Preparation of a Stable Sol Suspension of Pd-Loaded SnO2 Nanocrystals by a Photochemical Deposition Method for Highly Sensitive Semiconductor Gas Sensors

A stable sol suspension of Pd-loaded SnO2 nanocrystals, which is valid for both fundamental studies of semiconductor gas sensor and fabrications of a micro gas sensor, was fabricated by the photochemical deposition of PdCl42- onto SnO2 in an aqueous solution. UV light was irradiated on a mixture of a SnO2 sol obtained through a hydrothermal treatment of stannic acid gel in the presence of PdCl42- and ethanol/water at pH 2. A stable sol suspension of Pd-loaded SnO2 was successfully obtained by controlling the pH of the above suspension to 10.5 after UV irradiation. Thin-film type sensor devices (film thickness similar to 200 nm) using Pd-loaded SnO2 nanocrystal were successfully fabricated by a spin-coating method. Gas sensing measurements showed that the deposition of Pd on the SnO2 nanocrystals resulted in large electrical sensitization effect The maximum gas sensitization effect was obtained at 0.125 mol % Pd loading. Moreover, the Pd loading lowered the temperature, in which the maximum sensor response to H-2 was obtained, due to the efficient catalytic combustion of H-2 on Pd.