G. Ausanio

Generation of silicon nanoparticles via femtosecond laser ablation in vacuum

We demonstrate that femtosecond laser ablation of silicon targets in vacuum is a viable route to the generation and deposition of nanoparticles with radii of ≈5–10 nm. The nanoparticles dynamics during expansion has been analyzed through their structureless continuum optical emission, while atoms and ions, also present in the plume, have been identified by their characteristic emission lines. Atomic force microscopy analysis of the material deposited at room temperature has allowed the characterization of the nanoparticles size distribution. Taking into account the emissivity of small particles we show that the continuum emission is a blackbody-like radiation from the nanoparticles. Our results suggest that nanoclusters are generated as a result of relaxation processes of the extreme material state reached by the irradiated target surface, in agreement with recently published theoretical studies.

Ultrashort laser ablation of solid matter in vacuum: a comparison between the picosecond and femtosecond regimes

We have investigated the main features of ultrashort laser ablation of solid matter by using laser pulses of different durations, ranging from fs to ps timescales, and wavelengths, in the visible-near infrared spectral range. The analysis has been carried out on Si and Ni in terms of the two main characteristics of the ablation process: vacuum expansion of the ablated material and generation of nanoparticles of the target material. Fast photography and optical emission spectroscopy were used to characterize the plume expansion dynamics, while atomic force microscopy analysis of less than one layer deposits was employed to analyse the size distribution of the produced nanoparticles. Our analysis indicates that the properties characterizing the plume expansion in vacuum as well as the size distribution of the nanoparticles produced with laser pulses in the range of 100 fs–1 ps are almost independent of the specific material properties and laser pulse characteristics, thus representing general features of the process in these conditions.

Magnetic and morphological characteristics of nickel nanoparticles films produced by femtosecond laser ablation

We have used the technique of femtosecond (fs) laser ablation in a vacuum to produce films of nickel nanoparticles. A peculiarity of this fs laser deposition is the significant shape and orientation anisotropy of the nanoparticles, which are oblate ellipsoids with the major axis parallel to the deposition substrate. The deposited films present unique magnetic properties, and, in specific conditions, very high remanence ratios (up to 0.7) accompanied with relatively low values of saturation and coercive fields can be obtained. We have interpreted these results in terms of the mentioned anisotropies, and of the occurrence of a thermally induced in-plane tensile stress, which is a function of the nanoparticles size.

Synthesis of nanocrystal films via femtosecond laser ablation in vacuum

A new technique based on ultrashort laser ablation of solid targets in vacuum was used to synthesize films of individual nanocrystals of magnetic atoms (Fe and Ni). Laser pulses of 300?fs at 527?nm were used to produce a plume mainly constituted of nanoparticles of the target materials. After vacuum expansion, the plume was deposited on substrates at room temperature to produce ?1??m thick films. Atomic force microscopy and x-ray diffraction analyses of the deposited samples have demonstrated the possibility of producing films constituted of high quality, individual nanocrystals of the atomic targets, with an average size of ?20?nm, and a narrow size distribution. The ultrashort laser ablation and vacuum deposition proved to be a very versatile and simple technique for obtaining nanocrystal films of different materials.

Experimental evidence of stable water nanostructures in extremely dilute solutions, at standard pressure and temperature.

This paper presents the results of several experimental methods (FT-IR spectroscopy, UV-vis spectroscopy, fluorescence microscopy (FM), Atomic Force Microscopy (AFM)) evidencing structural changes induced in extremely diluted solutions (EDS), which are prepared by an iterated process of centesimal (1:100) dilution and succussion (shaking). The iteration is repeated until an extremely high dilution is reached, so that the composition of the solution becomes identical to that of the solvent--in this case water--used to prepare it. The experimental observations reveal the presence of supramolecular aggregates hundreds of nanometres in size in EDS at ambient pressure and temperature, and in the solid state. These findings confirm the hypothesis--developed thanks to previous physico-chemical investigations--that formation of water aggregates occurs in EDS. The experimental data can be analyzed and interpreted with reference to the thermodynamics of far-from-equilibrium systems and irreversible processes.

