Evidence of ω-phase in ion beam sputtered zirconium thin films

Zirconium thin films were sputtered at room temperature with Ar+ ion beam (1200 eV, 80 mA) on different substrates (Si, oxidized Si, amorphous quartz,...). Although classical 2 atom hcp a-phase was expected at normal pressure conditions, present paper proves the occurrence of the high pressure phase of zirconium: three atom hexagonal omega-phase. TEM diffraction patterns and grazing incidence X-ray diffraction spectra clearly show the existence of a phase different from the a-one. The unexpected phase was identified as the omega-one by means of CEEXAFS experiments. Moreover, results show that significant fraction of omega-phase coexists with alpha-grains which present a considerable increase of the interplanar distances. Substrate curvature induced by the deposit reveals an important compressive stress in the film. This residual stress is explained by conditions of non equilibrium maintained during the growth by the continuous ion bombardment of the subsurface region. Annealings performed at 700 degrees C show that the omega-phase relaxes in the alpha-phase. (C) 1999 Elsevier Science S.A. All rights reserved.