Electronic excitation effects on radiation damage in insulators under ion irradiation

To extract electronic excitation effects from the synergistic damage processes, we have studied photon-irradiation effects on insulators under heavy ion irradiation. Copper ions (Cu2+) of 3 MeV energy at an ion flux of 2 μA/cm2 and 2.3 eV photons at 0.2 J/cm2pulse were used to amorphous SiO2 (KU-1) and spinel MgO·2.4(Al2O3), either sequentially or simultaneously to fluences up to 5 × 1017 ions/cm2. Atomic force microscopy and cross-sectional TEM were conducted to study the surface morphology and internal microstructure, respectively. The simultaneous photon irradiation at high photon densities significantly enhanced surface damage for the insulators, but alleviated bulk defects. The electronic excitation gave rise to significant reduction in dislocation loops in MgO·2.4(Al2O3), whereas single ion irradiation produced copious dislocation loops. The results demonstrate that intense electronic excitation, coexistent with heavy ions, excite transient sub-gap states and the absorbed energy results in enhancement of atomic migration, either damaging the surface or annealing the internal defects.