Tiny devices promise new horizon for security screening and medical imaging

The devices use terahertz radiation, which can penetrate through materials such as plastics, wood and skin. This form of radiation, which falls between infrared and microwaves in the electromagnetic spectrum, does not damage living tissues as other forms such as X-rays can.

The devices are made from nanowires 100 times thinner than a human hair. They could be used in new, safe imaging technology with far higher resolution than current ultrasound devices used to detect small tumours.

A team of researchers from Strathclyde's Institute of Photonics, in the University's Department of Physics, developed a highly accurate micro-assembly technique to allow the construction of a 3D lattice of nanowire devices. The team used a specialised 'transfer printing' micro-assembly system to print semiconductor nanowire structures, with nanoscale accuracy, in orthogonal patterns onto metal antenna structures.

The study, published in the journal Science, is the result of a collaboration between Strathclyde, the University of Oxford, and the Australian National University (ANU), based in Canberra.

Professor Martin Dawson, one of Strathclyde's lead researchers on the project, said: "It is very exciting to see this collaborative work with our close colleagues at Oxford and ANU published in a journal as prestigious as Science. We have developed novel capabilities for printing of semiconductor nanostructures and microstructures at Strathclyde over the past few years and, combined with ANU's leading ability to grow semiconductor nanowires and Oxford's advanced light detection concepts this has led to very exciting results.

"It has been a pleasure to partner with our colleagues in this work and we look forward to further leading-edge results from the collaboration."

Dr Antonio Hurtado, a Senior Lecturer in Strathclyde's Institute of Photonics, who is also part of Strathclyde's lead team, said: "Building the THz detection systems was a great challenge that required the development at Strathclyde of extremely precise nanofabrication processes. These permitted us to use the semiconductor nanowires from ANU as 'building blocks' for their sequential integration in the 3D THz detectors designed at Oxford, whilst keeping the nanometric accuracy needed to assemble the systems. This has been a great combination of capability and a fantastic collaboration between the different teams involved in this work."

Other terahertz radiation systems, such as those used in airport security scanners, are based on simple intensity detection. However, improved imaging techniques can be implemented by making use of the fact that terahertz radiation, like all electromagnetic waves, contains polarisation information -- the direction of the electromagnetic fields as they propagate through space.

The orientation of the nanowires in the device allows terahertz radiation with different polarisations to be measured independently and given the compact device area, paves the way for future on-chip imaging systems.