Defect creation by MeV clusters in LiNbO 3

Single crystals of LiNbO ₃ (Y-cut orientation) were irradiated at room temperature with 3 MeV C ₆⁺ and 2.4 MeV C ₈⁺ clusters provided by CSNSM "ARAMIS" accelerator. The electronic stopping power was about 6.5 keV nm ^-1 in both cases. The fluences extended from 10 ¹⁰ to 4 × 10 ¹² C ₆⁺ or C ₈⁺ cm ^-2. Rutherford Backscattering Spectrometry in Channeling geometry (RBS/C) revealed the presence of extended defects, which cannot be due solely to nuclear stopping and which we ascribe to the high density of electronic energy associated with the correlated electronic stopping of the cluster components. The RBS/C analysis, providing a lattice disorder profile, confirms this interpretation: the damaged thickness closely corresponds to the cluster components correlation length (between 50 and 100 nm). The fluence evolutions of the disorder ratio, measured at the sample surface for C ₆ and C ₈ projectiles, correspond to damage cross sections close to 1.8 × 10 ^-13 cm ² in the two cases.