Laser-Printed Nanotech Makes Colors That Never Fade

To demonstrate the working principle of resonant laser printing, the researchers

printed several macroscopic images in various color tones. Here are examples of several famous paintings laser printed at 500 dots per inch. Credit: Technical University of Denmark Laser printers that "sculpt" images at miniscule scales could one day make color photos that don't fade over time the way ink does, according to a new study. Researchers at the Technical University of Denmark made a sheet of polymer and semiconductor metal that reflects colors that never fade, using tiny structures that diffract, absorb and reflect light of different wavelengths. A coating made of the material would never need repainting, and the resulting image would retain its vibrancy over time, the scientists said. This printing process also allows people to choose more specific colors, because exact wavelengths can be selected, meaning there's less guesswork involved with mixing pigments and comparing color charts, the researchers said. The same technique could be applied to making watermarks or even encryption and data storage, the researchers said. [The 10 Weirdest Things Created by 3D Printing]In this technique, the images are printed with a laser, which is fired at a sheet made of plastic on one layer and germanium on top of that. The sheets are made by depositing nanometer-thin layers of polymer and germanium into shapes, small cylinders and blocks, none measuring more than 100 nanometers across. (For comparison, an average strand of human hair is about 100,000 nanometers wide.) "We generate a nano-imprint," study lead author Xiaolong Zhu, a nanotechnology researcher at the Technical University of Denmark, told Live Science. Similar to what a laser printer does, the laser reshapes the tiny structures by melting them. Varying the intensity of the laser at tiny scales melts the structures differently, so they take on different geometries. This is why the image resolution can be so fine, the researchers said. An image from an inkjet printer or laser printer typically consists of 300 to 2,400 dots per inch. A nanometer-size pixel is thousands of times smaller, meaning a resolution of 100,000 dots per inch, the researchers said. In fact, the whole collection of pixels resembles a miniature city of skyscrapers, domes and towers.