Team uses patterned lithography instead of dye

Using tiny patterned metal nano-discs researchers at the Agency for Science, Technology, and Research (A*STAR) Institute of Materials Research and Engineering (IMRE) in Singapore have created [press release] a 100,000 dots-per-inch (dpi) print, the highest resolution color print ever produced.

According to the team industrial inkjet and laserjet printers can only reach a resolution of 10,000 dpi, while higher dpi research printers have only been capable of printing in a single color.

The key was to switch from a dye-based process or a lithography-type process.  Lithography refers to process that deposits coating material in a static pattern on another material.  

In the nano-printer, researchers use lithography to produce raised nano-patterns on a surface, which when coated in metal yield different colors.  Describes project leader, Dr. Joel Yang, "Instead of using different dyes for different colours, we encoded colour information into the size and position of tiny metal disks. These disks then interacted with light through the phenomenon of plasmon resonances."

"The team built a database of colour that corresponded to a specific nanostructure pattern, size and spacing. These nanostructures were then positioned accordingly. Similar to a child's 'colouring-by-numbers' image, the sizes and positions of these nanostructures defined the 'numbers'."

The etched image is colorless until the ultrathin metal film is applied.

Comments Dr. Yang, "But instead of sequentially colouring each area with a different ink, an ultrathin and uniform metal film was deposited across the entire image causing the 'encoded' colours to appear all at once, almost like magic!"
The patterned nanostructures (a) are colorless and gray scale, but once the metal thin film is added (b) high-density color is observed. [Image Source: A*STAR]

Dr. Karthik Kumar, another member of the research team, adds, "The resolution of printed colour images very much depends on the size and spacing between individual 'nanodots' of colour.  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."

A key component of enabling the printing of real-world test images was to run computer simulations of various nano-structures to build the palette.  The simulations were performed at A*STAR's Institute of High Performance Computing (IHPC).  Comments simulation leader Dr Ravi Hegde, "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."

There's the obvious application of this technology -- high resolution color printing.  But researchers say the technology could also be used for high-density optical storage and to create high-resolution reflective color displays.

Having published [abstract] the work in the prestigious peer-reviewed journal Nature Nanotechnology, A*STAR is now looking to patent and license the novel coloring method.

Sources: Nature Nanotechnology, A*STAR

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