Effect of interface morphology on intermetallics formation upon annealing of Al–Ni multilayer

Abstract

Following Benes rule, the initial phase formed at interface of Al–Ni multilayer on annealing is Al3Ni. On further annealing it should give rise to intermetallics Al3Ni2, AlNi and AlNi3, gradually increasing in Ni content. Using X-ray and polarized neutron reflectivity (PNR) we studied the depth dependent structure and magnetization of as-deposited and annealed Al–Ni multilayer, with thickness ratio of Al:Ni equal to 1:2 giving an overall atomic stoichiometry of 1:3 for Al:Ni. We identified asymmetric initial alloy phase formation at two interfaces, i.e. Ni on Al (Ni/Al) and Al on Ni (Al/Ni), of Al–Ni multilayer on annealing. The phases are identified as Al3Ni and Al3Ni2 at Al/Ni and Ni/Al interfaces respectively. Our results indicate that the asymmetric alloy formation at interfaces is directly correlated with the interface morphology of as-deposited multilayer. Higher roughness at Ni/Al interface changes the local concentration of elements at interface, which results into change in effective heat of formation of the alloys and thus makes Al3Ni2 more favourable at Ni/Al interfaces. PNR results also suggested that alloy layers are magnetically dead.