Monitoring the growth and reactivity of metal nanoclusters by in situ optical spectroscopy

A non-intrusive in situ surface differential reflectance spectroscopy (SDRS) is adapted on a magnetron sputtering deposition technique in order to study the optical properties of metal:dielectric nanocomposites in real-time during their alternate depositions. SDRS is helpful in studying optical properties of metal nanoclusters which are dominated by the surface plasma resonance (SPR), which is sensitive, not only to the morphology and organization of the nanoclusters, but also to their physical and/or chemical surroundings. Hence, to establish the correlation between the optical properties of nanoclusters and their nanostructure, post mortem high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and grazing-incidence small angle X-ray scattering (GISAXS) techniques are implemented. Following the signature SPR in real-time helps us not only to understand the different growth regimes through which the metal nanoclusters evolve, but also to study the effects caused by the physical and/or chemical treatments (such as, exposure of nanoclusters to different gases, either non-ionized or partially ionized, thermal annealing, and low-energy plasma annealing). Finally, the influence of a dielectric (Si3N4) capping matrix on the optical properties of the metal nanoclusters is equally studied after each physical and/or chemical treatment. In this way, the in situ optical spectroscopy allows us to monitor the optical properties of nanocomposites thin films during all the deposition steps and the additional post mortem structural characterization techniques help us to understand the different phenomena taking place at the nanoscale.