Effect of gold layer thickness on optical properties and sensing performance of triangular silver nanostructure array

Optical performance of the nanophotonic devices with pure silver nanostructure will be changed due to the oxidation and sulfuration. A hybrid Au-Ag triangular nanostructure is put forth for the purpose of preventing oxidation and sulfuration of Ag film. Effect of gold layer thickness on optical properties and sensing performance of the hybrid nanostructure array is systematically investigated through numerical simulation using the discrete dipole approximation (DDA) method. Theoretical results show that the oxide layer and sulfide layer leads to a significant red shift in the localized surface plasmon resonance (LSPR) lambda(max). The refractive index sensitivity (RIS) and figure of merit (FOM) of the hybrid nanostructure array strongly depend on thickness of the Au layer. It is found to possess the better RIS and FOM, when thickness of Au is 10 nm, thickness of Ag is 25 nm. Moreover, the hybrid nanostructure with the suitable Au layer thickness is fabricated by nanosphere lithography (NSL). The experimental results demonstrate that the measured spectrum is basically in agreement with the theoretical spectrum derived by the DDA calculation.