ELECTRONIC STOPPING EFFECTS IN FE60CO40 FILMS IRRADIATED WITH HIGH-ENERGY IONS

Thin films of the Fe60Co40 alloy produced by electron beam deposition under ultrahigh vacuum have been irradiated at liquid nitrogen tempera ture 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 c ontinuously measured as a function of the ion fluence at 77 K using in situ electrical resistivity measurements. The experimental results ar e analyzed to obtain the defect production efficiency which is the rat io of the experimental to the theoretical displacement cross section. It is found for the lightest ions, 40-186 MeV N, that the defect produ ction efficiency is lower than unity and can be understood on the basi s of elastic collision effects only. On the contrary, an important def ect production efficiency much higher than unity is observed in the ca se 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 e nergy deposition in electronic excitation in some metallic targets. A comparison and discussion are made regarding previous damage rate stud ies for other types of high electronic energy deposition in metallic t argets.