Periodic Reporting for period 1 - QTherm-2D (Development of a new first-principle Framework for Quantum Thermoelectricity — Application to 2D materials)
Période du rapport: 2018-05-15 au 2020-05-14
As the development of sustainable energy sources poses one of the greatest challenges for our society, the Marie Słodowska-Curie action QTherm-2D aims at exploring the emergence of thermoelectricity at the quantum scale and advancing realistic thermoelectrical nanodevices. On the one hand, the project addresses the fundamentals of thermoelectrical energy conversion at the nanoscale, such as the influence of decoherence, magnetic fields, and spin-orbit coupling on thermoelectrical energy conversion. And on the other hand, QTherm-2D advances the calculation of the thermoelectrical transport properties from first-principles for two-dimensional layered materials by considering electron-phonon interaction, doping, vacancies, and oxidation.
During the action of the QTherm-2D project the following work has been performed with results:
1. Realisation of state-of-the-art ab initio calculations of the thermal and electronic transport properties of 2D-layered Transition-Metal Trichalcogenides (TMTs), especially investigating the influence of electron-phonon interaction onto the thermoelectrical properties. We found that electron-phonon interaction drastically changes the thermoelectrical properties of 2D TMTs and need to be considered. Standard approximation for bulk materials as the constant relaxation time approximation or the estimation of the relaxation time via deformation potential cannot be applied for low-dimensional materials.
2. The project investigated the controlled thermal oxidation of individual TiS3 nanoribbons and its influence on the optoelectronic properties. The experiment (done by collaborators) shows that a thermal oxidation process can convert TiS3 nanoribbons into TiO2. The researcher has focused on the changes in the band structure of the system when passing from TiS3 towards TiO2. To calculate the electronic band structure, state-of-the-art ab-initio DFT and GW calculations have been performed. Those calculations indicate an increase in the bandgap of titanium oxysulfide when increasing the amount of oxygen and reducing the amount of sulfur. This presents a preliminary work for studying the influence of vacancies and oxidation on thermoelectrical performance.
3. Extensive analytical derivations have been performed to construct a zero- and a finite-temperature functional that can be used as a scalar potential in closed quantum dynamics. The zero-temperature functional has been tested and implemented and allows to describe dissipation in a closed quantum system towards the ground-state of the system.
4. The influence of decoherence on thermoelectrical transport has been studied and found that spatial decoherence can control energy and particle current in nanodevices and can hence be used to make thermoelectrical energy conversion more efficient.
5. Electronic current in lateral junctions with spin-orbit coupling and an exchange field has been studied. The researcher has found that the electrical current in those junctions can be controlled by rotating the magnetization of the bridge or by tuning the strength of the spin-orbit coupling.
The results have been exploited and disseminated in the following ways:
- Through three published peer-reviewed scientific publications
- Two manuscripts are written at the moment and will be submitted very soon
- Through realisation of five oral(1)/poster(4) presentations
- Through the realisation of two seminars
1. Realisation of state-of-the-art ab initio calculations of the thermal and electronic transport properties of 2D-layered Transition-Metal Trichalcogenides (TMTs), especially investigating the influence of electron-phonon interaction onto the thermoelectrical properties. We found that electron-phonon interaction drastically changes the thermoelectrical properties of 2D TMTs and need to be considered. Standard approximation for bulk materials as the constant relaxation time approximation or the estimation of the relaxation time via deformation potential cannot be applied for low-dimensional materials.
2. The project investigated the controlled thermal oxidation of individual TiS3 nanoribbons and its influence on the optoelectronic properties. The experiment (done by collaborators) shows that a thermal oxidation process can convert TiS3 nanoribbons into TiO2. The researcher has focused on the changes in the band structure of the system when passing from TiS3 towards TiO2. To calculate the electronic band structure, state-of-the-art ab-initio DFT and GW calculations have been performed. Those calculations indicate an increase in the bandgap of titanium oxysulfide when increasing the amount of oxygen and reducing the amount of sulfur. This presents a preliminary work for studying the influence of vacancies and oxidation on thermoelectrical performance.
3. Extensive analytical derivations have been performed to construct a zero- and a finite-temperature functional that can be used as a scalar potential in closed quantum dynamics. The zero-temperature functional has been tested and implemented and allows to describe dissipation in a closed quantum system towards the ground-state of the system.
4. The influence of decoherence on thermoelectrical transport has been studied and found that spatial decoherence can control energy and particle current in nanodevices and can hence be used to make thermoelectrical energy conversion more efficient.
5. Electronic current in lateral junctions with spin-orbit coupling and an exchange field has been studied. The researcher has found that the electrical current in those junctions can be controlled by rotating the magnetization of the bridge or by tuning the strength of the spin-orbit coupling.
The results have been exploited and disseminated in the following ways:
- Through three published peer-reviewed scientific publications
- Two manuscripts are written at the moment and will be submitted very soon
- Through realisation of five oral(1)/poster(4) presentations
- Through the realisation of two seminars
The QTherm-2D project has given the researcher the opportunity to obtain many different capacities. First of all, the researcher has become an expert in the theory of thermoelectrical transport and in the development of its foundations. This might play a very important role in the future search for sustainable energy sources which is still one of the greatest challenges of our society.
Secondly, the researcher has improved his computational skills and has become an expert in modeling thermoelectrical transport for realistic nanodevices from first principles. Especially, he has learned how to describe the influence of electron-phonon interaction on the thermoelectrical performance of nanoscale devices. This now provides the researcher with a complete framework to describe thermoelectrical phenomena for real systems from first principles, which is essential for the future search for high efficient thermoelectrical materials.
The obtained insights on quantum thermoelectrical energy conversion will allow other researchers in the field to further develop novel high-performance TE materials and outperform current technologies. Especially the fact, that the standard approach for calculating ZT within the constant relaxation time approximation does not perform well for low-dimensional system, might change the start-of-the-art methods: electron-phonon interaction from first-principles has to be considered and one needs to go beyond the constant relaxation time approximation when calculating the thermoelectrical performances of low-dimensional systems.
The obtained insights on quantum thermoelectrical energy conversion will allow other researchers in the field to further develop novel high-performance TE materials and outperform current technologies. Especially the fact, that the standard approach for calculating ZT within the constant relaxation time approximation does not perform well for low-dimensional system, might change the start-of-the-art methods: electron-phonon interaction from first-principles has to be considered and one needs to go beyond the constant relaxation time approximation when calculating the thermoelectrical performances of low-dimensional systems.