He reemission implanted in metals

• Published in: Journal of nuclear materials Vol. 453; no. 1-3; pp. 247 - 252
• Main Author: Tanabe, T.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2014
• Subjects: Blistering; Bubbles; Coalescing; Defects; Density; Fluence; Implantation; Migration
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2014.06.052

•Observation of He reemission of various metals under He+ implantation at wide temperature range.•Materials examined are aluminum (Al), Nickel (Ni) and molybdenum (Mo).•He reemission is quite temperature dependent and different with materials.•Three metals show similar dependence on temperature normalized with respective melting point.•He reemission is successfully correlated with He behavior in metals. Helium (He) reemission of Al, Ni and Mo under energetic He implantation (10–30keV) in wide temperature range is studied to understand behavior of implanted He in correlation with structure changes. The reemission behavior is categorized into 4 different temperature ranges with the normalized temperature (Tm) to the melting point of each metal. At elevated temperatures (well above ∼0.6Tm), interstitial He atoms and/or He-vacancy (ies) clusters can migrate remaining no structure change and showing smooth reemission without any burst. Between ∼0.25 and 0.6Tm, He reemission always accompanies significant structure modification. For ∼04–0.6Tm, implanted He coalesce to make bubbles and the bubbles can move to the surface. Bubble migration accompanies materials flow to the surface resulting in fuzz surface or columnar structure, depending on implantation flux. Slower bubble motion at ∼0.25–0.4 prohibits the material migration. Instead the bubbles coalesce to grow large and multi-layered blistering appears as periodic reemission behavior. Below ∼0.25Tm, He migration is too slow for bubbles to grow large, but bubble density increases up to a certain fluence, where neighboring bubbles start to coalesce. Accordingly, He release is mostly caused by mechanical failure or blister rapture. With increasing fluence, all defects (bubbles and dislocation loops) tangle or inter connected with neighboring defects and accordingly He migration to the surface along the tangled or connected defects is enhanced, resulting 100% reemission easily without making multilayered blistering.