Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 217-227).

Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 128-139).

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Thesis (Ph.D.)--Texas Christian University, 2006. / Title from dissertation title page (viewed Jan. 5, 2007). Includes abstract. Includes bibliographical references.

Le carbure de silicium est un des materiaux envisages pour des applications nucleaires tels que les reacteurs a fission de 4eme generation et les reacteurs a fusion. Dans ce cadre, le SiC serait soumis a des conditions extremes de temperatures et d’irradiation ainsi qu’a la presence de gaz issus des produits de fission ou d’activation qui necessitent de comprendre comment les proprietes physiques du SiC pourraient evoluer. Dans le present travail nous nous sommes attaches a etudier les phenomenes se deroulant a l’echelle atomique qui modifient la microstructure et peuvent degrader les proprietes macroscopiques. La premiere partie de cette these est consacree a la caracterisation de l’endommagement et notamment des defauts lacunaires crees dans le SiC par irradiation avec des ions lourds a differentes energies et differentes fluences au moyen de la spectroscopie d’annihilation de positons (PAS) complete par la spectrometrie Raman. Les resultats de cette etude mettent en evidence que l’importante perte d’energie electronique associee aux irradiations avec des ions lourds modifie la nature et la distribution des defauts en-dessous de 0.2 dpa. Au-dela, l’impact n’est pas visible. Pour un endommagement a fort dpa en regime de collisions elastiques, l’amorphisation peut etre atteinte. Elle se caracterise par la formation de volumes libres equivalents a l’hexalacune. La deuxieme partie est consacree a l’etude de l’interaction de l’helium avec les defauts lacunaires dans des echantillons de SiC implantes He 50 keV a deux fluences. La distribution des defauts lacunaires etudiee par PAS evolue avec la temperature et deux stades d’evolution majeurs ont ete mis en evidence, celui a plus haute temperature depend de la fluence. Des mesures de thermodesorption ont montre que le second stade coincidait avec la desorption de l’helium. Enfin, des mesures de RBS et NRA en mode canalisee ont permis de localiser l’helium dans la maille cristalline et d’observer qu’une fraction migrait en quittant des sites interstitiels tetraedriques a une temperature correspondante au premier stade. / Silicon carbide is one of the envisaged materials for nuclear applications such as GEN IV fission reactor and fusion reactor. In this framework, SiC will be exposed to extreme temperature and radiation conditions and gas presence coming from activation and fission products. It is needed to better understand how the SiC physical properties will evolve under these conditions. In this work, we have specially focused our studies on the phenomena occurring at atomic scale and which modify the microstructure leading to the degradation of the macroscopic properties. The first part of this thesis is devoted to the damage characterization and especially to the vacancy-type defects created in SiC by heavy ion irradiation at various energies and fluences by using positron annihilation spectroscopy and Raman spectroscopy. The results highlight that the important electronic loss energy associated to high energy heavy ion irradiations modify the defect nature and distribution below 0.2 dpa. Beyond this value, the impact is not visible. For a damage induced at high dpa in the elastic collision regime, the SiC is amorphised and this structure is characterized by the formation of free volume similar to the hexa-vacancy. The second part is focused on the study of helium interaction with vacancy-type defects in SiC samples implanted with 50 keV-He ions at two fluences. First, the defect distribution evolution as a function of the temperature has been studied by PAS and has evidenced two evolution stages depending on the fluence. Then, thermodesorption measurements have shown that the second stage coincide with the helium desorption. Finally, RBS and NRA measurements in channeling mode have allowed us to localize helium atom in crystal structure and to observe that a part of helium migrates from tetrahedral interstitial sites at a temperature corresponding to the first stage one.

No description available.

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

published_or_final_version / abstract / Physics / Master / Master of Philosophy

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy