Influence of the deposition conditions on the optical absorption of Ag-SiO_2 nanocermet thin films

摘要

We report a study of the influence of the deposition conditions on the morphological parameters (shapes, size distribution and ordering) of Ag nanoclusters embedded in SiO_2, deposited by different techniques of co-sputtering or multilayer deposition. The influence of the substrate temperature on the nucleation and growth process is also studied. The different cluster morphologies determined by various complementary techniques (transmission electron microscopy, scanning electron microscopy, atomic force microscopy) are then correlated with the optical absorption, showing that the fabrication process is the key factor to control the position, shape and width of the surface plasmon resonance peaks and to achieve the desired optical properties. Films deposited by co-sputtering from 2 targets on a substrate heated at 440 ℃ show a very narrow absorption peak at 370 nm corresponding to the plasma resonance in near spherical silver particles. In multilayered films, the absorption peak is shifted from 340 to 480 nm with a larger half-band width. In cermet films co-sputtered from composite target on a rotating substrate, two absorption peaks are observed due to the more elongated shape of the metal nanoparticles. The experimental results are analysed in the frame of the Maxwell Garnett theory.