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(a)-(h) Tapping mode AFM topological images of single-layer GO (a), rGO ((b)-(f), (h)), and graphene (g) sheets after charge injection. The white scale bars represent 1000 nm. The Z scale bar is placed on the right of each image. The GO sheets were either thermally reduced ((b)-(e)) at 130 °C with time period labeled on each image or reduced with hydrazine (f). The single-layer graphene sheet (g) was mechanically exfoliated from graphite flakes. The number labels 1-5 in (h) indicated rGO sheets (reduced at 130 °C for 120 min) that were charged with an AFM tip biased at 12 V, 9 V, 6 V, 3 V, and 0 V, respectively. (i) Raman spectra of rGO and graphene sheets, which displays a prominent G peak at 1582 cm−1, corresponding to the first-order scattering of the E2g mode.15 The intensity ratio (ID/IG)16 of the D band to the G band of the GO and rGO was labeled in each curve. (j) The plots of apparent height of the charged rGO sheets vs. tip bias in charge injection. The error bars are the standard variation of the apparent height of a charged rGO sheet.
Characterization of the charged nanostructures on the single-layered GO sheets. (a) and (b) Contact mode AFM images of square-shaped rGO nanostructures (indicated with arrows) generated by heating the areas with AFM tips heated to 125 °C (a) and 150 °C (b), respectively. (c) and (d) Lateral force microscope images taken simultaneously with (a) and (b), respectively. (e) and (f) SPFM images before charge injection. (g) and (h) Tapping mode topological images after charge injection at the reduced nanostructures. The white scale bars are 500 nm. The Z scale bar is shown on the right of each image.
The values of aR, aL, and δ of the parabolas shown in Figure 1(j).
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