Luisa Caneve

LIBS as a diagnostic tool during the laser cleaning of copper based alloys: experimental results

In spite of difficulties in quantitative LIBS analysis on copper based alloys, the very low invasiveness of the technique strongly sustains attempts to use it with cultural heritage materials, including ancient bronzes. Analytical results obtained with calibration curves and a calibration free model are compared here on a set of ancient roman coins. An attempt is presented to monitor the laser ablation process on bronze coins and artificially aged standards during the cleaning. The double pulse technique showed that LIBS analytical results could benefit from synchronization between the UV laser sources used, respectively, for cleaning (266 nm) and for LIBS analysis (335 nm).

The influence of the momentum transfer on the structural and optical properties of ZnSe thin films prepared by r.f. magnetron sputtering

Abstract ZnSe films were deposited at room temperature by radio frequency magnetron sputtering onto [100] oriented silicon substrates. Under the same deposition conditions three sets of samples were produced by varying the sputtering pressure (0.4, 0.5 and 0.9 Pa), and changing the sputtering power supply in the range 25–150 W. The effect of the different growth conditions on the structural and optical properties was investigated by using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) Spectroscopy. In particular, the dependence of the coatings residual strain, texture, refractive index and extinction coefficient on the parameter β, proportional to the momentum transfer was studied. According to the results, the ZnSe coatings were grown almost exclusively in the cubic phase with a small percentage of very disordered ZnSe hexagonal phases. At low β values, the films were found in a tensile in-plane stress state, then a stress inversion from tensile to compressive occurred at β=27 a.u. and the films remained in a compressive state for momentum values β>27 a.u.

Synthesis and characterization of ZnO nanorods with a narrow size distribution

The development of novel materials for energy harvesting applications or strain sensing has generated great interest towards zinc oxide (ZnO) nanostructures, and in particular towards the synthesis of ZnO nanowires or nanorods with well controlled morphology and properties. The high-yield mass production of such nanostructures by catalyst-free methods is a crucial aspect to enable a cost-effective large-scale development of new ZnO-based piezoelectric devices and materials. In the present work, we propose a method for the mass-production of high-purity ZnO-nanorods with a uniform size distribution, based on the combination of thermal decomposition of zinc acetate dihydrate and probe sonication in acetone. The quality of the produced ZnO nanorods is assessed through multi-technique characterization using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and photo-luminescence spectroscopy (PL). The adopted synthesis method is simple, cost effective and feasible for large-scale production. Various process parameters such as precursor amount and growth time have been found to play an important role in controlling the formation of the as grown nanostructures with high uniformity in size and morphology. Size distribution curves were employed to depict the effect of various process parameters for tailoring the morphology, homogeneity and aspect ratio of the nanorods. Our results reveal that the high crystallographic quality of ZnO nanorods grown by a long-time thermal decomposition method is not affected by probe sonication, which is proposed as a post-synthesis step necessary to produce ZnO nanorod powder with a uniform distribution of diameters and lengths.

Investigation of the mechanism of CO2 laser driven production of ultrafine sinterable (Si3N4 and SiC) powders

Abstract Silicon containing powders (Si3N4) and SiC) have been produced by TEA CO2 laser induced reactions in the gas phase. NH3 and several hydrocarbons (C2H4, C3H6, C2H2) have been used as additives to SiH4. The gas-phase decomposition process has been studied by detecting the entire luminescence spectrum emitted by early reaction products with an optical multichannel analyzer. Powder composition and morphology have been studied through IR spectrophotometry, X-ray diffraction at wide (WAXS) and small (SAXS) angles. The powder stoichiometry has been checked by using standard LECO systems for C and N determination.

Measurements of deuterium retention and surface elemental composition with double pulse laser induced breakdown spectroscopy

15th International Conference on Plasma-Facing Materials and Components for Fusion Applications, PFMC 2015

Quantitative elemental analyses of archaeological materials by laser-induced breakdown spectroscopy (LIBS): an overview

