Beautiful color printing for encoding high density data

Researchers at A*STAR (Agency for Science Technology and Research) based in Singapore have printed images at an extraordinary resolution of 100,000 dots per inch according to an Apr. 10, 2013 news item on ScienceDaily,

To print the image, the team coated a silicon wafer with insulating hydrogen silsesquioxane and then removed part of that layer to leave behind a series of upright posts of about 95 nanometers high. They capped these nanoposts with layers of chromium, silver and gold (1, 15 and 5 nanometers thick, respectively), and also coated the wafer with metal to act as a backreflector.

Each color pixel in the image contained four posts at most, arranged in a square. The researchers were able to produce a rainbow of colors simply by varying the spacing and diameter of the posts to between 50 nanometers and 140 nanometers.

When light hits the thin metal layer that caps the posts, it sends ripples — known as plasmons — running through the electrons in the metal. The size of the post determines which wavelengths of light are absorbed, and which are reflected …

Although the current process is not practical, it takes several hours to print an image there are some intriguing benefits,

Printing images in this way makes them potentially more durable than those created with conventional dyes. In addition, color images cannot be any more detailed: two adjacent dots blur into one if they are closer than half the wavelength of the light reflecting from them. Since the wavelength of visible light ranges about 380-780 nanometers, the nanoposts are as close as is physically possible to produce a reasonable range of colors.

The researchers believe there may be applications for anti-counterfeiting tags and encoding high density data.

You can read more about the work and find a citation and link to the researchers’ study published in Nature Nanotechnology at the ScienceDaily news item.

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