Visible and Near-Infrared Optical Properties of Indium Tin Oxide Nanoparticle Films

Highly doped semiconductors exhibiting optical transparency in the visible range, as Indium tin oxide (ITO), are widely used for many applications, including electrodes in screens, tablets, smartphones and solar cells. Those materials are commonly deposited via sputtering from bulk targets but more cost-effective and easier procedures for their deposition rely on the exploitation of nanoparticles, which allow the fabrication of very thin fillms starting from dispersions in many different solvents. A reliable determination of the optical properties, such as the complex refractive index dispersion, turns out to be very important to design devices for the aforementioned applications. Moreover, the recent research on plasmon-induced hot electron extraction with doped semiconductor nanocrystals will benefit from the knowledge of the refractive index dispersion in a broad range of wavelenghts. Altough the visible and near infrared refractive index dispersion has already been determined via transmission/reflection measurements, both in sputtered and nanoparticles films, a more reliable and precise determination via ellipsometry measurements is still missing.<br/>In this talk, the ellipsometry data and the complex refractive index dispersion of a dense sputtered ITO film and a more porous film made of ITO nanocrystals will be presented. The effective plasma frequency of the nanocrystals film is redshifted to roughly 3000nm compared with the 1800nm of the dense sputtered ITO. The data also allow to define the epsilon-near-zero wavelength range, which results interesting for many non-linear optical applications.