Catalina RUANO MERCHAN: Synthesis and characterization of 2D complex oxide thin films in the SrTiO3Pt(111)/Al203(0001) system

Abstract:
The formation of 2D dodecagonal quasicrystalline oxides (OQC), as related approximant phases were recently reported in thin films derived from BaTiO3 or SrTiO3 perovskites deposited on (111)-oriented Pt single crystal. These 2D structures add novel functionalities to the ultra-thin films of ternary oxides supported on metals when approaching the 2D limit. Here, we use a thin film stacking approach in which the single crystal is replaced by a Pt (111) buffer layer, deposited by MBE on an Al2O3(0001) substrate. An ultra-thin film of SrTiO3 was subsequently deposited by PLD. The film stacking is fully characterized by diffraction (LEED, RHEED, XRD), microscopy (STM, TEM, Nano-SAM) and spectroscopy (XPS, AES) techniques. We report the discovery of three OQC approximants obtained by reducing this system by annealing at high temperature under vacuum conditions. These phases can be described by three different tilings constructed with NGT elements. An atomic model determined by DFT, in agreement with the experimental observations, is proposed for each approximant. This thin-film approach can be useful for exploring the formation of complex 2D oxide phases in other metal-oxide combinations.

Keywords:
2D oxides, Oxide quasicrystal approximants, Thin film stacking, epitaxial growth, LEED, STM.

Composition of the jury:
> Reporters:   
- Mme Anouk GALTAYRIES, Maître de Conférences, Chimie ParisTech - PSL
- M. Rémi LAZZARI, Directeur de recherche, Sorbonne Université
> Examiners:
- M.Wolf WIDDRA, Professeur, Martin Luther Universität, Halle
- Mme Laurence MASSON, Professeure, AixMarseille Université
- M. Yannick FAGOT-REVURAT, Professeur, Université de Lorraine
> Direction of thesis:
- M. Vincent FOURNÉE, Directeur de thèse, Directeur de Recherche, Université de Lorraine
- Mme Muriel SICOT, Co-directrice de thèse, Chargée de recherche, Université de Lorraine
> Guest:
- M. Olivier COPIE, Chargé de recherche, Université de Lorraine