Francesco Gonella

Metal Nanocluster Composite Glasses

Publisher Summary This chapter is concerned with metal nanocluster composites formed by transition metal clusters embedded in silicate glasses, in which cluster concentration is below percolation limit (dispersed clusters); in particular, the systems are in the condition of quasi-static regime, where cluster radius is much smaller than the wavelength of the light used to probe its response and–most of all–the light used in a MNCG-based optoelectronic device. Composite materials formed by transition metal clusters embedded in glass matrices exhibit peculiar optical properties. The development of the cluster-matter field assumed a strong impact owing to the experimentalavailability of selected cluster beams and time-of-flight mass spectrometry techniques. In general, the problem of the modelization of the cluster behavior has followed either atomistic (bottom-up) approaches, which exploits ab initio techniques of the quantum chemistry, or top-down approaches, describing the cluster as a mesoscopic piece of bulk to be treated in the solid-state or statistical physics framework. This work gives particular emphasis to the third-order nonlinear optical properties, because their technological implications as well as their peculiarity in MNCGs deserve this detailed treatment. One of the greatest challenges for optics is the development of computer systems based on all-optical photonic switching devices replacing electronic ones, that is, with short time and energy consumption per switch.

Formation of copper and silver nanometer dimension clusters in silica by the sol‐gel process

Ag and Cu (pure and/or mixture) nanoclusters doped silica films were prepared by the sol‐gel process. In the case of Ag and Cu codoped silica films, Cu/Ag molar ratio was 1, 2, and 3 at constant (Ag+Cu)/SiO2 molar ratio of 0.175. Separated Ag and Cu nanoclusters are formed in the silica matrix. The size of the clusters and their distribution are dependent on the film composition. Optical absorption was measured from 185 to 800 nm. Intensity‐dependent nonlinear refractive index was measured for pure Cu and Ag–Cu (1:1 molar ratio) samples using z‐scan technique in the wavelength range from 570 to 596 nm. The measured nonlinear refractive index is of the order of 10−13 m2/W at a pulse repetition rate of 15.2 MHz.

Peculiarities and application perspectives of metal-ion implants in glasses

Abstract Ion implantation in insulators causes modifications in the refractive index as a result of radiation damage, phase separation, or compound formation. As a consequence, light waveguides may be formed with interesting applications in the field of optoelectronics. recently implantation of metals ions (e.g. silver, copper, gold, lead, etc.) showed the possibility of small radii colloidal particles formation in a thin surface layer of the glass substrate. These particles exhibit an electron plasmon resonance which depends on the optical constants of the implanted metal and on the refractive index of the glass host. The non-linear optical properties of such colloids, in particular the enhancement of optical Kerr susceptibility, suggest that the ion implantation technique may play an important role for the production of all-optical switching devices. In this paper an analysis of the state-of-the-art of the research in this field will be presented in the framework of ion implantation in glass physics and chemistry.

Interaction of high‐power laser light with silver nanocluster composite glasses

The size and size distribution of silver nanoclusters embedded in soda‐lime glasses (formed by ion irradiation of Ag+–Na+ ion‐exchanged waveguides) has been modified by high‐power laser irradiation. Optical transmittance in the visible range is found to increase above the energy threshold E*=0.3±0.1 J/cm2 for λ=532 nm and E*=5±1 J/cm2 for λ=1064 nm for pulse lengths of about 10 ns. Cluster size reduction has been observed. Small radii silver nanoclusters are also formed after laser irradiation of ion‐exchanged waveguides. The optical response of the composites has been determined by optical absorption spectroscopy. Transmission electron microscopy, x‐ray photoelectron and Auger electron spectroscopies, and Rutherford backscattering spectrometry have been used to characterize the composites.

Z-scan study on the nonlinear refractive index of copper nanocluster composite silica glass

We used the Z-scan technique for measuring the nonlinear refractive index n2 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, n2=(3.0±0.3)×10−12 cm2/W.

Annealing behavior of silver, copper, and silver–copper nanoclusters in a silica matrix synthesized by the sol‐gel technique

Silver, copper, and mixed silver–copper nanocluster‐doped silica thin layers were prepared by the sol‐gel process. Samples were heat treated in different annealing atmospheres (air, argon, or 5%H2–95%N2) in the temperature range 500–1100 °C. Specimens were characterized by optical absorption spectroscopy, Rutherford backscattering spectrometry, x‐ray diffraction, and transmission electron microscopy. Cluster growth and dissolution, as well as migration of metal atoms towards the sample surface, with a subsequent evaporation, were observed to occur at temperatures that depend on the annealing atmosphere. In the mixed silver–copper system, the formation of Ag–Cu phase‐separated clusters was observed.

Synthesis of silver clusters in silica-based glasses for optoelectronics applications

Abstract The techniques of silver–sodium ion exchange and Ag + ion implantation in glass have been successfully applied for producing silver clusters in soda-lime glass optical waveguides. Optical absorption spectroscopy, time and spectrally resolved photoluminescence, Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy and transmission electron microscopy measurements were made. Structural changes of the Ag + environment were observed in ion-exchanged samples prepared in liquids with different Ag + concentrations. Heat treatments in air and in H 2 atmospheres induced cluster formation in ion-exchanged samples through different reduction–migration mechanisms, whereas clusters formation in ion-implanted samples is related to the defect concentrations induced by the radiation damage.

LARGE THIRD-ORDER OPTICAL NONLINEARITY OF NANOCLUSTER-DOPED GLASS FORMED BY ION IMPLANTATION OF COPPER AND NICKEL IN SILICA

Composite glasses containing different metal nanoclusters were obtained by implanting copper, nickel, or copper+nickel ions in SiO2 glass. The nonlinear refractive index of the composites was determined by the Z-scan method at a wavelength of 770 nm and with a laser pulse duration of 130 fs. Values of n2 up to 0.68 cm2 gW−1 were measured in the case of the Cu+Ni implanted sample.

Spectroscopic investigation of silver in soda-lime glass

Abstract Spectral and time-resolved luminescence of silver in ion-exchanged soda-lime glass are investigated for samples with different Ag concentrations. The evolution of the observed spectroscopic features are correlated with structural changes in the silver environment from a marked ionic position with a weak influence of the surroundings to a configuration characterized by stronger silver–lattice coupling and Ag + –Ag + correlation effects.

Nanoparticle formation in silicate glasses by ion beam-based methods

Abstract Ion implantation (single or sequential) and ion irradiation of metal-doped matrices can be used to prepare metal nanocluster composite glasses. Some experiments are reviewed pointing out the effectiveness of these methods for controlled nanoparticle formation in silicate glasses.