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

Abstract

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 Ea=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 Ea, pre-exponential factor A) in the solid-state reaction in the Al/Au thin films, namely, Ea = 0.77 eV, log(A, s−1) = 9 for Al3Au8; Ea = 1.08 eV, log(A, s−1) = 13 for AlAu2; Ea = 1.13 eV, log(A, s−1) = 13 for Al2Au; and Ea = 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.