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Neighboring Cu grains with yellow/violet coloration and their characteristic step structure as revealed by PM and AFM images. (a), (c) yellow/violet and violet/yellow coloration at (90 + Δ°) and (90−Δ°) setting of the analyzer; (b) high-resolution PM image with rigorously crossed polarizer and analyzer. Note the parallel steps in each grain. The green lines indicate the average step edge direction; (d), (f) contact mode AFM image of the two grains; (e) schematic presentations of the step structure in the two grains, the shaded faces are roughly parallel with the surface of the Cu foil.
PM and AFM images of an individual graphene flake. (a) PM image in violet and (b) yellow orientation, note certain regions where no color is observed. The same grey coloration can be observed as for the Cu background; (c) topographic C-AFM image; (d) FF-AFM image, note the characteristic difference between graphene and Cu.
Intensity of linearly polarized light reflected from graphene over the same Cu grain as measured by microspectrometer. (a) Color changes with slightly off-crossed polarizers as the sample was rotated on the stage of the microspectrometer, the color code on right hand side indicated the intensity of the reflected light (100 correspond to color neutrality). (b) Color of the same Cu grain in (90 + Δ°) and (90−Δ°) positions as Δ is increased from 0° to 20°.
Ratio of reflected light intensities as in Fig. 3(b): (I+Δ − Iaverage)/Iaverage (black curve), (Iaverage − I −Δ)/Iaverage (red curve), and (I+Δ−I−Δ)/Iaverage (blue curve) as Δ increases from 0° to 90°.One may note that the color contrast is reduced as the analyzer approaches the parallel position with the polarizer.
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