Measured deviations from Rutherford backscattering cross sections using Li-ion beams

Bozoian et al. have developed an analytical theory which predicts the incident ion energy at which elastic-scattering cross sections begin to deviate from their Rutherford values as the result of nuclear perturbations. The predictions are in good agreement with experimental data for proton and helium-ion beams, and should be applicable to heavier projectiles. The theory has also been extended to account for isotopic variation of the incident beam. As a further test of the theory, we have performed a series of backscattering measurements using both 6Li and 7Li ion beams. Lithium-ion backscattering is of importance to thin-film analysis because it offers improved depth sensitivity and kinematic mass resolution as compared to helium. Elastic-backscattering cross sections for O, F, Al, and Ti were measured relative to those ofhigh-Z reference elements over an energy range of 2.5–9.25 MeV, and the energies at which they began to deviate from their Rutherford values were determined. The experimental results are compared to predictions from the analytical theory, and from optical-model calculations.