Tribological property of CeO2 films prepared by ion-beam-assisted deposition

Cerium oxide (CeO2) films were prepared by ion-beam-assisted deposition (IBAD). The films were synthesized on WC-Co and Si(100) substrates by depositing CeO2 vapor under simultaneous bombardment of O-2, Ar and Xe ions in the energy range of 1.0 to 5.0 keV. The elemental composition ratio (O/Ce) measured by Rutherford backscattering spectrometer (RBS) was in the range of 1.9 to 2.9, which was considerably higher than that expected from the stoichiometry. The X-ray diffractometry (XRD) patterns of CeO2 films prepared using O-2, Ar and Xe ion beams exhibited a single-phase CaF2 structure, which is typical of CeO2. By increasing the transport rate ratio of the ions to CeO2 vapor, the morphology of the specimens prepared using O-2 and Xe ion beams changed from a columnar grain to a granular one at transport ratios of 1.0 and 0.33, respectively. The defect density produced on the CeO2 film surface by ion irradiation was elucidated by Monte-Carlo simulation, leading to the result that the morphology change from columnar to granular is brought about at a threshold value in the defect density induced by ion bombardment. It was also been determined that the granular grain films have the very low friction coefficients of 0.15 at room temperature and 0.035-0.040 at 200 degreesC, respectively.