Local structure, optical and magnetic studies of Ni nanostructures embedded in a SiO2 matrix by ion implantation

Abstract

This work reports the formation of Ni nanostructures, their growth and saturation to form oxides by using ion implantation and thermal treatment in air at 600 degrees C. A quartz (SiO2) matrix was implanted with 100 keV Ni+ ions to doses in the range 5 x 10(15) -2 x 10(17) ions cm(-2). The formation of Ni nanoclusters was observed by high resolution x-ray diffraction (HRXRD), UV-visible optical spectroscopy, dc magnetization, AFM/ MFM and x-ray absorption spectroscopy (XAS). The cluster size distribution is narrow, with an average size of similar to 25 +/- 0.5 nm for the sample implanted at a dose of 1 x 10(16) ions cm(-2), but increases with implantation dose. Optical absorption spectra also show a clear signature of a surface plasmon resonance (SPR) peak at around 388 nm in accordance with the theoretical Mie's spectra. Temperature dependent zero-field-cooled and field-cooled magnetization measurements clearly indicate a superparamagnetic behavior, which is properly analyzed considering the size distribution of the magnetic nanostructures. The results show that the magnetic properties of the nanoparticles can be controlled by the implantation dose. A detailed investigation of the local structure using Ni K-edge NEXAFS/EXAFS suggests that the size of the Ni nanostructures is altered by implantation dose, reaching saturation in the form of oxides/silicates of Ni at a dose of 2 x 10(17) ions cm(-2).