Queen’s University Belfast: Researchers crack scientific mystery with 110-year-old experiment

The breakthrough, which was made by a group of students at Queen’s University Belfast, has revealed the electronic properties of an unusual nanoscale material for the very first time.

Using a modernised version of an old experimental geometry dating back to 1911, the researchers were able to measure for the first time the exact electronic properties of a “domain wall”. These are nanoscale, two-dimensional sheets which are embedded in some crystalline materials.

Domain walls can be more electrically conducting than the surrounding crystal. They are useful as nanoscale electrical connections, but their true potential lies in the fact that can also be created, destroyed, and moved around as required. This makes them very flexible and adaptable in comparison to current technologies, which all rely on fixed-in-place components.

Devices based on these mobile domain walls would be completely reconfigurable – they could change their function entirely or even heal themselves if they broke down. And all of this could take place in the blink of an eye, paving the way for an entirely different kind of electronic circuit.

To date, scientists have found it difficult to examine domain walls in detail. With widths down to only a few atoms – around ten-thousand times thinner than the width of a human hair – they are very small and not easy to access. Now, the Queen’s researchers have been able to shed light on the materials’ capabilities and this could lead the way for futuristic electrical circuits that can reconfigure and repair themselves.

Conor McCluskey, one of the students who led the experiment in the School of Mathematics and Physics at Queen’s, comments: “We have been able to use an experiment which is more than a century old to crack a modern-day mystery within nanotechnology. We have been able to show in detail exactly how the domain walls conduct electricity.

“We now know that the electrons that carry the electrical current within these domain walls move exceptionally fast at room temperature. They move at similar speeds to the electrons in graphene – which is a wonder material hailed for its conduction properties, and its discovery warranted a Nobel prize in 2004.

“Usually when an electron is carrying a current it eventually scatters off the atoms in the material. This blocks the electron on its journey and creates electrical resistance. We have found that charges in these domain walls can move for a very long time before they get scattered – on average they move quite fast. This property itself is quite useful for high-speed electronics, but combined with the fact that the domain walls themselves are entirely mobile and reconfigurable could be a game changer for nanotechnology.”

Conor adds: “Nanotechnology is at somewhat of a crossroads. Historically we have focussed on making electronic components smaller and smaller. That means you can fit more into your device, and as a result your device is more powerful. We’ve now reached a point where we can’t go any smaller without affecting the reliability of the components, the laws of physics don’t allow it.

“The next generation of devices will need to rely on materials which do something different, and mobile domain walls might offer us just that. Our discovery sheds some light on exactly what is happening in these domain walls to make them behave the way they do, and this understanding is key to creating real domain wall devices that work reliably.”

Professor Marty Gregg from the school of Mathematics and Physics at Queen’s comments: “There’s a great analogy from Professor Nava Setter, a pioneer in domain wall research, to describe the potential applications of domain walls in nanoelectronics. You can think of an electrical circuit as a city, a complex layout of buildings, all linked together by roads.

“Similarly, a circuit has electronic components linked together by electronic connections. If these electrical connections are instead provided by mobile and reconfigurable domain walls, it would be like having the ability to change the layout of the city roads in an instant, allowing you a direct path to your destination. Now, we are beginning to reveal the true electronic properties of the domain walls themselves. Rather than simply acting as connections, it seems like they can act as the functional components themselves. Sticking to the analogy, we can move and recreate the actual buildings in the city, rather than just the connections between them.”

He adds: “With circuits that can reconfigure or repair themselves, we could have tiny electronic devices that are extremely flexible and adaptable. This could make a huge difference to society. For example, the ability to repair electronic devices which are not easy to access, such as in medical implants, or onboard satellites in orbit, that would be a huge benefit.”