Fig. 1. (a) SERS performance of Al₂O₃@GO, PMN-PT@GO (P_s⁺) and PMN-PT@GO(P_s⁻) by employing R6G as the probe molecule under excitation of 532 nm laser. (b) Raman shift of G band of GO in Al₂O₃@GO, PMN-PT@GO (P_s⁺) and PMN-PT@GO(P_s⁻). (c) UV-vis spectra of the GO and R6G/GO. (d-f) Schematic diagram of GO doping when adsorbed on different surfaces of PMN-PT. (g-i) Contact potential differences (V_CPD) between Au probe and GO in (g) Al₂O₃@GO, (h) PMN-PT@GO (P_s⁺) and (i) PMN-PT@GO(P_s⁻) measured by a KPFM system. (j–l) Modulation mechanism of SERS enhancement of (j) Al₂O₃@GO, (k) PMN-PT@GO (P_s⁺) and (l) PMN-PT@GO(P_s⁻).

Fig. 2. Atomic structure of (a) intrinsic graphene, (b) graphene on up-polarized (P_s⁺) PMN-PT surface, (c) graphene on down-polarized (P_s⁻) PMN-PT surface for DFT calculation. The electronic band structure of (d) intrinsic graphene, (e) graphene on up-polarized (P_s⁺) PMN-PT surface, (f) graphene on down-polarized (P_s⁻) PMN-PT surface.

Fig. 3. (a, d) The temperature-dependent SERS spectra of R6G by employing (a) PMN-PT@GO(P_s⁻), (d) Al₂O₃@GO as a SERS substrate. (b) Schematic diagram of doping level of GO affected by PMN-PT@GO(P_s⁻) temperature. (c) Schematic illustration of the energy band structure of PMN-PT@GO(P_s⁻)/R6G and the electron transition process under 532 nm excitation laser. (e, f) SERS spectra of R6G with different concentrations on PMN-PT@GO(P_s⁻) at (e) 20 °C, (f) 0 °C. (g) SERS spectra of R6G with different concentrations on Al₂O₃@GO at different temperature.

Fig. 4. (a) SERS spectra of CV on PMN-PT@GO(P_s⁻) under excitation of 532 and 633 nm laser. (b) Schematic diagram of doping level of GO affected by PMN-PT@GO(P_s⁻) temperature. (c, d) Schematic illustration of the energy band structure of PMN-PT@GO(P_s⁻)/CV and the electron transition process under (c) 532 nm, (d) 633 nm excitation laser. (e, f) SERS spectra of CV on PMN-PT@GO(P_s⁻) under excitation of (e) 532 nm, (f) 633 nm laser at different temperature.

Fig. 5. (a, b) SERS spectra of PNTP on PMN-PT@GO(P_s⁻) under excitation of (a) 532 nm, (b) 633 nm laser at different temperature. (c) Schematic diagram of doping level of GO affected by PMN-PT@GO(P_s⁻) temperature. (d, e) Schematic illustration of the energy band structure of PMN-PT@GO(P_s⁻)/PNTP and the electron transition process under (d) 532 nm, (e) 633 nm excitation laser.