SERS-active WO_3-x thin films with tunable surface plasmon resonance induced by defects from thermal treatment

A series of WO_3-x thin films with defects were obtained by thermal treatments from laser irradiation and annealing, respectively. The corresponding tunability of localized surface plasmon resonance properties and the enhancement of Raman scattering intensity were realized due to the defects in the WO_3-x thin films after thermal treatments. With the changes of either laser power or annealing temperature, the crystalline quality of WO_3-x thin film was declined with a red shift of the surface plasmon resonance wavelength from 464 nm to 482 nm. The as-treated WO_3-x film shows good uniformity and reproducibility in Surface-enhanced Raman spectroscopy measurement, the detection limit for dye methylene blue can reach 10^-8 mol/L, and enhancement factor is 1.38 × 10⁶. Furthermore, the simulation result of finite-difference time-domain showed a substantial agreement with experimental results.