Velocity effect on the damage creation in metals in the electronic stopping power regime

Abstract

The energy deposited on target electrons by a swift heavy ion has been studied for several years. The deposited energy density in the vicinity of the ion path is large as the velocity of the incident ion is low. The influence of the ion velocity on irradiation effect induced by electronic energy loss (Se) has been clearly demonstrated after irradiation experiments performed on the insulator Y3Fe5O12 and suspected in metals. In that case the damage creation is enhanced at low ion velocities. In the present work, pure bismuth samples have been irradiated at 100 K by 42.9 MeV amu−1 Xe and 4 MeV amu−1 Kr ions with similar Se values (∼ 17 KeV nm−1). The resistivity increment Δϱ was measured in situ as a function of the ion fluence, Φt. The analyses of Δϱ(Φt) curves show that the Kr irradiation leads to a damage efficiency which is two to four times larger than that obtained after Xe irradiation. In addition, 2, 10 and 20 MeV amu−1 Pb-ion irradiations were performed at 20 K. The comparison of deduced latent track radii for the same Se values with previous results gives that lower velocity in irradiations produce larger tracks. These phenomena evidence that a strong ion velocity effect exists in bismuth. The thermal spike model with the ion velocity dependence of the initial energy deposition is used to determine the track radii as a function of Se values. We now find an agreement between calculated and experimental track radii in relation with the ion velocity. Moreover the electron number density ne of the quasi-free gas in bismuth is found to be 1.5 times the atomic density na (ne = 1.5na) and the Se threshold for continuous latent track formation, Set, is ranged from 24 to 31 keV nm−1 for ion energies ranging from 2 to 25 MeV amu−1.