The diffusion of Cu through electron-beam evaporated thin films was studied by monitoring electrical resistance changes, as a function of time, at 343 to 543K. It was found that the activation energy and the pre-exponential factor decreased with increasing Al content:

Ag-5.8at%Al:     D (cm2/s) = 4.96 x 10-14 exp[-0.39(eV)/kT]

Ag-9.2at%Al:     D (cm2/s) = 1.88 x 10-14 exp[-0.35(eV)/kT]

Ag-15.8at%Al:     D (cm2/s) = 3.86 x 10-15 exp[-0.27(eV)/kT]

Ag-18.2at%Al:     D (cm2/s) = 6.00 x 10-16 exp[-0.18(eV)/kT]

However, as a whole, the diffusion coefficient increased with increasing Al content. The enhancement of the diffusion coefficient, with increasing Al content, was attributed to the fact that the concentration gradient and the associated stress gradient at the interface and grain boundaries produced dislocations.

R.Roy, S.K.Sen: Thin Solid Films, 1993, 223[1], 189-95