Tilted domain matching epitaxy as an effective strain-relief mechanism in highly mismatched MgO/sapphire heterostructures

Epitaxial growth of MgO thin films on R-plane sapphire substrate was investigated through both experimental and theoretical approaches. X-ray diffraction shows a 002 -oriented MgO layer exhibiting a characteristic tilt of about 5° relative to the 01 1 ¯ 2 sapphire planes. To clarify the origin of this inclination, a geometrical model based on Domain Matching Epitaxy (DME) was developed, considering atomic configurations capable of minimizing interfacial strain through tilted growth. The simulations predict a theoretical tilt angle of 4.76°, in excellent agreement with the experimental value. The influence of the deposition temperature was also modeled and experimentally validated, showing that strain-free configurations occur near 550°C, resulting in optimal crystalline quality. This consistent theoretical–experimental correlation provides direct evidence that tilted growth acts as an intrinsic strain-relief mechanism in high-mismatch oxide heteroepitaxy, offering predictive insight into the orientation control of epitaxial oxide thin films.