Design and simulate the properties of triangular periodic nanoparticle arrays with the structure of bi-layer hexagonal lattice

In this study, the discrete dipole approximation (DDA) method was used to simulate the hybrid bi-layer hexagonal lattice of triangular periodic nanoparticle arrays (PNAs). The PNAs nanophotonic devices could be fabricated with pure silver, but their performances would be easily degenerated because of the oxidation (forming Ag₂O) and sulfuration (forming Ag₂S). Theoretical results show that the oxidation and sulfuration of Ag thin film lead to a significant red shift in the wavelength to reveal the maximum extinction efficiency (λ_max) and to a significant decrease in the maximum peak value of localized surface plasmon resonances (LSPRs). The structures with the bi-layer materials of Ag₂O–Ag and Ag₂S–Ag were used to prove the degeneration of the properties in the extinction spectra of the LSPRs by using DDA method for simulation. We would find that the maximum peak value of the wavelength of the extinction efficiency spectra critically decreased and λ_max had a red shift as the thicknesses of Ag₂O and Ag₂S increased. The structures with the bi-layer materials of Au–Ag and TiO₂–Ag were also used to investigate their extinction spectra of the LSPRs. The simulation results of DDA method found that the maximum peak value of the wavelength of the extinction efficiency spectra slightly decreased as the thicknesses Au and TiO₂ increased. Based on the Ag triangular nanostructure, the use of Au and TiO₂ to form hybrid Au–Ag and TiO₂–Ag triangular nanostructure cannot only be used to put forth of preventing oxidation and sulfuration but have a better performance than the Ag₂O–Ag and Ag₂S–Ag hybrid triangular nanostructures. Meanwhile, the thicknesses of TiO₂ or Au layers could be used to decide the refractive index sensitivity (RIS) and figure of merit (FOM) of the hybrid Au–Ag and TiO₂–Ag PNAs.