Understanding the Chemical Mechanism behind Photoinduced Enhanced Raman Spectroscopy

Abstract

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. Despite the explosion in recent demonstrations, the PIERS mechanism remains undetermined. Using X-ray and time-resolved optical spectroscopies, electron microscopy, cyclic voltammetry, and density functional theory simulations, we elucidate the atomic-scale mechanism behind PIERS. Stable PIERS substrates were fabricated using self-organized arrays of TiO 2 nanotubes with controlled oxygen vacancy doping and size-controlled silver nanoparticles. The key source of PIERS vs SERS enhancement is an increase in the Raman polarizability of the adsorbed analyte upon photoinduced charge transfer. A balance between improved crystallinity, which enhances charge transfer due to higher electron mobility but decreases light absorption, and increased oxygen vacancy defect concentration, which increases light absorption, is critical. This work enables the rational design of PIERS substrates for sensing.

Structural and optical properties of highly Ag-doped TiO2 thin films prepared by flash thermal evaporation

“…Alternatively, less common techniques such as traditional physical vapor deposition (PVD) methods including magnetron sputtering and laser ablation are utilized [35][36][37][38]. The choice of synthesis method impacts the photocatalytic and photoelectrochromic efficiencies of the resulting electrodes due to variations in porosity, crystallite sizes of oxide semiconductors, and the presence of structural defects [39].…”

Peculiarities of the Structure of Au-TiO2 and Au-WO3 Plasmonic Nanocomposites

“…Tungsten trioxide WO 3 is generally used as the electrochromic coating for smart windows due to its ability to change color depending on its stoichiometry [19,20]. Recently, there has been a growing trend of studying the photo-induced enhancement of Raman signal (PIERS) using composites based on the considered oxides with noble metal nanoparticles [21,22].…”

“…Depending on the synthesis method, the prepared electrodes have different photocatalytic and photo electrochromic efficiencies due to the different porosity and crystallite sizes of the oxide semiconductors. The presence of structural defects in the composite is also important [22]. Therefore, in this work, using Raman spectroscopy we have investigated the structural properties of Au-TiO 2 and Au-WO 3 composites obtained by the RF magnetron sputtering method.…”

Reusable SERS Substrates Based on Gold Nanoparticles for Peptide Detection

“…The electromagnetic mechanism is associated with plasmon excitation in metallic particles rich with electrons, as well as plasmon interaction in close proximity to the particle surface. The enhancement factor (EF) for the electromagnetic mechanism is typically about 10 5 –10 6 in comparison with regular Raman measurements, whereas the chemical mechanism adds another order or two to the EF due to charge transfer between either the molecules themselves [ 10 ] or the absorbed molecule and the substrate [ 11 , 12 ]. Thus, the enhancement factor could reach 10 6 –10 8 .…”