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Mapping dielectric response and charge distribution on the atomic scale reveals the origin of conductivity at the LAO/STO interface


1C. Cantoni, J. Gazquez, F. Miletto Granozio, M. P. Oxley, M. Varela, A. R. Lupini, S. J. Pennycook, C. Aruta, U. Scotti di Uccio, P. Perna, and D. Maccariello, “Electron transfer and ionic displacements at the origin of the 2D electron gas at the LAO/STO interface: direct measurements with atomic-column spatial resolution,” Advanced Materials, published online: 19 JUN 2012, DOI: 10.1002/adma.201200667.

Text Box:
Atom displacements in proximity of the LAO/STO interface shown by high-angle annular dark field imaging (top), and derived atomic model (bottom). Plots display the local polarization as derived from atomic displacements, and the injected electronic charge determined by the Ti valence as measured by electron energy loss spectroscopy.

A combination of scanning transmission electron microscopy and energy loss spectroscopy at the conducting interface between the insulators LaAlO3 (LAO) and SrTiO3 (STO) provides the first direct experimental evidence of a transfer of electrons from the LAO film to interfacial Ti atoms1. The functional properties of such epitaxial interfaces are important for the development of a new generation of multi-functional nanoscale electronic devices for future ultra efficient, self-adaptive, and fault-tolerant computers, but their physical origin has until now remained a highly controversial subject. A combination of atomic-scale measurements of lattice distortions and of electronic configuration shows that the transfer of charge occurs in response to a strong electric field generated by the interface itself, and finally provides a direct confirmation of the explanation proposed when the phenomenon was first discovered in 2004. In fact, results from state-of-the-art aberration-corrected electron probes with atomic-scale spatial resolution rule out any major contribution from extrinsic defects such as oxygen vacancies in STO.

 Oak Ridge National Laboratory