The work, as featured in Science Advances, was conducted by a consortium of UK-led physicists, led by the University of Leeds. The research involves studying vibrational properties of matter, or phonons, at the nanoscale. The team have created a powerful way to study ‘phonons’ - the collective oscillation of the nuclei of atoms, which can be thought of as waves that control the way that heat or sound carry through materials.
Thermoelectric materials are used in products that support everyday life, capturing waste heat and recycling it into electricity, for example recovering heat that is generated when a car brakes to recharge its battery, or using body heat to power wearable health monitoring devices. Like many other materials fields, there is a growing need in thermoelectrics for more effective, high performing materials to support the constant development of new products and applications, such as the automotive, medical and Internet of Things industries. Supported by powerful and versatile experimental techniques, the process of designing these materials is painstaking and meticulous, atom by atom.
At SuperSTEM, the Engineering and Physical Sciences Research Council’s (EPSRC) National Research Facility, the team used powerful electron microscopes which are able pinpoint and identify single atoms a million times smaller than a human hair. They developed a new technique that enables them to probe the specific properties of phonons, in volumes of material up to 20 orders of magnitude smaller than any other technique in existence. This new approach could provide a way to study how phonons are affected locally, when microscopic amounts of different chemicals are added at the atomic level, which is often the case in the development of new materials.
Dr Rebecca Nicholls, ESPRC Fellow in Materials for Energy Applications in the Department of Materials at Oxford, developed the theoretical framework which was used to interpret the experimental results. She explains: ‘Other techniques exist to study phonons, but none which allow us to look at the vibrations in such small volumes of material. The theoretical framework highlights these similarities and differences between the techniques and provides a way of interpreting, or even predicting, the results of experiments on other materials.’
The research was led by Professor Quentin Ramasse, Chair of Advanced Electron Microscopy at the University of Leeds and Director of SuperSTEM. Professor Ramasse said: ‘The technique we demonstrate has the potential to provide us with a deeper understanding into how small structural changes at the single atomic level can influence the performance of materials we use in our daily lives. What may appear as very fundamental research on complex properties of matter such as phonon propagation, can have profound implications for industrial and societal benefit.’
This research was carried out in collaboration with the University of London’s Royal Holloway, RMIT University (Australia) and industrial partner, Nion.