Interactions of water cluster ion beams with solid surfaces

In order to investigate the interactions of water cluster ion beams with solid surfaces, Si(100) substrates, SiO2 and metal films were irradiated at various ion doses and acceleration voltages, while the substrate temperature was kept at room temperature. The Rutherford backscattering spectroscopy (RBS) channeling measurement showed that the number of displacement atoms for the water cluster ion irradiation at ion doses larger than 1 × 10¹⁵ ions/cm2 was less than that for the Ar monomer ion irradiation at the same acceleration voltage. Furthermore, the sputtered depth of the Si and SiO2 surfaces increased with increase of the acceleration voltage. The sputtering yield at an acceleration voltage of 9 kV which was approximately 10 times larger than that for Ar monomer ion irradiation. The surface roughness of the Si substrates irradiated was less than 1 nm, and the smooth surface at a atomic level was obtained. For metal surfaces, the sputtering yield by the water cluster ion beams was also larger than that by Ar monomer ion beams. Furthermore, the contact angles for the sputtered surfaces were measured, and the wettability of the surface was investigated. The hydrophilic property was enhanced for the Si surface irradiated, although the Ti surface was hydrophobic. The change of the wettability by the water cluster ion irradiation was ascribed to the oxide layer formation on the Si and Ti surfaces.