Fig. 4: Visualizing the subsurface structure of extrinsically stacked FLG.

a Optical image. The orange dashed line is the overlapped area. b Topography of the red dashed rectangular region in Fig. 4a. PiFM images of the same region at (c). 1578 cm−1, (d). 1580 cm−1, (e). 1582 cm−1 and (f). 1588 cm−1. The white scale bar is 4 μm. g Normalized PiFM spectral shift on the crack. h Sketch of infrared phonon shift of layered graphene with respect to the compress or tensile strains. All the normalizations are conducted by the PiFM signal of substrate (SiO2)