Amorphization in aluminum oxide induced by ion irradiation

Amorphization in sapphire induced by irradiation has been observed for years but it is still in discussion whether displacements or implanted ions have an important role for the amorphization. In this work, we perform irradiation with high-energy heavy ions in thin film alpha-alumina below room temperature, so that the effects of atomic displacements, especially of damage cascades, can be revealed. Amorphization was detected at temperatures from 90 K to 230 K under irradiation with 600-900 keV xenon and krypton ions, while no amorphization was detected under irradiation with argon nor oxygen ions. The critical energy density to induce amorphization is estimated. Four stages on the crystalline-to-amorphous transformation was observed from the temperature dependence of the dose-to-amorphization. The effect of damage cascades on the irradiation-induced amorphization and defect kinetics resulting in an increase of the dose-to-amorphization will be discussed.