Design and fabrication of selective thin film absorbers on the basis of silver island films
The combination of a metal island film with a dielectric multilayer represents a novel approach to the preparation of spectrally selective absorbers. Metal island films show exceptional optical properties caused by the optical excitation of surface plasmon modes. The plasmon resonance frequency depends on the size and shape of the islands and is influenced by the deposition parameters. The first type of samples represents a silver island film in an ultrathin Al2O3 film. We analyzed these samples by means of spectrophotometry. The recorded spectra allow the calculation of the optical constants of the silver island films. These show a maximum absorption of up to 40%. Finally, we incorporated ultrathin metal-dielectric-composite films on a silver/alumina basis into multilayer stacks to design tailored spectrally selective absorber coatings. The stack absorption comes close to 100%.