Abstract
Alternative materials that can potentially replace Au and Ag in plasmonics and broaden its application potential have been actively investigated over the last decade. Cu and Al have been usually overlooked as plasmonic material candidates because they are prone to oxidisation. In this work the plasmonic performance of Cu and Al is investigated using numerical simulations of different nanostructures (spheres, cubes, rods and particle dimers) and taking into account the presence of oxidisation. It is shown that geometry can play a dominant role over material properties and the performance of Cu and Al becomes comparable to that of Ag and Au for systems of non-spherical particles and strong electromagnetic coupling among particles. This observation is experimentally confirmed by the fabrication and characterisation of Cu and Al metal island films. Optical characterisation of the samples reveals a comparable performance of these metals to that obtained for Ag and Au and suggests that Cu and Al metal island films can offer an efficient low-cost platform for solar energy harvesting, as shown in water vapour generation proof of concept experiments.
Highlights
Localised surface plasmons are collective electron oscillations taking place at the interface between a metal nanoparticle and its surroundings and can be excited by optical radiation.Sub-wavelength localisation, electromagnetic field enhancement, large absorption and extinction cross sections and sensitivity to environment modifications have enabled the design of multiple novel applications and the establishment of plasmonics as a promising research area for future technologies [1,2,3]
Its chemical reactivity limits device life-time and Au is often preferred over Ag
It is shown that geometry can play a dominant role over material properties and the performance of
Summary
Localised surface plasmons are collective electron oscillations taking place at the interface between a metal nanoparticle and its surroundings and can be excited by optical radiation. Sub-wavelength localisation, electromagnetic field enhancement, large absorption and extinction cross sections and sensitivity to environment modifications have enabled the design of multiple novel applications and the establishment of plasmonics as a promising research area for future technologies [1,2,3]. Optimal performance of most plasmonic applications imposes negative real part of the dielectric function and negligible losses as the basic criteria for material selection. Its chemical reactivity limits device life-time and Au is often preferred over Ag. In any case, Ag and Au possess some disadvantages such as scarcity, price, increased losses due to interband transitions and difficulty to tune the plasmon resonance beyond the visible range.
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