Silver Nanocluster Formation In Implanted Silica
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ABSTRACT Samples of fused silica were implanted at room temperature with 300 keV-Ag÷ for doses ranging from 0.gx1016 to 14X10' 6 ions/cm2 . A multi-technique approach including Rutherford backscattering spectrometry (RBS), x-ray diffraction (XRD), optical absorption and Raman scattering spectroscopies has been used to characterize silver precipitate. The Ag-depth profiles of samples implanted with doses higher than 6x1 016 Ag÷/cm2 show a bi-modal distribution, with the appearance of a secondary maximum near the surface. XRD spectra indicated the formation of silver nanocrystals of -10 nm in size within the heavily implanted samples. Optical absorption has been used to monitor the effects of ion doses on the optical properties of the metal clusters in the UV-Vis region. A single broad absorption band, due to surface plasmon resonance, is peaked at about 400 nm for low implantation doses. For doses higher than 4.3x10 16 Ag+/cm2 , a second broad band originates at higher wavelengths, peaking at 625 nm for the highest dose. The evolution of optical spectra is tentatively discussed in terms of the formation of silver particle aggregates with no longer spherical shape. An estimate of the mean size of silver nanoclusters of about 5.5 nm is obtained from low-frequency Raman scattering due to acoustic vibrations localized at the cluster surface. The discrepancies in the metal particle size obtained from XRD and Raman scattering measurements are discussed with respect to optical absorption data. INTRODUCTION Recent increase in research activities on semiconductor and metal nanocrystals embedded in solid transparent matrices is strongly motivated by the potential applications in the field of nonlinear processing devices and by the interest in fundamental physics on the excited states of these composite systems. Metal nanoclusters dispersed in transparent matrices present highly enhanced optical non-linearity due to quantum confinement of electrons, which strongly affects the optical properties of these composite systems. Therefore, as far as the opto-electronic applications are concerned, a very crucial step is the accurate control of cluster size during the synthesis process. Ion implantation provides a suitable route to precipitate metal colloids or semiconductor particles in dielectric matrix [1]. The major advantages of ion implantation in metal composite fabrication lie in its capability of incorporating much higher local concentration of metal particles in the host matrix compared to the melt quenching method. Furthermore, it allows for the depth-distribution control of the precipitated nanostructures. Basic properties of metal and semiconductor nanocrystals formed by high-dose ion implantation in fused silica and sapphire have been recently reviewed by White et al. [2]. Since the pioneering work of Arnold and Borders [3] most of the experimental investigations carried out on metal colloid composites were addressed to the characterization of structural and optical properties of metal nanoparticles in glass matrices [4,5
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