Ag triangular nanoplates are known to generate strong plasmonic resonances when excited by both light and electron beams. Experimental electron energy-loss spectra (EELS) and maps were acquired using an aberration-corrected JEOL-ARM microscope. The corner, edge and centre modes that are often observed in such structures were also observed in these measurements. In addition, novel higher order internal modes were observed and were found to be well reproduced by theoretical cal-culations using boundary element method (BEM). These modes are "dark modes" so are not observed in the optical extinction spectra. They are confined surface propagating modes and are analogous to laser cavity modes AbstractAg triangular nanoplates are known to generate strong plasmonic resonances when excited by both light and electron beams. Experimental electron energy-loss spectra (EELS) and maps were acquired using an aberration corrected JEOL-ARM microscope. The corner, edge and centre modes that are often observed in such structures were also observed in these measurements. In addition, novel higher order internal modes were observed and were found to be well-reproduced by theoretical calculations using boundary element method (BEM). These modes are "dark modes" so are not observed in the optical extinction spectra. They are confined surface propagating modes and are analogous to laser cavity modes.Keywords silver nanoparticles, localized surface plasmon resonance, electron energy-loss spectroscopy (EELS), boundary element method (BEM) Acknowledgements

Excessive corrosion of silver nanoparticles is a significant impediment to their use in a variety of potential applications in the biosensing, plasmonic and antimicrobial fields. Here we examine the environmental degradation of triangular silver nanoparticles (AgNP) in laboratory air. In the early stages of corrosion, transmission electron microscopy shows that dissolution of the single-crystal, triangular, AgNP (side lengths 50-120 nm) is observed with the accompanying formation of smaller, polycrystalline Ag particles nearby. The new particles are then observed to corrode to Ag2S and after 21 days nearly full corrosion has occurred, but some with minor Ag inclusions remaining.In contrast, a bulk Ag sheet, studied in cross-section, showed an adherent corrosion layer of only around 20-50 nm in thickness after over a decade of being exposed to ambient air. The results have implications for antibacterial properties and ecotoxicology of AgNP during corrosion as the dissolution and reformation of Ag particles during corrosion will likely be accompanied by the release of Ag + ions.

We use a combination of experimental measurements and density functional theory calculations to show that modification of the band structure of Cu by additions of Al causes an unexpected enhancement of the dielectric properties. The effect is optimized in alloys with Al contents between 10 and 15 at. % and would result in strong localized surface plasmon resonances at suitable wavelengths of light. This result is surprising as, in general, alloying of Cu increases its DC resistivity and would be expected to increase optical loss. The wavelengths for the plasmon resonances in the optimized alloy are significantly blue-shifted relative to those of pure Cu and provide a new material selection option for the range 2.2 to 2.8 eV.

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