Damage Evolution in Xe-Ion Irradiated Rutile (TiO2) Single Crystals

Abstract

AbstractRutile (TiO2) single crystals with (110) orientation were irradiated with 360 keV Xe2+ ions at 300K to fluences ranging from 2×1019 to 1×1020 Xe/m2. Irradiated samples were analyzed using: (1) Rutherford backscattering spectroscopy combined with ion channeling analysis (RBS/C); and (2) cross-sectional transmission electron microscopy (XTEM). Upon irradiation to a fluence of 2×1O19 Xe/m2, the sample thickness penetrated by the implanted ions was observed to consist of three distinct layers: (1) a defect-free layer at the surface (thickness about 12 nm) exhibiting good crystallinity; (2) a second layer with a low density of relatively large- sized defects; and (3) a third layer consisting of a high concentration of small defects. After the fluence was increased to 7×1019 Xe/m2, a buried amorphous layer was visible by XTEM. The thickness of the amorphous layer was found to increase with increasing Xe ion fluence. The location of this buried amorphous layer was found to coincide with the measured peak in the Xe concentration (measured by RBS/C), rather than with the theoretical maXimum in the displacement damage profile. This observation suggests the implanted Xe ions may serve as nucleation sites for the amorphization transformation. The total thickness of the damaged microstructure due to ion irradiation was always found to be much greater than the projected range of the Xe ions. This is likely due to point defect migration under the high stresses induced by ion implantation.