Selective Gas Metal Oxide Sensors: Fabrication of Multilayers by In-Situ Nanoparticle Aerosol Deposition

Flame Spray Pyrolysis was used to synthesize and directly deposit multilayers of metal oxides on sensor substrates. The nanoparticles are directly deposited from the aerosol phase by thermophoresis onto standard sensor substrates forming a highly porous film. FSP in combination with the direct deposition on sensor substrates is a very fast and clean single step process for sensor fabrication that results in a highly porous thick films having a large accessible surface This technology was used to fabricate Pd/SnO2 and undoped SnO2 sensors with Pd/Al2O3 filter layers on top. These layers were studied for their gas sensing properties and catalytic conversion for CH4, CO and ethanol. The realized multilayer sensors (Figure 1) with undoped and Pd-doped SnO2 were characterized and compared with their single layer coun-terparts. The presence of a Pd/Al2O3 filter layer on top of the sensing layer influenced the sensing behavior for all three gases and was found to be temperature- and gas-dependent. This sensor showed a remarkable performance for methane sensing, because it did not respond to CO and ethanol and therefore has a formidable selec-tivity for CH4. Thus, the sensor performance can be tuned (e.g. higher sensor signals or better selectivity) by choosing appropriate filters and sensing conditions (e.g. tem-perature). The results presented here underline that the FSP method for multilayer sensor fabrication is a promising candidate for further sensor development.