Preparation of a stable sol suspension of Pd-loaded SnO ₂ nanocrystals by a photochemical deposition method for highly sensitive semiconductor gas sensors

A stable sol suspension of Pd-loaded SnO ₂ 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 PdCl ₄ ^2- onto SnO ₂ in an aqueous solution. UV light was irradiated on a mixture of a SnO ₂ sol obtained through a hydrothermal treatment of stannic acid gel in the presence of PdCl ₄ ^2- and ethanol/water at pH 2. A stable sol suspension of Pd-loaded SnO ₂ was successfully obtained by controlling the pH of the above suspension to 10.5 after UV irradiation. Thin-film type sensor devices (film thickness ∼200 nm) using Pd-loaded SnO ₂ nanocrystal were successfully fabricated by a spin-coating method. Gas sensing measurements showed that the deposition of Pd on the SnO ₂ 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.