Solid-state reaction and structure in compositionally modulated zirconium-nickel and titanium-nickel films.

Abstract

Structure and solid-state formation of amorphous alloys have been studied in sputter-deposited zirconium-nickel and titanium-nickel multilayered samples. The as-deposited samples in both systems had an amorphous structure at very small composition-modulation wavelengths (l5 atomic planes of each constituent per layer), and a textured polycrystalline structure at a composition modulation wavelength of 200 atomic planes of each constituent per layer. Intermediate composition-modulation wavelength samples showed differences between the two systems with titanium-nickel samples showing structural coherence in the growth direction. Anneals produced amorphous phase growth in zirconium-nickel multilayered samples for all composition-modulation wavelengths. Amorphous phase growth was also observed in the titanium-nickel sample with a composition-modulation wavelength of 200 atomic planes per layer. The intermediate composition-modulation wavelength titanium-nickel samples which showed structural coherence did not react to form an amorphous phase. This attributed to the lack of an incoherent or disordered interfacial layer to act as a nucleus for amorphous phase growth. The kinetics of the amorphous phase growth process extracted by monitoring resistivity during the anneals revealed that growth followed a square-root-of-time law indicative of diffusion-limited layer growth process. Arrhenius plots of the reaction rate gave activation energies between 1.3 and 1.7 eV. A simple predictive scheme based on the thermodynamic driving force and relative atomic volumes is proposed for indicating whether a solid-state reaction will produce an amorphous phase.