Cation vacancies on both sublattices (V(Ti), V(Sr)) have been identified in homoepitaxial pulsed laser deposited SrTiO3 films using high intensity variable energy positron annihilation lifetime spectroscopy (PALS) measurements. Film nonstoichiometry was varied by varying laser fluence. PALS showed that on increasing the fluence above the Ti/Sr∼1 value, the concentration ratio [V(Sr)]/[V(Ti)] systematically increased. Reducing the fluence into the Ti-poor region below resulted in additional vacancy cluster defect formation. Vacancy concentrations greater than ∼50  ppm were observed in all films.

By combining structural and chemical thin film analysis with detailed plume diagnostics and\ud modeling of the laser plume dynamics, we are able to elucidate the different physical mechanisms\ud determining the stoichiometry of the complex oxides model material SrTiO3 during pulsed laser\ud deposition. Deviations between thin film and target stoichiometry are basically a result of two\ud effects, namely, incongruent ablation and preferential scattering of lighter ablated species during\ud their motion towards the substrate in the O2 background gas. On the one hand, a progressive\ud preferential ablation of the Ti species with increasing laser fluence leads to a regime of Ti-rich thin\ud film growth at larger fluences. On the other hand, in the low laser fluence regime, a more effective\ud scattering of the lighter Ti plume species results in Sr rich films

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Accommodation of nonstoichiometry in SrTiO 3 pulsed laser deposited (PLD) films was investigated using positron annihilation lifetime spectroscopy and (scanning) transmission electron microscopy. Increasing PLD laser fluence changed the stoichiometry from Ti to Sr deficient. Cation vacancy defects were detected, and the concentration ratio of Sr to Ti vacancies, [V Sr ]/[V Ti ], was observed to increase systematically in the Sr-deficient region, although no change in the electron microscopy lattice images was detected. Increasing Ti deficiency resulted in the accommodation of SrO layers in planar defects, and in the formation of vacancy cluster defects. A change from V Ti to V Sr defect positron trapping was also detected.

The electrical properties of the metallic interface in LaAlO3/SrTiO3 (LAO/STO) bilayers are investigated with focus on the role of cationic defects in thin film STO. Systematic growth-control of the STO thin film cation stoichiometry (defect-engineering) yields a relation between cationic defects in the STO layer and electronic properties of the bilayer-interface. Hall measurements reveal a stoichiometry-effect primarily on the electron mobility. The results indicate an enhancement of scattering processes in as-grown non-stoichiometric samples indicating an increased density of defects. Furthermore, we discuss the thermodynamic processes and defect-exchange reactions at the LAO/STO-bilayer interface determined in high temperature equilibrium. By quenching defined defect states from high temperature equilibrium, we finally connect equilibrium thermodynamics with room temperature transport. The results are consistent with the defect-chemistry model suggested for LAO/STO interfaces. Moreover, they reveal an additional healing process of extended defects in thin film STO.