O. De Pascale

Heavy metal concentrations in soils as determined by laser-induced breakdown spectroscopy (LIBS), with special emphasis on chromium

Soil is unanimously considered as one of the most important sink of heavy metals released by human activities. Heavy metal analysis of natural and polluted soils is generally conducted by the use of atomic absorption spectroscopy (AAS) or inductively coupled plasma optical emission spectroscopy (ICP-OES) on adequately obtained soil extracts. Although in recent years the emergent technique of laser-induced breakdown spectroscopy (LIBS) has been applied widely and with increasing success for the qualitative and quantitative analyses of a number of heavy metals in soil matrices with relevant simplification of the conventional methodologies, the technique still requires further confirmation before it can be applied fully successfully in soil analyses. The main objective of this work was to demonstrate that new developments in LIBS technique are able to provide reliable qualitative and quantitative analytical evaluation of several heavy metals in soils, with special focus on the element chromium (Cr), and with reference to the concentrations measured by conventional ICP spectroscopy. The preliminary qualitative LIBS analysis of five soil samples and one sewage sludge sample has allowed the detection of a number of elements including Al, Ca, Cr, Cu, Fe, Mg, Mn, Pb, Si, Ti, V and Zn. Of these, a quantitative analysis was also possible for the elements Cr, Cu, Pb, V and Zn based on the obtained linearity of the calibration curves constructed for each heavy metal, i.e., the proportionality between the intensity of the LIBS emission peaks and the concentration of each heavy metal in the sample measured by ICP. In particular, a triplet of emission lines for Cr could be used for its quantitative measurement. The consistency of experiments made on various samples was supported by the same characteristics of the laser-induced plasma (LIP), i.e., the typical linear distribution confirming the existence of local thermodynamic equilibrium (LTE) condition, and similar excitation temperatures and comparable electron number density measured for all samples. An index of the anthropogenic contribution of Cr in polluted soils was calculated in comparison to a non-polluted reference soil. Thus, the intensity ratios of the emission lines of heavy metal can be used to detect in few minutes the polluted areas for which a more detailed sampling and analysis can be useful.

Nanoparticle-Enhanced Laser-Induced Breakdown Spectroscopy of Metallic Samples

In this article, an increase of 1-2 orders of magnitude in laser-induced breakdown spectroscopy (LIBS) signals was obtained by depositing silver nanoparticles on metal samples. Nanoparticle-enhanced LIBS (NELIBS) was found to be a robust and flexible tool for the chemical analysis of metals because the sample emission signal did not appear to be affected much by the size and concentration of deposited nanoparticles (NPs) within the ranges of 10 nm for diameter and 1 order of magnitude for concentration. On the other hand, preliminary NELIBS tests on insulators and semiconductors did not show any significant enhancement with respect to conventional LIBS. In this article, we present a detailed investigation of the fundamental features of NELIBS spectra, in addition to some examples of analytical applications to the quantitative analysis of metal alloys.

Non-equilibrium plasma kinetics: a state-to-state approach

State-to-state approaches are used to shed light on (a) thermodynamic and transport properties of LTE plasmas, (b) atomic and molecular plasmas for aerospace applications and (c) RF sustained parallel plate reactors. The efforts made by the group of Bari in the kinetics and dynamics of electrons and molecular species are discussed from the point of view of either the master equation approach or the molecular dynamics of elementary processes. Recent experimental results are finally rationalized with a state-to-state kinetics based on the coupling of vibrational kinetics with the Boltzmann equation for the electron energy distribution function.

Optical emission spectroscopy and modeling of plasma produced by laser ablation of titanium oxides

Abstract In the present study, the time evolution of electron number density, of electron, atom and ion temperatures, of plasma produced by KrF excimer laser ablation of titanium dioxide and monoxide targets, are investigated by temporally and spatially resolved optical emission spectroscopy over a wide range of laser fluence from 1.7 to 6 J cm −2 , oxygen pressures of 10 −2 –10 −1 torr and in a vacuum. A state-to-state collisional radiative model is proposed for the first time to interpret the experimental results at a distance of 0.6 mm from the target surface, in vacuum and for a time delay from 100 to 300 ns from the beginning of the laser pulse. In particular, we concentrate our attention on problems concerning the existence of the local thermodynamic conditions in the laser-induced plasma and deviation from them, as observed in our experiment. The numerical model proposed for calculating the electron number density and the population densities of atoms and ions in excited states give good quantitative agreement with the experimental results of the optical emission spectroscopy measurements.

