Grain Growth and Gold Tracer Diffusion in Thin Films of Nanocrystalline Fe and Fe₉₅Zr₅

Abstract

Nanocrystalline Fe and Fe₉₅Zr₅ thin films with average grain sizes ranging from 5nm to 15nm made by e-beam codeposition have been investigated. The kinetics of grain growth during thermal annealing and 500keV Xe⁺ ion irradiation have been studied using dark-field transmission electron microscopy. In contrast to nanostructured pure elements produced by compaction of ultrafine powders, a considerable grain growth is observed at 673K in thin films of nanostructured Fe, but not in Fe₉₅Zr₅. The tracer diffusion of implanted gold have been investigated in these films and, for comparison, in crystallized, initially amorphous, Fe₈₀Zr₂₀. The broadening on annealing of the approximately Gaussian gold concentration profile was measured by Rutherford Backscattering Spectrometry. The diffusion constant corresponding to the time evolution of the tracer concentration can be expressed as D* = 8.4·10⁻¹⁰ m²/s exp(− 150 kJ mole⁻¹/RT) for Fe₉₅Zr₅ in the temperature region around 800K. The diffusion constant is close to that observed for crystallized Fe₈₀Zr₂₀ and amorphous Ni₆₅Zr₃₅ thin films. This is in contrast to the reported much higher diffusion constants for nanostructured metals made of compacted powders.