Fabio Marangi1
Politecnico di Milano1
Transparent conducting oxides play a significant role in nowadays electronic devices. Among those, indium tin oxide (ITO) is one of the most relevant materials used for transparent electrodes. Even if the fabrication of ITO-based electronic devices in the form of thin films is mainly carried out by means of sputtering, electrically conductive films may be obtained by the deposition of thin layers of ITO Nanocrystals (NCs) through spin coating and other related wet chemistry techniques. ITO NCs films show interesting properties deriving from the plasmonic behaviour of ITO in the form of small nanoparticles. Localized plasma frequency, which occurs in the infrared, can be tuned by playing around the shape and size of the nanocrystals but also strongly depends on the percentage of doping. Electrical properties of the films are strongly influenced by the properties of the single nanocrystals and morphology of the whole film. Processing conditions during the fabrication of the devices also affect the final conductivity of the films. Electrical conductivity of a number of ITO NCs thin films has been measured as a function of thickness of the films and processingtime and temperature, both in controlled atmosphere and in presence of air. Both optical and electrical properties of the films showed to be strongly affected by annealing temperature, regardless of being processed in air or in a controlled environment leading to different outcomes. In particular, films annealed at higher temperature showed greater electrical conductivity but poor optical response in the region of interest. The opposite was observed for lower annealing temperatures. The combination of all those tests allowed the definition of a recipe for the fabrication of ITO Nanocrystals with desired electrical properties and optical response. The plasmonic response of the films can be tuned after deposition, without acting at the single nanocrystal level in terms of doping, size and shape. Even if microscopically influenced by the single nanocrystal, the properties of the system as a film show a macroscopic behaviour deriving from the nanocrystals acting as a whole.