The thermal stability of the metastable fcc Zr1 - xAlxN thin films has been investigated by heating the samples in ultra high vacuum (P < 10- 7Pa). For this purpose, two films with chemical composition Zr0.65Al0.35N and Zr0.57Al0.43N were grown by reactive magnetron sputtering. The films were heated for duration of 60 min between 400-850 °C by steps of 50 °C. The structural evolution of the annealed films has been investigated by using X-ray diffraction (XRD), transmission electron spectroscopy (TEM) and by atomic force microscopy (AFM). Results show that up to annealing temperature of 600 °C the pristine structural and mechanical properties of all the films are retained. At annealing temperatures above 600 °C, important structural modification result as deduced from the shift of the XRD peaks towards the low 2θ values indicating changes in the unit cell dimension. Structural modifications are accompanied by hardness enhancement. In Zr0.57Al0.43N films annealed at 850 °C, chemical analysis by X-ray energy dispersive spectrometry evidenced Al-rich regions inhomogeneously distributed in the plane of the film. The results are discussed in terms of the transformation of the fcc Zr1 - xAlxN structure in a two-phase system composed of Al-poor Zr1 - xAlxN and low crystallized h-AlN via spinodal decomposition. © 2005 Elsevier B.V. All rights reserved.
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