Optical properties and structure characterization of sapphire after Ni ion implantation and annealing

Implantation of 64 keV64keV Ni ions to sapphire was conducted at room temperature to 1×1017 ions/cm21×1017ions∕cm2 with a current density of 55 or 10 μA/cm210μA∕cm2. Metallic Ni nanoparticles were formed with the 5 μA/cm25μA∕cm2 ion current and the NiAl2O4NiAl2O4 compound was formed with the 10 μA/cm210μA∕cm2 ion current. The crystals implanted with both current densities were annealed isochronally for 1 h1h at temperatures up to 1000 °C1000°C in steps of 100 °C100°C in an ambient atmosphere. Optical absorption spectroscopy, x-ray diffraction, transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy have been utilized to characterize the samples. The surface plasmon resonance (SPR) absorption band peaked at 400 nm400nm due to the Ni nanoparticles shifted toward the longer wavelength gradually with the annealing temperature increasing from 400 to 700 °C400to700°C. The SPR absorption band disappeared after the annealing temperature reached 800 °C800°C. NiO nanoparticles were formed at the expense of Ni nanoparticles with an increasing annealing temperature. The TEM analyses revealed that the nanoparticles grew to 6–20 nm6–20nm and migrated toward the surface after annealing at 900 °C900°C. The absorption band at 430 nm430nm from Ni2+Ni2+ cations in NiAl2O4NiAl2O4 did not shift with the increasing annealing temperature