Electrochromic Plasmonic Metasurfaces for Reflective Displays

Doctoral thesis, 2017

Plasmonic nanomaterials provide brilliant colors that arise from the ambient light coupling to the free electrons in metals. In the Roman empire, noble metal nanoparticles were used for staining glass in Church windows and tableware. Thanks to the extra-long lifetime of the plasmonic nanoparticles such glasswork still looks equally bright in color and can thus be used even after thousands of years. In comparison with organic dyes or paints, plasmonic nanomaterials provide strong stable colors even in ultrathin materials (hundreds of nanometers). If the colors can be electrically controlled this provides a novel technology for new display devices. In recent years, reflective (paper-like) displays become more and more interesting since they provide clear images in illuminated environments and are more friendly for human eyes compared to luminous display devices (LED, LCD). One of the most successful commercialized electronic papers is the E-ink technology (e.g. the popular KindleTM). However, one big problem of the E-ink technology on the market is that it only displays monochromatic texts or pictures. It has been known for some time that by implementing electrochemical control over the plasmonic nanostructures one can actively tune the optical response to some extent. Recently, it has also been shown that when combining conjugated polymers with the plasmonic nanomaterials the optical transmission can be modulated with high contrast and fast responding speed. In our work, a novel plasmonic nanomaterial combined with conjugated polymers works as an “electronic paper” in color with high contrast, fast response time (ms) and ultra-low power consumption (0.5mW/cm2). Especially, by using an ultrathin plasmonic nanostructure with a soft polymer layer the system is highly bendable with ultra-high optical reflection (>90 %), which opens up a new technology for electronic paper applications.