Exploiting quantum and phonon interference for molecular thermoelectricity and Seebeck sensing (MoQPI)

In any electrical device, unwanted heat produced by electronic components is usually wasted. A thermoelectric device can convert this waste heat to electricity through Seebeck effect. Generation of electricity from heat via the Seebeck effect is silent, environmentally friendly and requires no moving parts. Unfortunately current thermoelectric materials are difficult to process, have limited global supply and are not sufficiently efficient to meet the requirements of current energy demands. That is why there is a world-wide race to develop materials with a high thermoelectric efficiency.
To realise a high-performance thermoelectric material, both electron and phonon transport should be optimised. Since both electrons and phonons (vibrations) behave like waves, they can exhibit interference phenomena at a molecular scale, which could be used to optimise their transport properties. Therefore simultaneous control of room-temperature quantum interference (RTQI) of electrons and room-temperature phonon interference (RTPI) have the potential to underpin new design strategies for efficient molecular thermoelectricity.
This proposal, entitled 'MoQPI,' aims to design new highly-efficient thermoelectric materials for converting waste heat into electricity, by exploiting RTQI and RTPI in cross-plane (CP) sub-10nm thin films. Cross-plane structures are advantageous, because they do not suffer parallel heat paths through the substrate and can be engineered to suppress parasitic thermal conductance due to phonons. The radically-new CP nanostructured materials proposed in this Fellowship will be formed from single-molecules, parallel arrays of molecules in self-assembled monolayers (SAMs) and van-der-Waals (vdW) molecular nanoribbons sandwiched between metallic and/or graphene electrodes. I will exploit RTQI and RTPI simultaneously in many molecule systems and vdW molecular nanoribbons to yield a new generation of high-performance thermoelectric materials. Simultaneous assessment of quantum and phonon interference in molecular-scale thermoelectric materials will elucidate design strategies for the development of new generation of thermoelectric devices and consequently will change the community view on routes to engineer and realize highly efficient thermoelectric materials.
MoQPI will also develop innovative applications of the Seebeck effect for discriminating biological sensing. Using the Seebeck coefficient for sensing is advantageous compared with current methods based on electrical sensing, because two biological species that might possess similar conductances could have Seebeck coefficients with different signs or magnitudes. Furthermore, the electrical conductances of biomolecules such as DNA nucleobases are extremely low, which is problematic for conductance-based sensing, but advantageous for Seebeck sensing, since low electrical conductances typically lead to high Seebeck coefficients. Seebeck sensing using single molecules and molecular nanoribbons proposed in this proposal will generate ground-breaking knowledge needed for next-generation biosensing. MoQPI will also explore hybrid molecular structures for energy harvesting. The identification of simultaneous RTPI and RTQI enhanced energy harvesting and molecular sensing in ultra-thin-film molecular layers is the first step to realise new types of quantum technologies with important societal and economic impacts in the real world.

MoQPI is focussed primarily on delivering fundamental science, leading to significant academic impact. It will fill a gap in the UK's capability to use molecular scale thermoelectricity and maintain UK's leading position in the international race to exploit room-temperature quantum interference (RTQI) and room-temperature phonon interference (RTPI). The UKRI Strategic Prospectus highlights discovery and innovation in the physical sciences as being important for a Productive and Resilient Nation to increase UK competitiveness. MoQPI has creativity and innovative solutions at its core. The main beneficiaries of this proposal are academics and industries engaged in studying the conversion of heat into electricity and biomolecular sensing. The fundamental processes associated with molecular thermoelectricity in sub-nm molecular junctions, self-assembled monolayers and molecular nanoribbons have not been systematically studied and are a new direction for research. MoQPI will develop novel strategies for efficient conversion of heat to electricity by maximising phonon scattering to suppress thermal conductance and optimising electron transport to maximise Seebeck coefficient and electrical conductance. This will be the first time that RTQI and RTPI have been exploited simultaneously in the same device to design efficient thermoelectric materials with unprecedented performance. The project will lay the foundations for high performance thermoelectric thin-film devices and could lead to a step change in the understanding of thermoelectric processes. Furthermore, exploration of the entirely new concept of utilising molecular-scale thermoelectricity for molecular sensing "Seebeck sensing" will open new routes for selective sensing of biomolecules by utilising changes in the sign and magnitude of Seebeck coefficient as a recognition method. Together, these will have a strong influence on UK competitiveness in the field of molecular scale technology.
In the early stages of the project (month 18) a multidisciplinary workshop will be organised to bring together international academic colleagues and current and potential industrial partners to show-case the current status of the fields of molecular-scale thermoelectricity. A successful outcome of this project will also be very stimulating to the wider academic community and industrial partners who are engaged in the broad areas of synthesis and assembly of organic materials, mechanisms of charge transport, molecular electronics, sensors and surface science. Many companies in the UK e.g. Rolls-Royce (Birmingham), European Thermodynamics Ltd. (Leicester), Oxford Nanopore Technology (Oxford), NPL (Teddington), and Quantum Base (Lancaster) are likely to benefit directly or indirectly from this project which will foster the economic competitiveness of the UK.
MoQPI will also contribute to the UK's long-term strength in the field of molecular electronics by training PDRA and PhD students and developing their careers. The PDRA employed on the project will be ideally placed to learn new research-related and transferable skills and build strong independent research career. S/he will be especially equipped to develop and lead future programmes in molecular electronics. This aligns closely with UKRI's corporate plan 'Leading talent' for development of Future Leaders, both for academia and industry. One example of early impact will be additional modelling capabilities within the 'Gollum' transport simulation tool, which will be further developed during the Fellowship to describe electron and phonon transport in presence of environmental effects.