Insights into the Semiconductor SERS Activity: The Impact of the Defect-Induced Energy Band Offset and Electron Lifetime Change

Abstract

The significant boost in surface-enhanced Raman scattering (SERS) by the chemical enhancement of semiconducting oxides is a pivotal finding. It offers a prospective path toward high uniformity and low-cost SERS substrates. However, a detailed understanding of factors that influence the charge transfer process is still insufficient. Herein, we reveal the important role of defect-induced band offset and electron lifetime change in SERS evolution observed in a MoO 3 oxide semiconductor. By modulating the density of oxygen vacancy defects using ultraviolet (UV) light irradiation, SERS is found to be improved with irradiation time in the first place, but such improvement later deteriorates for prolonged irradiation even if more defects are generated. Insights into the observed SERS evolution are provided by ultraviolet photoelectron spectroscopy and femtosecond time-resolved transient absorption spectroscopy measurements. Results reveal that (1) a suitable offset between the energy band of the substrate and the orbitals of molecules is facilitated by a certain defect density and (2) defect states with relatively long electron lifetime are essential to achieve optimal SERS performance.

Precise Construction of Chiral Plasmonic Nanoparticles for Enantioselective Discrimination

“…In Figure a, the signal at around 1380 cm –1 of 2-NTT was distinctly amplified on the Au NP-based substrates. The enhancement factor (EF) of Au NPs@PSA200- b -PMA was calculated as 9.38 × 10 6 , which was comparable to the other SERS studies. − Due to the electromagnetic mechanism of Au NPs, the limit of detection for 2-NTT on Au NPs@PSA200- b -PMA was estimated to be 10 –7 M (Figure S19). In addition, the SERS performance of Au NPs of different sizes was explored.…”

Electrically configurable SERS-FET for the highly sensitive and selective detection of molecules

“…When the excited electron recovers from the CB to the defect level near the middle of band gap and is then re-excited by another photon, the resonance charge transfer between the LUMO and defect levels (Process 1) occurs. 40 However, the constant downward movement of the defect levels might disrupt the resonance transfer and then degrade the SERS performance (Process 2).…”

A WOx/MoOx hybrid oxide based SERS FET and investigation on its tunable SERS performance

“…The CM effect of semiconducting materials like TiO 2 , ZnO, MoS 2 , WSe 2 and MoO 3 has been extensively reported. 13–18 Practically, the SERS performance contributed by the CM is enhanced by regulating the defect density or levels to match the orbital energy levels of the adsorbed molecules, and boost the charge transfer efficiency. 19–21 For example, Cong et al reported impressive SERS performance measured on W 18 O 49 nanowires prepared by the hydrothermal method.…”