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- Context:
Helium irradiation onto tungsten surfaces brings about the growth of fuzzy
tungsten fibers in the diameter of several ten nano-meter. This material, which
is called "tungsten nano-structure", was found by the research on a plasma
facing tungsten material in the inside walls of nuclear fusion reactors. Because
the incident energy of the helium ions is less than that to sputter the tungsten
atoms from the surface, the growth of the fuzzy fibers can be regards as
self-organized growth. The formation process of the tungsten nano-structure is
not classified into the deposition and processing/etching, which are two kinds
of typical processes to create surface nano-structures. The formation mechanisms
of tungsten nano-structure have been not well understood. We have grappled with
the formation mechanisms of the tungsten-nano structure. The competition of
penetration and sputterinf in penetration process was solved by using binary
collision approximation. The He agglomeration in the diffusion process was
revealed by using density functional theory with the 'OpenMX'[1], and the burst
of He bubble in the surface is treated by molecular dynamics. As a result, we
explained that He creates bubble but H, Ne, Ar cannot create it with the
incident energy of less than 200 eV.
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