▎ 摘　　要

We observed graphene flakes on a SiO2/Si substrate and confirmed the variation in the thickness of the flakes by optical microscopy, Raman spectroscopy and scanning electron microscopy (SEM). We were able to clearly distinguish the thickness variation of the graphene provided a low primary electron acceleration voltage was used. It was found that different contrasts in SEM images at low acceleration voltages could be attributed to the fact that the generation of secondary electrons emitted from the graphene was affected by the different work functions that corresponded to the number of graphene layers. Copyright (C) 2012 John Wiley & Sons, Ltd.