Atomic scale compositions across DyScO/SrTiO interfaces
IFF-News June 1, 2009
by Martina Luysberg, Markus Heidelmann, Lothar Houben, Markus Boese, Tassilo Heeg, Jürgen Schubert, and Martin Roeckerath
It is well known, that the polar discontinuity at the LaAlO3/SrTiO3 interface is accommodated by a charge transfer. In consequence, a two dimensional electron gas is established, which makes the interface between the two insulating materials conductive. In a similar way a conducting interface is expected for the DyScO3/SrTiO3 interface, since LaAlO3 and DyScO3 comprise the same polarity and are band insulators holding similar dielectric constants and energy gaps. However, our electrical measurements on DyScO3/SrTiO3 multilayers reveal insulating behaviour.
High-resolution Z-contrast microscopy and electron energy loss spectroscopy are employed to measure the composition of individual atomic layers across the interfaces in a DyScO3/SrTiO3 multilayer system. An intermixing extending over two monolayers at the interfaces is observed for both, the Dy-Sr sublattice and the Sc-Ti sublattice. Furthermore, the valence of Ti is found to be constant throughout the layer system. Employing the ionic model the composition of the individual atomic layers can be trans¬lated into charges. Consid¬ering compensation between adjacent layers each of the lay¬ers is found to be neutral. Hence, the interfaces are expected to be insulating, which is confirmed by electric measurements. From this result it is concluded that in addition to charge accumulations, intermixing of cations can contribute to counteract the interface dipoles associated with the polar discontinuity.
Martina Luysberg, Markus Heidelmann, Lothar Houben, Markus Boese, Tassilo Heeg, Jürgen Schubert, and Martin Roeckerath: Intermixing and charge neutrality at DyScO3/SrTiO3 interfaces, Acta Materialia 57 (2009) 3192.