SAXS study of molybdenum irradiated with helium ions

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 cmsup(-2) up to total doses of 0.43-3.46 x 1018 ions cmsup(-2). The critical fluence producing blisters and the blister skin thickness were measured to be about 0.5 x 1018 ions cmsup(-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 x 1018 ions cmsup(-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 quantiatively the kinetics of formation of these bubbles. (orig.)