First principle calculations of energy of agglomerated helium in the period 6 elements

Difference of helium (He) agglomeration energies between period 6 elements, tantalum (Ta), tungsten (W), iridium (Ir) and gold (Au), is illustrated by using first principles calculations based on density functional theory (DFT). It is found that He in W and Ir can agglomerate more easily than Ta and Au. We investigate a relationship between the He agglomeration tendency and the growth of nanostructure by He plasma irradiation. Thus, the four metals are exposed to He plasma irradiation. Each metal has different structures after the He plasma exposure. Surface nanostructures of W and Ir are fuzzy fiber-like while these structures are not observed in Ta and Au. In the meantime, W and Ir have a tendency to agglomerate He atoms at a vacancy or interstitial sites easily. This correlation suggests that the He agglomeration may play a role for understanding the fuzz formation mechanism.