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Hydrogen sensing properties of nanostructured Pd/WO3 thin films: role of hydrophobicity during recovery process

In the present work the structural, optical and hydrogen sensing properties of Pd-capped tungsten oxide (Pd/WO3) thin films have been investigated. The nanostructured Pd/WO3 thin films have been prepared using DC magnetron sputtering on glass and Si(100) substrates at various oxygen partial pressures. The samples were hydrogenated at 2 bar hydrogen pressure in an operating temperature range 300–423 K. Optical transmittance spectra confirms fully transparent WO3 thin films deposited at oxygen partial pressure of 0.5 Pa while the transmittance drastically decreases to 50% for hydrogenated Pd/WO3 thin films. The influence of surface roughness and hydrophobicity of the Pd/WO3 thin films on the hydrogen sensing performance have been studied. Fast response time (1 sec) and an optimum recovery time (∼8 min) have been observed at a moderate temperature of 323 K for the samples having roughness ∼4.5 nm and contact angle ∼96°. Hydrophobicity of the surface provides short recovery time by opposing the existence of water-vapour on the surface.