Enhanced Raman scattering when scatterer molecules located in TiO₂/Ag nanojunctions

Abstract

The TiO2/4-mercaptopyridine (4-Mpy)/Ag sandwich structure has been fabricated by a self-assembly method and the enhanced Raman scattering of the molecule embedded in the nanojunction, known as surface-enhanced Raman spectroscopy (SERS), was studied. X-ray photoelectron spectroscopy (XPS) has been employed to investigate the formation process of TiO2/4-Mpy/Ag sandwich structure. Raman spectra of TiO2/4-Mpy/Ag sandwich structure were significantly enhanced relative to those observed on 4-Mpy adsorbed on Ag particles or TiO2/4-Mpy. A possible distribution of 4-Mpy molecules in the fabrication of TiO2/4-Mpy/Ag assemblies has been proposed. It shows that 4-Mpy molecules adsorb on the surface of the TiO2 NPs, and the 4-Mpy molecules connect with Ag NPs via the S atom. The analysis of XPS confirms the result obtained from Raman spectra of TiO2/4-Mpy/Ag assemblies. The SERS enhancement mechanism has discussed briefly in the article, and we ascribed it to the charge-transfer mechanism.

Effect of TiO2 on Altering Direction of Interfacial Charge Transfer in a TiO2‐Ag‐MPY‐FePc System by SERS

“…To elucidate the reasons for the considerable difference in the relative intensity of MPY, energy level schematics of the three kinds of systems for the CT processes were proposed in Figure . The energy level structures of the related components in the systems were in accordance with those in the previous reports . In the Ag‐MPY system (Figure A), the electron can be excited from the Fermi level of the Ag NPs and then transfer to the lowest unoccupied molecular orbital (LUMO) level of MPY under the 633 nm excitation with the energy of 1.96 eV.…”

Effect of TiO2 on Altering Direction of Interfacial Charge Transfer in a TiO2‐Ag‐MPY‐FePc System by SERS

“…To elucidate the reasons for the considerable difference in the relative intensity of MPY, energy level schematics of the three kinds of systems for the CT processes were proposed in Figure . The energy level structures of the related components in the systems were in accordance with those in the previous reports . In the Ag‐MPY system (Figure A), the electron can be excited from the Fermi level of the Ag NPs and then transfer to the lowest unoccupied molecular orbital (LUMO) level of MPY under the 633 nm excitation with the energy of 1.96 eV.…”

“…Thee nergy level structures of the related components in the systems were in accordance with those in the previous reports. [42,43] In the Ag-MPY system ( Figure 3A), the electron can be excited from the Fermi level of the Ag NPs and then transfer to the lowest unoccupied molecular orbital (LUMO) level of MPY under the 633 nm excitation with the energy of 1.96 eV.T he intensity of the b 2 mode of MPY adsorbed on the surface of the Ag NPs was enhanced intensely due to the CT mechanism based on Herzberg-Te ller contributions. [20,34] In the Ag-MPY-FePc system, FePc was coordinated with MPY,which led to some changes in the molecular electronic structure of the Ag-MPY and the generation of alarge electronic delocalization effect.…”

Charge Transfer Effects on Resonance-Enhanced Raman Scattering for Molecules Adsorbed on Single-Crystalline Perovskite

“…In Figure a, several observable bands located at 488 and 977 cm –1 are attributed to the crystal mode (Figure b), while the 621 cm –1 (C–C–C/N–CC out-of-plane bend), 1001 cm –1 (ring breathing), 1031 cm –1 (C–H in-plane bend), 1182 cm –1 (C–H in-plane symmetric bend), 1200 cm –1 (C–H in-plane antisymmetric bend), 1582 cm –1 (C–C stretch with deprotonated nitrogen), and 1602 cm –1 (C–C stretch with protonated nitrogen) are intrinsic to MPY. A more detailed assignment for Raman bands of MPY under different conditions is shown in Table . − …”