Chemical synthesis of In2O3 nanocrystals and their application in highly performing ozone-sensing devices

In2O3 nanocrystals were prepared by injecting In2O3 sols in a coordinating environment at 160 °C. In this way an innovative concept has been achieved, based on the use of self-limitating nanoreactors. By a proper control of the synthesis conditions, differently sized nanocrystals were obtained, the smallest having a size of about 3.5 nm. The nanocrystals were purified by thermal treatments and characterized by X-ray diffraction and high-resolution transmission electron microscopy, showing the presence of nanosized In2O3 single-crystals. Nanocrystals with a size of about 6 nm were dispersed in a solvent and deposited onto alumina substrates with pre-deposited heaters and electrodes. The resulting devices were tested towards ozone gas, obtaining responses ranging over several orders of magnitude even for low (60 ppb) ozone concentrations and short response and recovery times. This result is interpreted as a consequence of the small grain size of In2O3 but also of the mild processing, resulting in nanoporous, non-aggregated layers.