Structure and Optical Properties of Boron Nitride Capped Silver Nanoparticles Grown by Magnetron Sputtering

Nanostructured silver films have demonstrated plasmonic functionality but suffer from the effects of environmental degradation. We aim to overcome this issue by encapsulating the silver in hard transparent ceramics. Silver nanoparticles were grown on Si and borosilicate glass substrates by magnetron sputtering in the temperature range of RT-300°C. Subsequently the Ag nanoparticles were capped in-situ by a boron nitride layer. The morphology and structure of the films was investigated by transmission electron microscopy, while the optical properties were determined by spectroscopic ellipsometry and optical absorption spectroscopy. The results demonstrate that a dense BN capping layer prevents the Ag segregation to the surface, thus exposure to the atmosphere. The films have a composite structure with nanosized silver particles separated by the amorphous boron nitride matrix. In addition, the BN matrix prevents the coalescence of the supported Ag islands, which is observed for non-capped Ag films. In films with a nominal silver thickness below 10 nm the optical properties can be tuned by adjusting the growth and post-growth annealing parameters (nominal thickness, temperature, annealing duration). The structure-optical property relationship is discussed on the basis of plasmon-polariton resonance and the film morphology.