F. J. Gordillo-Vázquez

Spectroscopic measurements of the electron temperature in low pressure radiofrequency Ar/H2/C2H2 and Ar/H2/CH4 plasmas used for the synthesis of nanocarbon structures

This paper deals with optical emission spectroscopy studies of low pressure (0.1–0.5 Torr) capacitively coupled radiofrequency hydrocarbon/argon-rich plasmas used for the synthesis of nanocarbon structures. The main goal of this paper is to obtain the electron temperature of such far-from-equilibrium plasmas as a function of the pressure, the excitation power and the argon content. In doing so, we have found that the argon upper energy levels used for electron temperature estimation remain close to corona balance. The latter has allowed us to use a modified Boltzmann plot technique to derive the electron temperature. It was found that, for the plasmas investigated, an increase of the argon population density (from 10% to 95%) leads to a pronounced decrease of the electron temperature while an increase of the processing pressure produces a moderate increase of the electron temperature. Additionally, the increase of the power from 50 to 300 W produces a very slight growth of the electron temperature.

Electronic temperature and density of the plasma produced by nanosecond ultraviolet laser ablation of LiF

1.5 J cm ˛2 close to the threshold. It is found that, whereas Ne sin the range of 10 16 cm ˛3 d decreases by a factor of 2 as the distance to the target increases, Te exhibits a sharp decrease sfrom 1.85 eV to 0.66 eVd between 1 and 2 mm from the target and it remains practically constant for longer distances from the target. These results provide direct measurements of the electron temperature and density during nanosecond laser ablation of LiF.

Chemical and thermal impacts of sprite streamers in the Earth's mesosphere

This work was supported by the Spanish Ministry of Economy and Competitiveness, MINECO, under projects AYA2011-29936-C05-02 and ESP2013-48032-C5-5-R and by the Junta de Andalucia, Proyecto de Excelencia, FQM-5965. F.C.P.R. acknowledges MINECO for the FPI grant BES-2010-042367. A.L. was supported by a Ramon y Cajal contract, code RYC-2011-07801

Influence of the power on the processes controlling the formation of ECR-CVD carbon nitride films from CH4/Ar/N2 plasmas

Carbon nitride films have been synthesized by means of electron cyclotron resonance chemical vapour deposition (ECR-CVD) using different power values (50?212?W) at constant pressure conditions (0.03?mbar). Optical emission spectroscopy and mass spectrometry were used for the characterization of the plasma. The films were analysed using energy dispersive x-ray spectroscopies. It was found that all signal peaks in the optical emission spectra increased monotonically following the increase in microwave power. Moreover, we have observed that the radiative emission from the 4p(2p9) resonant state of Ar is the most affected by CH4 addition to a pure argon plasma. The latter suggests that a Penning mechanism controls the activation of CH4 molecules with increasing power levels at relatively low pressures. Besides, the increase of excited N atoms indicates a higher activity of the etching mechanisms of carbon nitride films with increasing power.

Influence of Ar and O2 atmospheres on the Li atom concentration in the plasma produced by laser ablation of LiNbO3

An analytic kinetic model is elaborated to determine the spatial evolution of the concentration of ground and excited Li atoms (up to the 3 2D level) present in the plasma generated by pulsed laser ablation of a LiNbO3 crystal in gas atmospheres (at 1 Torr) of different nature, both reactive (O2) and inert (Ar). Whereas the Li atom population densities in the plasma produced in gas are, in general, higher than those found in vacuum, the concentration of ground Li atoms close to the substrate is similar in vacuum and Ar, though lower than in O2. It is suggested that the reabsorption of radiation by the plasma is more important within O2 than in Ar since the absorber (ground Li) concentration is higher in O2 environments. A very reasonable qualitative agreement is found when comparing the Li I-670.8 nm spectral line emission intensity predicted by the model with that obtained experimentally in Ar and O2 atmospheres.

