Spatially selective narrow band and broadband absorption in Ag/SiO₂/Ag based trilayer thin films by oblique angle deposition of SiO₂ layer

Abstract We have experimentally demonstrated spatially selective absorption in Ag-SiO₂-Ag based trilayer thin films by tuning the deposition angle of SiO₂ layer. These structures generate cavity resonance which can be tuned across the substrate locations due to spatially selective thickness and refractive index of silicon oxide (SiO₂) film sandwiched between metallic silver (Ag) mirrors. Spatially selective property of SiO₂ film is obtained by oblique angle deposition technique using an electron beam evaporation system. The resonance wavelength of absorption in this trilayer structure shifts across the substrate locations along the direction of oblique deposition. The extent of shift in resonance increases with increase in angle of deposition of SiO₂ layer. 4.14 nm mm⁻¹ average shift of resonance wavelength is observed when SiO₂ is deposited at 40° whereas 4.76 nm mm⁻¹ average shift is observed when SiO₂ is deposited at 60°. We observed that the width of resonance increases with angle of deposition of the cavity layer and ultimately the resonant absorption disappears and becomes broadband when SiO₂ is deposited at glancing angle deposition (GLAD) configuration. Our study reveals that there is a suitable range of oblique angle of deposition from 40° to 60° for higher spatial tunability and resonant absorption whereas the absorption becomes broadband for glancing angle deposition.