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Thin films composed of tungsten oxide (WO 3 ) nanoclusters were fabricated by oxidizing supersonic cluster beam deposited tungsten films at various temperatures. Oxidation at 700 °C resulted in aggregation of the deposits, forming a percolated network of WO 3 spherical caps connected by fine links. The resistance response of the palladium-(Pd-) coated film sample to hydrogen (H 2 ) was investigated. The response rate was faster than those of other samples oxidized at lower temperatures. This is the result of the rapid electrical switching of the intercluster links between the highly resistive depleted state and conducting hydrogenated state. The possibility of improving the H 2 sensing response rate with the use of the percolated WO 3 film structure is illustrated.

The resistive H 2 sensing properties of palladium-coated highly porous tungsten oxide nanocluster films (Pd/WO 3 ), with the WO 3 layers having different thicknesses (11.2–153 nm) and electrodes at different positions, were investigated at 80 °C. The results were interpreted by using a model involving various mechanisms including surface catalytic dissociation of the H 2 and O 2 molecules, spillover and diffusion of the split species on the surface and inside the WO 3 layer respectively, and the interaction between the species. The validity of the model was further examined by investigating the influences of the WO 3 thickness and the electrode position on the H 2 sensing properties. The results of data analysis confirm the important role of the diffusion of the split species in the WO 3 layer. The optimum sensor is characterized by having an ultrathin WO 3 nanocluster film with a thickness ≈11 nm, which exhibits a strong sensor response; short response time and recovery time, and stable resistant output during the hydrogenation process.

Hydrogen- (H₂-) induced resistive response of palladium (Pd) coated tungsten oxide (WO₃) films prepared by using supersonic cluster beam deposition (SCBD) was investigated. An SCBD WO₃ film is found to be constructed of WO₃ nanoclusters of diameters of 3-5 nm. The nanoclusters are loosely connected to form a structure of high porosity around 66%. With this structure, the film exhibits many excellent room-temperature H₂ sensing properties, including high sensitivity, broad detectable range of H₂ concentration, low detection limit, fast response rate, excellent cyclic stability (2400 cycles), high selectivity against vapor of many organic compounds, mild ambient pressure dependence and many other advantages such as low power consumption, miniaturizability and high batch-to-batch reproducibility. These findings are useful for making new high-quality H₂ sensors for monitoring the leakage of H₂ and ensuring safe use of this gas.

Tungsten oxide (WO3) films were prepared by using magnetron sputtering. Substrate temperature and sputtering pressure were adjusted to vary the microstructure. The films were found to contain nanoclusters; while their size L, and porosity θ and surface roughness zRMS of the film can be varied. After adding a palladium coating on the film surface, the hydrogen (H2) sensing properties of the films, including sensitivity of detection, response time and recovery time were measured. Their dependences on L, θ and zRMS were analyzed and interpreted. The information achieved is useful for improving H2 sensor technology.

Hydrogen- (H2-) induced resistive response of palladium (Pd) coated tungsten oxide (WO3) films prepared by using supersonic cluster beam deposition (SCBD) was investigated. An SCBD WO3 film is found to be constructed of WO3 nanoclusters of diameters of 3?5?nm. The nanoclusters are loosely connected to form a structure of high porosity around 66%. With this structure, the film exhibits many excellent room-temperature H2 sensing properties, including high sensitivity, broad detectable range of H2 concentration, low detection limit, fast response rate, excellent cyclic stability (>2400 cycles), high selectivity against vapor of many organic compounds, mild ambient pressure dependence and many other advantages such as low power consumption, miniaturizability and high batch-to-batch reproducibility. These findings are useful for making new high-quality H2 sensors for monitoring the leakage of H2 and ensuring safe use of this gas.