Microstructural evolution of Fe/Ti multilayers submitted to in situ thermal annealing

Abstract

The Fe/Ti multilayers of nominal bilayer thickness of 4.0, 8.0 and 18.0 nm with alternating Fe and Ti sublayers thickness ratio of 1:1 were deposited by direct current magnetron sputtering on Si(100) substrates. The bilayer thickness of as-deposited Fe/Ti multilayers was measured as a modulation wavelength of 4.8, 8.5 and 19.0 nm, respectively, by small angle X-ray diffraction and cross-sectional transmission electron microscopy (XTEM). The three Fe/Ti multilayers were composed of pure metallic α-Fe and α-Ti according to wide angle X-ray diffraction and selected area diffraction. The Fe/Ti multilayers were in situ submitted to thermal vacuum annealing at the temperatures ranging from 523 K to 723 K for the annealing time of 3 h. With annealing at the lower temperature of 523 K, the intermetallic FeTi appeared in the Fe/Ti multilayers with small modulation wavelength of 4.8 nm. At 623 K, the intermetallic FeTi was formed with modulation wavelength of 8.5 nm. At the higher temperature of 723 K, the intermetallic FeTi was detected with modulation wavelength of 19.0 nm. The modulation wavelength of the Fe/Ti multilayers remained during the thermal annealing. The mixture of intermetallic FeTi and α-Fe phase was observed in the extended Fe sublayer of the Fe/Ti multilayers annealed at 723 K by XTEM, correspondingly the remaining Ti sublayer was obtained as a thinned sublayer. Coexistence of the intermetallic FeTi, α-Fe and α-Ti phases indicated that the dynamic factors have control of the intermixing between the Fe and Ti sublayers in the Fe/Ti multilayers during the thermal annealing.