Structural origins of optical properties of nanosized indium particle films: An ellipsometric insight

Abstract

Indium has attracted widespread attention due to its compelling optical properties for promising applications in plasmonics. In this work, we employ spectroscopic ellipsometry to investigate the optical properties of indium nanoparticle films with different size distributions fabricated by using electron beam evaporation. We propose a method to distinguish optical responses arising from electron behaviors in different structures by fitting the multi-oscillator Drude-Lorentz dispersion model. For the particle films with bimodal size distributions, localized surface plasmon resonances arising from electron oscillations in both large and small particles are modeled by applying two oscillators. The formation of densified structures, resulting from contacts of adjacent particles, is revealed by adding an oscillator with a center energy close to zero. The validity of the multi-oscillator model is qualitatively verified by using scanning electron microscopy and atomic force microscopy. Reflectance spectra justify quantitively the proposed model. This study is beneficial for the applications of nanostructured indium films in advanced plasmonic devices. The ellipsometric modeling on indium particle films provides a means of distinguishing the contributions of diverse electron behaviors to optical responses in complex nanostructures.