Formation of intermetallic phases and texture evolution in Ni0.95Mo0.05/Ti multilayer

This study presents a comprehensive investigation of the chemical and structural properties, particularly the texture, of glass/[Ni_0.95Mo_0.05/Ti]_N multilayer systems with period thicknesses ranging from 4 to 20 nm. A combination of X-ray diffraction (XRD), X-ray reflectometry (XRR), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS) was employed for the analysis. A gradual change in the preferred orientation of hexagonal α-Ti crystallites from (002) to (100) with increasing period thickness was revealed, which potentially explains the growth of layer waviness from the substrate to the surface with increase of period thickness. Crystallization of Ni_0.95Mo_0.05 in the form of solid solution was established. The formation of Ni_1-xTi_x intermetallic compounds at the interfaces was shown, with an average stoichiometry of x ≈ 0.5. These presumably comprise a mixture of Ni-rich and Ti-rich intermetallics. As the period thickness increases, crystallization of the intermetallics in the form of mixture of Ni₃Ti and Ti₂Ni as well as refinement (fragmentation) of the grains of the intermetallic compounds was revealed. The results obtained provide insights into the problem of creating sharp interfaces in multilayered systems, which is essential for the development of high-efficient reflective elements for neutron optics as well as for X-ray microscopy in the spectral range of the “water window".