Hydrogen sensor based on optical and electrical switching

We report about a hydrogen sensor using electrical and optical switching properties of Pd-based thin films. Palladium is well known for its ability to absorb high amounts of hydrogen due to palladium hydride formation. Series of different thickness Pd films (10–70 nm) were deposited on glass substrates by dc plasma sputtering. A CaF2 buffer layer was deposited between the glass support and the Pd-film in order to reduce the internal stresses and improve the mechanical stability of the sensor. A Pt diffusion barrier was deposited on the active film to prevent sensor poisoning. Pd-polymer nano-composite films were deposited by co-sputtering of Pd and polymer targets. The morphology and composition of the films were analysed by SEM, TEM and EDS. Electrical resistance and differential transmittance were measured depending on different concentrations and flows of the testing gas (0.5–10.0% hydrogen in nitrogen). A proportional dependence of the measured signal on the hydrogen concentration was found. The influence of different structures and morphologies on the switching properties was investigated.