The effect of C+ implantation on the interdiffusion of Cu/Au and Cu/Ni/Au thin-film structures was investigated at temperatures ranging from 200 to 600 °C, and for different annealing times at 400 °C. For comparison, unimplanted Cu/Ni/Au and Cu/C/Ni/Au thin-film structures were also studied. The implantation of carbon ions has very little effect on the interdiffusion of Cu and Au at the temperatures investigated. For the Cu/C/Ni/Au structure, very little Cu-Au interdiffusion was observed within the temperature range studied. However, spontaneous delamination of C/Ni/Au from Cu occurred at ≥400 °C. This must be due to the poor adhesion of C to Cu which is made worse at these temperatures by the thermal expansion mismatch. X-ray diffraction analysis revealed the formation of intermetallic CuAu compounds after annealing of the implanted and unimplanted Cu/Au and Cu/Ni/Au structures. The mechanisms of diffusion are considered to be associated with this intermetallic alloying, which results in the generation of vacancies that form the diffusion paths. In the case where alloying does not occur, diffusion is therefore limited by solid solubility.