Optical properties of porous anodic alumina membrane uniformly decorated with ultra-thin porous gold nanoparticles arrays.

In this paper, we directly develop a facile method to decorate a modified porous anodic alumina membrane (PAA) with an ultrathin porous film of gold nanoparticles with sub-gaps less than 25 nm and particle size less than 40 nm on the top surface and Au nanoparticles uniformly attached to the pore walls as well as the bottom of the pores, utilizing radio-frequency magnetron sputtering. The size as well as the interparticle distance of the gold nanostructures is adjusted by changing the structural properties of PAA membrane and the sputtering time. According to the measured reflection spectra, the saturation of interference color is significantly enhanced. As a result, the Au-coated PAA membrane exhibits a brilliant and tunable color. Field enhancement can be achieved in these structures through the excitation and constructive interference of surface plasmon waves. In addition, the role of localized surface plasmon and propagating surface plasmon was discussed. A four-layered model is presented to describe the reflectance data that show excellent agreement with the experimental data. The brilliant Au-coated PAA membrane is useful for decorative purposes and holds promise as an effective surface enhanced Raman scattering (SERS) substrate.