Influence of microstructure on dielectric function and plasmonic properties of silver nanoparticles grown by solid state dewetting: a spectroscopic ellipsometry study

Abstract

Abstract This work reports the microstructure influence on dielectric function and plasmonic properties of silver nanoparticles (Ag NPs). Ag NPs with varying microstructures were grown on corning glass substrate by solid-state dewetting (SSD) of sputtered silver thin films deposited by varying RF power. Dielectric function and plasmonic properties of Ag NPs were investigated from spectroscopic ellipsometry (SE) data using a quite unique model in terms of the combination of different oscillators. Drude–Lorentz model along with two Gauss oscillators was used to account for intraband, interband transitions and different modes of localized surface plasmon resonance (LSPR) of Ag NPs. It was observed that peak of imaginary part of pseudo dielectric function, which is due to LSPR of Ag NPs, shifted towards the lower energy at higher RF power due to increase in thickness of precursor films which subsequently resulted in to increase in particle size. A shift in the LSPR peak in absorbance spectra in UV–Vis-NIR spectroscopy was also observed. No LSPR peak is observed in SE or UV–Vis absorbance spectra for thick films deposited at high RF power due to the presence of continuous silver film even after annealing. This change in microstructure from nanoparticle formation to continuous films is also reflected in the values of void fraction and surface roughness calculated from SE using Bruggeman Effective Medium Approximation (BEMA). Field Emission Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), and X-ray diffraction (XRD) were used to probe the microstructure of Ag NPs. Root mean square (RMS) roughness evaluated from AFM matched well with surface roughness measured from SE.