New Insights into SERS Mechanism of Semiconductor–Metal Heterostructure: A Case Study on Vanadium Pentoxide Nanoparticles Decorated with Gold

Abstract

Recently, vanadium oxides and other semiconductor materials have been intensively studied to use them as nonplasmonic substrates for surfaceenhanced Raman scattering (SERS) spectroscopy due to their advantages such as greater uniformity, stability, and spectral reproducibility compared to plasmonic ones. The combination of vanadium pentoxide nanoparticles (V 2 O 5 NPs) with nanostructures of noble metals has shown considerable promise for enhancing the SERS signal, while maintaining the aforementioned advantages. We prepared V 2 O 5 / Au NP films by a novel, simple, fully solvent-and linker-free method: the gas-phase synthesis of vanadium NPs followed by their thermal annealing at 550 °C to obtain V 2 O 5 NP films, which were subsequently decorated with Au nanoislands. Using methylene blue (MB) solution as a test analyte, we observed a significant enhancement of the SERS signal (up to 65 times) from the V 2 O 5 /Au composite compared to those from pure V 2 O 5 substrates. The SERS enhancement in this case arises from the synergy of electromagnetic and chemical (charge-transfer) enhancement. The deposition of Au on the V 2 O 5 surface increases the charge-transfer contribution. Moreover, the additional enhancement is achieved due to electromagnetic field coupling between V 2 O 5 and Au or between neighboring Au nanostructures. The observation of two maxima of MB SERS signal from the V 2 O 5 /Au heterostructure for various Au deposition times brings new insights into the SERS mechanism of the semiconductor− metal heterostructure. Spectral mapping across the V 2 O 5 /Au substrates shows excellent homogeneity and spectral reproducibility (RSD of the SERS signal less than 10%). This study introduces an important step in designing novel semiconductor−metal SERSactive substrates. Our V 2 O 5 /Au heterostructures represent highly attractive substrates with improved stability and spectral reproducibility as compared to other nonplasmonic and plasmonic ones.