Interdiffusion in composition-modulated copper-gold thin films

Vapor-deposited Cu-Au thin films were produced containing composition modulations with wavelengths between 8 and 26 Å. The modulations produced satellite peaks in the x-ray diffraction patterns. Amplification factors and the corresponding diffusion coefficients were obtained by measuring the decay rate of the satellite intensities. The amplification factor reached a maximum at 17 Å and decreased at both shorter and longer wavelengths. Interdiffusion coefficients between 10−21 and 10−19 cm2/sec were measured over the temperature range 200–260 °C. The effective diffusion coefficient is linearly dependent on the function B2(λ) for λ≳10 Å. From the wavelength dependence of the measured diffusivities, a gradient-energy coefficient of −4.7×10−6 erg/cm was obtained and is in good agreement with theoretical estimates. These experimental results were compared with the predictions from a proposed model for diffusion on cubic lattices.