Abstract
The interest on nanocrystalline films, as a result of their outstanding properties associated with nanoscale and interface effects, has been recently extended to a range of metal oxides such as InOx and ZnO. These oxides are known for their fabrication simplicity, their high transparency in the visible and high reflectivity in the infrared regions, and have attracted a pronounced attention due. to their remarkable room temperature sensing properties to reactive atmospheres such as Ozone. They exhibit changes in conductivity from five to eight orders of magnitude, after photoreduction. with UV or laser irradiation and subsequent oxidation in reactive atmosphere, in a fully reversible manner. This combination of optical and electrical properties favors numerous applications as transparent conductive electrodes in flat panel devices and solar cells, coatings for architectural glasses and, more recently, as grating materials in optoelectronic devices.
A comparison of the room temperature ozone sensing properties of polycrystalline Zinc oxide and Indium oxide films to an ozone atmosphere has been carried out. Thin films, with a thickness of 10 mn to 1100 nm, have been produced by the DC magnetron sputtering technique. The initially high resistive as-grown films were brought to a high conducting state through a photoreduction process by UV light exposure and, subsequently, they were exposed to a controlled ozone atmosphere resulting in a strong increase of the resistivity of the films caused by re-oxidation. This treatment was shown to be fully reversible over many cycles of photoreduction and oxidation. The films exhibited resistivity changes of several orders of magnitude during the cycles. The sensor response, i.e. the ratio between the conductivity in the conductive state and the insulating state, has been studied for a variety of deposition parameters. Structural investigations carried out by XRD and AFM, revealed that there is a strong correlation between crystallinity, surface topology, and ozone sensitivity for the materials under investigation. The, highest sensor response of the films was always achieved at room temperature.