Solid-State Reaction in Cu/a-Si Nanolayers: A Comparative Study of STA and Electron Diffraction Data

The kinetics of the solid-state reaction between nanolayers of polycrystalline copper and amorphous silicon (a-Si) has been studied in a Cu/a-Si thin-film system by the methods of electron diffraction and simultaneous thermal analysis (STA), including the methods of differential scanning calorimetry (DSC) and thermogravimetry (TG). It has been established that, in the solid-state reaction, two phases are formed in a sequence: Cu + Si → η″-Cu₃Si → γ-Cu₅Si. It has been shown that the estimated values of the kinetic parameters of the formation processes for the phases η″-Cu₃Si and γ-Cu₅Si, obtained using electron diffraction, are in good agreement with those obtained by DSC. The formation enthalpy of the phases η″-Cu₃Si and γ-Cu₅Si has been estimated to be: ΔH_η″-Cu3Si = -12.4 ± 0.2 kJ/mol; ΔH_γ-Cu5Si = -8.4 ± 0.4 kJ/mol. As a result of the model description of the thermo-analytical data, it has been found that the process of solid-state transformations in the Cu/a-Si thin-film system under study is best described by a four-stage kinetic model R3 → R3 → (Cn-X) → (Cn-X). The kinetic parameters of formation of the η″-Cu₃Si phase are the following: E = 199.9 kJ/mol, log(A, s^-1) = 20.5, n = 1.7; and for the γ-Cu₅Si phase: E = 149.7 kJ/mol, log(A, s^-1) = 10.4, n = 1.3, with the kinetic parameters of formation of the γ-Cu₅Si phase being determined for the first time.