Influence of ion velocity on damage efficiency in the single ion-target irradiation system: Au-Bi₂Sr₂CaCu₂O_x

Based on the cross section measurement of the columnar defect along the ion path using high-resolution electron microscopy, we developed a method to study the influence of ion velocity on ion irradiation damage. The use of a single ion-target irradiation system avoids the influences of the different target materials and the different species of incident ions on the irradiation damage. By investigating the dependence of damage efficiency on the ion velocity, we can minimize the influence of the different ion effective charge on the ion irradiation damage. The application on the Au-Bi₂Sr₂CaCu₂O_x system shows that there is a critical velocity ν_c∼0.057c (c, the velocity of light) at which the damage efficiency is maximum. By reanalyzing the previous published data, we have found a similar critical velocity (ν_c∼0.055c) in the Xe-YIG (yttrium garnet) irradiation system, indicating it is a quite general phenomenon. From this observation, the irradiation damage process is divided into two stages. In the high ion velocity region the irradiation damage is ion velocity controlled and in the low ion velocity region the irradiation damage is the energy-density threshold controlled. The peak of damage efficiency corresponds to the turning point between two stages.