Damage creation threshold of Al2O3 under swift heavy ion irradiation

Among insulators, sapphire (Al2O3) is less sensitive than any amorphizable oxides regarding the irradiation with heavy ions in the electronic energy loss regime. Earlier experimental results indicated a critical energy loss for damage creation of around of 20 keV/nm, while calculations based on the inelastic thermal spike model predict a value of ∼10 keV/nm. In order to clarify this discrepancy, additional irradiation experiments were performed with different ions between Ni and U covering electronic energy losses between 10 and 43 keV/nm and kinetic energies in the range from 1 to 11 MeV/u. Irradiation effects were characterized by atomic force microscopy (hillock formation), profilometry (swelling), and channeling Rutherford backscattering (near-surface disorder). Combining the results from these measurements, an electronic energy loss threshold of 9.5 ± 1.5 keV/nm is extracted, indicating that the earlier threshold was overestimated and confirming the predictive power of the inelastic thermal spike model. Threshold predictions based on thermal spike model calculations are given for lower and higher beam energies.