Directed growth of amorphous silicon nanocups a) Scheme depicting the fabrication process of nanocup metasurfaces including i) metal deposition ii) spin coating of double layer resist iii) electron beam exposure iv) directed growth of a-Si via sputtering v) lift-off. b) Selected scanning electron micrographs of the a-Si nanocup arrays highlighting: open resonator structure, high uniformity, and nanometric character (sidewalls = 50 nm). c) Optical micrograph of an optical pattern illustrating the formation of vibrant colors alongside scanning electron micrographs showing the Moiré effect of the nanocup array. Due to the large image section, the optical micrograph (left) exhibits a brightness gradient caused by the non-uniform illumination of the sample. Credit: Advanced Optical Materials (2024). DOI: 10.1002/adom.202401501
“Color is crucial,” as pop artist Roy Lichtenstein famously said, but the significance of color extends far beyond art. From the creation of Prussian blue—the first synthetic pigment—to quantum dots in modern display technology, colors and their creation have always mirrored technological progress.
Researchers at ETH Zurich’s Laboratory for Nanometallurgy have developed a new fabrication method for non-primitive metasurfaces, by which the colors of these metasurfaces represent and visualize light-matter interactions. The paper is published in the journal Advanced Optical Materials.
To showcase the capabilities of these metasurfaces, the researchers recreated Lichtenstein’s iconic “Sinking Sun” at the nanoscale. This reproduction illustrates how specific resonant states—or, in simpler terms, colors—can be engineered through careful manipulation of geometry and materials. As a result, these metasurfaces are ideally suited for encoding information in ways that remain visually imperceptible, offering a robust deterrent against counterfeiting.
Generating Colors with Points a) Roy Lichtensteins “Sinking Sun,” ( Estate of Roy Lichtenstein) b) optical micrograph of nanoscale reproduction of the “Setting sun” with a-Si nanocup metasurface c) Optical micrograph illustrating the color change through chemical dealloying, i.e., the formation of a disordered optical cavity and consequent coupling between the aSi nanocups and the disordered cavity. The subfigures at the bottom present the color centers, i.e., the points generating the image. Credit: Advanced Optical Materials (2024). DOI: 10.1002/adom.202401501
