Relative humidity sensor based on a silver nano-grating made from DVD discs

A relative humidity sensor based on a silver nano-grating was proposed. By stripping and cleaning commercially available CD and DVD discs, polycarbonate plates with different grating periods are obtained. These plates as templates are coated with a layer of sputtered silver film to form silver nano-gratings, which exhibit refractive index sensing sensitivities of 517 nm/RIU and 742.9 nm/RIU, respectively. The finite-difference time-domain simulation results conform the excited surface plasmon polariton modes and localized surface plasmon modes on the nano-grating. By spin coating a layer of humidity-sensitive porous silica with optimized thickness, the silver nano-grating shows a relative humidity detection sensitivity of 0.23 nm/%RH.