The plasmonic properties of supported nanodisk arrays of the catalysts Pt and Pd are systematically characterized over a large size and spectral range (UV-VIS-NIR). Spectrally tunable Localized Surface Plasmon Resonances (LSPRs) with extinction cross-sections comparable to Au and Ag are found [1]. By measuring the absorption and scattering cross-sections for varying particle size the branching ratio for the two plasmon decay channels is obtained experimentally. The absorption channel – in contrast to Ag/Au – is found to dominate in Pt and Pd over the entire UV-VIS-NIR range of the LSPR-spectrum [2]. The intrinsic catalytic activity of Pt and Pd together with the dominant absorption LSPR decay channel, generating e-h pairs, makes these nanoparticles interesting candidates for studies of e-h transfer to HOMO/LUMO resonances of molecular adsorbates.
A novel plasmonic sensing principle, based on the spectral shift caused by a change in the bulk electronic properties of the particle by a new type of atom entering the lattice, is demonstrated with Pd as model system. The LSPR is used as very sensitive, non-destructive and real-time probe to study hydrogen uptake in Pd nanodisks in solid solution and as a metal hydride. Isotherms can be obtained obeying Sievert’s law in the α phase region and showing a typical hysteresis upon charging and discharging with two plateau pressures of 18 torr and 7.5 torr, respectively, for the α+β phase coexistence region. A simple model, where the spectral LSPR shift as well as the change in extinction are a linear function of the hydrogen content in the system over the α, the α+β and the β phase region is successfully used to calculate p-C isotherms from the LSPR data [3]. The agreement with literature for the bulk Pd-H system is excellent. These results provide a valuable novel experimental approach for studying hydrogen storage materials and open up a novel route towards ultra sensitive optical hydrogen sensors, both of high importance in a future hydrogen economy.
[1] C. Langhammer, Z. Yuan, I. Zoric and B. Kasemo, Nano. Lett. 6, 833 (2006).
[2] C. Langhammer, B. Kasemo and I. Zoric, J. Chem. Phys., submitted
[3] C. Langhammer, B. M. Clemens, I. Zoric and B. Kasemo, Nature Nanotechnol., submitted
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