Unraveling HI-supersaturation in low-energy ion/plasma-irradiated W surfaces

In the present work, H content and defect microstructures in the H supersaturated surface layer (HSSL) formed upon a fluence seriers were performed using ¹⁵N-¹H nuclear reaction analysis (NRA) and transmission electron microscopy (TEM). H concenration up to 16 at.% in HSSL was record-breakingly observed. Detailed experimental insights guide us to the conclusive role of defect sinks (e.g., free surface and vacancy clusters, etc.) in absorbing W self-interstitial atoms and materializing temporary Frenkel pairs (t-FP) as H-decorated vacancy-type defects under low-energy H ion/plasma irradiation. Fundamental effects of mobile hydrogen in irradiated materials and the possibility of SSL formation in W materials under fusion reactor conditions are discussed.