Printing to the limit: Nanotech resolution

Take it to the limit

 

The idea of the paperless office, or even the paperless, laboratory, is yet to be achieved and most of us are still very much familiar with printers, inkjets, laser printers, toners and cartridges. Twenty years ago the typical desktop printer could squeeze around 300 droplets of ink or the equivalent substance into a line an inch long (approximately 25 mm). And, borrowing from the print publishing industry users would allude to that machine having a print "resolution" of 300 dpi (dots per inch). Today, even an inexpensive printer can cram at least thirty times as many dots into the same distance offering 10,000 dpi printing.

10,000 dpi high resolution in printing produces images of great clarity and sharp text, but the keenest human eye can resolve dots at a much greater limits almost approaching the diffraction limit of light in fact and so technologists have for many years attempted to push the limits of printing still further. Now, a team in Singapore has used nanotechnology to take the concept of printing into a whole new area that would have had Gutenberg blushing. They have developed an innovative method that allows them to create sharp, full-colour images at an astounding 100,000 dpi resolution using metal-laced nanostructures. The technology sidesteps conventional inks and dyes entirely and offers an entirely new paradigm for data storage and archiving that lends itself more to the microfiche or microform system that dates back to the mid 19th Century rather than the digital optical storage media of the late 20th. The same technology could also be used to generate invisible watermarks for sensitive documents and security features for financial assets, including money and papers share certificates for instance. Forgers would have no way of spoofing such watermarks and security tags given the potential for incorporating a vast amount of information and detail in a tiny space with such high-resolution printing.

Writing in the journal Nature Nanotechnology, the team based at Singapore's A*STAR Institute of Materials Research and Engineering (IMRE) explain how they were inspired by stained glass windows, the kind of ecclesiastical architectural feature that adorns countless churches and cathedrals around the world. Stained glass is traditionally made by adding metal to the liquid glass before setting it in sheets. Science now understands that the wide range of beautiful colours seen in such glass is due to the scattering of light by nanoparticles of the added metal fragments. The Singapore team has used an analogous method involving adding precisely patterned metal nanostructures to a glass surface to scatter incident light to give them the colour they need at a particular point

Karthik Kumar says that size and spacing of the nanodots is critical to the final image quality. "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 colour dots, we were able to demonstrate the highest theoretical print colour resolution of 100,000 dpi." The team explains that rather than droplets of ink or dye being placed on the printed surface, the colour information is encoded in the size and position of tiny metal discs. The discs produce their specific colour through plasmon resonances. By building a database of colour information corresponding to a specific nanostructure pattern, size and spacing, the team can then use a single-mass microlithographic technique to position all the colours in a manner rather akin to a child's colouring-by-numbers picture. There is one critical difference, all the nanoparticles are added at once creating the full-colour image almost instantaneously.

Commercial printing

The IMRE team worked with colleagues in the Institute of High Performance Computing (IHPC) to design the pattern using computer simulation and modelling. IHPC's Ravi Hegde explains that, "The computer simulations were vital in understanding how the structures gave rise to such rich colours. This knowledge is currently being used to predict the behaviour of more complicated nanostructure arrays." The next step is to commercialise the technology and the team is working with Exploit Technologies Pte Ltd, their research centres' technology transfer wing, to engage potential investors and explore licensing.