Currently leading technologies for color printing, such as the inkjet and laserjet methods, deposit tiny dots of dye on a surface. The size of these dots is typically in the micrometer range, which means that the highest attainable resolution for these techniques is below 10,000 dpi. Approaches that yield finer dots have been demonstrated in research laboratories, but these techniques are so far limited to producing monochrome images and are not scalable. The method now developed at the A*STAR Institute of Materials Research and Engineering (IMRE), with the participation of the Institute of High Performance Computing (IHPC), provides a fundamentally different approach that is free of the technological limitations of colorant-based methods. "We use tiny metal nanostructures to create color," explains Joel Yang, the lead researcher on this project. "This is somewhat similar to staining glass, where different colors are produced by using different metals. We use only one metal, however, which we deposit in a thin, uniform layer on tiny posts of varying diameter."
The posts are only a few tens of nanometers in size, and Yang and his co-workers have now shown that, depending on the disks' diameter and density, different colors can be generated through a mechanism known as plasmon resonance. To demonstrate the power of their technique, Yang's team has created a 50 micrometer × 50 micrometer photorealistic full-color image with pixels at 250 nanometer pitch (see top image). This resolution is at the so-called optical diffraction limit, which is the fundamental resolution limit of any optical imaging system.
This new method now pushes the door for commercial uses wide open. "At the current stage, we can think already of a number of applications, including branding and brand protection for products meant for viewing under a microscope—bio-assays or microscope calibration kits, for instance—or the production of anti-counterfeit features," says Yang. "Following further development, there should be the potential for applications such as high-density optical data storage or coating all sorts of surfaces with colors that won't fade."
Importantly, with a view to commercial applications, the new technique can be scaled up. The creation of the nanostructures that make up the image may be quite involved. Once a master template is made, however, pattern-replication methods such as nano-imprint or photolithography can be used to mass-produce micro-images. Furthermore, technologies for imprinting large areas are available, too.
Indeed, first steps from laboratory to market have already been taken: One Singapore provisional patent is filed and another is pending. Furthermore, the team is working with Exploit Technologies Pte Ltd (ETPL), A*STAR's technology-transfer arm, to assess the interest of companies for collaborations, and to explore opportunities for licensing the technology.
Provided by Agency for Science, Technology and Research (A*STAR), Singapore
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