Thin films composed of metal nanoparticles (Au, Ag, Cu) dispersed in AlN: The influence of composition and thermal annealing on the structure and plasmonic response

In this work, thin films composed of gold (Au), silver (Ag), and copper (Cu) metals, dispersed in aluminium nitride (AlN), were prepared by reactive direct current magnetron sputtering, and post-deposition thermal annealing. The structure, morphology and optical response of the films were studied as a function of the composition and annealing temperature. The atomic concentration of the plasmonic metal (Au, Ag and Cu), ranged from 2 to 6 at% in Au, 4 to 11 at% in Ag and 3 to 10 at% in Cu. The formation of Au and Ag nanoparticles dispersed in the AlN matrix was observed only for the Au and Ag systems. The average sizes of the nanoparticles increased with the increase of the annealing temperature, up to 6 nm in the case of Au and 12 nm for the case of the Ag. The Au:AlN system revealed plasmonic response at temperatures of 500 degrees C and above, with clear localized surface plasmon resonance, LSPR, bands in the visible range (520-540 nm). The Ag:AlN films showed a LSPR band at lower temperatures (300 degrees C), at wavelengths around 380 nm, shifting to 410 nm at higher annealing temperatures. In some cases, Ag clusters were also formed on the top of the Ag:AlN films, leading to a nearly flat absorption band from visible to infrared wavelengths. In the case of the Cu:AlN thin films, the optical response did not exhibit any characteristics associated to the LSPR effect.