Sputtering and chemical modification of solid surfaces by water cluster ion beams

Water was introduced into a cluster source, and heated up to 150°C by a wire heater attached around the source. When the vapor pressure was larger than 1 atm, the vaporized water clusters were produced by an adiabatic expansion. The irradiation effects of water cluster ions on solid surfaces such as Si(100) and Ti substrates were investigated. The sputtered depth increased with increase of ion dose and acceleration voltage. The sputtering yield of the Si and Ti surfaces by the water cluster ion beams was approximately 10 times larger than that by Ar monomer ion beams at the same acceleration voltage. In addition, the XPS measurement showed that the sputtered surface had an oxide layer such as SiO_x and TiO_x. It was found from the depth profile of O_1s peak that the oxide layer thickness increased with increase of acceleration voltage, and it was about 10 nm at an acceleration voltage of 6 kV. Furthermore, the contact angles for the sputtered surfaces were measured, and they were about 80 degrees for the Ti surfaces and about 5 degrees for the Si surfaces, respectively. The contact angle for the unirradiated surface was about 45 degrees for Si surface and about 30 degrees for Ti surface, and the change of the contact angles was due to the oxide layer formation by the water cluster ion irradiation.