Fluence Dependence of Surface Morphology and Deuterium Retention in W Bulks and Nanocrystalline W Films Exposed to Deuterium Plasma

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.