Transparent, conducting ATO thin films by epoxide-initiated sol-gel chemistry: a highly versatile route to mixed-metal oxide films.

A robust synthesis approach to transparent conducting oxide (TCO) materials using epoxide assisted sol-gel chemistry is reported. The new route utilizes simple tin and antimony chloride precursors in aqueous solution, thus eliminating the need for organometallic precursors. Propylene oxide acts as a proton scavenger and drives metal hydroxide formation and subsequent polycondensation reactions. Thin films of antimony-doped tin oxide (ATO) were prepared by dip-coating of mixed metal oxide sols. After annealing at 600 °C in air, structural, electrical and optical properties of undoped and Sb-doped tin oxide films were characterized. Single layer films with 5 mol % Sb doping exhibited an optical transparency which was virtually identical to that of the plain glass substrate and an electrical resistivity of 2.8 × 10(-2) Ω cm. SEM and AFM analysis confirmed the presence of surface defects and cracks which increased with increasing Sb dopant concentration. Multiple depositions of identical ATO films showed a roughly 1 order of magnitude decrease in the film resistivity after the third layer, with typical values below 5 × 10(-3) Ω cm. This suggests that a second and third deposition fill up residual cracks and defects in the first layer and thus brings out the full performance of the ATO material. The epoxide-assisted sol chemistry is a promising technique for the preparation of mixed oxide thin film materials. Its superiority over conventional alkoxide and metal salt-based methods is explained in the context of a general description of the reaction mechanism.

Gas sensors based on nanostructured materials.

Gas detection is important for controlling industrial and vehicle emissions, household security and environmental monitoring. In recent decades many devices have been developed for detecting CO(2), CO, SO(2), O(2), O(3), H(2), Ar, N(2), NH(3), H(2)O and several organic vapours. However, the low selectivity or the high operation temperatures required when most gas sensors are used have prompted the study of new materials and the new properties that come about from using traditional materials in a nanostructured mode. In this paper, we have reviewed the main research studies that have been made of gas sensors that use nanomaterials. The main quality characteristics of these new sensing devices have enabled us to make a critical review of the possible advantages and drawbacks of these nanostructured material-based sensors.