Exploitable results
Reliable solid state gas sensors with high sensitivity, high response stability and long lifetimes have been developed for the detection of carbon monoxide, nitrogen oxides and methane, using nanostructured materials. The development of nanostructured sensing layers was addressed to both thick and thin film technology. Thick film sensors have been realised starting from nanosized powders produced by laser pyrolysis and wet precipitation methods. Powders of pure and doped titanium dioxide have been synthesized by laser pyrolysis and wet precipitation methods have been used for powder production. Sensors have been made from tin oxide and titania precursors. Good stability and sensitivity were reached. Also, pure and niobium or gallium doped titanium dioxide thick film sensors have been successfully prepared for carbon monoxide and methane detection. Sensors have been prepared starting from titanium dioxide-based powders. The performance, especially the stability, is promising. Thin film sensors with nanoscaled sensing layers have been realised based on silicon, sapphire and alumina substrates using physical vapour deposition (PVD) and rheotaxial growth and thermal oxidation (RGTO). Thin film sensors based on silicon substrates have been designed, optimized and tested, resulting in an adequate sensitivity. Sensors based on titanium tungstenide (TiWO3) (for nitrogen dioxide detection) and on tin oxide-gold and tin oxide-lead (for carbon monoxide and methane detection respectively have also been prepared. Finally a new experimental set up for impedance spectroscopy was built. This technique allows a better understanding of the physical phenomena underlying the sensor operation, especially the materials intergrain capacitance and inductance related aspects. Some of the developed sensors are performing significantly better than the present state of the art, resulting in important benefits for the industrial partners in the gas sensor market for combustion control in burners and vehicles engines.