X-RAY-DIFFRACTION CHARACTERIZATION AND SOUND-VELOCITY MEASUREMENTS OF W/NI MULTILAYERS

We present detailed structural characterization and shear elastic constant measurements of sputtered W/Ni multilayers. Structural refinement of the reflection x-ray-diffraction spectra was used to determine the out-of-phase lattice spacings of the constituent layers. The Ni(111) lattice spacing expands almost-equal-to 3% and the W(110) lattice spacing is constant with decreasing modulation wavelength LAMDA down to LAMBDA almost-equal-to 30 angstrom. Transmission x-ray diffraction was used to determine the in-plane structure. The W layers undergo an anisotropic contraction in plane with the [002] directions contracting almost-equal-to 2% and the [110BAR] remaining constant with decreasing LAMBDA. The Ni [220BAR] expands almost-equal-to 1.5% with decreasing LAMBDA. The Ni layer expands both in plane and out of plane, contradicting Poisson ratio arguments relating in-plane and out-of-plane strains. Below LAMBDA = 35 angstrom the multilayers undergo a structural transition in which both layers transform into a random close-packed structure. The shear velocity decreases almost-equal-to 22% with decreasing LAMBDA down to the disorder transition and then is LAMBDA independent. The results imply that there is a correlation between the origin of the elastic anomalies and amorphization.