Laser Printing of Plasmonic Color Images in Polymer-Embedded Nanorod Films

Nanoscale structures that support surface plasmons have been used extensively to create colorful images at the surface of materials. Approaches used include dispersion of nanoparticles, the dewetting of thin films, e-beam lithography to precisely control the size and distribution of nanostructures, and laser-based techniques that produce semi-random distributions of nanoparticles. While some impressive palettes have been rendered, they are either only produced at the sample surface, cannot be tuned with a laser after fabrication, are not embedded in a polymer matrix, or are limited to very few colors. Here, we report the laser printing of gold nanorods embedded in polyvinyl alcohol films for in situ color image generation. Laser-induced modification of the nanorod length via photothermal heating results in a shift in the longitudinal plasmonic peak of the rods, bringing their absorbance into the visible spectrum. Photothermal reshaping of the nanorods is confirmed by UV-vis spectroscopy and transmission electron microscopy. Electromagnetic finite element simulations are used to predict the resulting colors and are in good agreement with the experimental results. This plasmonic laser-printing approach allows the generation of a broad color palette and high-resolution images within a flexible polymer film, protecting the colors from environmental degradation.