Nanotip processing on TiO2 surfaces irradiated with fullerenes in the electronic regime

TiO2 single crystals, overlaid with a thin layer (5 nm) of Pt, were irradiated with C-60 clusters produced by the 15 MV tandem accelerator of the "Institut de Physique Nucleaire d'Orsay". The incident projectile energy was either 30 or 40 MeV, which corresponds to a slowing-down mainly governed by inelastic processes (electronic energy loss of 30 MeV C60 clusters in TiO2:61.1 keV nm(-1)). All the irradiations were performed at room temperature with fluences up to 10(11) clusters/cm(-2). Each cluster impact induces a surface modification leading to a surface nanoprotrusion. From atomic force microscopy (AFM) measurements, the surface nanotips have a mean height of 12 nm and a mean basal diameter of 34 nm for 30 MeV cluster irradiations. Rutherford backscattering spectrometry in channeling geometry (RBS-C) evidences the track damage created in TiO2 by the high electronic energy losses. Additional RBS analyses performed at grazing detection angle show that the roughness of the metallic film increases after irradiation. Both AFM and RBS results allow to conclude that the top part of the radiation-induced nanotips consists of TiO2 which has bursted the 5 nm platinum layer. (C) 2004 Elsevier B.V. All rights reserved.