Optical properties of thin metal films with nanohole arrays on porous alumina–aluminum structures

A multilayer system is formed by the deposition of a 10-35 nm thin Au or Ag film with 18-25 nm diameter holes on 75-280 nm thick layers of porous anodized aluminum oxide (AAO) supported by a bulk sheet of aluminum. We present a detailed study of system parameters, which influence the optical response, including the porosity, metal layer thickness and crystallographic orientation of the Al substrate. The spectral properties are mainly governed by the interference of the reflections from the Al substrate and the thin metal film separated by the AAO layer. An enhanced plasmonic attenuation component near 650 nm for the Au films with holes can be observed when the interferometric anti-reflection condition is fulfilled close to this particular wavelength.