Cheap plasmonics to enable full-colour fast switching e-paper

June 03, 2016 // By Julien Happich
Looking into ways to design high-resolution low cost display panels, researchers from Sandia National Laboratories and the Center for Nanoscale Science and Technology at the National Institute of Standards and Technology have re-visited the concept of e-paper by combining inexpensive electrochromic polymers with plasmonic structures.

Prof. A. Alec Talin and his colleagues presented their findings in the journal Nature Communications with the paper "High-contrast and fast electrochromic switching enabled by plasmonics", showing a candidate technology for the cheap manufacture of thin full colour displays with resolutions two orders of magnitude higher than today's high-definition displays, while boasting switching speeds in the range of milliseconds.

Instead of having to lay multiple layers and colour-specific electrochromic polymers sandwiched with dedicated control electrodes, Talin relied on Au and Al metallic nanoslit arrays (serving as the plasmonic structures) conformally coated with two ordinary electrochromic polymers, PANI and PolyProDOT-Me2. The arrays of vertical nanoscale slits (each slit only 60nm deep and 250nm wide with a pitch of 500nm) are perpendicular to the direction of the incoming light. When light hits the aluminium nanoslits, it is converted into surface plasmon polaritons (SPPs), which are electromagnetic waves containing frequencies of the visible spectrum that travel along the dielectric interfaces - here, of aluminium and electrochromic polymer.


Schematic diagram of a plasmonic electrochromic electrode incorporating (a) Au-nanoslit array and (b) reference planar electrochromic electrode. The pitch of the Au-nanoslit array is 500 nm. (c) Chemical structures of PANI in the reduced and oxidized form. SEM images of the fabricated Au-nanoslit electrode (d) before and (e) after deposition of a PANI to a thickness d≈15 nm. (f) Magnified SEM image from e. Scale bars, 300 nm (d,e). Scale bar, 100 nm (f).

The plasmonic structure would turn into a deep black by simply applying a tiny electric current across the top of the slit, cutting off the entering light and the SPPs within milliseconds. When the current was flicked off, light frequencies passed through the slits and instantly turned on the pixel.