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In this Thesis, a study of the electronic structure of two Ti-based oxidesystems, TiO2 thin films and the ultra-thin LaAlO3-SrTiO3 (LAO-STO)heterojunctions, is given. A weak room-temperature ferromagnetism (FM) has beendetected in slightly reduced TiO2 thin film and in other oxides; as thesematerials are insulating closed-shell systems, this phenomenon has beenclassified as "d0 magnetism". Since this magnetism could be related to thegrowth process and to the presence of defects (oxygen vacancies, VO), ananalysis of Ti electronic states (especially of Ti3+ energy levels) ismandatory. The first part of this work is devoted to the magneticcharacterization of a set of TiO2 and N-doped TiO2 samples, together with theanalysis of Ti 3d-related states carried out with X-ray photoemission (XPS) andresonant photoemission (ResPES). The hypothesis of clustered VO as the sourceof FM is then discussed in the light of the experimental and theoreticalresults. Another interesting oxide system in which the stoichiometry of Ti ionsplay a fundamental role is the LAO-STO interface. In fact, while LAO and STOseparately are two band insulators, the interface created by growing LAO on thetop of STO (001) has found to become metallic, hosting a 2D electron gas. Thesecond part of this Thesis is devoted to the study of conductive and insulatingLAO-STO interfaces, carried out by XPS, X-ray absorption (XAS) and with ResPES.The sample stoichiometry is evaluated through a comparison with LAO and STOsingle crystals. A resonance enhancement of the conductive Ti states,associated to Ti3+ ions, is reported and compared to theoretical calculations.On the basis of these results, the origin of metallic states in ultra-thinLAO-STO interfaces is properly addressed. In addition, a characterization ofthe structural disorder at the interface is shown, carried out withangle-resolved XPS.

Electronic structure of TiO2 thin films and LaAlO3-SrTiO3 heterostructures: the role of titanium 3d1 states in magnetic and transport properties