▎ 摘　　要

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. We found a distinct linear relationship between the relative secondary electron intensity from graphene and the number of layers, provided that 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 terms of its capability to characterize graphene samples with sub-micrometer squares in area on various insulating substrates. (C) 2010 The Japan Society of Applied Physics