Defect formation in a carbon onion upon irradiation with Ar ions

The interaction of an Ar ion with a C₆₀@C₂₄₀@C₅₄₀ carbon onion and an Ar ion beam with a C₆₀@C₂₄₀@C₅₄₀@C₉₆₀ carbon onion are studied by molecular dynamics. The energy threshold for the formation of a vacancy in a pentagon of the onion fullerene shell is examined in two temperature regimes (300 and 1000 K). The main types of defects formed in the onion structure at various incident ion energies are detected and described. It is shown that the pentagonal cycles with their nearest environment are the least stable regions in the carbon onion under irradiation. The results obtained provide direct confirmation of the possibility of formation of a diamond structure upon ion irradiation of carbon onions.