Angela De Bonis

Nanoparticles and thin film formation in ultrashort pulsed laser deposition of vanadium oxide.

The ultrashort pulsed laser deposition of vanadium oxide thin films has been carried out by a frequency-doubled Nd:glass laser with a pulse duration of 250 fs. The characteristics of the plasma produced by the laser-target interaction have been studied by ICCD imaging and optical emission spectroscopy. The results confirm that an emitting plasma produced by ultrashort laser pulses is formed by both a primary and a secondary component. The secondary component consists of particles with a nanometric size, and their composition and spatial angular distribution influence the deposited films. In fact, these films, analyzed by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and atomic force microscopy, are formed by the aggregation of a large number of nanoparticles whose composition is explained by a model based on equilibrium thermal evaporation from particles directly ejected from the target. On these basis, the presence in the films of a mixture of V(2)O(5) and VO(2) is discussed.

Interdisciplinary approach to cell-biomaterial interactions: biocompatibility and cell friendly characteristics of RKKP glass-ceramic coatings on titanium.

In this work, titanium (Ti) supports have been coated with glass-ceramic films for possible applications as biomedical implant materials in regenerative medicine. For the film preparation, a pulsed laser deposition (PLD) technique has been applied. The RKKP glass-ceramic material, used for coating deposition, was a sol-gel derived target of the following composition: Ca-19.4, P-4.6, Si-17.2, O-43.5, Na-1.7, Mg-1.3, F-7.2, K-0.2, La-0.8, Ta-4.1 (all in wt%). The prepared coatings were compact and uniform, characterised by a nanometric average surface roughness. The biocompatibility and cell-friendly properties of the RKKP glass-ceramic material have been tested. Cell metabolic activity and proliferation of human colon carcinoma CaCo-2 cells seeded on RKKP films showed the same exponential trend found in the control plastic substrates. By the phalloidin fluorescence analysis, no significant modifications in the actin distribution were revealed in cells grown on RKKP films. Moreover, in these cells a high mRNA expression of markers involved in protein synthesis, proliferation and differentiation, such as villin (VIL1), alkaline phosphatase (ALP1), β-actin (β-ACT), Ki67 and RPL34, was recorded. In conclusion, the findings, for the first time, demonstrated that the RKKP glass-ceramic material allows the adhesion, growth and differentiation of the CaCo-2 cell line.

Formation of Titanium Carbide (TiC) and TiC@C core-shell nanostructures by ultra-short laser ablation of titanium carbide and metallic titanium in liquid.

Laser ablation of bulk target in liquid allows to obtain stable nanoparticles and nanostructures, also in metastable phases, limiting the use of hazardous reagents and extreme reaction conditions. Titanium carbide (TiC) is a ceramic compound with several technological applications ranging from biocompatible materials to wear resistant coatings. The possibility to obtain core/shell structures expands its range of application due to the ability of modify the surface properties of the core ceramic material. TiC and metallic titanium targets have been ablated by means of an ultra-short laser source in different liquid media (water, acetone, n-hexane and toluene). The obtained colloidal solutions have been characterized by TEM, XRD and micro-Raman analysis. In all the used experimental conditions TiC nanoparticles have been produced. During water and acetone mediated ablations, the oxidation of titanium has been observed, whereas by using oxygen free solvents, such as n-hexane and toluene, core/shell TiC nanoparticles embedded in amorphous and graphitic carbon shell, respectively, have been obtained.

Laser ablation of GaAs in liquid: the role of laser pulse duration

The synthesis of gallium arsenide (GaAs) nanoparticles has attracted wide scientific and technological interest due to the possibility of tuning the GaAs NP (nanoparticle) band gap across the visible spectrum and their consequent use in optoelectronic devices. In recent years, laser ablation in liquid (LAL) has been widely used for the preparation of colloidal solutions of semiconducting and metallic nanoparticles, thanks to its flexibility. With the aim of highlighting the key role played by laser pulse duration on the ablation mechanism and on the properties of the obtained materials, laser ablation of a gallium arsenide target in acetone was performed using laser sources operating in two different temporal regimes: Nd:glass laser ( = 527 nm, pulse duration of 250 fs and frequency repetition rate of 10 Hz) and Nd:YAG laser ( = 532 nm, pulse duration of 7 ns and frequency repetition rate of 10 Hz). The ablation process was studied following the dynamics of the laser induced shock waves (SWs) and cavitation bubbles (CBs) by fast shadowgraphy, showing that CB dimension and lifetime is related to the laser pulse length. A characterization of the obtained materials by TEM (transmission electron microscopy) and microRaman spectroscopy have shown that quite spherical gallium oxide/GaAs nanoparticles can be obtained by nanosecond laser ablation. On the other hand, pure polycrystalline GaAs nanoparticles can be produced by using an ultrashort laser source.

