Optical characterisation of nanostructured Au/WO3 thin films for sensing hydrogen at low concentrations

Nanostructured gold/tungsten trioxide (Au/WO3) thin films based gasochromic sensors have been developed and investigated towards hydrogen (H2) at low concentrations. Using a novel wet chemical method, atomically precise gold (Au) nanoclusters were deposited onto tungsten trioxide (WO3) films supported on a quartz substrate. The Au/WO3 based sensors exhibited change in gasochromic properties upon exposure to H2 in the visible-NIR (800–1000 nm) range. The total absorbance in this range increased by approximately 2.5%, when exposed to H2 gas (0.06%) balanced in synthetic air at an operating temperature of 200 °C. The micro-structural properties of the films were studied via energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). EDX analysis of the Au/WO3 films on quartz substrates shows the presence of strong tungsten (W) and oxygen (O) peaks, which indicates that the films are mainly consisted of WO3. TEM investigation showed that the synthesised Au nanoparticles have average diameters of 2–5 nm after deposition. SEM investigations revealed agglomeration of the Au phosphine [Au9(PPh3)8(NO3)3] clusters to form nanoparticles on top of WO3 layer. At optimum operating temperature (200 °C), fast response (<2 min) and recovery in conjunction with a stable baseline occurs.