On the Novel Biaxial Strain Relaxation Mechanism in Epitaxial Composition Graded La_1−xSr_xMnO₃ Thin Film Synthesized by RF Magnetron Sputtering

摘要

We report on a novel method to fabricate composition gradient, epitaxial La_1−xSr_xMnO₃ thin films with the objective to alleviate biaxial film strain. In this work, epitaxial, composition gradient La_1−xSr_xMnO₃, and pure LaMnO₃ and La_0.67Sr_0.33MnO₃ thin films were deposited by radio frequency (RF) magnetron sputtering. The crystalline and epitaxy of all films were first studied by symmetric θ–2θ X-ray diffraction (XRD) and low angle XRD experiments. Detailed microstructural characterization across the film thickness was conducted by high-resolution transmission electron microscopy and electron diffraction. Four compositional gradient domains were observed in the La_1−xSr_xMnO₃ film ranging from LaMnO₃ rich to La_0.67Sr_0.33MnO₃ at the surface. A continuous reduction in the lattice parameter was observed accompanied by a significant reduction in the out-of-plane strain in the film. Fabrication of the composition gradient La_1−xSr_xMnO₃ thin film was found to be a powerful method to relieve biaxial strain under critical thickness. Besides, the coexistence of domains with a composition variance is opening up various new possibilities of designing new nanoscale structures with unusual cross coupled properties.