Effects of thermal annealing on the texture of La 0.67 Sr 0.33 MnO 3 thin films
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Klaus H. Dahmen Department of Chemistry & MARTECH, The Florida State University, Tallahassee, Florida 32306-4390 (Received 13 November 2000; accepted 10 April 2001)
Thin films of La0.67Sr0.33MnO3 (LSMO) were prepared at 670 °C on LaAlO3 (LAO) and SrTiO3 (STO) substrates by liquid-delivery metalorganic chemical vapor deposition. X-ray diffraction analysis 2/ and pole figure scans showed that the films are epitaxial with (001)LSMO//(001)LAO and (001)LSMO//(001)STO. The crystal structure of LSMO/LAO was indexed as face-centered cubic with a double cell and LSMO/STO as simple cubic. Electron microscopy revealed square facets and elongated grain features. Films heat-treated between 700 and 800 °C on LAO resulted in a structural change, while those on STO showed an increase in texture.
La0.67Sr0.33MnO3 (LSMO), famous for its impressive giant magnetoresistance (GMR) effect has been investigated due to its potential assistance in fuel cells, microelectromechanical system (MEMS) sensors, and other devices.1– 4 The influence of the microstructure on the properties of the LSMO epilayer (perovskite related structure) has been studied.1,3 Deposition on different substrates such as SrTiO3 (STO), MgO, and LaAlO3 (LAO) results in different lattice mismatch at the film–substrate interface which affects strongly its properties.5,6 Post annealed films of La1−xCax MnO3 (018 < x < 0.33) has been found to be critical to the MR properties.7 Here we report on the effects of thermal annealing on the texture of LSMO thin films deposited on LAO(001) and STO(001) single-crystal substrates. The films were deposited by liquid-delivery metalorganic chemical vapor deposition method (LD-MOCVD). Details of the deposition procedures have been described elsewhere;1,2 however, a brief description is given here. The reactor was operated under vacuum and heated to 670 °C with oxygen as the oxidant. The precursors were weighted and dissolved in diglyme with the help of a sonication. The solution was transported by argon to the reactor zone. The total pressure in the reactor was about 5 torr. The films were then heat-treated at 700 and 800 °C under argon/air (760 torr, 50% O2) between 2 and 6 h. The phase analysis was checked by 2/ scan
using Cu K␣ radiation. The in-plane texture was probed by pole figure through a series of scans. The films’ topography was analyzed by scanning electron microscopy (SEM) (JEOL JSM-840, Tokyo, Japan). The LAO(001) and STO(001) substrates were purchased from MTI Co., Richmond, VA and used as received without any modifications. The x-ray diffraction (XRD) 2/ scan of the asdeposited thin LSMO films on LAO is shown on Fig. 1. The films were epitaxially grown with (001)LSMO // (001)LAO and can be indexed as face-centered cubic (FCC) with a double cell lattice parameter. The XRD patterns revealed very small reflections at 32.45° and 58.45°, which correspond to (022) and (311), respectively. These reflections were not observed on the
a)
FIG. 1. XRD 2/ scan of as-deposited thin films of LSMO/LAO heterostructure.
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