Surface cracking of vitreous fused silica induced by MeV ion beam bombardment

Abstract

The surface cracking behavior of vitreous fused silica (suprasil II) induced by MeV^(35)C1 and^(19)F ions was observed. The crack density increases with ion fluence, reaches a maximum (for 17 MeV^(35)C1 at 1 × 10^(13 35)Cl/cm^2 and for 17 MeV^(19)F at 5 × 10^(13 19)F/cm^2) and then declines. The cracks close up for subsequent higher ion fluences. The surface cracking occurs in different ion fluence ranges with ion mass, for 17 MeV^(35)C1 5xl0^(12)-lxl0^(14 35)Cl/cm^2; for 17 MeV^(19)F, 1 × 10^(13)-3 × 10^(14 19)F/cm^2. No surface cracks were observed for 2 MeV H^+ for the ion fluence range of 5 × 10,^4-10^(17) ‘H/cm^2. The measurements of the defects in silica samples with EPR indicate that the surface cracking occurs in the transition region where the ion damage tracks partly overlap. We tentatively suggest that the surface cracking may result from heavy ion tracks in the insulating materials, and cracks close up at higher ion fluence due to the compaction of the irradiated area.