Implantation parameters affecting aluminum nano-particle formation in alumina

The formation of nano-dimensional metallic Al precipitates in alumina due to the reduction of the host matrix as a result of ambient temperature ion implantation of Y ions is examined. The formation and growth of Al precipitates are dependent on both the Y ion dose and the energy available to the matrix, as reported here. Reducing the ion dose from 5 × 1016 to 2.5 × 1016 ions/cm2 results in smaller precipitates; 10.7 ± 1.8 nm to 9.0 nm ± 1.2 nm, respectively, for incident ion energies of 150 keV, based upon particle size measurements obtained using energy filtered transmission electron microscopy. Below a fluence of 2.5 × 1016, particle formation is not detected. The energy available to the matrix was varied; first, by controlling the incident ion energy (varied between 60 and 150 keV) while holding the substrate at ambient temperature, and second, by controlling the substrate temperature (varied between 44 and 873 K) while holding the incident ion energy constant at 150 keV. Experiments conducted with incident ion energies of 110 keV or higher produce crystalline Al precipitates; whereas implantations at 100 keV produce amorphous Al particles and implantations at 60 keV produce no detectable precipitates. The implantations carried out as a function of temperature produce successively smaller precipitates with decreasing temperature to 77 K (6.7 ± 1.0 nm), below which no precipitates are detected. An Arrhenius activation energy for the formation of the aluminum precipitates of 1.7 kJ/mole has been calculated using the volume of precipitates formed as a function of inverse temperature. This low activation energy suggests that radiation enhanced diffusion (RED) is responsible for particle growth during these implantations.