Exploring the structure and electronic properties of individual hybrid GO/rGO flakes

Exploring surface charge dynamics: implications for AFM height measurements in 2D materials

“…Therefore, additional AFM interaction channels are necessary for accurate differentiation. As explained in [ 61 ], this distinction is achieved unequivocally by using the KPFM and 2ω elec electrostatic channels. In KPFM images ( Figure 1c ), GO flakes are identified by their signature localized charge domains related to its low conduction and disordered nature [ 76 ].…”

“…The 2ω elec signal ( Figure 1d ), related to the tip–sample capacitance [ 77 ], also allows one to discriminate GO from rGO. While a quantitative interpretation of the 2ω elec contrast in 2D materials necessitates further elucidation, it has proven reliable and robust for distinguishing materials with distinct electronic properties and, in particular, for identifying rGO with different reduction degrees [ 61 ]. In this channel, GO displays no contrast, whereas rGO shows a larger value compared with the substrate.…”

“…Moreover, we can examine a nanoscale heterogeneous sample, such as a partially reduced rGO flake. The transition from GO to rGO under reduction with hydrazine involves a non-homogeneous process, in which, at the intermediate reduction stages, the rGO flakes are composed of regions with different reduction degrees and, therefore, different properties [ 61 ]. As depicted in Figure 4a , when the tip–sample voltage is compensated (KPFM on), the height of rGO is roughly homogeneous along the flake.…”

“…Co-deposited samples of GO and rGO were prepared following the methodology outlined in [ 61 ]. In summary, ultradiluted (4 × 10 −4 wt %) dispersions of GO and/or rGO in Milli-Q type-I water (MQ water) were utilized.…”

“…KPFM was operated in the frequency modulation mode (FM-KPFM) with an AC voltage of 700 mV at 7 kHz using platinum-coated silicon tips (Olympus AC240TM-R3, k = 2 N/m and f 0 = 70 kHz). Using a dual lock-in amplifier (Zurich instruments, HF2LI), in addition to the KPFM channel, which provides information on the sample's SP, the 2ω elec capacitance signal was also recorded, as explained in [ 61 ].…”