Transport Properties of High-Temperature Jupiter-Atmosphere Components

Transport properties of high-temperature helium and hydrogen plasmas as well as Jupiter atmosphere have been calculated for equilibrium and nonequilibrium conditions using higher approximations of the Chapman–Enskog method. A complete database of transport cross sections for relevant interactions has been derived, including minority species, by using both ab initio and phenomenological potentials. Inelastic collision integrals terms, due to resonant charge-exchange channels, have been also considered.

Thermodynamics, Transport and Kinetics of Equilibrium and Non-Equilibrium Plasmas: A State-to-State Approach

Thermal non-equilibrium plasmas have been deeply investigated theoretically by means of the state-to-state approach, offering the unique opportunity of a detailed information about internal distributions affecting thermodynamics, transport coefficients and kinetics, properly accounting for the presence of excited states. The efforts made in the construction of knowledge on the dynamics of elementary processes occurring in the plasma with resolution on internal degrees of freedom, required by the method, are discussed. Boltzmann equation is solved for electrons self-consistently coupled to the chemical species collisional dynamics, reproducing very interesting features of strongly non-equilibrium internal distributions, characterizing plasmas.

Plasma-assisted pulsed laser deposition for the improvement of the film growth process

In this paper, results are reported on the characterization of thin films of titanium dioxide and chalcogenide glass doped with praseodymium by the technique of plasma-assisted pulsed laser deposition (PA-PLD) with biased substrate. This technique is shown to be able to prevent contamination of deposited films by particles ejected and to improve the pulsed laser deposition process for stoichiometry, morphology and optical properties of the films produced.

Electron energy distribution functions and second kind collisions

The role of second kind collisions (skc) in affecting the electron energy distribution function (eedf) is discussed in the light of old and new results. Different non-equilibrium situations are presented including low pressure and atmospheric plasmas. Special attention is devoted to the post-discharge conditions when the decay of electron temperature is such as to emphasize the role of skc in structuring the eedf. Finally, results for parallel plate reactors obtained by including self-consistent kinetics in a particle in cell with Monte Carlo collisions approach and 1D high enthalpy flows for aerospace applications are presented and discussed.

Measurement of vibrational, gas, and rotational temperatures of H2(X1Σg+) in radio frequency inductive discharge plasma by multiplex coherent anti-Stokes Raman scattering spectroscopy technique

Translational, rotational, and vibrational temperatures of H2 in radio frequency inductive discharge plasmas at pressures and power release ranges, respectively, of 0.5–8 torr and 0.5–2W∕cm3 have been measured by using multiplex coherent anti-Stokes Raman scattering (CARS) spectroscopy. Computational codes have been developed to determine the rotational and vibrational temperatures and to analyze H2 CARS spectrum for nonequilibrium conditions. The results show a decrease of the vibrational temperature from 4250 to 2800 K by increasing the pressure from 0.5 to 8 torr and a corresponding increase of the rotational temperature from 525 to 750 K.

Plasma kinetics in molecular plasmas and modeling of reentry plasmas

State-to-state non-equilibrium plasma kinetics is widely used to characterize cold molecular and reentry plasmas. The approach requires a high level of dynamical information, and demands a large effort in the creation of complete databases of state-resolved cross sections and rate coefficients. Recent results, emphasizing the dependence of elementary process probability on both the vibrational and rotational energy content of the H2 molecule, are presented for those channels governing the microscopic collisional dynamics in non-equilibrium plasmas, i.e. electron-impact induced resonant processes, vibrational deactivation and dissociation in atom–diatom collisions and atomic recombination at the surface. Results for H2 plasmas, i.e. negative ion sources for neutral beam injection in fusion reactors, RF parallel-plate reactors for microelectronics, atmospheric discharges and the shock wave formed in the hypersonic entry of vehicles in planetary atmosphere for aerothermodynamics, are discussed.