S. Martelli

Preparation and investigation of nanostructured SiC-nickel layers by electrodeposition

Nanocomposite layers have been obtained by electrochemical deposition of silicon carbide nanoparticles (mean diameter 20 nm) in a nickel plating bath. The influence of nanoparticles on nickel electroplating is studied by electrochemical impedance spectroscopy (EIS) at cathodic potential. Cathodic polarization diagrams have been determined in the electrolyte with and without nanoparticles. We show that incorporation of 20 nm SiC particles into nickel deposition modifies the impedance and cathodic polarization diagrams in correlation with the modification of the surface morphology and crystallinity of nickel matrix.

Composite Electrodeposition to Obtain Nanostructured Coatings

Nanocomposite coatings are obtained by electrochemical deposition of silicon carbide nanoparticles (mean diameter 20 nm) in a nickel plating bath. The influence of nanoparticles on nickel electroplating is studied by electrochemical impedance spectroscopy at cathodic potential, and cathodic polarization diagrams are performed in the electrolyte with and without nanoparticles. We show that incorporation of 20 nm SIC particles into nickel deposits modifies the impedance and cathodic polarization diagrams in correlation with the modification of the surface morphology and crystallinity of the nickel matrix

Structural and optical modification in hafnium oxide thin films related to the momentum parameter transferred by ion beam assistance

Abstract Hafnium oxide (HfO2) films were deposited on silica and glass substrates by ion (Xe+) assisted deposition with increasing ion momentum transfer to the growing film. The relationship among the ion momentum values, the crystalline phase and the refractive index (packing density) has been worked out by means of X-ray diffraction and spectrophotometric analysis. Compaction of the films by ion beam assistance is clearly evidenced by the changes in their microstructure. A three steps transition from a random monoclinic phase, via amorphous phase, up to an highly phase oriented (fiber texture), as a function of ion momentum, has been found.

LIF FILMS : PRODUCTION AND CHARACTERIZATION

Abstract LiF films were produced by thermal evaporation onto amorphous substrates kept (during evaporation) at temperatures ranging from ambient up to 350°C. The evolution through two polycrystalline states was analysed by X-ray diffraction techniques, which also revealed that the LiF film lattice parameter is equal to that of LiF crystal. The refractive index of the produced films was measured by transmission optical interferometry. Talisurf-6 profilometer measurements on the film surface show sharp edges and very smooth surfaces, which reflect the substrate surfaces.

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.

Production of iron-oxide nanoparticles by laser-induced pyrolysis of gaseous precursors

Laser-assisted pyrolysis in a continuous flow reactor has been applied to synthesise iron-oxide nanoparticles. The scope of the present contribution was to investigate the possibility of increasing the reaction yield in order to obtain powder amounts suitable for practical applications. To this aim, a gas mixture containing Fe(CO)5 and N2O has been submitted to CO2 c.w. laser pyrolysis. As a reaction sensitiser gas, SF6 has been preferred to C2H4 to avoid ethylene fragmentation in N2O presence and the formation of iron carbides. Due to unexpected SF6 dissociation, the synthesis process led to the preferential formation of iron fluoride compounds. Powder samples, submitted to calcining treatment (400°C, 3 h), showed an almost complete transformation to α- and γ-iron oxides retaining the nanostructure feature of the powder.

Influence of LiF film growth conditions on electron induced color center formation

Abstract The formation of laser active color centers in LiF films irradiated with low energy electrons has been investigated as a function of the film growth parameters. Spectroscopic measurements have shown that the formation efficiency of F-aggregate centers is higher in polycrystalline films than in single crystals and can depend on the film growth conditions, which in turn influence the surface to volume ratio, the void presence and the preferred orientation of the crystallites.

On the growth of LiF films by Pulsed Laser Deposition

Abstract The production of Lithium fluoride (LiF) films by Pulsed Laser Deposition is reported for the first time. The influence of several deposition parameters such as the laser energy density, the presence of a gas pressure (10−1 mbar of He) and the substrate temperature on the film quality is studied by using in-situ reflectivity measurements, Scanning Electron Microscopy and X-ray diffraction. Films deposited in vacuum are polycrystalline and fully textured along the 〈100〉 orientation, whereas those grown in He pressure present a more complicated structure. Films are generally rough, the roughness decreasing as the substrate temperature increases or the laser energy density decreases. The origin of this roughness is discussed in terms of the ablation mechanism taking place at the target.

Intense visible photoluminescence from coloured LiF films on silicon

Lithium fluoride films, about 1.5 μm thick, thermally evaporated onto silicon substrates were subjected to low energy electron bombardment. Intense photoluminescence, extending from green to red in the visible spectral range was measured at room temperature in the irradiated areas, due to the presence of the laser active F2 and F3+ colour centres.