Seeded Epitaxial Growth of PbTiO3 Thin Films on (001) LaAlO3 using the Chemical Solution Deposition Method

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Abstract
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 || [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.