Abstract
Multifunctional flexible Au electrodes based on one-dimensional (1D) arrays of plasmonic gratings are nanofabricated over large areas with an engineered variant of laser interference lithography optimized for low-cost transparent templates. Au nanostripe (NS) arrays achieve sheet resistance in the order of 20 Ohm/square on large areas (∼ cm2) and are characterized by a strong and dichroic plasmonic response which can be easily tuned across the visible (VIS) to near-infrared (NIR) spectral range by tailoring their cross-sectional morphology. Stacking vertically a second nanostripe, separated by a nanometer scale dielectric gap, we form near-field coupled Au/SiO2/Au dimers which feature hybridization of their localized plasmon resonances, strong local field-enhancements and a redshift of the resonance towards the NIR range. The possibility to combine excellent transport properties and optical transparency on the same plasmonic metasurface template is appealing in applications where low-energy photon management is mandatory like e.g., in plasmon enhanced spectroscopies or in photon harvesting for ultrathin photovoltaic devices. The remarkable lateral order of the plasmonic NS gratings provides an additional degree of freedom for tailoring the optical response of the multifunctional electrodes via the excitation of surface lattice resonances, a Fano-like coupling between the broad localised plasmonic resonances and the collective sharp Rayleigh modes.
Highlights
Plasmonics has gained considerable momentum due to the ever increasing ease in the methods of fabrication and characterization of optical nanoantennas and thanks to their multidisciplinary applications [1,2,3,4,5]
Conventional transparent conductive electrodes based on oxides such as indium tin oxide (ITO) suffer from serious delamination issues when applied to flexible devices such as electronic displays [28], touch screens, smart windows, flexible electronics [29] or transparent heaters [30] and a growing demand of alternative transparent electrodes based on metal nanowire networks is observed
In this paper we address these issues using a novel variant of laser interference lithography (LIL) which enables the production of plasmonic structures periodically arranged over large area, on low cost, transparent and flexible substrates
Summary
Plasmonics has gained considerable momentum due to the ever increasing ease in the methods of fabrication and characterization of optical nanoantennas and thanks to their multidisciplinary applications [1,2,3,4,5]. The spectral overlap of such dispersive propagating modes with the LSP resonances of the NS monomers or dimers strongly amplifies the local electromagnetic field [42] and qualifies the transparent electrodes as multifunctional templates featuring enhanced photon harvesting in the NIR spectral range with possible applications ranging from nanospectroscopy and biosensing to photovoltaics. In these experiments we employed Au as the active plasmonic element due to its chemical stability towards oxidation and tarnishing, as well as, to its excellent electrical conductivity. We stress that the described nanofabrication method could be adapted to other elements relevant for plasmonics providing a further handle for tailoring the plasmonic response
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