C. Maurizio

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.

Fast nonlinear refractive index of pure and alloy metallic nanoclusters in silica glass

Abstract Fast nonlinear refractive index and nonlinear absorption coefficient were measured at 527 nm of wavelength for composites formed by either copper or gold-silver alloy nanoparticles embedded in silica by the Z-scan technique. A single 6 ps long pulse from a Nd:glass laser was used in the Z-scan measurement, allowing to determine the fast (i.e., non-thermal) component of the nonlinear response. Both the composites exhibit relatively large (and negative for the Au–Ag alloy) nonlinear index. Transmission electron microscopy, optical absorption and extended X-ray absorption fine structure spectroscopies were also used to characterize the samples. Some figures of merit for the two samples were evaluated, as well as the third-order optical susceptibilities.

Silver nanocluster formation in ion-exchanged glasses by annealing, ion beam and laser beam irradiation: An EXAFS study

Extended X-ray absorption fine structure analysis is used to determine the silver local environment in silicate glasses doped by the Ag-alkali ion-exchange process, followed by different treatments, namely, ion irradiation, thermal annealing in reducing atmosphere, laser irradiation. The obtained results indicate that metal nanocluster composites with different cluster structures may be formed with these multistep methodologies, pointing out the role of the preparation parameters in giving rise to different features. Lattice parameters and cluster diameter were determined by grazing incidence X-ray diffraction.

SYNTHESIS OF GaN QUANTUM DOTS BY ION IMPLANTATION IN DIELECTRICS

GaN nanocrystals (in the wurtzite phase) were synthesized by sequential implantation of Ga and N ions into either crystalline (quartz, sapphire) or amorphous (silica) dielectrics, followed by annealing of the samples in flowing NH3 gas at 900 °C. GaN was formed by reaction of implanted Ga with NH3 combustion products and/or via conversion of Ga oxide/oxynitrides. A blueshift of the near-band-edge photoluminescence (quantum-confinement effect) was observed for GaN nanocrystals with size ⩽2–3 nm, present in all the substrates.

Nanocluster formation in silicate glasses by sequential ion implantation procedures

Abstract Cluster formation is studied after sequential double implantation (Cu, Ni; Ag, S) in silica and soda–lime glass. The structure and properties of nanocluster composites are investigated by optical absorption spectroscopy and transmission electron microscopy, evidencing the formation of core-shell structures. The presence of metal alloy clusters is also investigated by means of synchrotron-radiation-based techniques.

Nb clusters formation in Nb-doped magnesium hydride

Extended x-ray absorption fine structure spectroscopy, x-ray diffraction and transmission electron microscopy were used to analyze the Nb coordination and clustering in Nb-doped (5 at. %) h-Mg film samples deposited by rf magnetron sputtering. Results show that the catalytic effect of the Nb doping in the H2 absorption and desorption kinetics is connected with the formation of Nb nanoclusters dispersed in the host matrix. The H2 desorption from β-MgH2 is favored by local elastic stresses produced by β-NbH0.89 clusters on the MgH2 matrix that reduces the stability of the hydride phase and by preferential paths in the nanocomposite hydride.

Influence of annealing atmosphere on metal and metal alloy nanoclusters produced by ion implantation in silica

Abstract The evolution of binary alloy clusters in sequentially ion-implanted Au/Cu or Ag/Au silica glasses has been studied as a function of the annealing atmosphere. Alloy formation has been unambiguously evidenced in the as-implanted samples. In the case of Au/Cu system, the selective effect of reducing (hydrogen containing) or oxidizing (air) atmosphere during subsequent annealing can be used to either modify the structure of the alloy or to separate the two species, respectively. On the contrary, no remarkable difference between reducing or oxidizing post-implantation annealing can be evidenced in the Au/Ag system.

MAGNETIC PROPERTIES OF Co AND Ni BASED ALLOY NANOPARTICLES DISPERSED IN A SILICA MATRIX

Abstract A comparative study of the magnetic properties of Co and Ni based alloy nanoparticles (Ni–Co, Ni–Cu and Co–Cu) formed in a silica matrix by ion implantation is presented. Different ion doses and implantation sequences were realized in order to obtain different nanostructures. The structural and magnetic properties observed for the Cu50Ni50 nanoparticles are similar to those of the Cu60Ni40 bulk alloy. The crystal structure of CoxNi1−x (0⩽x⩽1) nanoparticles is similar to that of the corresponding bulk alloy. The magnetic properties depend on the ion-implanted dose and on the alloy composition. The samples prepared by implanting a 15×10 16 ions / cm 2 total dose contain nanoparticles, which are superparamagnetic at room temperature and their magnetic behavior is influenced by dipolar interparticle interactions. The magnetization of the CoNi samples at high magnetic field is larger than that of the corresponding bulk alloy and follows the same composition dependence of that quantity measured in the alloy.

Pd-based alloy nanoclusters in ion-implanted silica: Formation and stability under thermal annealing

Abstract In this work we report on the formation and stability under thermal annealing of Pd–Cu and Pd–Ag alloy nanoclusters obtained by sequential ion implantation in silica. The role of the annealing atmosphere on the alloy cluster formation and stability is investigated. A comparison is made with similar alloy-based systems obtained by sequential ion implantation in silica of Au–Ag or Au–Cu followed by annealing under similar conditions, in order to evidence the peculiar effect of the various metals in controlling the alloy evolution and/or decomposition.

On the optical absorption and nonlinearity of silica films containing metal nanoparticles

Abstract 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.