Due to their excellent conductivity and unique physical properties, carbon nanotubes (CNTs) are ideal for next-generation electronic devices. One of the most promising developments is their application in THz devices. Increasingly, THz imagers are emerging as a safe and viable alternative to conventional imaging systems across a wide range of applications, from airport security, food inspection and art authentication to medical and environmental sensing technologies.
The demand for THz detectors that can deliver real-time imaging for a broad range of industrial applications has spurred research into low-cost, flexible THz imaging systems. Yukio Kawano of the Laboratory for Future Interdisciplinary Research of Science and Technology, Tokyo Institute of Technology (Tokyo Tech), is a world-renowned expert in this field.
Kawano and his team have been investigating THz detection performance for various types of CNT materials – leading to the development of flexible THz imagers for CNT films that can be fine-tuned to maximize THz detector performance. Publishing their findings in ACS Applied Nano Materials, the THz imagers are based on chemically adjustable semiconducting CNT films.
By making use of a technology known as ionic liquid gating , the researchers demonstrated that they could obtain a high degree of control over key factors related to THz detector performance for a CNT film with a thickness of 30 micrometers. This level of thickness was important to ensure that the imagers would maintain their free-standing shape and flexibility, as shown in Figure 1.
“Additionally,” the team says, “we developed gate-free Fermi-level  tuning based on variable-concentration dopant solutions and fabricated a Fermi-level-tuned p?n junction  CNT THz imager.” In experiments using this new type of imager, the researchers achieved successful visualization of a metal paper clip inside a standard envelope (see Figure 2.)
The bendability of the new THz imager and the possibility of even further fine-tuning will expand the range of CNT-based devices that could be developed in the near future.
Moreover, low-cost fabrication methods such as inkjet coating could make large-area THz imaging devices more readily available.