Determination of the graphene-graphite ratio of graphene powder by Raman 2D band symmetry analysis

Graphene has many unique properties which make it an attractive material for many applications. Analytical methods to differentiate graphene from graphite, like the optical contrast technique, atomic force microscopy or conventional Raman analysis based on intensity ratios, require a specific sample preparation and substrate. Here we report a method to distinguish between few-layer graphene (with less than 10 layers) and graphite that is independent of a specific sample preparation or substrate. Our approach is based on the symmetry of the Raman 2D peak in graphene and its asymmetry in graphite. By evaluating the coefficient of determination R-2 of a Voigt profile fit we can establish a benchmark that discerns graphene from graphite. We found values above 0.985 to be characteristic of graphene. The results were confirmed by thickness measurements with atomic force microscopy. We applied this analysis to both individual graphene flakes and graphene flakes as a thick film. This method allows for fast characterisation of large quantities, a feature that is needed for industrial application. It can be used to determine the graphene content of flakes produced from graphite exfoliation and the efficiency of various production methods.