Materials Modifications with Cluster Beams: Bulk and Surface Modification

It is now well accepted that electronic excitation and ionization arising from the slowing down of swift heavy ions can lead to structural modifications in some metallic targets as it has been known for a long time in insulators. A rapid overview of some results obtained after GeV monoatomic heavy ion irradiations will be given. It will then be shown that new specific effects take place during irradiations with cluster ions. The projectiles used are energetic cluster beams: 10 to 40 MeV Au$\text{}_{4}$ or C$\text{}_{60}$ ions. The rates of linear energy deposition in electronic excitation are close for GeV monoatomic and for 10 MeV cluster ions, but the cluster ions have characteristic velocities which are one order of magnitude smaller than those of monoatomic ions. This leads to a strong spatial localization of the deposited energy during the slowing down process. The density of deposited energy can then reach values as high as a few 100 eV/atom. This very high density of energy deposited in the electronic system of the targets can lead to spectacular structural modifications: generation in the vicinity of the ion trajectories of isolated or agglomerated point defects, new crystalline phases, amorphized regions... After an overview of such damage induced in bulk metals, semiconductors, and insulators, we will discuss surface damage, consisting in the formation of bumps, craters, "lava-flows" on the target surface.