A method of printing metal-laced, nanometer-sized structures has created full-color images at 100,000 dots per inch (dpi), revolutionizing the way images are printed. The technology could be further developed for high-resolution reflective color displays and high-density optical data storage. Today’s ink-jet and laser-jet industrial printers can achieve only 10,000 dpi, while research-grade methods can dispense dyes for single-color images only. The novel breakthrough developed at A*Star’s Institute of Materials Research and Engineering (IMRE) uses no inks or dyes to achieve full-spectrum color images at 100,000 dpi. The development allows colors to be treated as a lithographic rather than inking matter. The team drew inspiration from stained glass, which traditionally is fabricated by mixing tiny fragments of metal into glass. Nanoparticles from these metal fragments scatter light passing through the glass, giving stained glass its colors. With the help of modern nanotechnology tools, the IMRE researchers used a similar concept to precisely pattern metal nanostructures, designing the surface to reflect the light to achieve colored images. Their findings appeared online Aug. 12 in Nature Nanotechnology. A colored nanoscale rendition of a standard test image used in image processing experiments. (a) Before the addition of metal in the nanostructures, the image has only gray-scale tones, as observed under an optical microscope. (b) Colors are observed using the same optical microscope after the addition of the metal layers to the nanostructures in specific patterns. (c) Zooming into the image with the same setup, the specular reflection at the corner of the eye is observed, showing the refined color detail that the new method is able to achieve. The region indicated (bottom right) is made up of nanostructures as observed in the electron micrograph. (Image: A*Star) "The resolution of printed color images very much depends on the size and spacing between individual ‘nanodots’ of color,” said Dr. Karthik Kumar, a key researcher." The closer the dots are together and because of their small size, the higher the resolution of the image. With the ability to accurately position these extremely small color dots, we were able to demonstrate the highest theoretical print color resolution of 100,000 dpi." Rather than use different dyes to achieve different colors, the scientists encoded color information into the size and position of tiny metal disks, said project leader Dr. Joel Yang. “These disks then interacted with light through the phenomenon of plasmon resonances. The team built a database of color that corresponded to a specific nanostructure pattern, size and spacing,” Yang said. “These nanostructures were then positioned accordingly. Similar to a child’s ‘coloring by numbers’ image, the sizes and positions of these nanostructures defined the ‘numbers.’ “But instead of sequentially coloring each area with a different ink, an ultrathin and uniform metal film was deposited across the entire image, causing the ‘encoded’ colors to appear all at once, almost like magic!” The IMRE researchers collaborated with A*Star’s Institute of High Performance Computing (IHPC) to design the pattern using computer simulation and modeling, which were needed to understand how such rich colors were achieved, according to Dr. Ravi Hegde of IHPC. “This knowledge is currently being used to predict the behavior of more complicated nanostructure arrays,” he said. The scientists are now working with Exploit Technologies Pte Ltd., A*Star’s technology transfer arm, to establish collaborators and to license the technology. For more information, visit: www.imre.a-star.edu.sg