Usingnanometer-size metamaterials, researchers at Missouri University of Science andTechnology have developed a technique to print images that uses the manipulationof light, rather than the application of ink, to produce colors. This"no-ink" printing method has been demonstrated by producing aMissouri S&T athletic logo just 50 micrometers wide.
In normalcolor printing, various semi-transparent inks are applied on top of each otherto produce the various hues of a picture. In the technique developed byMissouri S&T, instead of ink, microminiature perforations are made in a multi-layered structureconsisting of two thin films of silver separated by a film of silica45 nanometers thick. The uppermost layer of silverfilm, just 25 nanometers deep, is punctured with miniscule holes using a focused ion-beam millingmicrofabrication process.
Usingthis process, the researchers created holes with different diameters(ranging in size from 45 to 75 nanometers) corresponding to the desired absorption of light at variouswavelengths. As such, light shining ontothe logo at specific frequencies allowedresearchers to create different colors with reflected light instead of ink. This nano-scale "colorpalette" meant that the physical characteristics of the holes in the materialdetermined the color displayed to accurately reproduce the S&T athleticlogo.
"Unlikethe printing process of an inkjet or laserjet printer, where mixed colorpigments are used, there is no color ink used in our structural printingprocess – only different hole sizes on a thin metallic layer," said Dr.Jie Gao, assistant professor of mechanical and aerospace engineering at MissouriS&T.
Thenanoscale perforations used to provide this color are so small as to only be visiblewith the help of an electron microscope, but they allowed the researchers to reproducethe standard colors of the S&T logo, and also to manipulate the light toproduce four new colors to make an orange ampersand, a navy blue "Missouri", a magenta "S" and "T", and a cyan pickaxe symbol.
As the sandwiched silver/silica material acts asa plasmonic device, the Missouri S&Tteam believes that mechanical color printing on such materials providesa much higher printing resolution than conventionalcolor printing. This is because their research shows that the periodic holes on the surface of the silver film provides excitation of surface-plasmon polaritons (electromagnetic waves that travel along the surface of a metal-dielectric or metal-air interface) and create an optical magnetic dipole resonance which results in near-perfect light absorption and negligible reflection in the material.
As a combination of substances that provide functions or phenomena that act in ways notyet found in nature, the printing substrate is also a metamaterial. As such, its unique properties may allow it to be used in ways not previously possible in the areas of nanoscale visual arts, security tagging, andinformation storage. The researchers also believe that such a method of printing should also result in a reduced material count in relation to standard printingmethods, andcould lead to lower costs, easier recycling, and higher fidelity and stability in image reproduction.
The results of this research were recently published in the journal Scientific Reports.
Source: Missouri S&T
