ZnO gas sensors: A comparison between nanoparticles and nanotetrapods-based thick films

Nanostructured ZnO was obtained through two different synthetic processes: a traditional sol-gel (SG) route and a combination of vapor transport process and controlled oxidation methods. In SG synthesis, thermal decomposition of the precursor at 450 æC for 2 h in an oven led to pure zincite nanoparticles. Through the second method, instead, nanocrystalline structures in form of tetrapods (TP) were directly obtained during the synthesis process. Powder and film characterizations have been carried out by means of TG-DTA, SEM, TEM and XRD. Finally, electric measurements have been performed with the aim to compare conductive properties, surface barrier heights and gas sensing features, versus O3, NO2, CO and H2S. Despite the significant difference in morphology, it turned out that both types of sensors offered large responses to oxidizing gases at concentration suitable for environmental monitoring.