Self-assembled monolayer-enhanced hydrogen sensing with ultrathin palladium films

Xu, Tao; Zäch, Michael; Xiao, Z. L.; Rosenmann, Daniel; Welp, U.; Kwok, W. K.; Crabtree, G. W.

doi:10.1063/1.1929075

Cited by 219 publications

(198 citation statements)

References 23 publications

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“…It has been shown that the use of ultrathin discontinuous Pd films [11] offers a simple solution to realize a hydrogen sensor that could fulfill many of those requirements. Discontinuous films are commonly deposited by physical vapor deposition (PVD) techniques such as electron-beam evaporation.…”

Section: Introductionmentioning

confidence: 99%

Fast and robust hydrogen sensors based on discontinuous palladium films on polyimide, fabricated on a wafer scale

et al. 2010

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Fast hydrogen sensors based on discontinuous palladium (Pd) films on supporting polyimide layers, fabricated by a cost-efficient and full-wafer compatible process, are presented. The films, deposited by electron-beam evaporation with a nominal thickness of 1.5 nm, consist of isolated Pd islands that are separated by nanoscopic gaps. On hydrogenation, the volume expansion of Pd brings initially separated islands into contact which leads to the creation of new electrical pathways through the film. The supporting polyimide layer provides both sufficient elasticity for the Pd nanoclusters to expand on hydrogenation and a sufficiently high surface energy for good adhesion of both film and contacting electrodes. The novel order of the fabrication processes involves a dicing step prior to the Pd deposition and stencil lithography for the patterning of microelectrodes. This allows us to preserve the as-deposited film properties. The devices work at room temperature, show response times of a few seconds and have a low power consumption of some tens of nW.

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Section: Introductionmentioning

confidence: 99%

Fast and robust hydrogen sensors based on discontinuous palladium films on polyimide, fabricated on a wafer scale

et al. 2010

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“…3,4 In particular ultrathin palladium ͑Pd͒ films have been recently attracting increased attention as an application in resistive hydrogen ͑H 2 ͒ gas sensing for fuel cell safety systems. 5,6 Here, the volume expansion that occurs in Pd nanoclusters at hydrogenation 7,8 is exploited to reversibly narrow or even close the film-inherent nanogaps. New percolation pathways are thus formed and lead to a decrease in electrical resistance ͓see Fig.…”

mentioning

confidence: 99%

“…13͒ or selfassembled monolayers. 6 However, the characteristics of the interjacent transition regime itself and related changes in electrical response to hydrogen have not been studied yet. Our investigations show that this transition is of a gradual nature and is characterized by a semicontinuous film regime 2,14 that results in characteristic physical properties and distinct responses at H 2 exposure.…”

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confidence: 99%

The transition in hydrogen sensing behavior in noncontinuous palladium films

Kiefer

Villanueva

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et al. 2010

Applied Physics Letters

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The morphological transition in ultrathin palladium ͑Pd͒ films around the percolation threshold and the related transition in hydrogen sensing behavior is investigated. We find that besides the transition from continuous to discontinuous Pd, an intermediate -semicontinuous-state must be considered. It shows hydrogen sensing features of both continuous and discontinuous film types, simultaneously. This study focuses on the discontinuous-semicontinuous transition. Experimental evidence is supported by studying the evolution of the electrical resistance with temperature, under hydrogen exposure and after thermal annealing. The results are highly relevant for the optimization of nanogap based hydrogen sensors.

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“…14,15 Bimorph micro-and nano-mechanical structures are a convenient solution from the point of view of their compatibility with standard top-down techniques developed in the semiconductor industry over the years 16 and their ultra-low power consumption. However, deflection-based (or amplitude-based) mechanical sensors, regardless of the transduction technique, suffer from the fact that any external source of noise directly offsets the electrical signal that is the output from the device and thereby reduces the resolution of the sensor.…”

Section: Introductionmentioning

confidence: 99%

Ultra-low power hydrogen sensing based on a palladium-coated nanomechanical beam resonator

2012

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Hydrogen sensing is essential to ensure safety in near-future zero-emission fuel cell powered vehicles. Here, we present a novel hydrogen sensor based on the resonant frequency change of a nanoelectromechanical clamped-clamped beam. The beam is coated with a Pd layer, which expands in the presence of H 2 , therefore generating a stress build-up that causes the frequency of the device to drop. The devices are able to detect H 2 concentrations below 0.5% within 1 s of the onset of the exposure using only a few hundreds of pW of power, matching the industry requirements for H 2 safety sensors. In addition, we investigate the strongly detrimental effect that relative humidity (RH) has on the Pd responsivity to H 2 , showing that the response is almost nullified at about 70% RH. As a remedy for this intrinsic limitation, we applied a mild heating current through the beam, generating a few mW of power, whereby the responsivity of the sensors is fully restored and the chemo-mechanical process is accelerated, significantly decreasing response times. The sensors are fabricated using standard processes, facilitating their eventual mass-production.

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Self-assembled monolayer-enhanced hydrogen sensing with ultrathin palladium films

Cited by 219 publications

References 23 publications

Fast and robust hydrogen sensors based on discontinuous palladium films on polyimide, fabricated on a wafer scale

Fast and robust hydrogen sensors based on discontinuous palladium films on polyimide, fabricated on a wafer scale

The transition in hydrogen sensing behavior in noncontinuous palladium films

Ultra-low power hydrogen sensing based on a palladium-coated nanomechanical beam resonator

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