Linear hydrogen gas sensors based on bimetallic nanoclusters

This work reports on the fabrication of hydrogen gas sensors based on bimetallic palladium-copper nanoclusters. The nanoclusters were generated by sputtering and inert-gas condensation inside an ultra-high vacuum (UHV) compatible system, and self-assembled on an insulating substrate with a pair of pre-formed interdigitated gold/nichrome electrodes. Nanocluster deposition was stopped once their coverage on the substrate reached the percolation threshold. Electrical properties of the fabricated sensors were investigated by means of electrical conductance measurements, and assigned to charge carrier transport within network of metallic islands that is dominated by tunnelling. The produced devices were utilized as conductometric gas sensors. Herein, a constant voltage was applied across the interdigitated electrodes, and the change in electrical current signal was measured which reflects gas concentration. All fabricated sensors showed increase in the conductance upon exposure to hydrogen which can be assigned to the increase in tunnelling current due to the decrease in the size of the gaps between the nanoclusters or the establishment of conducting paths through the network of percolating nanocluster film. The sensors were found to be sensitive at low concentrations of hydrogen at room temperature, and exhibit a linear relationship between hydrogen concentration and the sensitivity. Therefore, those sensors have the potential to be used for practical life applications.