Spray-on plasmonics enable tunable colours at video rate

May 13, 2019 //By Julien Happich
A team of researchers from the University of Cambridge have devised a novel way to leverage plasmonics for stable colours that can be electrically tuned across different wavelengths, at speed.

In a paper titled “Scalable electrochromic nanopixels using plasmonics” published in Science Advances, the researchers describe electrochromic nanoparticles with a multilayered plasmonic composite architecture filled with a dielectric spacer. The nanoparticles-on-mirror (NpoM) as they call them (because the particles are coated onto a metallic mirror), strongly confine light within the individual gaps to the underlying mirror, producing extremely localized cavity resonances and precisely tuned colour scattering independent and insensitive to the angle and polarization of incident light.

The electrochromic eNPoMs consist of colloidal gold nanoparticles (Au NPs) encapsulated in a conductive polymer shell (polyaniline or PANI for short), which are then cast onto a planar gold mirror. The shell thickness obtained through the encapsulation process defines the critical gap spacing to the underlying mirror as well as the spacing between neighboring particles (which the authors say reduces their optical coupling and inhibits aggregation). That is why even when designed at large scale, each individual NPoM acts as an independent active nanopixel.

The eNPoM changes colour as a function of the redox state of the thin (0 to 20nm) PANI shell surrounding each Au NP on the Au mirror substrate (altering the resonant gap). Right: Redox reaction of PANI in the gap (PANI0, fully reduced; PANI1+, half oxidized; PANI2+, fully oxidized)

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