Metamaterial Boosts Infrared Spectroscopy’s Sensitivity

A metamaterial absorber developed by researchers from the Korea Institute of Machinery and Materials (KIMM) under the Ministry of Science and ICT and UNIST is able to significantly enhance the detection of harmful substances or biomolecules. The proposed metamaterial described in the research gathers and releases light energy simultaneously, inducing a greater intensity of light that can be absorbed by molecules. The amplified signals allow more distinct (precise) results, particularly when working with small traces of substances.

The material is able to enhance infrared absorption spectroscopy through hundredfold amplification of detection signals and features cross-shaped nano-antennas, formed in a metal-insulator-metal configuration. The middle insulating layer had a thickness of 10 nm, and the material’s designers employed vertical nanogaps — smaller than the wavelength of infrared light — to maximize light absorption by molecules.

SEM image of the metamaterial absorber developed by KIMM and UNIST (left). Top view shows cross-shaped antenna. Side view of the microstructure of the metamaterial absorber developed by KIMM and UNIST (center). Structure of the metamaterial absorber developed by KIMM and UNIST (right). Figure shows 10-nm vertical nanogaps. Courtesy of the Korea Institute of Machinery and Materials.

“The proposed metamaterials achieved a record-high difference of 36% in our demonstration on a monolayer with a thickness of 2.8 nm,” said Inyong Hwang, a researcher in the department of electrical engineering at UNIST.

Though high-resolution beam lithography was required to form the microstructure on metamaterial surfaces, the team’s surface enhanced infrared absorption (SEIRA) platform relies on more affordable nanoimprint lithography and dry-etching processes. The metamaterial may therefore be mass produced through affordable manufacturing processes.

“Using the nanoimprint process, we can obtain metamaterials in the metal-insulator-metal configuration and process them into desired patterns. On top of that, the dry-etching process allows mass production of microstructured metamaterials,” said Joo-Yun Jung, principal researcher at KIMM.

“Our study is the first to induce near-field enhancement and resolve near-field exposure using vertical gaps. The technique is expected to have vast applications, especially for infrared sensors used in the detection of biomolecules, harmful substances, and gases,” added UNIST professor Jongwon Lee.

The research was published in Small Methods (www.doi.org/10.1002/smtd.202100277).