Formation of multilayer films for gas sensing by in situ thermophoretic deposition of nanoparticles from aerosol phase

Dry aerosol synthesis applying the flame spray pyrolysis was used to manufacture and directly (in situ) deposit tin dioxide nanoparticles on sensor substrates. For the first time this technique was used to synthesize a combination of two porous layers for gas-sensor fabrication. Two different sensing layers were deposited on ceramic substrates, i.e., pure tin dioxide and palladium-doped tin dioxide. The top layer was a palladium-doped alumina as a filter. The fabricated sensors were tested with methane, CO, and ethanol. In the case of CH₄, the pure tin dioxide sensor with the Pd/Al₂O₃ filter showed higher sensor signals and improved selectivity with respect to water vapor compared to single tin dioxide films. At temperatures up to 250 °C the Pd doping of the tin dioxide strongly increased the sensitivity to all gases. At higher temperatures the sensor signal significantly decreased for the Pd/SnO₂ sensor with a Pd/Al₂O₃ filter, indicating high catalytic activity.