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Lun. 14/10/2019 11:00 Salle des Séminaires, Bâtiment 21, Etage 4 (à confirmer) LOURENÇO-MARTINS Hugo (Göttingen University) Measuring optical excitations at the nanoscale with structured-electron spectroscopies (Nanostructures quantiques propriétés optiques) Electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) consists in sending fast electrons onto a nano-material and analyzing the energy losses undergone by these electrons. During the last decade, STEM-EELS became a privileged technique to study optical or electronic excitations at the nano-scale (e.g. plasmons [1], excitons [2] or surface-phonons [3]) as it provides both the spectral and spatial resolutions required to explore these type of phenomena. However, conventional STEM-EELS suffers from different drawbacks: contrary to optical spectroscopies, its spectral resolution is limited to few meV at the very best, it does not provide any temporal information and it is blind to the phase of the optical excitation. All these issues can be circumvented by structuring the wavefunction of the probe electron in the TEM, either in the spatial domain (e.g. generation of vortex electron [5]) or in the temporal domain (e.g. generation of ultrashort electron wavepacket [6]). Pour plus d'informations, merci de contacter Cassabois G. |
