Kinetics of intermetallic phase formation in multilayer Al/Pt thin films

https://doi.org/10.1016/j.jallcom.2025.185110

Complex investigations of a solid-state reaction process were carried out in bilayer and multilayer thin films of Al/Pt and (Al/Pt)₁₅ by the methods of simultaneous thermal analysis, transmission electron microscopy, in situ electron diffraction, and X-ray diffraction. The solid-state reaction between the aluminum and platinum layers was found to start with the formation of an amorphous a-Al₂Pt phase. The sequence of the phase formation in the solid-state reaction was determined to be the following: Al+Pt→a-Al₂Pt→Al₃Pt₂→Al₂₁Pt₈→Al₄Pt. Thermokinetic modeling of the solid-state reaction was made in the Al/Pt films under study. The “An” type of reaction (n-dimensional formation of grains followed by crystallite growth) was shown to most accurately correspond to the formation of the a-Al₂Pt phase. The formation of the Al₃Pt₂ phase was revealed to occur in two sequential stages: the first stage corresponds to the “Bna” type of reaction (a chain mechanism of grain formation followed by fast crystallite growth), while the second stage belongs to the “R3” type of reaction (three dimensional diffusion along grain boundaries and/or a reaction on grain boundaries which proceeds according to the type of a contracting sphere). With regard to the Al₂₁Pt₈ and Al₄Pt phases, their formation process can be best described by a kinetic model which consists of two parallel reactions. The “An” type of reaction corresponds to the formation of the Al₂₁Pt₈ phase, with the “Cn-Х” type of reaction (a reaction with autocatalysis with grain formation following the chain mechanism) corresponding to the formation of the Al₄Pt phase. Kinetic parameters of the phase formation for a-Al₂Pt, Al₃Pt₂, Al₂₁Pt₈ and Al₄Pt, were determined, with those for Al₂₁Pt₈ and Al₄Pt found for the first time.