Kyoto Institute of Technology develops high-sensitivity infrared sensor using semiconducting CNTs with no cooling required

Associate Professor Yoshiyuki Nonoguchi, Professor Takeshi Yamao, and Assistant Professor Yuhi Inada from the Department of Materials Science, Kyoto Institute of Technology and Professor Yukio Kawano and Assistant Professor Kou Li from the Faculty of Science and Engineering, Chuo University, in collaboration with the Sensing Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), announced the development of a high-sensitivity infrared sensor using semiconducting carbon nanotubes (CNTs) controlled into different types of electrical properties: p-type (where the primary charge carriers are holes) and n-type (where the primary charge carriers are electrons). Because the sensor enables non-destructive observation of internal structures using infrared radiation that can penetrate clothing and plastics, it is expected to find broad application in security inspection, quality control, medical diagnosis, next-generation communications, and related fields. Their findings were published in Small Structures on February 2.

Infrared radiation has the property of passing through many organic materials, but because its energy is low, cooling is required to detect it with high sensitivity. Developing a sensor that can be used simply and at low cost has therefore been an ongoing challenge.

In this study, semiconducting single-walled carbon nanotubes were isolated at high purity, and thin films chemically controlled into p-type and n-type, each with distinct electrical properties, were then combined.

In the sensor developed by the researchers, infrared radiation is efficiently absorbed and converted into heat via collective oscillations of electrons in the carbon nanotubes. This is known as plasmon resonance, a phenomenon in which specific wavelengths of light are strongly absorbed and converted to heat, causing a localized rise in temperature. The sensor operates by exploiting the "thermoelectric effect," which converts this temperature difference into an electrical signal. Sensitivity was improved approximately 11-fold compared with conventional materials that contain a mixture of metallic CNTs.

This improvement is attributed to the superior ability of semiconducting nanotubes to convert heat into electricity (thermoelectric performance), as well as their efficient heating through the strong absorption of infrared radiation via plasmon resonance.

It was also demonstrated that chemical doping treatment reduces heat dissipation, generating a larger temperature difference.

The researchers reported that the simultaneous control of three properties (plasmon resonance, thermoelectric performance, and doping) is what led to the improvement in sensitivity.

Going forward, the researchers will advance applied research toward future social implementation, including potential integration into wearable devices.

Nonoguchi commented: "In this research, we achieved highly sensitive infrared detection without the need for cooling by using semiconducting carbon nanotubes. Because a high voltage output can be obtained, we anticipate future applications in miniaturized and portable inspection devices. Going forward, we will continue to promote industry-academia collaboration while pursuing further improvements in sensitivity and broader application development at the university level."

Journal Information
Publication: Small Structures
Title: Synergistic Plasmonic-Thermoelectric Enhancement in Semiconducting Carbon Nanotubes for Infrared Light Detection
DOI: 10.1002/sstr.202500834