Full colour e-posters could reach 10,000 dpi

October 17, 2016 // By Julien Happich
Researchers from the Chalmers University of Technology (CUT) have demonstrated that plasmonic nanostructures combined with electrically-tuneable polymers could yield just any colour on demand.

Designing a flexible sheet of e-paper pixels as a proof-of-concept, the researchers claim the technology could cut today's electrophoretic e-papers power consumption more than ten folds while allowing very high resolutions on large scale formats, for posters or foldable e-readers less than a micrometre thin.

Publishing their findings in the Advanced Materials journal in a paper titled "Plasmonic Metasurfaces with Conjugated Polymers for Flexible Electronic Paper in Color", Andreas Dahlin and his PhD student Kunli Xiong report a seemingly simple reflective display architecture.

Using parallel lithographic processing steps compatible with large areas and plastic films, they created plasmonic metasurfaces made up of: a base reflection layer of silver, 150nm thin; a spacer layer made of alumina whose thickness determined the reflective colour obtained by Fabry–Pérot interference; and last a 20nm thin layer of gold patterned with nanoholes 150nm apart. The reflective colour of the base plasmonic metasurface can be varied across the whole colour spectrum through the alumina deposition process, choosing a thickness from 40 to 95nm (the primary colours red, green, and blue corresponding to an alumina thickness of 48, 93, and 83nm respectively).

a) Schematic of the metasurface. b) Electron microscopy image of the nanoholes from above. c) A sample on PET support with a colour palette generated by a gradient in the alumina thickness. d) A photo of samples with the primary colours under ambient light. e) Reflection spectra in air of the red, green, and blue samples for different angles.

"The nanohole array in the thin gold film enhances the coloration since it enables coupling to surface plasmons and provides strong resonant scattering", the paper explains.