Determination of the Number of Graphene Layers: Discrete Distribution of the Secondary Electron Intensity Derived from Individual Graphene Layers

Using a scanning electron microscope, we observed a reproducible, discrete distribution of secondary electron intensity stemming from an atomically thick graphene film on a thick insulating substrate. The discrete distribution made it possible to uniquely relate the secondary electron intensity to the number of graphene layers. Furthermore, we found a distinct linear relationship between the relative secondary electron intensity from graphene and the number of layers, provided a low primary electron acceleration voltage was used. Based on these observations, we propose a practical method to determine the number of graphene layers in a sample. This method is superior to the conventional optical method in its capability to characterize graphene samples with sub-micrometer squares in area on various insulating substrates.