Researchers have developed flexible, bendable terahertz (THz) imagers based on chemically adjustable semiconducting carbon nanotube (CNT) films. The CNT films can be tuned to maximize THz detector performance. Flexible THz imagers could expand the scope of THz applications to include wraparound, wearable technologies and large-area photonic devices. Resting on a fingertip, the carbon nanotube terahertz (CNT THz) imager can easily wrap around curved surfaces (a). Just by inserting and rotating a flexible THz imager attached to the fingertip, damage to a pipe was clearly detected (b). Courtesy of ACS Applied Nano Materials. A team at Tokyo Institute of Technology (Tokyo Tech) used an electronic-double-layer technique with ionic liquids to obtain an on/off resistance ratio for a semiconducting-separated CNT film with a thickness of 30 μm. This level of thickness ensured that the imagers would maintain their free-standing shape and flexibility. The researchers further developed gate-free Fermi-level tuning based on variable-concentration dopant solutions and tuned the Fermi level at an optimal gate voltage to maximize the THz detector performance. The development of a gate-free tunable doping technology based on a variable-concentration dopant solution enabled the fabrication of a Fermi-level-tuned p-n junction CNT THz imager. In experiments using the new THz imager, researchers achieved successful visualization of a metal paper clip inside a standard envelope. The carbon nanotube terahertz (CNT THz) imager enabled clear, nondestructive visualization of a metal paper clip inside an envelope. Courtesy of ACS Applied Nano Materials. The chemically tunable doping capability demonstrated by the team could facilitate the realization of flexible THz imaging applications and, when combined with a low-cost fabrication method such as an inkjet coating process, could lead to large-area THz photonic devices. The bendability of the new THz imager and the possibility of even further fine-tuning could open the way for a range of CNT-based devices. Because of their excellent conductivity and unique physical properties, CNTs are an attractive option for next-generation electronic devices. Increasingly, THz imagers are emerging as a safe, viable alternative to conventional imaging systems across a range of applications, from airport security, food inspection, and art authentication to medical and environmental sensing technologies. The research was published in ACS Applied Nano Materials (doi:10.1021/acsanm.8b00421).
