Understanding the Chemical Mechanism behind Photoinduced Enhanced Raman Spectroscopy

Photoinduced enhancedRaman spectroscopy (PIERS) is a new surfaceenhanced Raman spectroscopy (SERS) modality with a 680% Raman signalenhancement of adsorbed analytes over that of SERS. Despite the explosionin recent demonstrations, the PIERS mechanism remains undetermined.Using X-ray and time-resolved optical spectroscopies, electron microscopy,cyclic voltammetry, and density functional theory simulations, weelucidate the atomic-scale mechanism behind PIERS. Stable PIERS substrateswere fabricated using self-organized arrays of TiO2 nanotubeswith controlled oxygen vacancy doping and size-controlled silver nanoparticles.The key source of PIERS vs SERS enhancement is an increase in theRaman polarizability of the adsorbed analyte upon photoinduced chargetransfer. A balance between improved crystallinity, which enhancescharge transfer due to higher electron mobility but decreases lightabsorption, and increased oxygen vacancy defect concentration, whichincreases light absorption, is critical. This work enables the rationaldesign of PIERS substrates for sensing.

Automated summary

Photoinduced enhanced Raman spectroscopy (PIERS) is a new surface enhanced Raman spectroscopy (SERS) modality with a 680% Raman signal enhancement of adsorbed analytes over that of SERS. In this study, the atomic-scale mechanism behind PIERS is elucidated using various spectroscopic and simulation techniques. The key factor contributing to the PIERS enhancement compared to SERS is the increase in Raman polarizability of the adsorbed analyte through photoinduced charge transfer. This work provides insights for the rational design of PIERS substrates for sensing applications.