Kinetics of diffusion and phase formation in a solid-state reaction in Al/Au thin films

https://doi.org/10.1016/j.jallcom.2024.175500

The kinetics of diffusion and formation of Al-Au intermetallic compounds in a solid-state reaction between layers of aluminum and gold has been studied by the method of in situ electron diffraction. The phase sequence in the solid-state reaction in Al/Au thin films is found to depend on the atomic ratio of aluminum and gold at the initial state. Specifically, with the atomic ratio being Al:Au=2:1, one observes the formation sequence: Al₃Au₈→AlAu₂→Al₂Au, while with the ratio Al:Au=1:4, the sequence is Al₃Au₈→AlAu₄. The observed change in the sequence is explained using the theoretical model of EHF (Effective Heat of Formation). The kinetic parameters of the diffusion of gold through the layer of reaction products in the Al/Au thin films have been determined, including the apparent activation energy of the diffusion E_a=1.17 eV and pre-exponential factor D₀=120 cm²/s. Based on the data obtained by in situ electron diffraction, the kinetic parameters of the phase formation have been estimated by the Kissinger-Akahira-Sunose method. In addition, the kinetic parameters of the formation of the Al-Au intermetallic compounds have been determined (apparent activation energy E_a, pre-exponential factor A) in the solid-state reaction in the Al/Au thin films, namely, E_a = 0.77 eV, log(A, s⁻¹) = 9 for Al₃Au₈; E_a = 1.08 eV, log(A, s⁻¹) = 13 for AlAu₂; E_a = 1.13 eV, log(A, s⁻¹) = 13 for Al₂Au; and E_a = 1.35 eV, log(A, s⁻¹) = 16 for the phase AlAu₄. The kinetic parameters of the formation of the AlAu₄ phase have been estimated for the first time.