Inverse Calibration Free fs-LIBS of Copper-Based Alloys

Abstract In this work the analysis by Laser Induced Breakdown Spectroscopy (LIBS) technique of copper-based alloys having different composition and performed with fs laser pulses is presented. A Nd:Glass laser (Twinkle Light Conversion, λ = 527 nm at 250 fs) and a set of bronze and brass certified standards were used. The inverse Calibration-Free method (inverse CF-LIBS) was applied for estimating the temperature of the fs laser induced plasma in order to achieve quantitative elemental analysis of such materials. This approach strengthens the hypothesis that, through the assessment of the plasma temperature occurring in fs-LIBS, straightforward and reliable analytical data can be provided. With this aim the capability of the here adopted inverse CF-LIBS method, which is based on the fulfilment of the Local Thermodynamic Equilibrium (LTE) condition, for an indirect determination of the species excitation temperature, is shown. It is reported that the estimated temperatures occurring during the process provide a good figure of merit between the certified and the experimentally determined composition of the bronze and brass materials, here employed, although further correction procedure, like the use of calibration curves, can be demanded. The reported results demonstrate that the inverse CF-LIBS method can be applied when fs laser pulses are used even though the plasma properties could be affected by the matrix effects restricting its full employment to unknown samples provided that a certified standard having similar composition is available.

Silica Xerogel Obtained by Ultrashort Laser Irradiation of Tetraethyl Orthosilicate

The formation of an opaque solid foam was induced by the direct interaction between tetraethyl orthosilicate (TEOS) and an ultrashort femtosecond laser source(Nd:glass, 527 nm, 10 Hz, 250 fs). The product, which resulted to be a silica xerogel, was characterized by different techniques. In particular, information about the morphology was obtained by scanning and transmission electron microscopy (SEM and TEM), while the presence of different functional groups was studied through IR measurements. Since the properties of this kind of material can be improved by functionalizing it with metal nanoparticles, a palladium metal target was ablated in liquid TEOS. TEM images show that palladium was present in the form of nanoparticles and EDX measurements confirm the presence of the metal inside the silica network.

Ultrashort Pulsed Laser Ablation of Magnesium Diboride: Plasma Characterization and Thin Films Deposition

A MgB2 target has been ablated by Nd:glass laser with a pulse duration of 250 fs. The plasma produced by the laser-target interaction, showing two temporal separated emissions, has been characterized by time and space resolved optical emission spectroscopy and ICCD fast imaging. The films, deposited on silicon substrates and formed by the coalescence of particles with nanometric size, have been analyzed by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, micro-Raman spectroscopy, and X-ray diffraction. The first steps of the films growth have been studied by Transmission Electron Microscopy. The films deposition has been studied by varying the substrate temperature from 25 to 500°C and the best results have been obtained at room temperature.

Ultrashort pulsed laser deposition of ITO thin films

Pulsed Laser Deposition of indium tin oxide in the femtosecond regime has been performed in our laboratory. Plume diagnostics has been carried out by means of a fast Intensified Coupled Charge Device (ICCD) camera. Optical emission spectroscopy has been applied to characterize the transient species produced in the femtosecond regime. The time evolution of emission lines has been discussed and compared with that obtained for nanosecond regime. The films, deposited on glass substrates, has been analysed by scanning electron microscopy, energy dispersive x ray analysis, x ray photoelectron spectroscopy and x ray diffraction. The results obtained from femtosecond ablation show that the processes in the short pulse regimes are very different from the nanosecond one. In particular the plume angular distribution shows a characteristic high cosine exponent and the composition of the deposits is completely stoichiometric and independent from the laser fluence, even if to obtain crystalline films a substrate temperature of 600 °C is needed. Preliminary data indicate that the deposited films are suitable for gas sensor applications.