Aerosol synthesis of chemoresistive gas sensors: Materials, structures and performances

The sensing performance of nanoparticle films obtained by aerosol synthesis is investigated as a function of material composition (e.g. SnO₂, TiO₂, WO₃), film morphology and layout. It is shown that highly porous (98%) films are obtained by direct deposition from the gas phase. Utilization of a flame spray pyrolysis (FSP) reactor as particle source was found to be a flexible alternative for the synthesis of single and multi oxides at high production rates. More in detail, low content Si-doping of SnO₂ or WO₃ FSP-made nanoparticles drastically increased their response to ethanol and acetone, respectively. This was attributed to the high thermal stability of these nanocomposites at the elevated operation temperatures of metal oxide gas sensors. However, mechanical stabilization of these films was required to avoid their disintegration. Sufficient mechanical stabilization was obtained by rapid in-situ annealing with an impinging particle free flame leading to highly sensitive metal oxide-based gas sensors. In conclusion, aerosol synthesis of chemoresistive gas sensors is critically reviewed focusing on the opportunities offered by novel flame methods, such as FSP, while assessing some of its current limitations.