© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 www.advmat.de www.MaterialsViews.com wileyonlinelibrary.com COMMUNICATION Layer Selective Control of the Lattice Structure in Oxide Superlattices Alex Frano, Eva Benckiser, Yi Lu, Meng Wu, Miguel Castro-Colin, Manfred Reehuis, Alexander V. Boris, Eric Detemple, Wilfried Sigle, Peter van Aken, Georg Cristiani, Gennady Logvenov, Hanns-Ulrich Habermeier, Peter Wochner, Bernhard Keimer,* and Vladimir Hinkov* A large-scale research effort has recently been undertaken to understand and tailor the properties of transition metal oxides (TMOs) by hetero-epitaxial growth. Advances in layer deposi- tion methods have enabled the creation and exploration of novel interface and surface states, metastable crystalline and electronic phases, and low-dimensional electron systems. [1,2] In contrast to most semiconductor heterostructures, TMOs often possess soft structural degrees of freedom, such as tilt distortions of the metal-oxygen octahedra, which facilitate lat- tice relaxation in epitaxial films and superlattices (SLs) and may profoundly influence the electronic structure. Detailed knowl- edge and control of the lattice structure is therefore impor- tant for the prediction, understanding, and manipulation of the electronic properties of TMO heterostructures. Here we present an x-ray diffraction and electron microscopy study of epitaxial LaNiO 3 (LNO) and LaAlO 3 (LAO) films as well as LNO- LAO SLs, which have attracted widespread interest spawned by proposals of orbital reconstructions, superconductivity, and spintronic phenomena. [3–8] Our data indicate that the overall thickness of a SL can serve as a control parameter for the lattice symmetry of its individual components. Specifically, both com- mensurate and incommensurate structures can be realized in LNO-LAO SLs with identical composition, but different thick- ness. This finding provides new perspectives for the creation of misfit layer compounds analogous to the well known Bi-based high-temperature superconductors [9] and thermoelectrics. [10] Pulsed laser deposition was used to grow LNO and LAO films as well as LNO-LAO SLs on single-crystalline, [001]-ori- ented LaSrAlO 4 (LSAO) substrates. Bulk LNO and LAO crys- tallize in the trigonally distorted perovskite structure R ¯ 3c, with pseudocubic ( PC) lattice constants 3.837 and 3.789 Å, respec- tively. The structure of LSAO is tetragonal ( I4/ mmm), with unit cell (u.c.) parameters a = b = 3.756 Å and c = 12.636 Å. LSAO thus applies compressive strain to both components of the SL. The SL bilayer periodicities and total thicknesses ( T) were obtained from specular X-ray diffraction (XRD) patterns, as described elsewhere. [6,11] Here, we report reciprocal space maps (RSMs) to fully char- acterize the lattice strain state and symmetry, and transmission electron microscopy (TEM) patterns to obtain complementary real-space information of the SL structure. We will use PC h, k, l- indexing for both LNO and LAO. RSMs will be shown in units of q x, y,z = 2 π/ d x, y,z , using the substrate reference to define the lattice spacing d x, y,z . Before discussing the data on the superlattices, we pre- sent reference measurements on 100 nm thick LNO and LAO films grown on LSAO. Figure 1a shows a representative RSM in the ( q y , q z )-plane around the (015) reflection of a LAO film. The peaks at (1.673(1),8.239(1)) Å -1 reveal a structure with an in-plane lattice constant matching the one of LSAO (shown as a white solid line) and a c-axis lattice constant of 3.8128(5) Å. Together with the ( q x , q y ) map around (005) shown in Figure 1b, these data demonstrate that the diffraction pattern is composed of single, unsplit Bragg peaks. We also surveyed the diffracted intensity at several accessible half-order positions. Following the Glazer approach, [12] their extinction rules can be used to deter- mine the rotation pattern of the metal-oxygen octahedra. The LAO film exhibited half-order peaks at all ( h/2, k/2, l/2) with h, k, and l odd, except ( h/2 = k/2 = l/2). These selection rules are consistent with octahedral rotations of the kind a - a - c - : equal rotation angles along a and b and different rotation around c, all out of phase. [12] This rotation pattern is described by the monoclinic space group C2/ c, isostructural with LNO films and SLs on different substrates reported elsewhere. [13,14] Within our experimental resolution, no peak splitting was observed DOI: 10.1002/adma.201303483 A. Frano, Dr. E. Benckiser, Y. Lu, M. Wu, Dr. A. V. Boris, Dr. G. Cristiani, Dr. G. Logvenov, Prof. H.-U. Habermeier, Dr. P. Wochner, Prof. B. Keimer, Prof. V. Hinkov [+] Max-Planck-Institut für Festkörperforschung Heisenbergstr. 1, D-70569, Stuttgart, Germany E-mail: b.keimer@fkf.mpg.de; hinkov@physik.uni-wuerzburg.de A. Frano Helmholtz-Zentrum Berlin für Materialien und Energie Wilhelm-Conrad-Röntgen-Campus BESSY II Albert-Einstein-Str. 15, D-12489, Berlin, Germany Prof. V. Hinkov Quantum Matter Institute University of British Columbia Vancouver, B.C., V6T 1Z1, Canada Dr. M. Castro-Colin, Dr. E. Detemple, Dr. W. Sigle, Prof. P. van Aken Max-Planck-Institut für Intelligente Systeme Heisenbergstr. 3, 70569, Stuttgart, Germany Dr. M. Reehuis Helmholtz-Zentrum Berlin für Materialien und Energie Lise-Meitner Campus Hahn-Meitner-Platz 1, D-14109, Berlin, Germany [+] Physikalisches Institut und Röntgen Center for Complex Materials Sys- tems, Universität Würzburg, 97074 Würzburg, Germany Adv. Mater. 2013, DOI: 10.1002/adma.201303483