Hi-res Enfina EELS explains conductivity in oxide interfaces
In a report entitled Metallic and Insulating Oxide Interfaces Controlled by Electronic Correlations (Jang, et al) published in the February 2011 issue of Science, the investigators used Gatan's high-resolution Enfina®ER EELS spectrometer to study the influence of oxide electronic properties on the formation of two-dimensional electron gases at complex oxide interfaces.
By growing a single atomic layer of a rare earth oxide in a strontium titanate matrix, a two-dimensional structure is created. Depending on the rare earth selected, the layer can be an insulator (Sm, Y) or a conducting 2-D electron gas (La, Pr, Nd). Using a dedicated cFEG STEM and special high-vacuum, high-resolution Gatan Enfina®ER EELS spectrometer, the authors showed that charge transfer is not reason for the change in conductivity. Rather than charge transfer, it is the strength of electronic correlations that dictates the transport properties of oxide interfaces.
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Image: Figure 3: STEM and EELS analysis. (A) High-angle annular dark field (HAADF) image of a 10-uc SrTiO3/1-ML LaO film grown on SrTiO3. The rectangular box represents the region of EELS line scans. (B) EELS spectra of T-L2,3 and O-K edges obtained from 2D line scans across the interface shown in (A). The spacing along the line scan between consecutive EELS spectra is 2.8 Å. The spectra at the LaO layer are highlighted by thicker lines. For the spectra for Ti L2 and L3 edges, peak broadening and less pronounced peak splitting at the interface are clearly observed. (C) HAADF images of 10-uc SrTiO3/1-ML LaO/SrTiO3 and 10-uc SrTiO3/1-ML SmO/SrTiO3 heterostructures. Both samples show no obvious defects or dislocations, indicating coherent interfaces. (D) Selected area Ti-L2,3 EELS spectra obtained at the interfaces for 10-uc SrTiO3/1-ML LaO/SrTiO3 and 10-uc SrTiO3/1-ML SmO/SrTiO3 heterostructures. The arrow is a guide for comparison.
Metallic and Insulating Oxide Interfaces Controlled by Electronic Correlations.
Science 18 February 2011: Vol. 331 no. 6019 pp. 886-889. DOI: 10.1126/science.1198781.
H. W. Jang1, D. A. Felker2, C. W. Bark1, Y. Wang3, M. K. Niranjan3, C. T. Nelson4, Y. Zhang4,5, D. Su6, C. M. Folkman1, S. H. Baek1, S. Lee1, K. Janicka3, Y. Zhu6, X. Q. Pan4, D. D. Fong7, E. Y. Tsymbal3, M. S. Rzchowski2, and C. B. Eom1
1Department of Materials Science and Engineering, University of Wisconsin–Madison, Madison, WI 53706, USA. 2Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA. 3Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska–Lincoln, Lincoln, NE 68588, USA. 4Department of Materials Science and Engineering, University of Michigan–Ann Arbor, Ann Arbor, MI 48109, USA. 5National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, P.R. China. 6Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA. 7Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA.
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