Creixement epitaxial de pel·lícules fines d’òxids funcionals complexos per mètodes químics ecològics i sostenibles
- Autores: Wang Hailin
- Directores de la Tesis: Narcís Mestres Andreu (dir. tes.), Benjamín Martínez Perea (codir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2020
- Idioma: catalán
- ISBN: 9788449098598
- Tribunal Calificador de la Tesis: Amílcar Labarta (presid.), José Santiso López (secret.), Adrián Carretero Genevrier (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia de Materiales por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Perovskites oxides are of strong interest due the huge potential range of applications they offer with a particularly simple structure, such as spintronics, magneto-optic devices, or catalysis, and most of these applications require the use of thin films and heterostructures. Most of the electronic properties of perovskites are determined by the physics associated with the transition metal and the corner-sharing oxygen anions of the BO6 octahedra therefore, in double perovskite structures, the ordered arrangement of cations in the B-site position is of major relevance.
Chemical solution deposition (CSD) techniques are promising methodologies to achieve epitaxial oxide thin films combining high performance with high easy scalability, environment friendly fabrication and low cost. In this thesis, the polymer-assisted deposition (PAD), an aqueous CSD method, is used to prepare derivatives of lanthanum manganite perovskite films, including La0.92MnO3, La0.7Sr0.3MnO3, La2CoMnO6 and La2NiMnO6 films on SrTiO3 and LaAlO3 substrates. La0.92MnO3 and La0.7Sr0.3MnO3 display ferromagnetic metallic conducting properties, La2CoMnO6 and La2NiMnO6 are ferromagnetic insulating. All these films have Curie temperatures near room temperature.
Firstly, we introduced the basic concepts related to perovskite oxides, including the structure and the magnetic properties, and the methods to grow oxide thin films. Secondly, more detailed processes of PAD method and characterizations will be presented. The third part is a compilation of articles of the La0.92MnO3, La2CoMnO6 and La2NiMnO6 films. All the films were prepared by PAD method. The thermal behavior of the mixed metal polymer precursor solution was traced by combining differential scanning calorimetry and thermogravimetric analysis. The structural features were studied by X-ray diffraction. The thickness was measured with X-ray reflectivity. The surface topography of the films was measured by AFM. Static magnetic properties were measured using a SQUID magnetometer. The scanning transmission electron microscopy (STEM) measurements together with electron energy loss spectroscopy (EELS) was used to confirm the full Co/Mn cationic ordering in La2CoMnO6 films, and ALBA synchrotron radiation facilities were used to investigate the disordering in La2NiMnO6 films. The dynamic magnetic properties of La0.92MnO3 thin films and La0.92MnO3/Pt bilayers as a function of temperature were studied by using a ferromagnetic resonance spectrometer.
The results show that the particular crystallization and growth process conditions of PAD (very slow rate, close to thermodynamic equilibrium conditions) promote high crystallinity and quality of the films, as well as favors spontaneous B-site cationic ordering, almost full B-site cationic ordering can be achieved in La2CoMnO6 while the ordering factor in La2NiMnO6 films is around 80%. The La2CoMnO6 and La2NiMnO6 samples prepared by rapid thermal annealing (RTA) have similar magnetic properties to the counterpart films prepared by using conventional annealing processes, showing only slight differences in the microstructure. On the other hand, ferromagnetic resonance (FMR) measurements in La0.92MnO3 films and La0.92MnO3/Pt bilayers indicate a clear increase of the magnetic damping in the later, which may be indicative of the transfer of spin momentum from La0.92MnO3 to the Pt layer by spin pumping. This fact demonstrates that PAD technique allows obtaining complex oxide thin films of high microstructural quality suitable for spintronics applications.
Our results make evident the CSD-PAD method can be competitive with physical methods allowing obtaining complex oxide epitaxial thin films of high quality. In particular, the growth conditions of PAD are prone to promote spontaneous B-site cationic ordering in double perovskite oxide.
