AMORPHIZATION OF AL2O3 BY ION-INDUCED DENSITY REDUCTION

Al2O3 at room temperature amorphizes at an anomalously high ion implantation dose, corresponding to hundreds of displacements per atom (dpa). We have performed X-ray reflectometry and Monte Carlo simulations, which show that amorphization near the. surface is preceded by a progressive reduction in density caused by high-energy-transfer elastic collisions which knock Al and O atoms deeper into the crystal. Electron microscopy shows that the reduction in density is at least partially accommodated by void formation. We propose that the accumulation of these and other low-density defects such as vacancy clusters and nuclei of amorphous and lower-density crystalline phases of Al2O3 may serve as a mechanism for high-dose amorphization.