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Coloring with Barely-There Coating

Monday, January 5, 2015

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A new lightweight, ultra-thin color coating technology for smooth and rough surfaces is gaining traction at Harvard University.

The technology could potentially be used anywhere the weight of paint matters, such as the external fuel tank of NASA’s space shuttle, or where a decorative pearlescent look is sought, according to researchers at Harvard’s School of Engineering and Applied Sciences.

Mikhail Kats
Eliza Grinnell / SEAS Communications / Harvard University

Student Mikhail Kats and his team at Harvard's School of Engineering and Applied Sciences have discovered new ways to create colorful coatings using minimal materials.

The team first demonstrated the coloring technique on smooth surfaces in 2012.

A Rough Step

The team essentially spray-painted an ultra-thin germanium coating onto gold, changing the color.

Recently, the group took the technology a step further, coating a rough surface. The findings were published in the journal Applied Physics Letters.

“I cut a piece of paper out of my notebook and deposited gold and germanium on it,” according to Ph.D. student Mikhail Kats, “and it worked just the same.”

Wide Range of Applications

While it sounds simple, the finding has big implications. It suggests that ultra-thin coatings could be applied to essentially any rough or flexible material, from wearable fabrics to stretchable electronics, according to the university.

gold films
Mikhail Kats, Romain Blanchard, and Patrice Genevet / Harvard University

Gold films colored with nanometer-thick layers of germanium show a range of color possibilities.

“This is a way of coloring something with a very thin layer of material, so in principle, if it's a metal to begin with, you can just use 10 nanometers to color it, and if it's not, you can deposit a metal that's 30 nm thick and then another 10 nm,” said Federico Capasso, the Robert L. Wallace professor of applied physics and Vinton Hayes research fellow in electrical engineering.  

“That's a lot thinner than a conventional paint coating that might be between a micron and 10 microns thick.”

Coating Technique

In the lab, Kats uses an electron-beam evaporator to apply the gold and germanium coating to the paper.

He seals the paper sample inside the machine's chamber, and a pump sucks out the air until the pressure drops to a staggering 10-6 Torr (a billionth of an atmosphere).

paper
Eliza Grinnell / SEAS Communications / Harvard University

Kats cut a piece of paper out of his notebook to test the coating technique on rough surfaces. The paper was coated using about 30 nanometers of gold. The germanium (at right) was applied to the paper using an electron-beam evaporator. When deposited on top of the gold, it turned violet.

A stream of electrons strikes a piece of gold held in a carbon crucible, and the metal vaporizes, traveling upward through the vacuum until it hits the paper. Repeating the process, Kats adds the second layer.

A little more or a little less germanium makes the difference between indigo and crimson.

The school’s Office of Technology Development is seeking commercial opportunities for the new color coating technology and welcomes inquiries from interested parties.

   

Tagged categories: Coatings technology; Color; Design; Metal coatings; Nanotechnology; Research

Comment from john lienert, (1/5/2015, 9:06 AM)

the perfect "time and material " job


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