Film microstructure-deposition condition relationships in the growth of epitaxial NiO films by metalorganic chemical vap
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Film microstructure-deposition condition relationships in the growth of epitaxial NiO films by metalorganic chemical vapor deposition on oxide and metal substrates Anchuan Wang, John A. Belot, and Tobin J. Marks Science and Technology Center for Superconductivity, The Materials Research Center, and the Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113 (Received 27 March 1998; accepted 26 August 1998)
High-quality epitaxial or highly textured NiO thin films can be grown at temperatures of 400–750 ±C by low-pressure metalorganic chemical vapor deposition (MOCVD) on MgO, SrTiO3 , C-cut sapphire, as well as on single crystal and highly textured Ni (200) metal substrates using Ni(dpm)2 (dpm dipivaloylmethanate) as the volatile precursor and O2 or H2 O as the oxidizer/protonolyzer. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive detection (SEM/EDX), and atomic force microscopy (AFM) confirm that the O2 -derived NiO films are smooth and that the quality of the epitaxy can be improved by decreasing the growth temperature and/or the precursor flow rate. However, low growth temperatures (400–500 ±C) lead to rougher surfaces and carbon contamination. The H2 O-derived NiO films, which can be obtained only at relatively high temperatures (650–750 ±C), exhibit slightly broader v scan full width half-maximum (FWHM) values and rougher surfaces but no carbon contamination. Using H2 O as the oxidizer/protonolyzer, smooth and highly textured NiO (111) films can be grown on easily oxidized single crystal and highly textured Ni (200) metal substrates, which is impossible when O2 is the oxidizer. The textural quality of these films depends on both the quality of the metal substrates and the gaseous precursor flow rate.
I. INTRODUCTION
Nickel oxide thin films have recently drawn considerable attention for applications as diverse as battery electrodes,1 electrochromic smart windows,2–7 biasing layers in magnetoresistive heads and spin valves,8–15 and as a transparent conducting oxide.16–18 In addition, it has been reported that NiO thin films are compatible with the high temperature superconductor, YBCO (YBa2 Cu3 O72x ),19 and thus represent a promising candidate for buffer layers in coated conductor applications. Because of this wide range of potential applications, a variety of NiO thin film deposition techniques have been investigated, including sputtering,2,5,7,11–14,16 pulsed laser deposition,3 reactive evaporation,20 spray pyrolysis,17 thermal deposition,3 and metal-organic chemical vapor deposition (MOCVD).4,9 In these reports, the NiO films obtained are predominantly amorphous or randomly oriented polycrystalline. Among the various deposition techniques, MOCVD, with precise control over film thickness and composition, high deposition rates, conformal coverage, and low deposition temperatures, would appear to be ideally suited for growth of highly oriented or epitaxial NiO films for coated conductor applications. To this end, we
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