Swift-uranium-ion-induced damage in sapphire

Single crystals of α-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ were irradiated at Ganil with ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ ions using four different energies: 0.48, 1.72, 2.78, and 3.40 MeV/u. All the irradiations were performed at a temperature of ≊80 K, with fluences extending from 1.2×${10}^{12}$ to 2.5×${10}^{12}$ ions ${\mathrm{cm}}^{\mathrm{-}2}$. The samples were characterized by Rutherford backscattering spectrometry in channeling geometry (RBS-C) and optical absorption measurements. RBS-C analyses evidence the lattice disorder induced by collective electronic excitations. Depending on the electronic stopping power (dE/dx)e (up to 44.2 keV ${\mathrm{nm}}^{\mathrm{-}1}$), the damage cross section ${\mathit{A}}_{\mathit{e}}$ varies between 0.3 and 2.1×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^2$. Optical absorption spectroscopy exhibited the characteristic bands associated with oxygen vacancies. The kinetics of F centers were determined in order to precisely determine the respective contributions of the nuclear and electronic processes in point-defect generation.