Criteria for surface plasmon resonance energy of metal nanoparticles in silica glass

Absorption spectra of silica glasses implanted by Ni negative-ions of 60 keV to 3.8 x 10(16) ions/cm(2) were studied with excluding incoherent multiple reflection (ICMR) due to substrates. Two absorption peaks of 3.3 and 6.0 eV due to Ni nanoparticles were observed. To our knowledge, this is the first direct observation of the 6.0 eV peak which was usually smeared by ICMR. A next concern is identification of the surface plasmon resonance (SPR) of Ni nanoparticles from the two peaks, 3.3 and 6.0 eV. However, two types of well-known SPR criteria predict completely different energies each other, 2.8 and 5.9 eV, respectively. Validity of these criteria is discussed. It is found that one of the criteria includes a non-realistic assumption. Moreover, both the criteria are found to give just an absorption maximum and do not specify the SPR. Using different size dependences between sp-electrons (surface plasmon) and d-electrons, an alternative criterion is proposed. The 3.3 eV band is identified as the SPR of Ni nanoparticles in SiO2. (C) 2004 Elsevier B.V. All rights reserved.