Thèses

Jeudi 6 Octobre 2022 à 14h00.

Synthesis, high pressure behaviour and metastable phases of SixGe1−x alloys

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Directeur de thèse / thesis director :

Vittoria Pischedda, Maître de Conférences, Université Lyon 1

Membres du jury / jury members :

Natalia Dubrovinskaia, Professeure des Universités, University of Bayreuth, Germany Rapporteur
Alexandre Courac, Maître de conférence, Sorbonne universités, Paris Rapporteur
Fannie Alloin, Directrice de Recherche CNRS, INP, Grenoble Examinatrice
Patrice Melinon, Directeur de recherche CNRS, Université Lyon 1 Examinateur
Panczer Gerard, Professeur des universités, Université Lyon 1 Examinateur
Neeraj Sharma, Professeur associé , New South Wales University, Australia Examinateur

Résumé / Abstract :

Understanding the transition pathway toward metastable phases in SiGe alloys is a key issue for future generations of semiconductor and energy-related technology. High pressure techniques have proven to be a very efficient method of exploring new phases and properties in germanium and silicon, leading to the discovery of a large number of metastable phases with exotic properties. However, there is only a few exper- imental reports on the high-pressure behaviour of SixGe1−x alloys, mainly due to the difficulty to synthesize homogeneous SiGe alloys of good quality. In this study, we first present synthesis pathways toward homogeneous polycrystalline SiGe alloys of different compositions using arc melting and high temperature treatments. Then, we report the high pressure behaviour of Ge and SiGe alloys studied using Paris-Edinburgh press and diamond anvil cells coupled with in-situ characterization techniques such as Raman spectroscopy and X-ray diffraction. Upon compression, the behaviour of the stable SiGe diamond phase is reported along with transition toward the β-metallic phase. During decompression, the formation of new metastable structures named SiGe-R8 and SiGe- BC8 is observed in SiGe alloys. Temperature is discussed as a key parameter to drive the diamond to β-metallic transition in large volume presses, possibly allowing synthesis of large quantities of metastable phases. The experimental results are discussed in comparison to those reported in the literature and using DFT simulations.

Keywords : [SiGe alloys, synthesis, high pressure, metastable phase]

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