Absorption spectra of Ni nanoparticles in silica glass (SiO2) fabricated by negative-ion implantation of 60 keV Ni to 4x1016 ions/cm2 were determined from three sets of spectra, i.e., transmittance, reflectance of implanted-surface side and that of rear-surface side, of the same samples, to exclude incoherent multiple reflection (ICMR) due to substrates. Although the absorption spectrum of as-implanted state is smeared with defect absorption, two absorption bands at 3.3 and 6.0 eV due to Ni nanoparticles are observed after annealing at 800°C in vacuum. However, a predicted peak energy from a criterion for surface plasmon resonance (SPR), εm'(ω) + 2 εd'(ω) = 0, was in 2.8 eV, far away from the observed peaks. Another criterion, (εm' + 2εd')2 + (εm'')2 = minimum, gives the peak energy of 5.9 eV. From decomposition of the dielectric constants into free- and bound-electron contributions, we conclude that the 3.3 eV peak is SPR-like, although the contribution of the bound-electrons to the 3.3 eV peak is not small. Size dependence also supports the assignment of the 3.3 eV peak. The large contribution of the bound electrons is due to a nature of the partially filled 3d orbitals of Ni. This is contrast to the closed 3d orbitals of Cu, and probably is the origin of the broad peak width.
The magnetic nanoparticles are fabricated in silica glass (SiO2) using high-flux implantation of nickel negative-ions of 60 keV. Photo-absorption measurements and the cross-sectional transmission electron microscopy (XTEM) observation confirm formation of metallic Ni nanoparticles in SiO2, and exclude possible formation of Ni silicides (Ni3Si, Ni2Si, NiSi) and oxides (NiO) as major products. The mean diameter of the nanoparticles was in ~2.9 nm, and the depth distribution was similar to the prediction from the TRIDYN code with taking account of the sputtering. Temperature- and field- dependences of magnetization show that the nanoparticles are in the super-paramagnetic state with a blocking temperature of ~27 K.
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