Composition and Growth-Temperature Effect on the Microstructure of Epitaxial La_1−x Sr_x MnO₃ (x = 0, 0.2) Thin Films on (001) LaAlO₃

La_0.8Sr_0.2MnO₃ (LSMO) and LaMnO₃ (LMO) thin films epitaxially grown on (001) LaAlO₃ substrate at 700 and 800°C were studied using cross-section and plan-view transmission electron microscopy. In both LSMO and LMO films deposited at 700°C, a two-layered structure was observed: a continuous cubic perovskite layer epitaxially grown on the substrate followed by epitaxially grown orthorhombic column nanostructures. The orthogonal nano columns in LSMO were very well defined with a narrow size distribution. The LMO films exhibited a somewhat distorted orthogonal shape for the nanostructured columns and a wider size distribution. LSMO and LMO epitaxial films deposited at 800°C consisted of only a continuous single layer of cubic perovskite. These results reveal that formation of epitaxial column nanostructures in the La_1-xSr_xMnO₃ thin films strongly depends on the growth temperature. Sr substitution on La sites in La_1-xSr_xMnO₃ can improve uniformity of column size distribution and perfection of the orthogonal shape of nano columns.