Ion-beam induced effects at 15 K in α-Al2O3 of different orientations

Ion-beam induced effects in alpha-Al2O3 of c, a, and r orientations were studied by Rutherford backscattering spectrometry (RBS) in channeling configuration using 1.4 MeV He ions. 150 keV Ar, 150 keV K, or 80 keV Na ions were step by step implanted at 15 K followed immediately by the RBS analysis without changing the sample environment. Defect annealing was observed during the RBS measurement, which is attributed to the electronic energy loss of the He ions. A similar effect occurs due to the electronic energy loss of the implanted ions, resulting in a reduced defect concentration between surface and profile maximum. The electronic energy loss of ions may change the charge state of defects, thus enhancing their mobility and causing defect annealing. The results suggest that within the collision cascade of individual ions in perfect sapphire only point defects are produced, the concentration of which is well reproduced by SRIM calculations taking into account suggested values of the displacement energies of E-d(Al)=20 eV and E-d(O)=50 eV for aluminum and oxygen, respectively. The lower efficiency for point defect production measured in c-oriented material can be explained by the heavily reduced visibility of Al atoms sitting on vacant octahedral sites, which are hidden in this direction. Point defect recombination is observed when the collision cascades start to overlap. Above a critical concentration point defects are altered into clusters which rapidly grow during further irradiation until a saturation is reached.