Figure 2: Bias-dependent diffraction spectra with graphene gratings in different electrolytes.

(a) Normalized diffraction intensity I_d/I_d^CNP as a function of V_bias at 3,000 cm⁻¹, which probes only the graphene grating response. The black dots and black line are experimental data and fitting, respectively, for graphene gratings in a 12 mM NaCl solution. The diffraction intensity shows a local maximum at CNP (V_bias=1.0 V). The red dots and red line are experimental data and fitting, respectively, for graphene gratings in a 11 mM CTAB solution. I_d also exhibits a local maximum at CNP, which is shifted to V_bias=0.2 V. (b) Simulation of the graphene conductivity in the NaCl solution as a function of Fermi level. Red, Re(σ_g); green, Im(σ_g); black, |σ_g|²∝I_d. (c,d) The solid lines show normalized diffraction spectra I_d(ω)/I_d^CNP (ω) at different V_bias. Two CH₂ vibrational resonances at 2,916 and 2,848 cm⁻¹ are observed from polymer residues for the as-prepared graphene grating in a NaCl electrolyte (c). More pronounced CH₂ resonances are observed for graphene gratings in the 11 mM CTAB electrolyte due to CTAB adsorption at the interface in (d). The dashed lines are theoretical fitting of the diffraction spectra as described in the text.