Individual Pd nanowire hydrogen sensors fabricated by electron-beam lithography

Abstract

We report on the hydrogen gas(H2)sensing performance of lithographically patterned Pd nanowires as a function of the nanowire thicknessand H2 concentration. A combination of electron-beam lithography and a lift-off process has beenutilized to fabricate four-terminal devices based on individual Pd nanowires with widthw = 300 nm, lengthl = 10 µm, andthickness t = 20–400 nm from continuous Pd films. The variation of the resistance and sensitivity at 20 000 ppmH2 of Pd nanowires was found to be much lager than at 10 000 ppmH2, which can beexplained by an α–β phase transitionoccurring at 20 000 ppm H2. This is confirmed by the observation of hysteresis behavior in the resistance versusH2 concentration for Pd thin films. The response time was found to decrease with decreasing thickness regardlessof H2 concentration due to a higher surface-to-volume ratio and a higher clamping effect. A single Pd nanowire witht = 100 nm was found tosuccessfully detect H2 at a detection limit of 20 ppm. Our results suggest that lithographically patternedPd nanowires can be used as hydrogen gas sensors to quantitatively detectH2 over a wide range of concentrations.