Plasmonic colourations are promising for flat panel display applications due to their full-colour gamuts and high spatial resolution. However, it cannot be readily tuned and requires expensive lithographic techniques. In this work, the concept of plasmonic nanopixels is proposed. These are fabricated by positioning electrochromic conductive polymer (e.g. polyaniline) coated gold nanoparticles onto a metal mirror, and termed an electrochromic nanoparticle on mirror (eNPoM). The tight confinement of light inside this well-defined and tiny gap volumes allows independent tuning of the individual nanoparticles, which act as active nanopixels. The scheme works by switching the charge state of the polymer shell electrically, thus rapidly shifting the resonant scattering colour of the eNPoM across over 100 nm wavelength ranges, in response to less than 1 V. As the whole construction process is solution-based, electrically-driven colour-changing metafilms can be fabricated by coating these nanopixels onto films to generate distinct vivid colours. In conjunction with commercially available printing techniques, flexible patterned devices are demonstrated, offering possibilities to make fully-printed wearable plasmonic devices including displays, electronic textiles, or sensors. The whole process is lithography-free and thus readily allows to be extended with large scale processing tools, such as roll-to-roll manufacturing. Furthermore, intriguing directional optical dynamics are experimentally demonstrated in eNPoMs with ultra-thin metal films. The plasmonic nanocavities not only create optical response controllable by the gap material properties which benefits for making new functional optical devices, but also allow for substantial field enhancement in the gap, offering an excellent platform for probing light-matter interactions at the nanoscale. The nanoeletrochemistry is explored within these nanopixels. Optical dynamics of eNPoMs made with different conductive polymers are investigated with dark-field and Raman spectroscopy in real-time while voltage is applied. The modulation of the optical response reveals the redox mechanisms inside the tiny gap.
Plasmonics, Metamaterials, Hybrid Nanophotonics
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