Determining the thickness of chemically modified graphenes by scanning probe microscopy

The thickness of unreduced and chemically reduced graphene oxide sheets deposited on different substrates was measured by different scanning probe microscopy (SPM) variants. Inaccurate and inconsistent results are obtained when thickness is derived as a sheet-to-substrate height, which is the typically employed approach to determine such a parameter. Measuring overlapped regions between different sheets leads to more realistic thickness values, which clearly reflect, for example, the removal of oxygen functionalities from graphene oxide following chemical reduction. The results underline the precautions that are required to draw valid conclusions from SPM-derived thickness data of chemically modified graphenes.