Alloy Nanoplasmonics: PdAu Alloy Nanoparticles for Hysteresis-Free Plasmonic Hydrogen Sensing

Ferry Anggoro Ardy Nugroho Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden Carl Wadell Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden Emil Lidström Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden Christoph Langhammer Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden

The notion of a hydrogen economy has catalyzed the development of various fields, like the use of nanostructured metal-hydride systems as signal transducer in plasmonic hydrogen sensors. [1] For this application, to date, Pd has been the transducer material of choice since it readily absorbs and releases hydrogen at room temperature and, more importantly, also exhibits localized surface plasmon resonance. However, the usage of pure Pd for hydrogen sensing purpose in real devices is not ideal. It exhibits wide hysteresis upon hydrogen sorption, which creates the problem of ambiguous readout depending on the sensor’s history. Alloying Pd with another metal (e.g. Au, Ag) is one possible solution to reduce the hysteresis and thus eliminate this problem. [2]

In this work we present a generic means to fabricate arrays of well-defined alloy plasmonic nanoparticles. Specifically, we fabricate quasi-random PdAu alloy nanodisks using Hole-mask Colloidal Lithography[3], in combination with alternating deposition of layers of Pd and Au followed by annealing at 500oC to promote alloy formation. For the application as hysteresis-free signal transducer in hydrogen sensors we find that increasing the Au content in the alloy nanoparticles significantly lowers the width of the hysteresis. Moreover, the sensitivity towards hydrogen at low H2 concentrations in the sensor environment increases up to eight times compared to pure Pd. Notably, this improved performance is obtained without compromising the signal-to-noise ratio of the sensor.

As we have shown before, plasmonic hydrogen sensing is also very useful to scrutinize more fundamental aspects of metal-hydrogen interactions at the nanoscale. Therefore we also utilize our PdAu nanoparticle arrays to shed light on the thermodynamics and kinetics of metal hydride formation as a function of alloy composition, and report on the most important findings.

References

[1] C. Wadell, et al., ACS Nano, Article ASAP DOI: 10.1021/nn505804f

[2] R. C. Hughes, et al. J. Appl Phys. 62, 1074 (1987).

[3] H. Fredriksson, et al., Adv. Mater. 19 4297 (2007).

ferryn@chalmers.se

Annealing alternating layers of Pd and Au produces alloy of PdAu with excellent control over the composition. On each side of the system the hydrogen absorption and desorption isotherms are shown. The hysteresis is vanished in the alloy system.









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