Enhanced interdiffusion in amorphous Ni–Zr thin films under tensile strain

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Abstract
Amorphous thin films of Ni-Zr have been deposited on different substrates using electron-beam evaporation. The films were compositionally graded and, in order to determine the interdiffusivity [dtilde] the time evolution on annealing of their depth profiles were measured using Rutherford backscattering spectrometry. Owing to the difference between thermal expansions of the film and substrate, strain was induced on heating to the annealing temperature. The observed interdiffusivity at 523 K in Ni-Zr films deposited on single crystals of NaCl, giving a tensile strain in addition to the initial strain, was found to be four to seven times larger than for Ni-Zr films deposited on sapphire, where no or only a small compressive additional strain was built up. The difference between the strain contributions from these substrates was estimated from available thermal expansion data to be 0.8%.