Fig. 4

Residue coverage comparison between the as-prepared and mechanically cleaned area. a TEM image of the as-prepared graphene region. b TEM image of the mechanically cleaned graphene region. The red box is the field of view of panel (c). c Close-up TEM image showing the pristine graphene lattice without surface residue. The marked red hexagons represent the honeycomb lattice of graphene. d HAADF-STEM image of the partially cleaned graphene sample. The dark bottom region is from the mechanically cleaned region. The images in the dashed two boxes were used for the intensity analysis shown in panels (e) and (f). e Histogram of the pixel intensities shown in box e. The two peaks from relatively high- and low-intensity regions were deconvoluted from the histogram. f Histogram of the pixel intensities shown in box f. The three sub-peaks were deconvoluted from the histogram