Effect of annealing on the optical absorption of Ni nanoparticles in MgO single crystals

Ni+ ion implantation with an energy of 64 keV in MgO single crystals was conducted at room temperature up to a fluence of 1 × 1017 ion/cm2. The as-implanted crystals were annealed isochronally at temperatures up to 900 °C. Optical absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) have been utilized to characterize the changes of optical properties and the microstructure of the annealed samples. XPS results showed that the charge state of implanted Ni was still mainly in metallic Ni0 after annealing at 900 °C. TEM analysis revealed metallic Ni nanoparticles with depth-dependant dimensions of ∼1–10 nm in the annealed sample. Optical absorption spectroscopy indicated that the Ni nanoparticles exhibited a broad surface plasmon resonance absorption band in annealed samples and the band shifted to a longer wavelength with the increasing annealing temperature.