Electronic stopping effects in Fe 60Co 40 films irradiated with high energy ions

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Thin films of the Fe 60Co 40 alloy produced by electron beam deposition under ultrahigh vacuum have been irradiated at liquid nitrogen temperature with high energy ions, 40–186 MeV N ions and 445 MeV Ag ions, on the French accelerator GANIL in Caen. The damage production has been continuously measured as a function of the ion fluence at 77 K using in situ electrical resistivity measurements. The experimental results are analyzed to obtain the defect production efficiency which is the ratio of the experimental to the theoretical displacement cross section. It is found for the lightest ions, 40–186 MeV N, that the defect production efficiency is lower than unity and can be understood on the basis of elastic collision effects only. On the contrary, an important defect production efficiency much higher than unity is observed in the case of the 445 MeV Ag irradiation where the slowing down of ions occurs mainly via inelastic collisions. These observations are new evidence of the spectacular damage creation which can be induced by very high energy deposition in electronic excitation in some metallic targets. A comparison and discussion are made regarding previous damage rate studies for other types of high electronic energy deposition in metallic targets.