Ultra-fast electrical circuits demonstrated by NUS and A*Star scientists
Ultra-fast electrical circuits demonstrated by NUS and A*Star scientists: a focused electron beam was used to probe the optical properties of two silver plasmonic resonators bridged by a layer of molecules with a length of 0.5 nanometres Tan Shu Fen, National University of Singapore

Scientists at the National University of Singapore and A*Star have demonstrated a super-fast electrical circuit which operates at frequencies of hundreds of terahertz - tens of thousands times faster than the microprocessors we have today.

The research, Quantum Plasmon Resonances Controlled by Molecular Tunnel Junctions, was led by assistant professor Christian Nijhuis of the National University of Singapore's Faculty of Science and Dr Bai Ping and Dr Michel Bosman from A*Star.

Their paper, published in the journal Science, explains a breakthrough process known as quantum plasmonic tunnelling, which could be used for super-fast computing speeds, nano-optical circuitry and single molecule detection.

Using light to transfer data

Light operates at extremely high frequencies of 100 terahertz. Photonics (the science of light) is used to carry data across optical fibre cables but these ultra-fast properties do not work with the state-of-the-art nano-scale microprocessor chips we have today, which can only reach very small length scales.

"Present-day technology is stuck around 3GHz computers. Every year we add more transistors and more memory but our computers don't get faster due to fundamental limitations in how processors are wired," Nijhuis told IBTimes UK.

"The electrical charge carried through metal wires has speed limits due to capacity side-effects and it's really limited. The idea is to use light coupled to the wires, [so] instead of the electrons going through the wires, they move along over the surface and that could go up to 10,000 times faster.

"We all know that light is super-fast, the fastest thing in the universe. It would be brilliant if you could do things with light."

It has long been known that it is possible for light to be captured when it interacts with certain types of metal, in the form of plasmons – ultra-fast oscillations of electrons which can be manipulated at the nanoscale.

Quantum plasmonic tunnelling

In 2012, A*Star scientists theorised that it would be possible to create an electrical circuit that made use of quantum plasmonic tunnelling, and their theory has finally been proved.

In order to capture the light over longer, tiny silver plasmonic resonator structures were used with a length scale between them of only 0.5 nanometres. The system could only be seen using an advanced electron microscope.

"If light, or a plasmon, is absorbed by one of the silver nanocube structures, it creates an electric field, which can induce tunnelling of electrons from one particle to the other and vice versa. That tunnelling process can then sustain a new plasmon mode, and that plasmon mode is the fundamental proof of concept that high speed nanoscale optoelectronics is possible," explained Nijhuis.

The scientists discovered that the speed of the transfer of electrons could be controlled by varying the molecular properties of the devices, and the next step is to create devices that can be integrated with real electronic circuits that can transfer electrons accurately and produce a high yield.