Amorphization of sapphire induced by swift heavy ions: A two step process

Single crystals of α-Al2O3 were irradiated with 0.7 MeV/amu Xe ions at the GANIL accelerator with fluences extending from 5 x 1011 to 2 x 1014 ions/cm2. The samples were characterized by Rutherford Backscattering Spectrometry in Channelling geometry (RBS-C) and surface profilometry for swelling measurements. RBS-C analysis evidence the presence of two incident ion effects on sapphire targets: the creation of partial disorder that saturates at ∼40% with a damage cross section of 7 x 10-14 cm2, followed by a complete disorder starting from the surface and appearing at fluence larger than ∼1.2 x 1013 ions/cm2. A correlation between relative disorder and swelling is observed. This study is in agreement with the appearance of amorphization of α-Al2O3 at high fluence as observed by Aruga et al. [T. Aruga, Y. Katano, T. Ohmichi, S. Okayasu, Y. Kazumata, Nucl. Instr. Meth. Phys. Res. B 166-167 (2000) 913-919]