Thèses

Mardi 23 Mai 2023 à 14h00.

Novel ultra-dense thin film and alternative micro-structured scintillators for synchrotron X-ray imaging

''Directeur de thèse / thesis director : Christophe Dujardin, Paul Antoine Douissard

Membres du jury / jury members :
Patrice Camy
Paul Antoine Douissard
Christophe Dujardin
Alexandra Pena Revellez
Anne Pillonnet
Audrey Potdevin

Invitée: Thu Nhi Tran Caliste

Résumé / Abstract :
The development of scintillators with high stopping power for high spatial resolution X-ray imaging at synchrotrons has been performed by employing two approaches. The first approach was to grow thin Single Crystalline Films (SCFs) of high density and high effective Z number by Liquid Phase Epitaxy (LPE). This aimed to reach a high spatial resolution while maximizing the absorption efficiency of the films. Before attempting to develop the LPE procedures, the compounds were investigated with a Geant4, Monte Carlo simulation tool, combined with subsequent analytical calculations to evaluate their scintillating spatial response. Ultra high density com- pound, Lu2Hf2O7, and other hafnates have, in this framework, been successfully grown on ZrO2:Y substrates. The atomic structure of the films was confirmed to be iso-structural with the substrate and have a low lattice mismatch. It was observed that various elements could enter the structure, and the flexibility of the hafnate system for LPE growth is thereby realized. The grown films of Lu2Hf2O7 doped with europium were detected to scintillate, however, the substrate itself displays low-intensity emission. The films have a low light output but deliver a good spatial response, validated by MTFs as well as radiography and tomography experiments. The second approach was to grow state-of-the-art SCF scintillators in a micro- structured manner by LPE. The aim was to increase the stopping power by having tall pillars containing light while maintaining a good spatial response. LSO:Tb and GGG:Eu, were grown micro-structured onto laser-treated LYSO:Ce and GGG substrates, respectively. The morphology of the pillars varies depending on the compound and the substrate orientation. The atomic structures and luminescent properties are comparable to their normal SCF counterparts, therefore a proof of concept has been demonstrated.

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