Tailoring of morphology and orientation of LaNiO3 films from polymeric precursors

The aim of this work was to prepare lanthanum nickel oxide (LaNiO₃, LNO) thin films of different morphology and orientation. The precursor solutions were prepared by a chemical method from citric salts of lanthanum and nickel. Films were deposited using spin-on technique on Si (1 0 0) substrates. Tailoring of the films orientation and morphology has been attained through two thermal treatment processes with different heating devices: tubular furnace (process 1) and hot plate (process 2). Films were annealed at 600 and 700 °C, with heating rates: 20 °C/min (process 1) and 1 °C/min (process 2). Annealing times were from 30 min to 20 h. LNO films were characterized by AFM and X-ray diffraction analysis. Depending on the heating process applied, the obtained films showed very different structures, from completely amorphous to well crystallized and highly oriented. Films treated by process 1 were polycrystalline, had smaller oval grains and lower roughness parameters than films heated on a hot plate. Due to the low heating rate and heating from the substrate side, films obtained through process 2 were highly (1 1 0) oriented with elongated grains aligned along one direction.