Periodic Reporting for period 1 - exciTitania (Excitonic quasiparticles in Titania)
Okres sprawozdawczy: 2017-09-01 do 2019-08-31
In exciTitania, we have worked towards the clarification of some intriguing characteristic of TiO2, including the anomalous dependence of its electronic and optical properties with the temperature, and its unexpected behaviour respecting the coherent motion of its crystal lattice. We have employed state-of-the-art theoretical calculations in close collaboration with researchers conducting advanced spectroscopy measurements.
We have got remarkable new insights into the excitonic nature of TiO2. We discovered novel properties of titania single crystal and nanoparticles which could be used, for example, to build low cost sensors with specific functions. We also elucidated the mechanisms behind the generation of the coherent motions of the atoms in the material. Our investigation has also shed light to the migration of the charge carriers in TiO2, which, with further research, may explain why this semiconductor has so exceptional features for the degradation of air pollutants.
We found the deformation potential coupling as the dominant mechanism for the generation and detection of coherent acoustic phonons in TiO2 nanoparticles and single crystals. These coherent acoustic phonons are responsible for a huge modulation of the exciton peak amplitude as well as a giant exciton energy shift in bulk TiO2. The detection and generation of these phonons are observed close to an exciton resonance at room temperature. Our calculations reveal that this exciton resonance exhibits extraordinarily large photo elastic coefficients, comparable to those found for quantum confined nanoparticles in the visible spectrum. These findings pave the way for the design of exciton control schemes using strain pulses.
For the proper description of the electron-phonon interaction in TiO2, we have joined efforts with theoreticians working on a framework that can describe the effects of multiple phonons using a single arrangement of the atomic positions in a supercell. The combination of this scheme with many body perturbation theory has resulted so far in the accurate account of the zero point renormalisation of the electronic gap of TiO2. This had never been accomplished before.
The results obtained within this project have been presented in the following conferences and seminars:
-2017 Seminar at Duke University, USA, “Excitonic quasiparticles in TiO2”
-2018 Seminar at UPV/EHU, Basque Country, Spain “Excitonic quasiparticles in TiO2”
-2018 Seminar at University of Oxford, UK “Excitonic quasiparticles in TiO2”
-2018 9th International Conference on Spontaneous Coherence in Excitonic Systems, Montreal, Canada “Excitonic quasiparticles in TiO2”
-2019 DESY NanoLab annual kickoff meeting, Zeuthen, Germany “Bulk and 2028surface properties of TiO2 photocatalyst”
-2019 World Congress on Laser, Optics and Photonics, Barcelona, Spain “Excitonic quasiparticles in TiO2”
All results and internal reports have been brought multiple time to discussion with our collaborators for their further exploitations. Some of our findings have been published in high impact international journals with open access. The rest will be published in the near future, always making them accessible free of charge.