Resonance energy of surface plasmon of nickel nanoparticles in silica glasses

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.