Firstly, we prepared the graphene sample lying on the TEM grid as reported before. Briefly, paraffin was melted and spin-coated on top of the Cu-supported graphene. Then the Cu-foil was etched using 10 wt% Na2S2O8 solution to obtain a paraffin-reinforced graphene. Then it was washed with water for 3 times and subsequently transferred to the TEM grid. The transferred film was dried at 45°C for 2 days.