Heteroepitaxial growth of lanthanum aluminate films derived from mixed metal nitrates

Epitaxial lanthanum aluminate (LaAlO₃) thin films were deposited on single-crystal substrates by pyrolysis of spin-on mixed nitrate precursors. The films are epitaxial without any second phase. TEM micrographs show that all of these films have pores with sizes ranging from 5 to 30 nm. Grain boundaries are not observed. Selected area diffraction shows that the films are single-crystal-like, despite the porosity. All the films are smooth and crack-free. The precursors first decompose into an amorphous mixture. Heterogeneous nucleation occurs on the lattice-matched, single-crystal substrate surface. The epitaxial films grow upward and consume the amorphous regions. The crystallization temperature of LaAlO₃ is lower for thin films than for bulk samples due to nucleation on the substrate. The crystallization of LaAlO₃ does not exhibit linear growth kinetics. The Johnson–Mehl–Avrami exponent of growth is between 1.4 and 1.5. This deviation from the linear growth model (n = 1) can be attributed to continuous nucleation on the substrate/film interface.