Invited Paper NS-TuM1
Atomic-Scale Studies of Complex Oxide Interfaces Using Aberration-Corrected Z-Contrast Imaging and EELS

Tuesday, October 16, 2007, 8:00 am, Room 616

Interfaces in complex oxide materials have been an enduring theme in materials physics, where the interplay of the reduced dimensionality, proximity effects, as well as surface relaxation, reconstruction and segregation creates interfacial states that are distinct from their bulk counterparts. It has long been recognized that the perovskite oxides provide a unique opportunity to bring materials with diverse and even mutually exclusive properties into intimate contact, thereby creating interfaces with excellent structural and chemical compatibility that potentially can be implemented in novel electronic devices. In recent years, novel techniques have been developed in analytical scanning transmission electron microscopy (STEM) that can be used to directly study the atomic-scale structure-property relationships of interfaces in complex oxides, both at room and LN₂ temperature. In particular, by using aberration-corrected Z-contrast imaging and electron energy-loss spectroscopy (EELS), the structure, composition and bonding can all be characterized directly with a spatial and energy resolution that cannot be achieved by any other technique. Here, we will demonstrate that the combination of aberration-corrected Z-contrast imaging and EELS can be used to analyze a wide range of properties in complex oxide materials, such as CMRs, high-k dielectrics and high-temperature superconductors. In particular, I will concentrate on my recent discovery of the cooperative doping-effect in the high-T_c superconductor YBa₂Cu₃O_7-x (YBCO), where the presence of grain boundaries causes a significant reduction in the critical current density (J_c). I will explain the atomic-level origin of the improved J_c across grain boundaries in Ca-doping YBCO, and propose a number of potential dopants to further improve the materials properties.¹ Further, I will discuss the effects of oxygen vacancy segregation on the dielectric property of ultra-thin SrTiO₃ on GaAs(001)² and conclude with our recent discovery that the Co-ion spin-state in Co-based perovskite oxides can be directly measured by EELS.

¹ Klie, R.F., J.P. Buban, M. Varela, A. Franceschetti, C. Jooss, Y. Zhu, N.D. Browning, S.T. Pantelides, and S.J. Pennycook, Nature, 2005. 435(7041): p. 475-478.
² Klie, R.F., Y. Zhu, E.I. Altman, and Y. Liang, Applied Physics Letters, 2005. 87(14).