fig6

Figure 6. Measurement of surface energy or forces of supported 2D materials. (A) Schematic of the surface force balance apparatus based on graphene-coated epoxy cylinders and summary of the measured surface energy (based on JKR theory)^[107]; (B) Schematic of nanoindentation experiments on graphene-coated silicon oxide substrates and the measured force-separation relationships^[110]; (C) Schematic illustration of an AFM tip coated with a thin graphite layer that is brought into contact with 2D materials (top panel) and typical force-distance curves measured on BN, MoS₂, and graphite^[112]. Figures are adapted from references^{[107,110,112]} with permission. AFM: Atomic force microscope; FLG: few layer graphene; JKR theory: the Johnson-Kendall-Roberts theory; SLG: single layer graphene; 2D: two-dimensional.