Damping resonance and refractive index effect on the layer-by-layer sputtering of Ag and Al2O3 on the polystyrene template

In this study, an ordered metal oxide-metal composite system was designed. By changing the thickness of film of Ag/Al₂O₃ nanoparticles (NPs), the red and blue shifts of local surface plasma resonance (LSPR) were realized in the proposed system and discussed by damping resonance theory and Mie's scattering theory to demonstrating the relationship between wavelength (λ) and particle diameter (D). With the increasing of sputtering time of Ag, the SPR of Ag was red shifted under the influence of damped vibration, obtaining that square of wavelength (λ²) is proportional to D. The surface plasma resonance (SPR) of Ag/Al₂O₃ showed an obvious blue shift, and then red shift suddenly, which is affected by the competition between damping resonance and refractive index. When the blue shift occurs, the change of wavelength (∆λ) is exponentially related to the diameter (D). The modulation of LSPR of the proposed composite nano-metal materials will have a potential application in SPR sensor and surface enhanced Raman scattering (SERS).