Proceedings of nanoGe Fall Meeting 2018 (NFM18)
DOI: https://doi.org/10.29363/nanoge.nfm.2018.265
Publication date: 6th July 2018
Using a combination of steady-state and ultrafast deep-ultraviolet (UV) we have identified the nature of the transitions at the optical gap of the much studied anatase TiO2 nanoparticles. The first excitation is a strongly bound 2-dimensional exciton in the 3D lattice of the material.[1] We also find that coherent acoustic phonons confined in the nanoparticles selectively modulate the oscillator strength of the 2D exciton, and theory shows that the deformation potential is at the origin of the coherent phonon wavepackets.[2] Further studies of the charge electron and hole trapping in anatase TiO2[3] and in ZnO[4] using ultrafast X-ray spectroscopy will be presented.
Finally, time resolved X-ray studies of CsPbBr3 perovskite NPs reveal the nature of the electron-hole recombination across the band gap, with the electrons being delocalized in the conduction band, while holes form small polarons in the valence band.[5]
[1] Strongly bound excitons in anatase TiO2 single crystals and nanoparticles
E. Baldini, L. Chiodo, S. Moser, J. Levallois, E. Pomarico, G. Auböck, A. Magrez, L. Forro, M. Grioni, A. Rubio and M. Chergui. Nature Communications 8 (2017) 13
[2] Phonon-Driven Selective Modulation of Exciton Oscillator Strengths in Anatase TiO2 Nanoparticles
E. Baldini, T. Palmieri, A. Dominguez, P. Ruello, A. Rubio and M. Chergui. Nanoletters (under review)
[3] Femtosecond X-ray absorption study of electron localization in photoexcited anatase TiO2
F. G. Santomauro, A. Lübcke, J. Rittmann, E. Baldini, A. Ferrer, M. Silatani, P. Zimmermann, S. Grübel, J. A. Johnson, S. O. Mariager, P. Beaud, D. Grolimund, C. Borca, G. Ingold, S.L. Johnson, M. Chergui
Scientific Reports 5 (2015) 14834-1-6
[4] Revealing hole trapping in ZnO nanoparticles by time-resolved X-ray spectroscopy
Thomas J. Penfold, Jakub Szlachetko, Fabio G. Santomauro, Alexander Britz, Wojciech Gawelda, Gilles Doumy, Anne Marie March, Stephen H. Southworth, Jochen Rittmann, Rafael Abela, Majed Chergui and Christopher J. Milne. Nature Communications 9 (2018) 478
[5] Localized holes and delocalized electrons in photoexcited inorganic perovskites: Watching each atomic actor by picosecond X-ray absorption spectroscopy
Fabio G. Santomauro, Jakob Grilj, Lars Mewes, Georgian Nedelcu, Sergii Yakunin, Thomas Rossi, Gloria Capano, André Al Haddad, James Budarz, Dominik Kinschel, Dario S. Ferreira, Giacomo Rossi, Mario Gutierrez Tovar, Daniel Grolimund, Valerie Samson, Maarten Nachtegaal, Grigory Smolentsev, Maksym V. Kovalenko, and Majed Chergui. Structural Dynamics 4 (2017) 044002
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