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″-Cu 3 Si → γ-Cu 5 Si. It has been shown that the estimated values of the kinetic parameters of the formation processes for the phases η″-Cu 3 Si and γ-Cu 5 Si, obtained using electron diffraction, are in good agreement with those obtained by DSC. The formation enthalpy of the phases η″-Cu 3 Si and γ-Cu 5 Si 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″-Cu 3 Si phase are the following: E a = 199.9 kJ/mol, log( A , s -1 ) = 20.5, n = 1.7; and for the γ-Cu 5 Si phase: E a = 149.7 kJ/mol, log( A , s -1 ) = 10.4, n = 1.3, with the kinetic parameters of formation of the γ-Cu 5 Si phase being determined for the first time.