Anodization parameters influence on anodic aluminum oxide formed above the silver island film

Optical properties of hybrid plasmonic thin film structure in the form of anodic alumina porous matrix above silver island film on the quartz substrate have been investigated. Silver nanoparticle film in the bottom of the structure has been obtained by physical vapor deposition in a vacuum chamber. The silver island film with the island of average diameter of 100 nm has been formed after annealing in the air atmosphere. Above the silver nanoparticle film an aluminum film has been deposited by the E-beam evaporation. As a result of one-step straight anodization, a nanoporous alumina thin film has been formed. The obtained structures were investigated, using spectroscopy and electron microscopy methods. The structure reflectance and optical density spectra have been obtained and analyzed for different anodization times and currents. To compare the results, the reflectance and optical density spectra have been obtained for silver nanoparticles and anodic alumina. When anodization times are increased, structure reflection coefficient spectra become more like the same characteristic for anodic aluminum oxide, which can be explained by film oxidation. At the same time a red shift of reflectance spectrums is observed in the structures with bigger maximum anodization currents. This effect has been observed in other works and can be explained by the increasing distance between the pores. A numerical modeling of optical properties with the help of Mie calculator for the structure with the nanoparticle size of 100 nm has shown that the results of the modeling can be compared to the experimentally obtained optical density spectra. The modeling was performed using spherical approximation. To obtain more precise results for alumina film thickness and nanoparticle optical properties, a silver nanoparticle form factor has to be considered. The results of this work can be used in sensors, optical coatings and photon sources fabrication methods. These can be used in screens, optical schemes and many other plasmonic devices