Fluence dependence of surface morphology and deuterium retention in w bulks and nanocrystalline w films exposed to deuterium plasma

Abstract

The surface morphology of pure W bulks and nanocrystalline tungsten films was investigated after exposure to a low‐energy (100 eV/D), high‐flux (1.8 × 1021 D m−2s−1) deuterium plasma. Nanocrystalline tungsten films of 6 μm thickness were deposited on tungsten bulks and exposed to deuterium plasma at various fluences ranging from 1.30 × 1025 to 5.18 × 1025 D m−2. Changes in surface morphology from before to after irradiation were studied with scanning electron microscopy (SEM). The W bulk exposed to low‐fluence plasma (1.30 × 1025 D m−2) shows blisters. The blisters on the W bulk irradiated to higher‐fluence plasma are much larger (~2 μm). The blisters on the surface of W films are smaller in size and lower in density than those of the W bulks. In addition, the modifications exhibit the appearance of cracks below the surface after deuterium plasma irradiation. It is suggested that the blisters are caused by the diffusion and aggregation of the deuterium‐vacancy clusters. The deuterium retention of the W bulks and nanocrystalline tungsten films was studied using thermal desorption spectroscopy (TDS). The retention of deuterium in W bulks and W films increases with increasing deuterium plasma fluence when irradiated at 500 K.