Dommage de surface et profils de teneur en gaz piégé dans le cuivre sous irradiation D'He + DE 20 keV

Abstract

Surface damage due to 20 keV He + irradiation of OFHC Cu was studied by optical and scanning electron microscopy, and by gas trapping profile measurements with proton backscattering and elastic recoil detection. Both annealed (1 h at 773 K) and unannealed Cu were implanted, at 300 K(0.22 T m ) and 500 K(0.37 T m ), up to fluences of 3 × 10 18 cm −2. Additional results with thin (1 μm) evaporated films and stressed cold-rolled foils (3 μm) were obtained. At 500 K in bulk OFHC Cu pores and/or large (∼1 μm) but scattered blisters appear; at 300 K in bulk or thin film Cu blisters are large and abundant. In all these cases a very large ( ⩾1.5 × 10 17 cm −7) and sudden release of deeply implanted helium takes place, leading to a depleted profile at a depth of about 90 nm ( ≈R p ). In contrast in cold-rolled foils the blisters are small (∼0.4 μm) and the profiles are undepleted. These results are explained by fissuration of helium-pressurized cavities. At high fluence blisters disappear, leaving a porous structure at 500 K and a rough micro-relief at 300 K; the helium profiles are flat and very wide (2–3 R p ). Blister disappearance, absence of flaking, and porous structure are discussed in terms of the width of the profiles and the formation of a helium-saturated, highly damaged (recrystallized), and permeable layer.