Wide-Gamut Plasmonic Color Palettes with Constant Subwavelength Resolution.

Unlike dye-based colorants, for which dilution results in a decrease in color saturation, a reduction of nanostructure density in plasmonic prints could increase color saturation instead. This interesting observation can be explained by the absorption cross-section of the nanostructure being larger than its physical cross-section. In this paper, we demonstrate the correlation between absorption cross-section and nanostructure density and use it to realize saturated colors by fabricating metal-insulator-metal aluminum nanostructures that support gap-surface plasmons (GSPs). We obtained structures with absorption cross-sections that exceed 10 times their physical cross-sections. The large absorption cross-sections of the GSP structures herald a color-mixing scheme where nanostructures of different hues are combined within subpixels at a constant pitch. The pitch is chosen such that the total absorption cross-section of individual constituents of the cell occupies the unit size area. Using a constant pitch of 320 nm, hence preserving the print resolution, our structures exhibit 45% coverage of the sRGB color space. By employing absorption cross-sections of the nanostructures, we produced black and saturated green pixels, which have been challenging to achieve in plasmonic color printing. The effects of square and hexagonal arrangements on color saturation are investigated, and point mixing effects are observed between individual nanostructures.