Seeded Epitaxial Growth of PbTiO 3 Thin Films on (001) LaAlO 3 using the Chemical Solution Deposition Method
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Seeded epitaxial growth of PbTiO3 thin films on (001) LaAlO3 using the chemical solution deposition method J. H. Kima) and F. F. Lange Materials Department, College of Engineering, University of California, Santa Barbara, California 93106 (Received 7 May 1998; accepted 29 October 1998)
Epitaxial PbTiO3 (PTO) thin films were grown on (001) LaAlO3 (LAO) substrates by a preseeded, two-step process via spin coating a Pb–Ti double alkoxide precursor solution. In the first step, a substrate was preseeded with epitaxial islands of PTO by coating the substrate with a very thin layer of the precursor solution and heat treating to 800 ±C for 1 h. The isolated islands had an epitaxial orientation relationship of [100] (001)PTO k [100] (001)LAO . In the second step, another PTO thin film was deposited by spin coating to produce an epitaxial film via grain growth from the seeded islands. The sequence of epitaxy during heating between 400 and 800 ±C was characterized by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy (TEM). This sequence was compared to the case where the LAO substrate was not seeded. Regardless of whether the substrate was seeded or not, perovskite PTO grains nucleated and grew within the pyrolyzed, amorphous film. Films grown on the unseeded substrates were, at best, only highly textured, polycrystalline films. TEM observations showed that only a low number of epitaxial nuclei formed at the substrate/film interface due, apparently, to the large strain energy associated with the large lattice mismatch (,4%) between PTO and LAO. Other, unoriented, PTO grains that nucleated within the amorphous film were not consumed as the epitaxial grains grew larger with increasing temperature. On the other hand, good epitaxial films could be produced when the number density of epitaxial nuclei was increased by first forming a seeded substrate.
I. INTRODUCTION
Considerable attention has been recently paid to the preparation of high quality ferroelectric epitaxial PbTiO3 (PTO) thin films to take full advantage of its anisotropic properties for optical and electronic applications. A number of techniques have been developed to grow epitaxial PTO thin films on single-crystal substrates, such as sputtering,1 chemical vapor deposition,2 pulsed laser deposition,3 and chemical solution deposition.4 Among them, the chemical solution deposition is of particular interest because of its good control of stoichiometry, ease of fabrication, and low temperature synthesis. The chemical solution deposition method is relatively new and requires a greater understanding of the relation between processing and defects in order to optimize film quality. Epitaxy mechanism for the formation of PTO thin films on (001) SrTiO3 (STO) single-crystal substrates was reported by Seifert et al.4 At room temperature, PTO has a tetragonal structure of which lattice parameters are a 0.3904 nm and c 0.4152 nm (cya 1.064), and a Curie temperature of 4
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