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Fingertip-Wearable Terahertz Imagers by Fermi-Level Tuning in Semiconducting-Separated Carbon Nanotube Films

 Tokyo Institute of Technology announced on June 28, 2018 that a research group led by Associate Professor Yukio Kawano has succeeded in developing fingertip-wearable terahertz (THz) imagers by fine tuning of Fermi-level in semiconducting-separated carbon nanotube (CNT) films. Scientific details were published in ACS Applied Nano Materials*.

 THz imagers are emerging as safe and viable imaging systems across a wide range of applications, such as airport security, inspection of industrial components, and medical sensing. Flexible and wearable devices with microscale are required to sense THz signals thorough complicated structures. Although thermal photo-voltaic effect in CNT is expected to respond the demand, sensitivity has been limited, especially in free standing thick CNT films due to the lack of ability to tune the Fermi level.

 The research group has solved the problem by devising Fermi-level-control, and developed flexible and bendableTHz imagers with CNT films. At first, semiconducting CNTs are separated from the ordinary mixture with metallic CNTs. Then, electronic-double-layer technique with ionic liquids has shown to tune the Fermi level and to get on/off resistance ratio (2758) for the CNT film with a thickness of 30μm. The THz detector performance is maximized by tuning Fermi level at an optimal gate voltage. In addition, chemical doping to CNT films using NaOH-crown ether solution enabled the fabrication of a Fermi-level-tuned p-n junction to realize voltage-free CNT THz imager. Fingertip-wearable THz imagers are fabricated and placed inside a tube to detect successfully defects of the tube using THz wave irradiation.

*Daichi Suzuki, Yuki Ochiai, Yota Nakagawa, Yuki Kuwahara, Takeshi Saito, and Yukio Kawano, "Fermi-Level-Controlled Semiconducting-Separated Carbon Nanotube Films for Flexible Terahertz Imagers", ACS Applied Nano Materials, 2018, Vol. 1, No. 6, pp 2469-2475, DOI: 10.1021/acsanm.8b00421; Publication Date (Web): June 6, 2018