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PROCESSUS ÉLÉMENTAIRES DE NUCLÉATION : UN OUTIL POUR L'ÉTUDE DES TRANSITIONS DE PHASES DANS LES AGRÉGATS

Fabien Chirot 1
1 Agrégats (LCAR)
LCAR - Laboratoire Collisions Agrégats Réactivité
Abstract : "What can be learned from sticking atoms onto clusters ? ". The present work answers (partly) this question. The original design of our experimental apparatus allows controlling the sticking collision of an atom onto a size selected thermalized free cluster. This makes measuring absolute sticking cross-sections possible. We show that, for sodium clusters, the measured sticking cross section's scaling law is not the one predicted by the widely used
geometrical hard-sphere model. This behavior can be partly reproduced using a harpooning model for the sticking collisions. We discuss the inuence of that non-geometrical scaling law for the cross section on the description of the nucleation processes, and in the frame
of the microreversible theories of cluster evaporation.
Another interesting application of controlled sticking collisions is nanocalorimetry. We show that caloric curves can be measured from the number of atoms that can be
stuck onto a cluster. This new nanocalorimetry method allows studying phase transitions in clusters with an accuracy at least as good as the other existing methods'. We prove this by measuring melting temperatures and latent heats of fusion for sodium clusters as small as Na30+. Finally, we discuss these results in the frame of a 2-level model for melting.
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https://tel.archives-ouvertes.fr/tel-00176908
Contributor : Fabien Chirot <>
Submitted on : Thursday, October 4, 2007 - 6:39:58 PM
Last modification on : Wednesday, January 27, 2021 - 4:52:03 PM
Long-term archiving on: : Thursday, September 27, 2012 - 12:51:04 PM

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  • HAL Id : tel-00176908, version 1

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Fabien Chirot. PROCESSUS ÉLÉMENTAIRES DE NUCLÉATION : UN OUTIL POUR L'ÉTUDE DES TRANSITIONS DE PHASES DANS LES AGRÉGATS. Physique Atomique [physics.atom-ph]. Université Paul Sabatier - Toulouse III, 2007. Français. ⟨tel-00176908⟩

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