E. Borsella

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.

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.

Laser synthesis and crystallographic characterization of ultrafine SiC powders

High purity, ultrafine SiC powders have been produced from gas phase reactants (SiH{sub 4}, C{sub 2}H{sub 2}) in a CO{sub 2} laser induced process. The flow reactor designed to operate with a medium power (10--50 W) continuous wave CO{sub 2} laser source is described. The mechanism of gas phase reactions involved has been investigated by means of on-line optical diagnostics. Powders produced have been characterized by means of conventional chemical and spectroscopic methods. The x-ray results point out a growth mechanism by coalescence; i.e., whole islands move in the flame to take part in binary collisions, analogously to that observed for particles produced by inert gas evaporation.

Laser‐driven synthesis of nanocrystalline alumina powders from gas‐phase precursors

Carbon dioxide laser synthesis from gaseous precursors has been successfully applied to produce nanosized Al2O3 particles. Trimethylaluminum [Al(CH3)3] and nitrous‐oxide (N2O) were used as gas phase reactants. Ethylene (C2H4) was added as sensitizer gas. The as‐synthesized powder particles showed considerable carbon contamination and an amorphouslike structure. After thermal treatment at 1200–1400 °C, the powder transformed to hexagonal α‐Al2O3 with very low carbon contamination, confirmed by x‐ray diffraction, x‐ray photoelectron spectroscopy, and chemical analysis. The thermally treated powder was composed of spherical single‐crystal nanoparticles with a mean size 〈D〉 of 15–20 nm, as determined by x‐ray diffraction, electron microscopy, and Brunauer–Emmett–Teller specific surface measurements. The laser synthesized Al2O3 particles are suitable dispersoids for intermetallic alloy technology.

Synthesis of TiC and SiC/TiC nanocrystalline powders by gas-phase laser-induced reaction

In the development of advanced ceramic nanocomposites, the production of titanium-based nanopowders has assumed importance, especially since recent results showed that mechanical properties of SiC matrices could be significantly improved by the incorporation of TiC second phase and vice versa. Nanosized TiC and TiC/SiC powders were synthesized by CO2 laser-induced reactions. A TiCl4 and hydrocarbons mixture was irradiated for titanium carbide production; the addition of SiH4 gave rise to the composite powders. The results of the powder characterization, obtained mainly by X-ray photoelectron spectroscopy, X-ray-induced Auger Spectroscopy and X-ray diffraction, are discussed in detail to correlate the reaction parameters to the composition and morphology of the products. Both TiC and SiC/TiC nanopowders showed a high reactivity to the air exposure, as evinced by the surface oxidation of the particles. Nevertheless, a quite good yield was obtained for nanocomposites of β-SiC matrix with the addition of up to 20% TiC phase.

Evidence of energy transfer in an aluminosilicate glass codoped with Si nanoaggregates and Er3+ ions

The enhancement of the Er3+ ions’ photoluminescence (PL) emission at 1.54μm in a Si and Er coimplanted aluminosilicate glass is investigated in detail. A postimplantation thermal treatment has been performed to recover the damage induced by the implantation process and to promote Si aggregation. It will be shown that 1h treatment in N2 atmosphere is not sufficient to induce Si precipitation for temperatures up to 500°C. Nevertheless, the most intense Er3+ PL emission at 1.54μm is achieved after a thermal treatment at 400°C. Such emission has been investigated by pumping in and out of resonance, showing a very efficient energy transfer process in the whole excitation wavelength range (360–515nm). These results suggest that good energy transfer mediators could be small Si aggregates and not only crystalline clusters. For the best performing sample, the effective Er excitation cross section has been measured to be higher than 10−17cm2 at 379 and 390nm and about 2×10−16cm2 at 476nm, that is, several orders of...

Resonance structure of multiple-photon excitation in symmetric and asymmetric tops☆

Abstract IR multiphoton resonances have been observed in the absorption spectra of C 2 F 5 Cl, CF 3 Br and CF 3 I excited by means of a continuously-tunable CO 2 laser. Their preliminary assignment, based on available spectroscopic data, shows the relevance of hot bands and Fermi resonances in the first steps of the non-linear laser excitation. The significance of multiphoton resonances for laser chemistry and isotope separation is discussed briefly.

Composite ceramic powders obtained by laser induced reactions of silane and amines

Ultrafine, ternary (Si/C/N) ceramic powders have been produced after CO 2 laser initiated reactions between silane and mono- or dimethylamine. Various spectroscopic diagnostics and chemical analyses, including ir spectrophotometry, x-ray photoelectron spectroscopy, and x-ray diffraction analysis have been employed to correlate the parameters involved in gas-phase reactions and the powder final composition.

Observation of structure in the quasicontinuum of multiple-photon-excited C2 F5Cl

Abstract We report the observation of strong spectral structure in the dissociation yield of C 2 F 5 Cl excited by two CO 2 lasers, as a function of the second, non-resonant laser, observed under molecular-beam conditions. This structure is associated with combination bands revealed by matrix-isolation spectroscopy.

SURFACE ANALYSIS STUDY OF THE OXIDATION OF ORGANOTIN FILMS DEPOSITED BY ARF EXCIMER LASER CHEMICAL VAPOR DEPOSITION

ArF excimer laser photolysis of gas phase tetramethyltin was used to deposit thin organotin films on Si. In situ Auger electron spectroscopy and x-ray photoelectron spectroscopy (XPS) film analysis, showed the presence of C and Sn, which, according to C 1s and Sn 3d5/2 peak deconvolution, were organized in highly branched polymeric chains likely containing H as well. The film was oxidized at room temperature by exposure to controlled quantities of O2 up to 5.4×1012L. Sn 3d5/2, C 1s, and O 1s XPS peaks monitoring allowed us to follow the sequence of the oxidative reactions. It resulted that oxygen attacks first the Sn–H and Sn–C sites leading to the elimination of H2O and C containing volatile compounds, which determines a rearrangement of the cleaved bonds and an overall decrease of the measured C content. After this fast phase, oxygen is inserted in the Sn–Sn and Sn–C bonds, with formation of Sn–O–Sn, Sn–O–C, and Sn–C–O species. At the highest oxygen doses the dominating SnO2 component shows that almost ...