SOLID-STATE AMORPHIZATION REACTION IN SPUTTERED AND EVAPORATED NI/ZR MULTILAYER FILMS

Ni/Zr multilayer films with single-layer thicknesses of a few hundred nanometres were prepared by electron beam evaporation and by DC magnetron sputtering. The films were subsequently annealed under high-vacuum conditions at temperatures between 570 and 640 K where the progress of the solid state amorphisation reaction was monitored by in situ measurements of the electrical conductivity. From these measurements the interdiffusion coefficient D was derived. The samples were characterised by X-ray diffraction with Cu K alpha 1 radiation in Seemann-Bohlin geometry and Rutherford backscattering with 25 MeV 16O ions. Analysis of X-ray diffraction patterns shows that the Zr layers of evaporated samples are under tensile stress, whereas those of sputtered samples are nearly unstrained or under a small compressive stress. In sputtered films, D is about an order of magnitude smaller than in comparable evaporated films which is interpreted as a result of the different stress states. These results agree with the interpretation of the author's recent irradiation experiment. A correlation between the Zr crystallite size and D is found such that D decreases with increasing crystallite size. X-ray patterns also indicate that the nucleation of the amorphous phase depends on the crystallographic orientation in the Zr layers.