Formation of surface nanostructures on rutile (TiO_2): comparative study of low-energy cluster ion and high-energy monoatomic ion impact

摘要

The formation of nanostructures on rutile (TiO_2) surfaces formed after the implantation ofkiloelectronvolt-energy Ar_n~+cluster ions and megaelectronvolt- to gigaelectronvolt-energymultiply charged heavy ions (I~(q+), Ta~q(+)and U~(q+)) is studied. Despite the differences in stoppingand energy transfer mechanisms between the kiloelectronvolt-energy cluster ions andmegaelectronvolt-energy monoatomic ions, their impacts lead to a similar type of surfacedamage, namely craters. For the cluster ion implantation the craters are caused by themultiple-collision effect (dominated by nuclear stopping) and the high density of energy andmomentum transferred to the target, while for the case of megaelectronvolt multiply chargedions the craters are probably formed due to the Coulomb explosion and fast energy transfercaused by the electronic stopping. At ion energies in the gigaelectronvolt range, nanosizeprotrusions, so-called hillocks, are observed on the surface. It is suggested that electronicstopping leads to the formation of continuous tracks and the transferred energy is high enoughto melt the material along the whole projectile path. Elastic rebound of the tension between themolten and solid state phases leads to liquid flow, expansion and quenching of the melt, thusforming the hillocks. Atomic force microscopy measurements carried out under differentenvironmental conditions (temperature and atmosphere) suggest that the damaged material atthe nanosize impact spots has very different water affinity properties (higher hydrophilicity orwater adsorption) compared with the non-irradiated rutile surface.