Featured Research

from universities, journals, and other organizations

New device hides, on cue, from infrared cameras

Date:
November 26, 2012
Source:
Harvard University
Summary:
Now you see it, now you don't. A new device can absorb 99.75 percent of infrared light that shines on it. When activated, it appears black to infrared cameras.

Artist's rendition of the experimental setup used to measure the reflectivity of the vanadium-sapphire device.
Credit: Modified from an illustration by Kirill Nadtochiy

Now you see it, now you don't. A new device invented at the Harvard School of Engineering and Applied Sciences (SEAS) can absorb 99.75% of infrared light that shines on it. When activated, it appears black to infrared cameras.

Composed of just a 180-nanometer-thick layer of vanadium dioxide (VO2) on top of a sheet of sapphire, the device reacts to temperature changes by reflecting dramatically more or less infrared light.

Announced November 26 in the journal Applied Physics Letters, and featured on its cover, this perfect absorber is ultrathin, tunable, and exceptionally well suited for use in a range of infrared optical devices.

Perfect absorbers have been created many times before, but not with such versatile properties. In a Fabry-Pιrot cavity, for instance, two mirrors sandwich an absorbing material, and light simply reflects light back and forth until it's mostly all gone. Other devices incorporate surfaces with nanoscale metallic patterns that trap and eventually absorb the light.

"Our structure uses a highly unusual approach, with better results," says principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS. "We exploit a kind of naturally disordered metamaterial, along with thin-film interference effects, to achieve one of the highest absorption rates we've ever seen. Yet our perfect absorber is structurally simpler than anything tried before, which is important for many device applications."

With collaborators at Harvard and at the University of California, San Diego, Capasso's research group took advantage of surprising properties in both of the materials they used.

Vanadium dioxide is normally an insulating material, meaning that it does not conduct electricity well. Take it from room temperature up to about 68 degrees Celsius, however, and it undergoes a dramatic transition. The crystal quickly rearranges itself as the temperature approaches a critical value. Metallic islands appear as specks, scattered throughout the material, with more and more appearing until it has become uniformly metallic.

"Right near this insulator-to-metal transition, you have a very interesting mixed medium, made up of both insulating and metallic phases," says coauthor Shriram Ramanathan, Associate Professor of Materials Science at SEAS, who synthesized the thin film. "It's a very complex and rich microstructure in terms of its electronic properties, and it has very unusual optical properties."

Those properties, when manipulated correctly, happen to be ideal for infrared absorption.

Meanwhile, the underlying sapphire substrate has a secret of its own. Usually transparent, its crystal structure actually makes it opaque and reflective, like a metal, to a narrow subset of infrared wavelengths.

The result is a combination of materials that internally reflects and devours incident infrared light.

"Both of these materials have lots of optical losses, and we've demonstrated that when light reflects between lossy materials, instead of transparent or highly reflective ones, you get strange interface reflections," explains lead author Mikhail Kats, a graduate student at SEAS. "When you combine all of those resulting waves, you can coax them to destructively interfere and completely cancel out. The net effect is that a film one hundred times thinner than the wavelength of the incident light can create perfect absorption."

The challenge for Capasso, Ramanathan, Kats, and their colleagues was not only to understand this behavior, but also to learn how to fabricate pure enough samples of the vanadium dioxide.

"Vanadium oxide can exist in many oxidation states, and only if you have VO2 does it go through a metal-insulator transition close to room temperature," Ramanathan explains. "We have developed several techniques in our lab to allow exquisite compositional and structural control, almost at the atomic scale, to grow such complex films. The resulting phase purity allows us to see these remarkable properties, which otherwise would be very difficult to observe."

Because the device can be easily switched between its absorbent and non-absorbent states, the possible applications are quite wide ranging and include bolometers (thermal imaging devices) with tunable absorption, spectroscopy devices, tunable filters, thermal emitters, radiation detectors, and equipment for energy harvesting.

"An ideal bolometer design needs to absorb all of the infrared light that falls on it, turning it to heat, and correspondingly its resistance should change a lot per degree change in temperature," notes Kats. "In principle, our new perfect absorber could be used to make incredibly sensitive thermal cameras."

Harvard's Office of Technology Development has filed patent applications on the novel invention and is actively pursuing licensing and commercialization opportunities.


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 et al. Ultra-thin perfect absorber employing a tunable phase change material. Appl. Phys. Lett., 101, 221101 (2012) DOI: 10.1063/1.4767646

Cite This Page:

Harvard University. "New device hides, on cue, from infrared cameras." ScienceDaily. ScienceDaily, 26 November 2012. <www.sciencedaily.com/releases/2012/11/121126131340.htm>.
Harvard University. (2012, November 26). New device hides, on cue, from infrared cameras. ScienceDaily. Retrieved October 20, 2014 from www.sciencedaily.com/releases/2012/11/121126131340.htm
Harvard University. "New device hides, on cue, from infrared cameras." ScienceDaily. www.sciencedaily.com/releases/2012/11/121126131340.htm (accessed October 20, 2014).

Share This



More Matter & Energy News

Monday, October 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-Fuel Impala

Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-Fuel Impala

3BL Media (Oct. 20, 2014) — Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-fuel Impala Video provided by 3BL
Powered by NewsLook.com
Would A Travel Ban Even Work In Stopping Ebola Spread?

Would A Travel Ban Even Work In Stopping Ebola Spread?

Newsy (Oct. 19, 2014) — The U.S. currently isn't banning travel from Ebola-stricken areas, but it's at least being considered. Some argue though it could be counterproductive. Video provided by Newsy
Powered by NewsLook.com
Tech Giants Push Back After FBI Suggests Less Encryption

Tech Giants Push Back After FBI Suggests Less Encryption

Newsy (Oct. 19, 2014) — FBI Director James Comey's stance on encryption technology isn't receiving much support from the tech community. Video provided by Newsy
Powered by NewsLook.com
Microneedle Patch Promises Painless Pricks

Microneedle Patch Promises Painless Pricks

Reuters - Innovations Video Online (Oct. 18, 2014) — Researchers at The National University of Singapore have invented a new microneedle patch that could offer a faster and less painful delivery of drugs such as insulin and painkillers. Video provided by Reuters
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