Elastic constants of beta tungsten thin films studied by picosecond ultrasonics and density functional theory

摘要

Tungsten thin films are used for various applications and sometimes exhibit an A15 structure (beta-W). They have some superior properties in comparison to the bcc structure (alpha-W), such as a higher superconducting transition temperature and larger spin Hall angle. However, elastic constants of beta-W are unclear, which restricts mechanical applications and reliable density-functional-theory calculations. In this study, we synthesized alpha-W, beta-W, and mixed-phase W films and determined their elastic constants by picosecond ultrasonics. We also calculated the elastic constants based on density functional theory and reveal that beta-W has a larger elastic anisotropy and smaller shear modulus. Our calculation further indicates a stable stacking faulted beta-W, which leads to a monoclinic structure.