Layered silver nanoparticles embedded in a BaF_2 matrix: optical characterization

Abstract

Multilayer stacks of silver and BaF(2) alternate layers have been deposited by thermal evaporation on a silica substrate with the aim to obtain Ag clusters dispersed in a BaF(2) insulator matrix. The Ag layer thickness was approximately 1.2 nm; the thickness of the BaF(2) layer was approximately 25 nm. The samples were thermally treated for a 1 h thermal annealing process at 500 degrees C. These kinds of multilayer device also have several applications in the field of optics for the realization of antireflection coatings. However, optical characterization of dielectric matrices that contain layered metallic nanoparticles still remains an unsolved problem in the field of nanostructured optical coatings. Therefore, the surface plasmon resonance peak that appears in the optical absorption spectra because of the formation of Ag nanoclusters inside the BaF(2) insulator matrix has been monitored and fitted by numerical codes. In particular, a previously published theoretical model, based on the Maxwell-Garnett effective medium theory, modified to take into account the effects that are due to the particle shapes and the spatial arrangement of the clusters, has been employed to fit the optical absorption spectra.