Metal island films show exceptional optical properties, which are interesting for linear and non-linear optics. One of the perspective applications of metal islands in optics utilizes the surface plasmon excitation for the design of spectrally selective absorbers. The absorption behaviour of metal islands can be influenced by the dielectric function of the metal, the size and the shape of the clusters and the properties of the embedding medium. It is possible to affect these factors and to prepare materials with tailored optical absorption properties.
We describe the optical properties of silver island films embedded in SiO2 and Al2O3. Despite of the presentation of spectrophotometric data and the film morphology as investigated by Transmission Electron Microscopy (TEM), we demonstrate the correlation between silver island geometry and optical response as well as their dependence on the deposition parameters. The results confirm that the silver cluster surface plasmon absorption line position and width depend on the deposition temperature and the cluster ambient. The optical data could be theoretically reproduced by means of the Rigorous Coupled Wave Approximation (RCWA).
We further demonstrate that the absorptance of the silver clusters may be enhanced up to nearly 100% when the clusters are embedded into a suitable designed multilayer stack.