Giovanni Mattei

Finite depth square well model : Applicability and limitations

An investigation of the finite depth square well model is presented in this article: model features and limitations, concerning size dependent band gap of semiconductor quantum structures, are presented and discussed. Model predictions are compared with large sets of experimental data for III–V, II–VI and lead salt semiconductor quantum dots and quantum wires. Matrix influence on the confinement is studied by modeling experimental results for colloidal CdS, CdSe, CdTe and InP quantum dots. The effect of quantum structure dimensionality is investigated and successfully simulated for colloidal CdSe and InP experimental data and Si first-principle calculations. Finally, model limitations for narrow band gap semiconductors are studied and discussed.

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.

Sub-nanometric metallic Au clusters as efficient Er3+ sensitizers in silica

Silica films co-implanted with Er and Au ions show an enhancement of rare earth photoluminescence after gold introduction in the matrix. Er excitation originates in a broad spectral region, from the red to the near ultraviolet. We have investigated the influence of gold aggregation on the optical properties of co-doped samples by varying the temperature of post-Au implantation annealing in the 400–900°C range. Optical measurements and extended x-ray absorption analysis support the hypothesis of an energy transfer process mediated by sub-nanometric Au aggregates with metallic character that are optically activated mostly through electron interband transitions between d and sp-conduction levels.

Cobalt nanoclusters in silica glass: Nonlinear optical and magnetic properties

Fused silica plates were implanted with Co ions at room temperature at the energy of 50 keV and to the fluence of 4×1016 ions cm−2. The formation of metal nanoclusters was observed by transmission electron microscopy. The cluster size distribution is narrow with a mean-diameter value of about 3 nm. Atomic in-depth distribution was determined by Rutherford backscattering spectrometry, whereas the cobalt chemical state was characterized by electron spectroscopies. Nonlinear refractive index n2 is of the order of 0.2 cm2 G W−1, as determined by the Z-scan technique at a wavelength of 770 nm for 130 fs long pulses at a 76 MHz repetition rate. Zero-field-cooled and field-cooled magnetization curves at the liquid-helium temperature exhibit features of superparamagnetic behavior that are characteristic of assemblies of single-domain nanoparticles.

Au–Cu alloy nanoclusters in silica formed by ion implantation and annealing in reducing or oxidizing atmosphere

The formation of binary alloy clusters in sequentially ion-implanted Au–Cu silica glass has been studied as a function of the annealing atmosphere. Alloy formation has been unambiguously evidenced in the as-implanted samples. The selective influence on Au precipitation of either oxygen or hydrogen annealing atmosphere leads to separation of gold and copper or to Au–Cu alloy cluster formation, respectively.

Alloy nanoclusters in dielectric matrix

Abstract Sequential ion implantation in dielectric matrix determines three different cluster morphologies: separated systems, alloy clusters and core–shell clusters. Post-implantation thermal treatments influence the alloy stability as a function of the annealing atmosphere (oxidizing, inert or reducing). Case studies will be given for the three different structures