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This work studies the behavior of Ag+ ions incorporated in different silica-based glassy matrices. To this end, Ag-doped silica coatings, prepared via sol-gel and deposited on pure silica and soda-lime glasses, are investigated by means of structural and optical spectroscopy techniques. Silver tends to segregate towards the interface during the annealing process, but in the case of soda-lime glassy substrates the exchange process favors its diffusion into the substrate. The environment of Ag+ ions during the annealing process determines their final oxidation state. In the pure silica matrix, Ag+ ions are found to be unstable and tend to reduce to Ag0, with the subsequent formation of metallic nanoparticles. However, the presence of network formers and modifiers gives rise to the appearance of nonbridging oxygen, which allows the stabilization of Ag+ ions in the matrix. [ABSTRACT FROM AUTHOR]

Following the recent finding that luster decorations in glazes of historical pottery consist of copper and silver nanoparticles dispersed in a glassy medium, the glaze in-depth composition and distribution of copper nanoparticles, copper ions, and their local environment have been studied in original samples of gold and red luster. The study has been fully carried out by nondestructive techniques such as Rutherford backscattering spectrometry, ultraviolet and visible spectroscopy, x-ray fluorescence, and extended x-ray absorption fine structure (EXAFS). Elemental analyses indicate that gold decorations are characterized by silver and copper, while red decorations by copper only. The color is determined mainly by metal nanoparticles. Specifically, silver nanoparticles determine the gold color, while the red color is determined by nanoparticles of copper. EXAFS measurements, carried out at the Cu K edge, indicate that in both gold and red luster copper is mostly the oxidized form (Cu[SUP+] and Cu[SUP2+]) with a large prevalence of Cu[SUP+]. States and local environment of copper ions are similar to those found in copper-alkali ion-exchanged silicate glass samples. This strongly supports the view that luster formation is mediated by a copper- and silver-alkali ion exchange as a first step, followed by nucleation and growth of metal nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: In the framework of metal nanocluster composite glasses for photonic application, (gold+copper)-containing silica films were synthesized by radiofrequency co-sputtering deposition technique by varying the Au/Cu ratio. To obtain the formation of metallic (alloy) nanoclusters, the deposited samples were annealed in reducing atmosphere at 900°C. The linear and nonlinear optical properties of the composite glasses were investigated. In particular, the nonlinear ultrafast optical response was measured by means of the Z-scan technique at a wavelength of 527nm with single 6ps pulse configuration. Significant refractive and absorptive effects were observed in all the annealed samples. The two main figures of merit related to the performance of materials for optical switching device application were evaluated for all samples, showing interesting values for the Cu-rich composites. [Copyright &y& Elsevier]

Abstract: In this work we investigated the Au–Cu binary nanophase diagram by means of structural and compositional characterization of alloy nanoclusters synthesized in silica by means of rf-cosputtering technique. In order to obtain the formation of metallic nanoclusters, as deposited samples have been annealed in reducing atmosphere at 900°C. A good agreement with the bulk alloy phase diagram has been found: in particular the fcc cubic alloy solid solution is present in all the investigated compositions from pure Au to pure Cu, with a lattice parameter following the modified Vegard’s law typical of the bulk alloy. Three ordered phases are also present corresponding to the Au:Cu atomic ratios of 3:1, 1:1 and 1:3. The linear and non-linear optical properties of the nanocomposites have been measured: the surface plasma resonance red-shifts with increasing the Cu content in the alloy and it spans the entire region from that of pure Au (530nm) to that of pure Cu (570nm). [Copyright &y& Elsevier]

