Laser-induced the enhancement of Raman scattering performance in WO_3-x/Ag composite films

Non-stoichiometric tungsten oxide (WO_3-x) has controllable defects, high charge density, and good synergy with other materials to exhibit good surface-enhanced Raman scattering (SERS) properties. Its heterojunction structure provides an opportunity to develop high-quality and low-cost SERS substrates. This study obtained WO_3-x/Ag composite thin films were obtained by Nd: YAG fiber pulsed laser modification at ambient conditions. The effects of interactions between heterojunctions and laser modification on the samples' morphology, composition, and optical properties were investigated. The absorption peaks exhibited a red shift by varying the laser scan speeds, and the SERS properties of the sample were evaluated by methylene blue (MB) dye. The results show that the laser-modified WO_3-x/Ag films have good stability as SERS substrates. The characteristic peaks of MB can still be detected after 90 days in the air. The WO_3-x/Ag films also have good homogeneity and a low detection limit, with a limit of detection (LOD) as low as 10^-7 M, and an enhancement factor as high as 1.34 × 10⁴. The simulated results by the finite difference in time domain (FDTD) showed substantial agreement with those of the experimental ones.