Inverse kirkendall mixing in collision cascades

We study ion-beam mixing of metallic bilayer interfaces using classical molecular-dynamics simulations of 5 keV collision cascades in the vicinity of Co/Cu and Ni/Cu (111) interfaces. We find that the production of vacancies and interface roughening is asymmetrical. On average, more Cu is introduced into the Co or Ni parts than vice versa, and more vacancies are produced in the Cu, indicative of an inverse Kirkendall effect in collision cascades. The effect is explained by the difference in melting points leading to different recrystalli-zation rates of the two materials.