Power/Performance Bits: June 17

Nanotubes boost terahertz detectors
Researchers at Rice University, Sandia National Laboratories and the Tokyo Institute of Technology have developed novel terahertz detectors based on carbon nanotubes that could improve medical imaging, airport passenger screening, food inspection and other applications.

Unlike current terahertz detectors, the devices are flexible, sensitive to polarization and broad bandwidth and feature large detection areas. They operate at room temperature without requiring any power and take advantage of the terahertz range of the electromagnetic spectrum.

Because terahertz waves are much smaller in energy than visible light, they said, finding materials that absorb and turn them into useful electronic signals has been a challenge. However, thin films of highly aligned carbon nanotubes developed at Rice have been configured to act as compact, flexible terahertz sensors.

Terahertz waves easily penetrate fabric and other materials and may provide less intrusive ways for security screenings of people and cargo. Terahertz imaging could also be used to inspect food without adversely impacting its quality.

Perhaps the most exciting application offered by terahertz technology, could be as a possible replacement for magnetic resonance imaging (MRI) technology in screening for cancer and other diseases since the potential improvements in size, ease, cost and mobility of a terahertz-based detector are phenomenal, the researchers said. With this technology, a handheld terahertz detection camera could conceivably be designed that images tumors in real time with pinpoint accuracy and without the intimidating nature of MRI technology.

A nanotube detector attached to two gold electrodes is able to detect terahertz waves. The nanotubes are doped to provide negative and positive regions. The detector developed by Rice University, Sandia National Laboratories and the Tokyo Institute of Technology could improve many imaging applications. (Source: Kono Laboratory/Rice University)

Deciphering carbon nanotubes
According to researchers at the University of Cambridge, what links legendarily sharp Damascene swords of the past with flexible electronics and high-performance electrical wiring of the future are the fact that they all owe their remarkable properties to different structural forms of carbon. The field of carbon nanotubes is at a very exciting stage researchers are beginning to understand what governs their growth and how they behave in industrially relevant environments.

History’s deadliest swords and their astonishing qualities are thought to have come from a combination of specific impurities in the iron ore and how hot and how long they were fired – a process that some scientists believe may have unwittingly created carbon nanotubes (CNTs) within them. These thin, hollow tubes are only a single carbon atom in thickness. Like their carbon cousin, graphene – in which the atoms lie flat, in a two-dimensional sheet – they are among the strongest, most lightweight and flexible materials known.

What makes carbon nanoforms such as graphene and CNTs so exciting, the researchers said, are their electrical and thermal properties and the fact that their potential use in applications such as lighter electrical wiring, thinner batteries, stronger building materials and flexible devices could have a transformational impact on the energy, transport and healthcare industries.

All of the superlatives attributed to the materials refer to an individual, atomically perfect, nanotube or graphene flake, and the frequently pictured elephant supported by a graphene sheet epitomizes the often non-realistic expectations. The challenge remains to achieve high quality on a large scale and at low cost, and to interface and integrate the materials in devices, they reminded.

But it is on the electrical front that they meet their greatest challenge. The process of manufacture is being scaled up through a Cambridge spin-out, Q-Flo; however, electrical conductivity is the next grand challenge for CNT fibers in the laboratory. To understand and develop the fiber as a replacement for copper conductors will be world-changing, with huge benefits.

Researchers can now not only see and resolve the intricate structures, but new characterization techniques allow real-time videos to be taken of how they assemble, atom by atom. They are beginning to understand what governs their growth and how they behave in industrially relevant environments, which allows their properties, alignment, location and interfaces with other materials to be better controlled — key to unlocking their commercial potential.

For high-end applications in the electronics and photonics industry, achieving this level of control is not just desirable but a necessity. The ability to produce carbon controllably in its many structural forms widens the ‘materials portfolio’ that a modern engineer has at their disposal. With carbon films or structures already found in products such as hard drives, razor blades and lithium ion batteries, the industrial use of CNTs is becoming increasingly widespread, driven, for instance, by the demand for new technologies such as flexible devices and our need to harvest, convert and store energy more efficiently.