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Localized surface plasmons (LSPs) of metallic nanoparticles decay either radiatively or via an electron-hole pair cascade. In this work, the authors have experimentally and theoretically explored the branching ratio of the radiative and nonradiative LSP decay channels for nanodisks of Ag, Au, Pt, and Pd, with diameters D ranging from 38 to 530 nm and height h=20 nm, supported on a fused silica substrate. The branching ratio for the two plasmon decay channels was obtained by measuring the absorption and scattering cross sections as a function of photon energy. The former was obtained from measured extinction and scattering coefficients, using an integrating sphere detector combined with particle density measurements obtained from scanning electron microscopy images of the nanoparticles. Partly angle-resolved measurements of the scattered light allowed the authors to clearly identify contributions from dipolar and higher plasmonic modes to the extinction, scattering, and absorption cross sections. Based on these experiments they find that absorption dominates the total scattering cross section in all the examined cases for small metallic nanodisks (D<100 nm). For D>100 nm absorption still dominates for Pt and Pd nanodisks, while scattering dominates for Au and Ag. A theoretical approach, where the metal disks are approximated as oblate spheroids, is used to account for the trends in the measured cross sections. The field problem is solved in the electrostatic limit. The spheroid is treated as an induced dipole for which the dipolar polarizability is calculated based on spheroid geometry and the (bulk) dielectric response function of the metal the spheroid consists of and the dielectric medium surrounding it. One might expect this model to be inappropriate for disks with D>100 nm since effects due to the retardation of the incoming field across the metallic nanodisk and contributions from higher plasmonic modes are neglected. However, this model describes quite well the energy dependence of the dipolar resonance, the full width at half maximum, and the total extinction cross section for all four metallic systems, even when 100≤D≤500 nm, indicating that the combined contribution of the effects not included in the model is small for the systems studied. For this reason the authors have extended the use of the same model to study scattering/absorption branching ratios. The main conclusions include the following. (i) Both the magnitude and peak position in extinction cross section are well accounted for by the model. (ii) The branching ratio for radiative and nonradiative decay is reasonably well accounted for. (iii) The model fails to account for the correct magnitudes of the measured absorption and scattering cross sections for larger particles in the case of Ag and Au. Possible reasons for this discrepancy are discussed. [ABSTRACT FROM AUTHOR]

Fuel cells have the potential to play an important role in sustainable energy systems, provided that catalysts with higher activity and stability are developed. In this work, it is found that thin alloy films of single-target cosputtered platinum-yttrium exhibit up to seven times higher specific activity (13.4 ± 0.4 mA cm−2) for the oxygen reduction reaction (ORR) than polycrystalline platinum, and up to one order of magnitude higher mass activity (3.5 ± 0.3 A mg−1) than platinum nanoparticles. These alloys have the highest reported ORR activity for an as-deposited material, i.e., without any additional chemical or thermal treatment. The films show an improvement in stability over the same materials in nanoparticulate form. Physical characterization shows that the thin films form a platinum overlayer supported on an underlying alloy. The high activity is likely related to compressive strain in that overlayer. As sputtering can be used to mass-produce fuel cell electrodes, the results open new possibilities for the preparation of platinum-rare earth metal alloy catalysts in commercial devices. [ABSTRACT FROM AUTHOR]

In indirect nanoplasmonic sensors, the plasmonic metal nanoparticles are adjacent to the material of interest, and the material-related changes of their optical properties are used to probe that material. If the latter itself represents another metal in the form of nanoparticles, its deposition is accompanied by charge transfer to or from the plasmonic nanoparticles in order to equalize the Fermi levels. We estimate the value of the transferred charge and show on the two examples, nanoparticle sintering and hydride formation, that the charge transfer has negligible influence on the probed processes, because the effect of charge transfer is less important than that of nanoparticle surface energy. This further corroborates the non-invasive nature of nanoplasmonic sensors. [ABSTRACT FROM AUTHOR]

TiO 2 +Pt plasmonic solids with 1 wt% Pt and different TiO 2 supports (anatase nanoparticles (TNP), polycrystalline nanorods (a-TNR) and single-crystal anatase nanorods (TNR)) were synthesized using the wet impregnation technique and tested as photo, thermal and photothermal catalysts in gas-solid and gas-liquid-solid reactions. Due to the different charges of the TiO 2 support surfaces, Pt particles with different sizes, crystallinities and degrees of interaction with the TiO 2 supports were formed during the synthesis. The heights of the Schottky barrier (SBH) were 0.38 eV for the a-TNR+Pt, 0.41 eV for the TNP+Pt, and 0.50 eV for the TNR+Pt samples, respectively. The low visible-light-triggered photocatalytic activity of the TNR+Pt catalyst toward the oxidation of water-dissolved bisphenol A (BPA) is attributed to its high SBH and active site deactivation due to the adsorption of BPA and/or BPA oxidation products. The highest photothermal catalytic H 2 -assisted NO 2 reduction rate was expressed by the TNR+Pt catalyst. This can be ascribed to the presence of a narrow particle size distribution of small Pt particles, the absence of the Pt catalysed reduction of the TNR support at higher temperatures, and the lower rate of re-injection of "hot electrons" from the TNR support to the Pt particles. [Display omitted] • Synthesized TiO2 +Pt solids can be used as photo, thermal and photothermal catalysts. • The nature of the TiO2 support affects the interaction between Pt and TiO2. • The Schottky barrier enables the separation of charge carriers in TiO2+Pt catalysts. • Visible-light illumination of TiO2 +Pt lowers the deNOx process ignition temperature. • The role of the Schottky barrier depends on the nature of catalytic application. [ABSTRACT FROM AUTHOR]