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Abstract: The formation mechanism of a high density of nanovoids by annealing amorphous Al2O3 thin films prepared by an electron beam deposition method was investigated. Transmission electron microscopy observations revealed that nanovoids ∼1–2nm in size were formed by annealing amorphous Al2O3 thin films at 973K for 1–12h, where the amorphous state was retained. The elastic stiffness, measured by a picosecond laser ultrasound method, and the density, measured by X-ray reflectivity, increased drastically after the annealing process, despite nanovoid formation. These increases indicate a change in the amorphous structure during the annealing process. Molecular dynamics simulations indicated that an increase in stable AlO6 basic units and the change in the ring distribution lead to a drastic increase in both the elastic stiffness and the density. It is probable that a pre-annealed Al2O3 amorphous film consists of unstable low-density regions containing a low fraction of stable AlO6 units and stable high-density regions containing a high fraction of stable AlO6 units. Thus, local density growth in the unstable low-density regions during annealing leads to nanovoid formation (i.e., local volume shrinkage). [Copyright &y& Elsevier]

Abstract: The composition and temperature dependence of the elastic properties and phase stability of quaternary Ti–Nb–Ta–Zr β-phase alloys with a body-centered cubic structure, developed for biomedical applications, were investigated using their single crystals, in order to clarify the origin of the low Young’s modulus in polycrystals. Transmission electron microscopy observations clarified that α″ martensitic transformation occurred in a temperature range that depended on the β-phase stability below room temperature. Electromagnetic acoustic resonance measurements clarified that the shear moduli c′ and c 44 of single crystals softened upon cooling from room temperature and became rather low near the martensitic transformation start temperature, i.e. the lower limit of β-phase stability. An analysis by the Hill approximation indicates that low c′ and c 44 caused the low Young’s modulus, and thus it is probable that the softening in c′ and c 44 is the origin of the low Young’s modulus. [ABSTRACT FROM AUTHOR]