Abstract: Prescribed nanocluster composite glass features require the control of the cluster formation and growth, and therefore the definition of effective preparation protocols. In this work, copper-containing silica films were synthesized by sputtering co-deposition of copper and silica in a radiofrequency magnetron sputtering apparatus. The composite system was sequentially thermally-treated in different annealing environment (oxidizing and/or reducing). Characterization of samples along the various preparation steps was performed by Rutherford backscattering spectrometry, X-ray diffraction, and optical absorption spectroscopy. The copper behavior during the composite formation was complex: copper migration and aggregation depend critically on the annealing conditions, and quite different stable structures actually result, such as fcc Cu and/or monoclinic CuO nanoparticles. [Copyright &y& Elsevier]

Abstract: The fast component of the nonlinear refractive index, n 2, of a composite film formed by alloy nanoparticles embedded in silica was measured by Z-scan technique, in conditions free from cumulative heating effects. By using a single 6ps long laser pulse at 1Hz, 527nm of wavelength, a negative sign of n 2 was evidenced. An explanation of this result is suggested, based on the dielectric confinement effect. The fast refractive index value, in modulus, is of the order of 10−10 cm2/W. [Copyright &y& Elsevier]

Abstract: The size, the size distribution, the structure and the concentration of the metallic particles embedded in a host dielectric matrix determine the linear and non-linear optical properties of this kind of composite glasses. In this work, copper-containing silica films about 0.5μm thick were prepared by radio frequency magnetron co-sputtering deposition technique, and then heat-treated in oxidizing and/or reducing atmospheres. The characterization of the samples was performed by optical absorption spectroscopy, Rutherford backscattering spectrometry and transmission electron microscopy. The investigated preparation protocols actually allow to control the final composite structure. Preliminary results indicate that some nanocomposite films have non-linear optical properties in the ps regime. [Copyright &y& Elsevier]

Composite systems with metallic nanoparticles embedded in dielectrics present peculiar physical properties which are attractive in several application fields. In the case of transition elements, the magnetic properties of the metal clusters embedded in a dielectric matrix mainly depend on the particle size and structure. In this work, silica films containing cobalt atoms were synthesized by RF magnetron co-sputtering deposition technique, with cobalt concentration of a few atomic percent. X-ray diffraction and transmission electron microscopy showed the presence of hcp cobalt nanoclusters in the as-deposited sample with the highest cobalt concentration. After deposition, thermal treatments were performed to promote cobalt compounds or nanoparticle formation. The thermal treatments were able to change the oxidation state of cobalt atoms, as well as the structure of metallic cobalt nanoclusters (from hcp to fcc), their final size depending on both the preparation parameters and the subsequent annealing atmospheres. [Copyright &y& Elsevier]

Transition element nanoclusters embedded in dielectric matrix are important for their optical and magnetic properties. In this work, composite silica films with cobalt atomic concentration up to 10% were synthesized by radiofrequency (rf) magnetron co-sputtering deposition technique. The composite systems structure could be triggered by varying the deposition parameters and by using a subsequent thermal treatment to promote the nanocluster formation. Magnetic measurements showed that the embedded cobalt nanoparticles act as superparamagnets, with coercive field and blocking temperature related to their size and structure (hcp or fcc). [Copyright &y& Elsevier]

Metal nanocluster composite glasses (MNCGs) have been the subject of both experimental and theoretical investigation because of their peculiar optical properties. In particular, the enhanced third-order optical nonlinearity could be exploited in the all-optical switching device technology. Nevertheless, several factors such as thermal stability, wavelength tunability, response time regime, recycling frequency, laser-induced damage and optical absorption come into play in the definition of the material suitability. In this work, we present some results on MNCG films prepared by ion implantation. Nonlinear refractive index values are also presented for rf sputtered films, evidencing the presence of thermal nonlinearity in the optical response. Figures of merit that must be satisfied for ultrafast all-optical switching application of MNCGs are evaluated for this composite. [ABSTRACT FROM AUTHOR]

