Researchers in Singapore are pushing the boundaries of printed color. In a recent issue of Nature Nanotechnology, Joel Wang and coworkers report a method of printing diffraction-limited pixels using the structural color of metallic nanostructures. Structural color refers to materials which derive their pigment from the interaction of tiny mico- or nanometer structures with light, rather than the absorption of light that occurs in most organic dyes. The light scattered by silver, for examples, can be different colors depending on the structure (size, shape, aspect ratio) of the metal at the nano-scale. In this recent paper, the idea of structural color is refined to create extremely high resolution printing. Specifically, arrays of nanometer-scale glass posts are coated with silver; the size and spacing of the posts controls the color of each pixel consisting of a 2×2 post subarray. The result is a remarkably reproduced Lena image, a standard test in the imaging community.
Though the execution is cutting edge and has high tech implications like optical storage, metal nanoparticles have been used as colorants since the Roman Empire. Centuries ago glassmakers unknowingly synthesized gold and silver nanoparticles in vibrantly hued stained glass. One spectacular example is the Lycurgus Cup. When illuminated from the inside, the cup displays the strong scattering and absorption properties of these nanoparticle that arise due to their surface plasmon. Basically, the conduction electrons in the metal particles couple strongly to incident light, either scattering or absorbing the light with high efficiency. Ancient artisans may have had less understanding of nanostructures than contemporary scientists, but they we able to harness their spectacular properties without the use of a transmission electron microscope. The recent work in Nature Nanotechnology pushes this ancient technology to its physical limit.
Pictures from the original report.