The potentiality of composite elastic magnets as novel materials for sensors and actuators

Abstract In the last decade the progress of standard magneto-elastic materials is going toward its physical limits. New horizons are recently opened by the development of artificial composites having both elastic and magnetic properties. The working principle of these elastomagnetic materials is not depending on intrinsic magnetostriction, but on the coupling between magnetic moments of the particles and particles themselves. The possibility to study the physical mechanism that relates the elastic and magnetic properties in the new scenery furnished by composites of magnetic particles in an elastic matrix is very promising from the basic knowledge point of view. On the other side, the potential competitiveness in several applications justifies the increasing efforts to improve the production and to perform technical characterization of these magnetoelastic composites in different experimental conditions.

Direct magnetostriction and magnetoelastic wave amplitude to measure a linear displacement

The change of the magnetization intensity induced by a tensile stress in magnetoelastic ribbons can be useful to evaluate a point displacement of an elastic body under deformation. The same measurement can be performed by means of the change in the amplitude of resonant magneteolastic waves, when a longitudinal stress is produced in the ribbons. A comparison between the two techniques is reported in this paper, with the aim to separate the sensitivity limits and the optimum method in different experimental conditions. It is shown how a large stress sensitivity of magnetization is related to a high stress sensitivity of the magnetoelastic waves amplitude but in a different range of applied stress. Generally, the first technique is most useful to investigate a large range of displacement (from 1 μm up to 1 cm) with a good linearity but a decreasing precision if the displacement increases, while the second technique is the most sensitive and also precise (0.01 μm) if little displacement ranges are to be investigated.

Ultrashort laser ablation of bulk copper targets: Dynamics and size distribution of the generated nanoparticles

We address the role of laser pulse fluence on expansion dynamics and size distribution of the nanoparticles produced by irradiating a metallic target with an ultrashort laser pulse in a vacuum, an issue for which contrasting indications are present in the literature. To this end, we have carried out a combined theoretical and experimental analysis of laser ablation of a bulk copper target with ≈50 fs, 800 nm pulses, in an interval of laser fluencies going from few to several times the ablation threshold. On one side, molecular dynamics simulations, with two-temperature model, describe the decomposition of the material through the analysis of the evolution of thermodynamic trajectories in the material phase diagram, and allow estimating the size distribution of the generated nano-aggregates. On the other side, atomic force microscopy of less than one layer nanoparticles deposits on witness plates, and fast imaging of the nanoparticles broadband optical emission provide the corresponding experimental charac...

Critical influence of target-to-substrate distance on conductive properties of LaGaO3/SrTiO3 interfaces deposited at 10−1 mbar oxygen pressure

We investigate pulsed laser deposition of LaGaO3/SrTiO3 at 10−1 mbar oxygen background pressure, demonstrating the critical effect of the target-to-substrate distance, dTS, on the interface sheet resistance, Rs. The interface turns from insulating to metallic by progressively decreasing dTS. The analysis of the LaGaO3 plume evidences the important role of the plume propagation dynamics on the interface properties. These results demonstrate the growth of conducting interfaces at an oxygen pressure of 10−1 mbar, an experimental condition where a well-oxygenated heterostructures with a reduced content of oxygen defects is expected.

Sol-gel synthesis, characterization and bioactivity of poly(ether-imide)/TiO2 hybrid materials

Novel organic-inorganic hybrid materials were synthesized by the sol-gel method from a multicomponent solution containing titanium butoxide, 6 weight % (wt%) or 12 wt% poly(ether-imide) (PEI), water and chloroform. The structure of the interpenetrating network is realized by hydrogen bonds between the Ti-OH group (H-donator) in the sol-gel intermediate species and the carboxylic group (H-acceptor) in the repeating units of the polymer. By Fourier transform infrared (FTIR) analysis the presence of hydrogen bonds between organic-inorganic components of the hybrid materials were proved. The morphology of the hybrid materials was studied by scanning electron microscopy (SEM). The structure of a molecular level dispersion was disclosed by an atomic force microscope (AFM), pore size distribution and surface measurements. The AFM and SEM analyzes confirmed that the PEI/TiO2 samples can be considered homogenous organic/inorganic hybrid materials because in both the compositions studied the average domains were less than 400 nm in size. The bioactivity of the synthesized hybrid materials was demonstrated by the formation of a layer of hydroxyapatite on the surface of the PEI/TiO2 samples soaked in a fluid simulating the composition of human blood plasma (SBF), demonstrated by SEM and energy dispersive spectroscopy (EDS) microscopy.