| Control over defects at interfaces and the associated potentials barriers represent a collective theme, which is pervasive in a wide variety of devices and structures, crossing multiple disciplines - from basic sciences to engineering to applied technologies. With the rapid emergence of multifunctional oxide systems, the analysis and control of dopants and oxygen defects - especially at interfaces - are the most prominent challenges in realizing next generation devices. In this context, the aberration corrected scanning transmission electron microscopy (STEM) represents truly the next frontier in microscopy, promising atomic level analysis of the defects which control the multifunctional properties of materials and devices. In this thesis, for the first time, a synergistic combination of these two emerging intellectual developments is used. This thesis provides a clear and compelling account of the possibility to manipulate dopant and oxygen defects at the atomic-level in SrTiO3. The core of the thesis is dedicated to atomic scale characterization of Grain Boundary (GB) cores using aberration corrected STEM imaging in conjunction with Electron Energy Loss Spectroscopy (EELS).; As a first case study, it is demonstrated that not only is it possible to manipulate the dominating oxygen defects at interfaces to obtain contrasting transport characteristics, but that modern aberration corrected STEM is able to provide a deterministic atomicscale analysis of such defects. It was discovered that the reduced GB is characterized by presence of Ti3+ rich periodic units. The formation of these units is a direct result of electron (left behind by escaping oxygen) localization on Ti atom.; The second case study focuses on transition metal (Mn) enriched GBs. It is demonstrated that by reducing the GB, it is possible to manipulate oxygen vacancy concentration as well as variable valence states exhibited by Mn (as Mn2+ and Mn3+). Aberration corrected STEM imaging and atomic scale EELS confirmed that there were definite changes in GB core structure as well as electronic structure. These changes were due to the localization of electrons on Ti site as well as Mn site.; I believe that the proposed defect design approach and analysis protocol would open new pathways to tailor the electronic properties of next generation devices, with an appropriate control over oxygen defects via solute doping and thermal treatment schemes. |
