Surface/Interface Properties in Oxide Thin Films and Heterostructures Unveiled by Aberration-corrected STEM/EELS

조회수 : 375 등록일 : 2016.05.24 21:41

일시 : 2016.05.25 17:00
소속 : 성균관대학교 에너지과학과
발표자 : 김영민
장소 : R404
 The surfaces and interfaces of perovskite transition metal oxides having correlated electrons exhibit a wide variety of electronic, magnetic and ionic phenomena that is not observed in their bulk counterparts, which make them invaluable for multiple applications in functional nano-devices. Keys to fundamental understanding of the surface/interface behavior of these materials often lie on local and global changes in combination of structural distortions and chemical factors like compositional gradients or oxygen vacancy formation. Local crystallographic scanning transmission electron microscopy (STEM) with advanced aberration correction technique can provide atomic-scale insight into coupled structural order parameter changes with picometer precision and advanced electron energy loss spectroscopy (EELS) techniques can determine chemical identity at a single atom level. In this work, to decouple the relevant chemical and physical mechanisms at the surface/interfaces of (LaFeO3)m/(SrFeO3)n superlattice heterostructures, we used the combined quantitative crystallographic STEM analysis with advanced EELS and density functional theory (DFT) calculations. We will show that polar order in the (LaFeO3)m/(SrFeO3)n superlattice made up of two non-polar oxides can be induced by means of oxygen vacancy ordering, thus suggesting vacancies can lead to new functionalities and possibly new applications. More interestingly, we demonstrate that by creating oxygen vacancies and reducing the surface structure, exotic phase showing a half-metallic ferromagnetic behavior can be stabilized, while the bulk remains antiferromagnetic and insulating.
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