Featured Research

from universities, journals, and other organizations

Applied physics as art: Spray-paint ultrathin coatings change color with only a few atoms' difference in thickness

Date:
October 14, 2012
Source:
Harvard University
Summary:
Researchers have demonstrated a new way to customize the color of metal surfaces by exploiting a completely overlooked optical phenomenon. For centuries it was thought that thin-film interference effects, such as those that cause oily pavements to reflect a rainbow of swirling colors, could not occur in opaque materials. However, even very "lossy" thin films, if atomically thin, can be tailored to reflect a particular range of dramatic and vivid colors.

Gold films colored with nanometer-thick layers of germanium.
Credit: Photo courtesy of Mikhail Kats, Romain Blanchard, and Patrice Genevet

In Harvard's Pierce Hall, the surface of a small germanium-coated gold sheet shines vividly in crimson. A centimeter to the right, where the same metallic coating is literally only about 20 atoms thicker, the surface is a dark blue, almost black. The colors form the logo of the Harvard School of Engineering and Applied Sciences (SEAS), where researchers have demonstrated a new way to customize the color of metal surfaces by exploiting a completely overlooked optical phenomenon.

For centuries it was thought that thin-film interference effects, such as those that cause oily pavements to reflect a rainbow of swirling colors, could not occur in opaque materials. Harvard physicists have now discovered that even very "lossy" thin films, if atomically thin, can be tailored to reflect a particular range of dramatic and vivid colors.

Published in the journal Nature Materials (online) on October 14, the finding opens up new possibilities for sophisticated optical devices, as well as consumer products such as jewelry and new techniques in the visual arts.

The discovery is the latest to emerge from the laboratory of Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS, whose research group most recently produced ultrathin flat lenses and needle light beams that skim the surface of metals. The common thread in Capasso's recent work is the manipulation of light at the interface of materials that are engineered at the nano- scale, a field referred to as nanophotonics. Graduate student and lead author Mikhail A. Kats carried that theme into the realm of color.

"In my group, we frequently reexamine old phenomena, where you think everything's already known," Capasso says. "If you have perceptive eyes, as many of my students do, you can discover exciting things that have been overlooked. In this particular case there was almost a bias among engineers that if you're using interference, the waves have to bounce many times, so the material had better be transparent. What Mikhail's done -- and it's admittedly simple to calculate -- is to show that if you use a light-absorbing film like germanium, much thinner than the wavelength of light, then you can still see large interference effects."

The result is a structure made of only two elements, gold and germanium (or many other possible pairings), that shines in whatever color one chooses.

"We are all familiar with the phenomenon that you see when there's a thin film of gasoline on the road on a wet day, and you see all these different colors," explains Capasso.

Those colors appear because the crests and troughs in the light waves interfere with each other as they pass through the oil into the water below and reflect back up into the air. Some colors (wavelengths) get a boost in brightness (amplitude), while other colors are lost.

That's essentially the same effect that Capasso and Kats are exploiting, with coauthors Romain Blanchard and Patrice Genevet. The absorbing germanium coating traps certain colors of light while flipping the phase of others so that the crests and troughs of the waves line up closely and reflect one pure, vivid color.

"Instead of trying to minimize optical losses, we use them as an integral part of the design of thin-film coatings," notes Kats. "In our design, reflection and absorption cooperate to give the maximum effect."

Most astonishingly, though, a difference of only a few atoms' thickness across the coating is sufficient to produce the dramatic color shifts. The germanium film is applied through standard manufacturing techniques -- lithography and physical vapor deposition, which the researchers compare to stenciling and spray-painting -- so with only a minimal amount of material (a thickness between 5 and 20 nanometers), elaborate colored designs can easily be patterned onto any surface, large or small.

"Just by changing the thickness of that film by about 15 atoms, you can change the color," says Capasso. "It's remarkable."

The researchers have already performed the same treatment on silver, making it appear gold, as well as a range of pastel colors.

Harvard's Office of Technology Development has filed a patent application and is working with the Capasso lab to pursue the commercialization of this new technology, either through a start-up company or through licensing to existing companies. Application areas being explored include consumer products and optical devices, such as filters, displays, photovoltaics, detectors, and modulators.

This work was supported in part by the U.S. Air Force Office of Scientific Research and a National Science Foundation (NSF) Graduate Research Fellowship. Some of the work was performed at the Harvard Center for Nanoscale Systems, a member of the NSF-supported National Nanotechnology Infrastructure Network.


Story Source:

The above story is based on materials provided by Harvard University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Mikhail A. Kats, Romain Blanchard, Patrice Genevet, Federico Capasso. Nanometre optical coatings based on strong interference effects in highly absorbing media. Nature Materials, 2012; DOI: 10.1038/nmat3443

Cite This Page:

Harvard University. "Applied physics as art: Spray-paint ultrathin coatings change color with only a few atoms' difference in thickness." ScienceDaily. ScienceDaily, 14 October 2012. <www.sciencedaily.com/releases/2012/10/121014162912.htm>.
Harvard University. (2012, October 14). Applied physics as art: Spray-paint ultrathin coatings change color with only a few atoms' difference in thickness. ScienceDaily. Retrieved October 23, 2014 from www.sciencedaily.com/releases/2012/10/121014162912.htm
Harvard University. "Applied physics as art: Spray-paint ultrathin coatings change color with only a few atoms' difference in thickness." ScienceDaily. www.sciencedaily.com/releases/2012/10/121014162912.htm (accessed October 23, 2014).

Share This



More Matter & Energy News

Thursday, October 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

3D Printed Instruments Make Sweet Music in Sweden

3D Printed Instruments Make Sweet Music in Sweden

Reuters - Innovations Video Online (Oct. 23, 2014) Students from Lund University's Malmo Academy of Music are believed to be the world's first band to all use 3D printed instruments. The guitar, bass guitar, keyboard and drums were built by Olaf Diegel, professor of product development, who says 3D printing allows musicians to design an instrument to their exact specifications. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Chameleon Camouflage to Give Tanks Cloaking Capabilities

Chameleon Camouflage to Give Tanks Cloaking Capabilities

Reuters - Innovations Video Online (Oct. 22, 2014) Inspired by the way a chameleon changes its colour to disguise itself; scientists in Poland want to replace traditional camouflage paint with thousands of electrochromic plates that will continuously change colour to blend with its surroundings. The first PL-01 concept tank prototype will be tested within a few years, with scientists predicting that a similar technology could even be woven into the fabric of a soldiers' clothing making them virtually invisible to the naked eye. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Jet Sales Lift Boeing Profit 18 Pct.

Jet Sales Lift Boeing Profit 18 Pct.

Reuters - Business Video Online (Oct. 22, 2014) Strong jet demand has pushed Boeing to raise its profit forecast for the third time, but analysts were disappointed by its small cash flow. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Internet of Things Aims to Smarten Your Life

Internet of Things Aims to Smarten Your Life

AP (Oct. 22, 2014) As more and more Bluetooth-enabled devices are reaching consumers, developers are busy connecting them together as part of the Internet of Things. (Oct. 22) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins