Atomic-Scale Chemical Imaging of Composition and Bonding at Perovskite Oxide Interfaces

Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) has proven to be a powerful technique to study buried perovskite oxide heterointerfaces. With the recent addition of 3$^{rd}$ order and now 5$^{th}$ order aberration correction, which provides a factor of 100x increase in signal over an uncorrected system, we are now able to record 2D maps of composition and bonding of oxide interfaces at atomic resolution [1]. Here, we present studies of the microscopic structure of oxide/oxide multilayers and heterostructures by STEM in combination with EELS and its effect on the properties of the film. Using atomic-resolution spectroscopic imaging we show that the degradation of the magnetic and transport properties of La$_{0.7}$Sr$_{0.3}$MnO$_3$/SrTiO$_3$ multilayers correlates with atomic intermixing at the interfaces and the presence of extended defects in the La$_{0.7}$Sr$_{0.3}$MnO$_3$ layers. When these defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in 5 unit cell thick manganite layers, almost 40\% thinner than the previously reported critical thickness of 3-5 nm for sustaining metallic ferromagnetism below T$_c$ in La$_{0.7}$Sr$_{0.3}$MnO$_3$ thin films grown on SrTiO$_3$.\\[4pt] [1] D.A. Muller, L. Fitting Kourkoutis, M. Murfitt, J.H. Song, H.Y. Hwang, J. Silcox, N. Dellby, O.L. Krivanek, Science 319, 1073-1076 (2008).