‘Painting with light’ | ASU News

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April 21, 2022

ASU professor invents new method of color printing

A new process developed by researchers at Arizona State University enables color printing on a micro-scale with a simple and inexpensive additive manufacturing process.

Chao Wang, Assistant Professor of Electrical Engineering at ASU’s Ira A. Fulton Schools of Engineering, invented a solution-based additive manufacturing process to “paint with light” on glass and plastics. Wang’s new printing method uses light to control the photochemical reduction of metallic microstructures on an engineered optical material.

The technique opens up new avenues for microscale color printing, including printing on surfaces such as wearable optical devices and flexible displays. It also enables the creation of high-resolution color images without applying complex and expensive semiconductor processing techniques.

A peer-reviewed manuscript on this work, “Structural Color Printing via Polymer-Assisted Photochemical Deposition,” authored by Wang, Yu Yao, associate professor of electrical engineering at Fulton Schools, and students working in their labs, has been submitted. recently published in the journal Lumiere Research: Science & Applications.

Wang’s new technology is based on polymer-assisted photochemical metal deposition, or PPD. The new technology is used at room temperature, is non-toxic and provides a solution-based additive manufacturing process that requires no heating, vacuum deposition or etching steps. This enables the printing of ultra-thin and smooth silver surfaces to act as the top light-absorbing film in the engineered optical material, which also includes thick, reflective films on the back.

According to Wang, this breakthrough grew out of the team’s previous work in creating a new additive manufacturing technique for 3D printing high-quality metal objects.

“This is an extension of that work,” says Wang. “Unlike conventional metal printing techniques that rely on high-temperature laser heating, our developed technology is a solution-based printing process. Here we show that it is also applicable to creating structures more complex photonics.

The team introduced a polymer into the precursor solution that works like ‘sticky hands’ to link the reduced metal nanoparticles together into continuous, smooth films. This means that the printed metallic film is a composite of metallic nanoparticles and a small amount of sticky polymer.

ASU researchers were able to print blue, green, yellow and orange images with high contrast using Chao Wang’s new polymer-assisted photochemical metal deposition process. To demonstrate his versatility in printing, the paper’s first author, Shinhyuk Choi, an electrical engineering graduate student in Wang’s lab, printed images of a character named Stitch in blue and purple (d), an image a cactus in green and yellow (e), and versions of the ASU logo in orange and yellow (c and f). Figure (a) shows a schematic illustration of the polymer-assisted photochemical deposition, or PPD, print setup and an example of a printed ASU logo (scale bar: 500 μm, or approximately 0.0197 inch). In figure (b), a 3D diagram shows the printing of a stack of multilayer films in microstructures. The figures (dh) are demonstrations of the feasibility of printing complex structures with different colors. The photo in figure (g) shows a Fabry-Perot cavity fabricated on a polyethylene terephthalate, or PET, plastic substrate with a smooth flex. Figure (h) shows optical images of a colored logo produced by the Department of Electronic Engineering – Tsingha University, Wang’s alma mater, on a dielectric-coated metal layer with a scale bar representing 100 μm (approximately 0.0039 thumb). Images courtesy of Chao Wang

To vividly display color in prints, the authors designed an optical material as a thin-film, multi-layered structure called a Fabry-Perot cavity. It works similarly to the colored pigments in paints which absorb light of specific wavelengths. Absorption of the Fabry-Perot cavity is affected by both the thickness of the printed metallic films – controllable even when they are less than 10 nanometers – and by the dimensions of the designed film stack on which the films are printed. .

“The photons interact with the structures in the cavity to absorb a particular wavelength of light allowing you to display a new color,” says Wang.

In this process, ultraviolet light is used to program a photochemical reduction of silver in a solution at room temperature. Therefore, light is used directly to “imprint” color pixels down to micrometric sizes.

“It was a really fun experiment to be able to use light to create microstructures that can, in turn, control light,” says Wang. “It’s a good example of how multidisciplinary thinking helps research.”

Top image courtesy of Unsplash

Erik Wirtanen

Web Content Communications Administrator, Ira A. Fulton Schools of Engineering


480-727-1957[email protected]


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