HETEROEPITAXIAL GROWTH OF LANTHANUM ALUMINATE FILMS DERIVED FROM MIXED-METAL NITRATES

Epitaxial lanthanum aluminate (LaAlO3) thin films were deposited on si ngle-crystal substrates by pyrolysis of spin-on mixed nitrate precurso rs. The films are epitaxial without any second phase. TEM micrographs show that all of these films have pores with sizes ranging from 5 to 3 0 nm. Grain boundaries are not observed. Selected area diffraction sho ws that the films are single-crystal-like, despite the porosity. All t he films are smooth and crack-free. The precursors first decompose int o an amorphous mixture. Heterogeneous nucleation occurs on the lattice -matched, single-crystal substrate surface. The epitaxial films grow u pward and consume the amorphous regions. The crystallization temperatu re of LaAlO3 is lower for thin films than for bulk samples due to nucl eation on the substrate. The crystallization of LaAlO3 does not exhibi t linear growth kinetics. The Johnson-Mehl-Avrami exponent of growth i s 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 in terface.