Metamaterial Improves IR-Sensors

A new device for surface enhanced infrared absorption spectroscopy: Infrared light is trapped by tiny gaps in the metal surface, where it can be used to detect trace amounts of matter. (Source: U. Buffalo)

Scientists searching for traces of drugs, bomb-making components and other chemicals often shine light on the materials they’re analyzing. Especially infrared absorp­tion spectro­scopy is used to sleuth out perfor­mance-enhancing drugs in blood samples and tiny particles of explosives in the air. While infrared absorpt­ion spectro­scopy has improved greatly in the last hundred years, researchers are still working to make the tech­nology more sensitive, inex­pensive and versatile. A new light-trapping sensor, developed by a Uni­versity at Buffalo-led team of engineers makes progress in all three areas.

“This new optical device has the potential to improve our abi­lities to detect all sorts of bio­logical and chemical samples,” says Qiaoqiang Gan, associate professor of electrical engi­neering in the School of Engi­neering and Applied Sciences at UB. The sensor works with light in the mid-infrared band of the electro­magnetic spectrum and consists of two layers of metal with an insu­lator sandwiched in between. Using atomic layer depo­sition, researchers created a device with gaps less than five nano­meters between two metal layers. Impor­tantly, these gaps enable the sensor to absorb up to 81 percent of infrared light, a signi­ficant improvement from the 3 percent that similar devices absorb.

For surface-enhanced infrared absorp­tion (SEIRA) spectro­scopy the sensor acts as a substrate for the materials being examined. It boosts the sens­itivity of SEIRA devices to detect molecules at 100 to 1,000 times greater reso­lution than pre­viously reported results. The increase makes SEIRA spectro­scopy comparable to another type of spectro­scopic analysis, surface-enhanced Raman spectro­scopy, which measures light scat­tering as opposed to absorp­tion. The SEIRA advance­ment could be useful in any scenario that calls for finding traces of molecules, says Ji. This includes but is not limited to drug detec­tion in blood, bomb-making materials, fraudulent art and tracking diseases. Researchers plan to continue the research, and examine how to combine the SEIRA advance­ment with cutting-edge SERS. (Source: U. Buffalo)

Reference: D. Ji et al.: Efficient Mid-Infrared Light Confinement within Sub-5-nm Gaps for Extreme Field Enhancement, Adv. Opt. Mat., online 3 July 2017; DOI: 10.1002/adom.201700223

Link: Dept. of Electrical Engineering, State University of New York at Buffalo, Buffalo, USA

 

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