INSTITUTO DE FISICA LA PLATA
Unidad Ejecutora - UE
congresos y reuniones científicas
Local structure around Fe impurities in rutile TiO2
A. MUDARRA; C. RODRIGUEZ TORRES; L. A: ERRICO
Workshop; 1st Internacional Workshop on Semiconductor Devices Modeling and Electronic Materials & IEEE EDS 2010 Mini-Colloquim; 2010
GEMIDE, Facultad de Ingenieria
Conferencia invitada.Expositor: L. A. Errico Impurities play a fundamental role in semiconductor physics. When semiconducting oxides are doped with appropriate impurities it can develop new and unexpected physical properties, which could have important technological applications. In all cases, the impurity-induced properties strongly depend on the electronic structure of the host-impurity system, which is in turn sensitive to the electronic and structural distortion induced by the impurity on the crystal lattice. Thus, the understanding and accurate determination of those distortions is of paramount importance, but this is not a simple task and the detailed understanding of the electronic structure of doped semiconductors is in many cases still an unresolved problem. TiO2 is one of the most investigated single crystalline systems in the surface science of metal oxides. This oxide is used as a photocatalyst, in solar cells, as a gas sensor, as a white pigment in paints and cosmetics, as a corrosion-protective coating, as an optical coating and plays an important role in bio-implants and earth sciences, among others. TiO2 is also of significant interest in magnetism. Several oxide-based dilute magnetic semiconductors (DMS) have been reported to be robust room temperature ferromagnets. In particular, the Co-doped TiO2 system, the first reported to be ferromagnetic, has received much attention. However, contradictory experimental as well as theoretical results were obtained, and it is uncertain whether the ferromagnetic signal (FM) found in some cases is intrinsic or comes from extrinsic magnetic phases. Conjectures were usually based on macroscopic experimental results but relatively little attention was given to the local structure around the dopants. Knowledge of the local environment of the dopant is essential to understand the mechanisms giving rise to magnetic order in these compounds. We present an investigation of Fe-doped TiO2 rutile thin films. In order to characterize these samples we used x-ray absorption experiments, 57Fe Mössbauer spectroscopy and magnetometry. Results from iron K-edge near-edge and extended x-ray absorption fine structure confirm that Fe3+ replaces Ti4+ in the TiO2 structure increasing the metal-anion bond length. Combining these results with ab initio calculations, which provide the structural relaxations and the hyperfine parameters at the Fe site, we were able to characterize the local structure of Fe in rutile TiO2 unambigously. The result for structural, hyperfine and magnetic properties calculated using density-functional theory, if oxygen vacancies are present in the ironoxygen octahedral. The role of the vacancies in the magnetic ordering and the results for Fe in anatase TiO2 and rutile SnO2 are also discussed.