Abstract
Columnar defects are produced in semiconductor and insulator materials by swift heavy ion irradiation. It has been considered that the electronic stopping power of irradiating ions is the dominant factor in the formation of defects. However, our recent results suggest that ion-velocity is also an important parameter for use in describing this phenomenon. In the present study, we investigate the columnar defects produced in the Bi2Sr2CaCu2O8 (Bi-2212) superconductor by heavy ion irradiation (Au8+,12+, I8+,29+, Br12+, and Ni11+) in the energy range of 60–600 MeV. From transmission electron microscopy, it is shown that the diameters of columnar defects become smaller and their distribution become narrower with an increase in ion velocity. This is explained as an effect of nuclear collision by calculation of the mean free path for the irradiated ions. The present results imply that nuclear collisions strongly affect the formation of columnar defects, even for swift heavy ion irradiation.