résumé
Raman spectroscopy (RS) of graphene and related materials (GRM) is being considered as a fast, versatile, powerful and non-destructive characterization technique. RS is indeed sensitive to the number of layers, their stacking order, the defects nature and density, doping and strain. This wealth of information should make RS the ideal “turnkey” experiment for routine characterization purposes.[1] However, graphene/multi-layer graphene Raman bands lineshapes also depend on the uniformity across the probed area (strain, doping, numer of layers…) and on the substrate (optical interference effects, dielectric screening…). An accurate interpretation of Raman spectra becomes then very complex and deserves the combined use of complementary diagnosis. In this talk, we focus only on single-layer graphene and present how RS can be used to separate and estimate strain and doping in graphene. Indeed, it was shown that the correlation analysis of the Raman G and 2D bands of graphene can be used to optically separate the effects of strain and charges and quantify them.[2] Here, using an optical doping technique,[3] we extract and discuss the relative dependencies of the G, 2D and 2D’ bands frequencies as a function of strain and at zero doping. We further highlight the advantages of using the 2D’ instead of the 2D. Finally, based on an example where a sharp gradient of charges concentration is present in the sample, we discuss the impact on Raman signatures of charges heterogeneities with a characteristic length scale smaller than the laser spot size.[1] A.C. Ferrari, D.M. Basko, Raman spectroscopy as a versatile tool for studying the properties of graphene, Nat. Nano., 8, 235 (2013).[2] Ji Eun Lee, Gwanghyun Ahn, Jihye Shim, Young Sik Lee, Sunmin Ryu, Optical separation of mechanical strain from charge doping in graphene, Nat. Comm. 3, 1024 (2012).[3] A. Tiberj, M. Rubio-Roy, M. Paillet, J.-R. Huntzinger, P. Landois, M. Mikolasek, S. Contreras, J.-L. Sauvajol, E. Dujardin, A.-A. Zahab Reversible optical doping of graphene Scientific Reports 3, 2355 (2013).