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(a) AFM topographic image of GO layers on a gold substrate. Panel (b) depicts a surface potential map of the same region where equipotential areas corresponding to different coverages can be appreciated. Coverage is marked with the number of ML on the substrates as n ML. (c) Profile performed on the surface potential map following regions with different coverages (The red line in (b) indicates schematically the paths followed to perform the profile). (d) AFM topography image and (e) surface potential map of GO layers on a highly p doped Silicon substrate. (f) Profile performed on (e) following regions with different coverage (the red line in (e) indicates schematically the paths followed to perform the profile). (g) AFM topography image and (h) surface potential map of GO layers on a HOPG substrate. (i) Profile performed on (h) following regions with different coverages (the red line in (h) indicates schematically the paths followed to perform the profile). (j) This graph summarizes our experimental results: plot of the surface potential difference (in absolute value) as a function of the number of monolayers layers of GO flakes on Si (black), HOPG (red), and gold (green) substrates.
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(a) AFM topographic image of GO layers on a Si substrate. The upper-right region corresponds to a multilayered region with height of 15 nm (i.e., 12 layers). In the central area, we observe a bilayered GO. Panels (b) and (c) are surface potential maps of the same region as panel (a) acquired before and after chemical reduction of the GO layers. The profiles shown in panel (d) correspond to the same path on the surface potential before and after reduction. Here, we observe that the surface potential difference between layers decreases after chemical reduction. The expected saturation behaviour can also be observed for the 12 monolayers layers region.
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(a)–(d) KPFM images of the same region of GO deposited on HOPG under different environmental conditions. Sample temperature (T) and environmental RH are indicated in white in each image. The images are equalized saturating the substrate in order to optimize the visual discrimination of layers when possible. The red line indicates schematically the paths followed to perform the profiles shown in panel (e). The paths followed are the same in the four images. In the profiles depicted in panel (e), we can observe how the surface potential smears out with increasing relative humidity. At 30%, humidity changes in the surface potential can hardly be appreciated.
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