Dense palladium nanoparticle arrays with controlled coverage for fast hydrogen sensors

We report the application of dense palladium nanoparticle arrays for room-temperature hydrogen sensor with sub-second response time. The palladium nanoparticle arrays were fabricated in between a pair of interdigital electrodes by means of gas phase cluster beam deposition. The coverage of the nanoparticles was controlled by in-situ monitoring the conductance between the electrodes. We demonstrate that the conductance of the arrays is dominated by quantum tunneling through nanojunctions between the closely spaced nanoparticles. Unlike conventional thin film-based resistive hydrogen sensors this sensor showed an inverse relationship between increased hydrogen concentration and resistance. With a careful control on the nanoparticle coverage, a linear dependence of the relative change of the conductance on the logarithm of hydrogen concentration was shown. The sensor can produce a stable response to hydrogen concentration lower than 0.62%.