Stability and Structural Characterization of Epitaxial NdNiO 3 Films Grown by Pulsed Laser Deposition
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Stability and Structural Characterization of Epitaxial NdNiO3 Films Grown by Pulsed Laser Deposition Trong-Duc Doan, Cobey Abramowski, and Paul A. Salvador Carnegie Mellon University, Department of Materials Science and Engineering, Pittsburgh, PA, 15213-3890 ABSTRACT Thin films of NdNiO3 were grown using pulsed laser deposition on single crystal substrates of [100]-oriented LaAlO3 and SrTiO3. X-ray diffraction and reflectivity, scanning electron microscopy, and atomic force microscopy were used to characterize the chemical, morphological and structural traits of the thin films. Single-phase epitaxial films are grown on LaAlO3 and SrTiO3 at 625°C in an oxygen pressure of 200 mTorr. At higher temperatures, the films partially decompose to Nd2NiO4 and NiO. The films are epitaxial with the (101) planes (orthorhombic Pnma notation) parallel to the substrate surface. Four in-plane orientational variants exist that correspond to the four 90° degenerate orientations of the film's [010] with respect to the in-plane substrate directions. Films are observed to be strained in accordance with the structural mismatch to the underlying substrate, and this leads, in the thinnest films on LaAlO3, to an apparent monoclinic distortion to the unit cell. INTRODUCTION Thin film deposition of complex oxides having interesting properties, such as ferroelectricity, magnetoresistivity, superconductivity, optical activity, has attracted great attention for the development of advanced and novel devices (see for example [1]). Moreover, thin film deposition has also proven to be an important tool for synthesizing new and metastable phases and for allowing certain strain states to be accessed, which can lead to a variation in the film's structure and properties. Because advanced multilayer structures and complex device architectures require deposition of thin films with controlled structural and physical properties at very small length scales, it is imperative to understand the nature of materials as epitaxial thin films and their difference to their bulk counterparts if many of the potential applications are to be realized. In this communication we describe how the structure of the metastable perovskite oxide NdNiO3 is affected by the growth conditions, underlying substrate, and overall film thickness. The perovskite nickelates, of the stoichiometry ANiO3 (A = Lanthanide, Y), are of interest because of their physical properties, which include a sharp, thermally driven metal-insulator transition. The temperature at which this transition occurs, TMI, is known to be a strong function of the A cation and of external pressure[2-4]. Such electronic properties render these materials useful as metallic electrodes [5, 6] in ferroelectric devices, as optical switches, as bolometers, and as actuators. From a fundamental scientific perspective, the first order metal-insulator transition that occurs is of great interest because it is not a common feature of complex oxides and it is strongly coupled to the structural parameters (bond angles and distances) an
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