Blister formation in rutile TiO₂(1 0 0) films by helium irradiation

Incident energy, fluence of helium ion and temperature for blister formation in rutile TiO₂(1 0 0) films were investigated. Epitaxial rutile TiO₂(1 0 0) films were grown on α-Al₂O₃(0 0 0 1) substrates by pulsed laser deposition. The films were irradiated at room temperature and 95 K with 4 keV helium ions up to fluence range from 1.0 × 10¹⁶ to 2.3 × 10¹⁷ ions/cm². The surface morphology of TiO₂ films was observed by scanning electron microscope and atomic force microscope. Rutherford backscattering spectroscopy with channeling was used to determine the depth profile of radiation-induced damage. In the case of room temperature irradiation with fluences higher than 2 × 10¹⁶ ions/cm², helium blisters with 100-200 nm sizes in TiO₂ films were observed. Furthermore, helium irradiation at 95 K resulted in smaller size blisters (∼50 nm). It is suggested that the size of blisters in TiO₂(1 0 0) films is strongly affected by the temperature during the helium irradiation. The photo-induced superhydrophilicity of TiO₂ films was improved by high fluence helium irradiation, which caused blister growth.