STRUCTURAL-CHANGES IN CO ZR MULTILAYERS DURING ANNEALING BELOW THE CRYSTALLIZATION TEMPERATURE/

The local structure of two multilayer systems Co/Zr of different layer thickness during annealing well below the crystallisation temperature was determined by means of extended X-ray absorption fine structure ( EXAFS), performed at Co K edge as well as at Zr K edge. By taking addi tionally wide angle X-ray scattering (WAXS) measurements into consider ation, the averaged EXAFS signal summing up contributions of all exite d atoms in the sample could be separated into parts belonging to the c rystalline and amorphous phases which occurred in the intermediate sta tes of the system Co/Zr simultaneously. The existence and conservation of fibre textures within the crystalline layers and the conservation of periodicity in chemical composition perpendicular to the layer plan e could be proved. Moreover, intensities of the 0002 and 10-11 reflect ions of Zr provided reasonable starting models for fitting crystalline Zr to a subshell model of close lying shells. Coordination numbers ob tained for the crystalline phases of Co and Zr agreed well with the bu lk data. Looking from the position of either absorbing species the ato mic radial distribution was evaluated. Zr neighbours dominated for Zr as well as for Co central atoms. Around Co atoms we found Co at typica l distances of 2.45, 2.78 and 3.06 Angstrom; around Zr the Zr neighbou rs occupied neighbour shells at 3.07 and 3.30 Angstrom. Distances betw een unlike atoms were found to be 2.65 and 2.81 Angstrom. These values describe single symmetric contributions of asymmetric pair distributi ons derived on the basis of multiple Gauss analysis. From EXAFS and WA XS we concluded that the amorphous part of the layer system is initial ly dominated by a Zr-rich phase which competes with a second amorphous phase of an approximate composition Co50Zr50 during the the subsequen t stages. As the reaction proceeds the latter grows while the Zr-rich phase is reduced. (C) 1998 Elsevier Science S.A.