Strain Relaxation and Functional Properties of o -LuFeO 3 /SrTiO 3 (001) Thin Films

Orthorhombic LuFeO 3 ( o -LuFeO 3 ) has attracted increasing interest owing to its distinctive multiferroic behavior and tunable optical response. High-quality epitaxial growth, coupled with atomic-scale structural characterization, is indispensable for advancing fundamental understanding and enabling practical device applications. In this study, high-quality o -LuFeO 3 thin films were epitaxially grown on SrTiO 3 (001) substrates via pulsed laser deposition. Comprehensive structural characterization confirms phase-pure, c -axis-oriented films with atomically sharp interfaces. To mitigate lattice mismatch, the films adopt a 45° in-plane rotational alignment, i.e., LuFeO 3 110∥SrTiO 3 100. Geometric phase analysis (GPA) and Burgers circuit reconstruction reveal a periodic network of misfit dislocations and the coexistence of 90° rotational domains originating from symmetry breaking at the heterointerface. Thickness-dependent analyses demonstrate a reduction in the out-of-plane lattice parameter with decreasing film thickness; the critical thickness for misfit dislocation formation lies between 10 and 20 nm, with the 10 nm film remaining nearly fully coherent. The 45 nm-thick films exhibit weak ferromagnetism at room temperature and possess a direct optical bandgap of 2.8 eV. These results provide atomic-scale insights into strain relaxation mechanisms in ferrite-based heterostructures and establish a foundation for the rational design of functional oxide devices.