LIBS is one of the most promising techniques for rapid, in-situ elemental analyses of artworks. It does not require sample preparation, it is almost non destructive (micro sampling) and information both about major and trace elements could be obtained simultaneously. LIBS has been used to recognize the elements present in different archaeological materials and has been also proposed for on-line monitoring during the object cleaning by lasers. Quantitative determination of the material composition can supply useful information to restorers and help the object cataloguing. However, the analytical LIBS measurements on the archaeological materials were rarely reported, mainly due to difficulties to obtain the corresponding matrix-matched standards, required for the initial calibration. Alternatively, Calibration-Free (CF) approach could be used on some class of materials if all the major sample elements are detected and if the laser plasma preserves the material stochiometry. The latter condition is sometimes missing, as in the case of bronzes under nanosecond pulse laser ablation. We have developed a theoretical model for laser ablation of quaternary copper alloys, which allows for correction of the missing plasma stochiometry in CF approach. The model also predicts the optimal calibration for this type of material. In our recent work, we also obtained quantitative LIBS results on marbles by realizing the calibration standards starting from doped CaCO3 powders and by applying the corrections on the plasma parameters, different for the laboratory standards and marbles. Semi-quantitative LIBS results have been also obtained on multi-layered renaissance ceramics by subtraction of the contribution to plasma of each ceramic layer.

Residual stress and adhesion in ion-assisted hafnia coatings on glass

Thin film mechanical properties are strongly influenced by the features of the employed deposition technique. Ion beam-assisted evaporation permits good control of the parameters involved in the process and offers several advantages in processing coatings with expected performance. In this paper, the generation of residual stresses depending on the ion bombardment conditions and their effect on the adhesion behaviour of hafnium dioxide IBAD thin films were investigated. Stresses, which were tensile or compressive depending on the momentum parameter RE1/2 values, where R is the ion-to-atom arrival ratio and E is the ion energy, were measured with a mechanical profilometer by the curvature change of the sample before and after the deposition. The scratch test technique was used to evaluate the adhesion failure load (Lc) of the HfO2 thin films and is correlated with the stress present in the samples themselves. The analysed samples showed an increase in critical load as the momentum parameter value increased...

Development of nanocomposites for conservation of artistic stones

Properties of consolidant and protective materials modified with nanoparticles were analysed in this study following their application onto marble samples. For this purpose, different solutions of an acrylic resin with dispersed SiO2 and TiO2 nanoparticles were prepared. The relative durability of Paraloid B72, an acrylic resin used as consolidant and modified by nanoparticles, was evaluated comparatively by means of diverse diagnostic techniques, namely, scanning electron microscopy, laser-induced fluorescence, ultrasonic sound, colorimetry, total immersion water absorption and contact angle. The results demonstrate that nanoparticles enhance the effectiveness of consolidant and protective material because they induce substantial changes of surface morphology of the coating layer.

IR multiple-photon excitation of polyatomic molecules: a route towards nanostructures

The availability of high power IR laser sources in the 1980s paved the way to new attractive experiments for driving chemical reactions, based on the selective excitation of vibrational modes in polyatomic molecules up to and above the dissociation threshold. The process was first studied in the collisionless regime for applications to laser isotope separation and selective chemistry, and later in collision-assisted conditions leading to the synthesis of nanostructures. In particular, the mechanisms of IR laser pyrolysis of SiH4 and hydrocarbons were investigated in order to control the production of silicon- and carbon-based nanoaggregates. For this purpose, different on-line diagnostics were utilized to monitor the gas-phase reaction intermediates and the process of particle nucleation and growth. The basic principles of the process of multiple-photon excitation of polyatomic molecules and its applications to the synthesis of nanostructures will be reviewed in this paper. Peculiar optical properties of silicon nanoparticles and carbon nanotubes obtained as final products of the developed processes will be described in relation to remarkable applications in several fields.

Control of the size and density of ZnO-nanorods grown onto graphene nanoplatelets in aqueous suspensions

Zinc oxide nanorods (ZnO-NRs) with high density and chemical purity were grown onto unsupported graphene nanoplatelets (GNPs) in aqueous suspensions, using two different growth approaches namely: a hydrothermal method and ultrasonic probe sonication. The size and density of the ZnO-nanorods grown onto graphene nanoplatelets were controlled through seed layer deposition and through the proper setting of the process parameters, in particular through the control of the fluidodynamics of the colloidal suspension during the growth. The highest growth density of the ZnO nanorods having a diameter of ∼45 nm was obtained onto GNPs seeded by the probe sonication method and through the hydrothermal method in dynamic conditions. XRD and XPS investigations confirmed that all produced ZnO-GNP composites are characterized by high crystallinity and purity, although solution dynamics affected their UV luminescence. The proposed approaches enable the controlled high-density growth of crystalline ZnO-NRs onto GNPs in an aqueous suspension, at a low cost, and are suitable for large scale production.