Effect of gold-coating on the plasmon properties of silver nanostructure arrays

We report that gold-coating has a significant effect on the plasmon properties of both triangular and rhombic Au-Ag nanostructure arrays. Both finite-difference time-domain and discrete dipole approximation methods are used to calculate the optical properties of the nanostructure array. We changed the thickness of the gold-coating and the refractive index of the medium surrounding the nanostructure array and obtained the maximum refractive index sensitivity. The electric field distribution of the triangular nanostructure array is also explored by a FDTD method. The calculated results show that gold-coating has a significant effect on the plasmon properties of the triangular and rhombic Au-Ag nanostructure array and the rhombic nanostructure array has a higher refractive index sensitivity than the triangular nanostructure array.