Microstructural characteristics of conductive SrRuO 3 thin films formed by pulsed-laser deposition
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Microstructural characteristics of conductive SrRuO3 thin films formed by pulsed-laser deposition P. Lu Department of Materials Science and Engineering, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801
F. Chu, Q. X. Jia, and T. E. Mitchell Materials Science and Technology Division, MS K765, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 10 February 1997; accepted 10 November 1997
Transmission electron microscopy and high-resolution electron microscopy have been used to study microstructural properties of conductive SrRuO3 films grown by pulsed laser deposition on (001) LaAlO3 and (001) SrTiO3 substrates. It was found that the SrRuO3 films deposited on both substrates consist of mixed domains of [001] and [110] orientations, with orientation relationships that can be described as (i) (001)f k (001)s and [110]f k [100]s and (ii) (110)f k (001)s and [001]f k [100]s , respectively. The SrRuO3 films deposited on SrTiO3 , in particular, were found to have a layered domain structure, with the [110] domain grown initially on the substate, followed by growth of the [001] oriented domain with increasing thickness. The films on SrTiO3 are strained and have a coherent interface with the substrate. The SrRuO3 films deposited on LaAlO3 , on the other hand, contain a high density of structural defects such as stacking faults and microtwins on the (022) planes. Microtwins as large as 50 nm in thickness are observed in the films deposited on LaAlO3 . Possible causes for the observed structural defects in the films are discussed.
I. INTRODUCTION
In recent years, there has been considerable interest in epitaxial growth of conductive oxides for various applications.1–7 In superconducting devices for use in integrated circuits, the conductive oxide films have been used as buffer layers for growth of high-temperature superconducting YBa2 Cu3 O72x (YBCO) thin films and also as normal metals in superconductor-normal metal-superconductor (SNS) junctions.8–12 In ferroelectric nonvolatile memory applications, epitaxially grown conductive oxides have been employed as electrodes, on which epitaxial device structures with excellent properties can be fabricated.13–16 Among the various conductive oxides, SrRuO3 has been extensively investigated recently for thin film applications.7–9,15–17 The material has a GdFeO3 -type orthorhombic structure with lattice constants of a 0.5573 nm, b 0.5538 nm, and c 0.7856 nm. The structure can be considered as a pseudo-cubic perovskite with a lattice constant of ,0.3928 nm. It has a relatively high electrical conductivity (a roomtemperature resistivity of 280 mV ? cm for single crystals), and is thermally and chemically stable and structurally compatible with superconducting, ferroelectric, and high dielectric constant materials. SrRuO3 has been epitaxially deposited by off-axis sputtering and pulsed laser deposition (PLD) on different 2302
J. Mater. Res., Vol. 13, No. 8, Aug 1998
substrates.7–9,15–18 Epitax
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