Full color images at 100,000 dpi now possible

Printing technology is advancing at a rapid rate and it’s good to see where it is heading towards. Above is a picture which is one of the first in a series of full color images in 100,000 dpi glory, and that’s about 100,000 dots per inch! Scientists have been able to achieve this using nano technology. This technology uses printing method which makes use of tiny pillars which are just tens of nanometers tall, and the images come in full color.

The method can be used for printing small watermarks or secret messages which are invisible to a naked eye. It may also find its use in very high density data storage discs in the future. The opportunities for this technology are endless. Each of the pixel in the ultra high resolution images produced using this technology is made up of four nanoscale posts which are capped with silver and gold nanodisks. As far as the explanation for coloration of pixel goes, it is possible to control the color of light which they reflect by adjusting the diameters and spaces between the nanoscale posts which are just tens of nanometers. Scientist at Agency for Science, Technology and Research (A*STAR) in Singapore came up with a full palette of colors using the effect called structural color. In order to test the working of the principle, they went ahead and decided to print a 50×50 micrometre version of the ‘Lena’ test image, a colored portrait with abundant colors, and is commonly used to test standard in the printing world.

Materials scientist Joel Yang first took a notice of this effect when he was examining metal nanoparticles under a light microscope. “We saw that we could control the colors, from red to blue, by controlling the size of the particles,” he says. What he found was pretty exciting because the metal nanostructure were found to resonate with a particular wavelength of light depending on their size. The effect is well known to physicists as ‘plasmon resonance’ for a long time now, and light at the correct wavelength makes the electrons on the surface of the metal nanostructure to resonate, and basically this controls the color which the structure reflects. Though a well known concept, Yang is the first person to exploit this theory by printing high resolution images in full color.

For demonstration purpose, when the team printed the Lena image, they used the electron beam lithography in order to create a pattern of silicon wafer using a collection of posts that were made using insulating material. Once the posts were created, metal nanodisks were placed on the posts and later coated the wafer’s surface with metal. This enabled the image to be bright as the wafer reproduced the colored light from the pillars. “The colors appeared all at once after we applied the metal,” says Yang.

The images that were created using Yang’s technique have about 100,000 dots per inch. Comparing this number with common inkjet or laser printers that we use daily isn’t possible as they are able to produce ink spots which are few micrometers in size, and the highest quality printer is able to produce images with a maximum resolution of 10,000 dots per inch. Although Yang’s images were printed over areas that were large enough for a naked eye to see comfortably, “they would look higher than high definition”, says Teri Odom, a chemist at Northwestern University in Evanston, Illinois. It is worth noting that an average human with perfect eyesight cannot distinguish objects which are smaller than, say 20–30 micrometers.

When placing the pixels very closely, there are certain restrictions. Even under the microscope, optical images have ultimate resolution limit. There’s a phenomenon called diffraction, in which when two objects are placed together very closely, the light that reflects off them will undergo diffraction, thus blurring both the objects for the viewer, and the diffraction limit decides the constraint on how closely the pixels can be placed with respect to each other. The distance between two objects is equal to half the wavelength of the light used for imaging is called diffraction limit. Considering the wavelength of middle of color spectrum is around 500 nanometers, it means that pixels cannot be placed closer than 250 nanometers without blurring, and the technology which Yang has developed places the pixels exactly at this distance.

Apart from the resolution itself, stability of the image is also important. The life span of print is very important when it comes to stuff like photographs, and this is where the new technology shines. In addition to resolution, the structural color also adds image stability. The metal and insulating materials which are used in making of these images are durable. “They do not fade over time, unlike organic dyes and colorants,” says Guo.

This technology surely makes today’s printing world pretty much outdated. What are your thoughts on this new method? Are you happy with the direction printing technology is heading towards? Let us know using the comment form below.

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