Diffusion in Thin Bi-Metal Films of Au–Cu

For the study of diffusion in thin films, bulk methods such as radioactive tracers and sectioning techniques are not readily applicable because of the limited size and thickness of the specimens. This paper describes the use of electron microprobe spectroscopy as the analytical method for the detection of diffusion of Au into Cu films. Films prepared by evaporating 1500 Å of Cu on top of 100 Å Au were examined with the electron beam of the microprobe normal to the Cu film surface. Characteristic AuMα radiation was monitored at various accelerating voltages. This radiation requires a minimum of 2.2 kV for excitation beam voltage. It was not observed for as-deposited sandwich films until the beam was accelerated at 6 kV. The diffusion of Au into the Cu film, after various heat treatments, could be detected by the enhancement of the AuMα intensity and by the decrease of the minimum beam voltage necessary to just detect the characteristic AuMα signal. Data was obtained for the varying annealing conditions and were used to estimate the activation energy for the diffusion of the Au into the Cu film. The average value for E was found to be 0.8 eV ± 0.2 eV.