Optical properties of silver clusters formed by ion irradiation |
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Authors: | JC Pivin MA García H Hofmeister A Martucci M Sendova Vassileva M Nikolaeva O Kaitasov J Llopis |
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Institution: | (1) Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, batiment 108, 91405 Orsay Campus, France, FR;(2) Departamento de Física de Materiales, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain, ES;(3) Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany, DE;(4) Dipartimento di Ingegneria Meccanica, Universita di Padova, via Marzolo 9, 35131 Padova, Italy, IT;(5) Central Laboratory for Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee blvd., 1784 Sofia, Bulgaria, BG |
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Abstract: | Precipitation of silver clusters in silica is achieved by different methods: ion implantation, ion beam mixing of superimposed
layers and ion irradiation of films deposited by means of co-sputtering or sol-gel technique. Main features of the nanoparticles
depending on the preparation method are investigated by TEM. The optical extinction resonance of these clusters is analysed
in terms of sizes and interaction between the clusters on the basis of calculations. We found that resonances in sputtered
and gel films with low metal concentrations are well described by plasmon polaritons in isolated clusters and calculations
based on Mie theory allow the study of their growth under irradiation. This theory is not appropriate to describe the optical
response of silver clusters in silica implanted with Ag concentrations higher than 5 at.% or in ion beam mixed films, because
of the interaction between clusters. Using an effective medium model, it is demonstrated that the random dispersion of clusters
in implantation films causes fluctuations and, on average, an increase of the clusters polarization. On the contrary, the
particular arrangement of the clusters with a bimodal size distribution in ion beam mixed films induces a screening effect
between the clusters of largest size.
Received 10 January 2002 / Received in final form 26 April 2002 Published online 19 July 2002 |
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Keywords: | PACS 61 46 +w Nanoscale materials: clusters nanoparticles nanotubes and nanocrystals – 78 40 -q Absorption and reflection spectra: visible and ultraviolet |
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