SAXS study of molybdenum irradiated with helium ions

Abstract

Defects produced by helium ion irradiation have been investigated by means of small-angle X-ray scattering (SAXS) measurements, transmission electron microscope (TEM) and scanning electron microscope (SEM) observations. He + ions with projectile energy of 2 MeV were implanted in thin high-purity molybdenum foils with dose rates of 7–56 μA cm −2 up to total doses of 0.43–3.46 × 10 18 ions cm −2. The critical fluence producing blisters and the blister skin thickness were measured to be about 0.5 × 10 18 ions cm t-2 and 2.8 ± 0.4 μm, respectively, from SEM observations. Two types of bubbles were observed by TEM. The angular dependence of SAXS intensity was explained by the superposition of three Gaussian-shaped scattering curves, suggesting three different types of irradiation defects. Type II, which had a dimension of 4–7 nm, was identified with polygonal bubbles observed by TEM. This type appeared beyond the critical dose of 0.6 × 10 18 ions cm −2 . Type III, which had a dimension of 0.6–2.7 nm, was identified with finer bubbles observed by TEM and distinguishable from type II. The SAXS results have been applied to evaluate quantitatively the kinetics of formation of these bubbles.