HIGH-RESOLUTION CHARACTERZATION OF LOW-DIMENSIONAL DEFECTS IN SrTiO3

Abstract

<p>Strontium titanate (SrTiO₃) has a wide range of applications in the electronic industry and attracts growing world-widely interest recently because of novel discoveries at its surfaces, interfaces and with selected dopants. The understanding of some of the structural properties of SrTiO₃ and its optical properties have been lagging due to limited characterization techniques available to study single monolayers and dopants in this material.</p> <p>In the present thesis, pure SrTiO₃ single crystals with (2x1) and c(4x2) surface patterns were synthesized and samples (Pr, Al) doped SrTiO₃ were prepared through ion implantation. The atomic and electronic structures of these samples were investigated by various high-resolution imaging and spectroscopic techniques available in an aberration-corrected transmission electron microscope. Particularly, the direct imaging of individual light atoms and vacancies within a bulk material containing heavier elements was demonstrated for the first time via the STEM-annular dark-field (ADF)/annular bright-field (ABF) images. In addition, the first electron energy-loss spectroscopy (EELS) 2-dimensional maps of dopants located in a lattice were obtained. These results provided a solid foundation regarding the mechanism of red light emission in doped SrTiO₃. More importantly, a new experimental approach allowing the effective extraction of weak EELS signals from low-dimensional defects was developed and successfully applied to understand the chemical state and coordination of Ti cations within a single monolayer on a reconstructured SrTiO₃surface and the local defect configurations of injected Pr⁺ and Al⁺ ions within SrTiO₃ single crystals.</p>