Abstract
Raman spectroscopy is commonly used to determine the number of layers of few-layer graphene (FLG)samples. In this work, we focus on the criteria based on the G-band integrated intensity and on the laseroptical contrast. Limitations due to stacking order are discussed and lead to the conclusion that it isnecessary to combine Raman and optical contrast to avoid misinterpretation. Both methods enable todistinguish unambiguously between single layer graphene and multilayer graphene. However, neithereach method separately nor the combination of the two enable a determination of the number of layers forall possible stacking orientations. Importantly, since the two methods always significantly disagree whenthey fail, the comparison of the values deduced by each method allows to discriminate if the determinednumber of layers can be specified or not. Other important parameters (substrate, laser wavelength,objective numerical aperture) are discussed to define a reliable method to determine the number ofgraphene layers in FLG and its domain of validity. The proposed method which combines Raman andoptical contrast measurements, carried out with a 532 nm laser and using a 100x objective with anumerical aperture of 0.9, allows the determination of the number of layers for (up to 5) FLG on thefollowing substrates: (i) glass (soda lime glass or similar with refractive index between 1.50 and 1.55) and(ii) oxidized silicon (SiO2 on silicon, with a SiO2 thickness of 90 ± 5 nm). The method is however limited tohigh quality graphene and FLG with small defect density and low residue.