ABSTRACTSamples of fused silica were implanted at room temperature with 300 keV-Ag+ for doses ranging from 0.8×1016 to 14×1016 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 6×1016 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 4.3×1016 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.
Unusually large fluorescence quantum yield for a near-infrared emitting DNA-stabilized silver nanocluster
