Microstructural properties of solution-deposited La_(0.7)Sr_(0.3)MnO_3 and LaMnO_3 thin films

摘要

The microstructural properties of solution-deposited La_(0.7)Sr_(0.3)MnO_3 and npndoped LaMnO_3 films have been studied. Several factors such as the choice of substrate, method of surface cleaning, annealing atmosphere, and precursor solution concentration were considered. Films with smoother surfaces were observed on SrTiO_3 (100) and LaAlO_3 (100) crystals, due to the near matching of the film-substrate lattice constants and thermal-expansion coefficients. In contrast, substrates such as Si (100) yield films with a rougher morphology. Variations in the crystalline quality and surface morphology of the films were demonstrated, simply by altering the precursor solution concentration and the surface condition of substrate. The local structure of the films was studied by Raman spectroscopy, which indicated enrichment in the oxygen content, differing from ideal oxygen stoichiometry (or from films annealed in inert gas atmosphere). This latter effect was shown to be more effective in the case of LaMnO_3, where a structural transition from rhombohedral to orthorhombic was observed by changing the annealing atmosphere from ambient air to pure N_2 gas, and is suggested to be the main origin of the anomalous conductivity increase reported in the literature in air or O_2-annealed manganite films with respect to stoichiometric bulk La_(1-x)(Sr,Ca)_xMnO_3.