Concentration of Li atoms in plasmas produced from laser ablation of LiNbO3

An analytic kinetic model capable to predict the spatial and temporal evolution of the population densities of ground and excited state Li atoms (up to the 32D level) in nonequilibrium laser-generated plasmas from LiNbO3 targets is presented. The model is especially useful as a nonequilibrium diagnostic tool for determining the concentrations of Li atoms from available measurements of electron density (Ne) and temperature (Te). In addition, the present approach is able to determine the electron kinetic mechanisms contributing to populate and depopulate the Li atom ground and excited states in laser-produced plasmas. A very reasonable qualitative agreement is found when comparing the model predicted Li atom densities with those obtained experimentally. Thus, the proposed approach can be used as a useful tool to optimize the processes involved in pulsed laser deposition of LiNbO3 thin films.

Drift and clustering of daughter negative ions of H2O in parent gas

The mobility of daughter negative ions of H2O in parent gas has been measured with a pulsed Townsend technique over the density-reduced field strength, E/N, range 9?100?Td and a pressure range 2?16?Torr. It has been found that the mobility of the anions is dependent on the gas pressure. Using a transport theory considering the influence of the permanent dipole field of H2O, we have found that the pressure-dependent mobilities can be associated with a series of cluster ions of the type OH?(H2O)n (n?=?1?3), with the mass of the cluster species increasing with the total gas pressure. Also, the mobility of H? and OH? could be estimated. Using a Townsend avalanche simulator we have been able to explain the measured ionic currents in terms of an ion?molecule reaction scheme with a single set of swarm and reaction coefficients for each value of the density-reduced field strength, E/N, at several pressures. Regarding the positive ions, the only drifting ion is H3O+, the mobility of which could be estimated. The rate constants relative to the formation of the OH?(H2O)n (n?=?1?3) species were also derived from this study.

Influence of the excitation frequency on CH4/H/H2 plasmas for diamond film deposition: electron energy distribution function and atomic hydrogen concentration

The influence of the excitation frequency f = ω/2π of the applied electric field on the period average electron energy distribution function (EEDF) and on the atomic hydrogen concentration found near the deposited diamond films (substrate) and in the bulk of CH4(5%)/H/H2 plasmas produced in RF and MW discharges is estimated. This is done through the solution, as a function of the reduced effective electric field, of a stationary homogeneous electron Boltzmann equation (EBE) and the solution, in terms of the atomic hydrogen mole fraction, of a simple kinetic model for the plasma mechanisms underlying the production and loss of atomic hydrogen. The physical basics underlying the approach followed to solve the EBE, including discussion of EEDF time-modulation effects, are discussed in the light of recent results by Loureiro (1993 Phys. Rev. E 47 1262) on time-dependent kinetics of pure H2 plasmas. Correlations are established between the results, obtained under various discharge conditions, from plasma-enhanced chemical vapour deposition (PECVD) experiments of diamond-like carbon (DLC) and diamond thin films, and the calculated EEDF, atomic hydrogen concentrations (in the plasma and near the substrate) and mechanisms underlying the production and loss of atomic hydrogen in the plasma.

Statistical-mechanical calculations of thermal properties of diatomic gases

The impact of rotational–vibrational dynamics of molecules on the molecular partition functions, law of mass action and thermodynamic functions of partially dissociated diatomic gases is discussed. A group of 11 gases, expected to have their partition functions the most sensitive to the molecular rotational–vibrational properties, is selected for rigorous and detailed studies, and the partition functions, dissociation degrees and free energies of the gases are calculated (using various models of molecular rotational–vibrational dynamics) and compared in a broad range of temperature and particle density.

Ion concentrations in plasmas produced from 193 nm excimer laser irradiation of LiNbO3 in vacuum and gas atmospheres

We have calculated the concentration of ions in the plasma produced upon ablation of LiNbO3 with a low fluence ArF excimer laser in vacuum and different gas environments (Ar and O2). The model shows that Li and Nb ions (with the amount of Li ions being greater than that of Nb ions) are the most abundant in the plasma with their concentrations being always above their corresponding neutral densities. In addition, we show that the concentration of excited Nb ions is relatively important while no excited Li ions are predicted. We found that the concentration of both Li and Nb ions in O2 is slightly higher than in Ar and vacuum. Moreover, the calculated spatial evolution of the ionic species suggests that a significant fraction of the predicted ion concentration is not produced by electron–atom ionization events within the plasma; on the contrary, they might have been produced in the LiNbO3 crystal through a nonthermal mechanism and then ejected from the target after the laser pulse.