We used the Z-scan technique for measuring the nonlinear refractive index n[sub 2] of a thin composite film formed by copper nanoparticles embedded in silica glass. By varying the number of pulses of the laser shot, we evidenced heating effects induced by the laser during measurements. We were able to estimate the nonthermal refractive-index value, n[sub 2]=(3.0±0.3)x10[sup -12] cm[sup 2]/W. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Sequential ion implantation of Au and Fe ions has been performed in silica. Despite the fact that the two species are not miscible in the bulk, structural characterizations show that the nanoparticles produced are a Au–Fe alloy. The crystalline structure of the nanoparticles is fcc with a lattice parameter of 0.395nm. The nanocomposite is ferromagnetic at 3K, with a magnetic moment per Fe atom equal to 1.4μ B and it shows a hysteresis loop with a coercive field of 24mTorr. Due to alloying, the optical absorption spectrum does not exhibit the typical surface plasmon resonance of gold nanoparticles. The sample exhibits a change of its optical and structural properties when is annealed at 600°C. [Copyright &y& Elsevier]

Abstract: Glass layers for planar light waveguides prepared by Ag–Na ion exchange of different silicate glasses in molten salt baths are annealed and/or irradiated with a laser beam in the UV region, with different energy density values and total pulse numbers. The samples are mainly characterized by optical absorption spectroscopy, luminescence spectroscopy, and Rutherford backscattering spectrometry, in order to determine the role of irradiation parameters and of the host matrix structure in the aggregation phenomena. Photoluminescence spectroscopy gave information regarding the presence of Ag multimeric aggregates, the primal seeds for the growing (nano)crystals. The appearance of the plasmon resonance band in the optical absorption spectra proved the formation of Ag clusters and allowed the evolution steps of the clusterization process to be followed as a function of the energy deposited during the laser irradiation. [Copyright &y& Elsevier]

Abstract: The magnetic properties of Co–Cu/silica nanocomposites prepared by sequential ion implantation have been investigated. The nanostructure is formed of 4nm average size particles dispersed in silica matrix and with mainly FCC structure. The hysteresis loops at 3K indicate that the nanoparticles have uniaxial anisotropy with values smaller than that of single Cobalt implants. The samples are characterized by a superparamagnetic behavior with blocking temperatures that depend on the Co/Cu implanted ratio, and the blocking temperature distributions are narrower than those obtained by taking into account only the particle size distribution. Results are discussed considering size effects and that the nanoparticles are formed of a Co–Cu solid solution or only of Co. [Copyright &y& Elsevier]

Abstract: The nanostructural and magnetic properties of Fe–Pd/SiO2 granular solids prepared by sequential ion implantation have been investigated. Nanostructural features depend on the relative Pd/Fe implanted dose and, in particular, in the Pd50Fe50 sample 2–6nm size nanoparticles with the disordered FCC structure are formed. At low temperatures Fe–Pd composites have open hysteresis loops with coercivity fields of some mT and large magnetic moment per Fe atom (2.8μB). In only-Fe and Fe–Pd composites the nanoparticles are superparamagnetic at room temperature and the blocking temperature increases from 20K, for the only-Fe sample, to 110K, for Fe50Pd50 sample. [Copyright &y& Elsevier]

Metal quantum-dot composite glasses can exhibit an enhanced optical Kerr susceptibility, χ(3), whose real part is related to the n2I coefficient of the intensity-dependent refractive index. We used the Z-scan technique for measuring the n2I’s of micrometric composites films formed by copper with nanometer sized particles embedded in silica glass by means of radiofrequency magnetron sputtering technique, followed by thermal annealing in reducing atmosphere, to promote cluster growth. A single 6 ps long pulse at a repetition rate of 1 Hz was used to determine the picosecond fast (noncumulative, electronic) response of the composites. We obtain n2I from (0.48±0.24)×10−11 to (2.0±1.0)×10−11 cm2/W and β of (3.1±1.6)×10−7 to (8.5±4.2)×10−7 cm/W in the explored range of Cu/SiO2 composition. [Copyright &y& Elsevier]