Determination of anisotropic elastic constants of superlattice thin films by resonant-ultrasound spectroscopy

Superlattice thin films are expected to show elastic anisotropy because of lattice misfits at interfaces among different elements. This study demonstrates that resonant-ultrasound spectroscopy and laser-Doppler interferometry can determine anisotropic elastic constants of superlattice thin films. Mechanical resonance frequencies of a layered specimen composed of a substrate and deposited thin film depend on the elastic constants, mass densities, and dimensions of the substrate and thin film. X-ray diffraction measurement determines accurately the total thiskness of a multilayer thin film. Therefore, the elastic constants of the multilayer thin film can be derived from measured resonance frequencies, provided that mode identification on observed resonance frequencies is achieved. We measure the resonance frequencies by a piezoelectric tripod and identify the vibration modes by measuring the displacement distributions on the specimen surface using laser-Doppler interferometry. We apply the present method to a Co/Pt multilayer [Co (4 Å) Pt (16 Å)] 500 showing the perpendicular magnetic anisotropy. The in-plane elastic constants are larger than those of bulks by 1%-7%. This is attributed to internal strain due to lattice misfit at the Co-Pt interfaces through interatomic anharmonicity. © 2005 American Institute of Physics.Nakamura N., Ogi H., Hirao M., et al. "Determination of anisotropic elastic constants of superlattice thin films by resonant-ultrasound spectroscopy", Journal of Applied Physics, 97(1), 013532 (2005) https://doi.org/10.1063/1.1828221