Silicon quantum dots in thermoelectric material applications

Major advances in efficient, clean and secure energy conversion and use are needed if we are to reduce global greenhouse gas emissions, for example to meet the EU's commitment of a reduction of 80% by 2050. Thermoelectric materials are able to take advantage of wasted or unutilized heat sources, such as in furnaces, car exhausts, and solar cells. As a result, thermoelectric materials have become an area of great interest. These materials are able to convert a temperature gradient into electrical power, and vice versa, without mechanical intervention. The power output from current commercial modules produced are however, modest, but power generated from these devices are then used elsewhere for low power applications, e.g. powering sensors or safety feedback loops. We have successfully synthesized Phenyl-acetylene functionalized Silicon quantum dots (SiQDs) which are showing potential to provide highly efficient thermoelectric materials. These conjugated ligands would allow transport of electrons through the conjugated orbitals. A preliminary characterization of this system, in the bulk, shows an electric conductivity in the region of 24 S.m-1, thermal conductivity 0.10 Wm-1K-1 and a Seebeck coefficient of 4148 muVK-1 at 300 K, with an estimated figure of merit ZT in the region of 0.6. Knowledge of the microscopic conduction rates and mechanisms of these materials would be invaluable in our attempts to improve these materials by design. The present application is to use the uniquely elegant method of Muon spectroscopy to measuring these microscopic properties.

The outcomes will ultimately be of importance to sections of society well beyond the confines of chemical sciences and academia and are likely to impact on, for example, the automotive industry and the energy sector. The discovery of new materials and of processes leading to new materials has, as history shows, always had a profound impact on people's everyday life, well beyond what was originally thought possible - man-made polymers discovered in the 1930s-50s being prime examples. Similarly, successful thermoelectric devices of adequate efficiency and acceptable manufacturing costs can be envisaged to be produced on a very large scale using the principles established in this programme. Such devices may eventually replace current thermoelectric technology, have the potential of becoming part of everyday life.
Users and beneficiaries of this research will therefore be initially the international academic community and industrial as well as governmental research laboratories worldwide. They will encompass a wide range of disciplines, i.e. chemists, physicists, theoreticians, engineers, and eventually extend to production and marketing. This project must be seen part of a large international effort in nanoscience and nano-based materials and cannot be taken in isolation from the exchange of ideas that is an intrinsic aspect of any major scientific development.