A. Marquez

Pontifical Catholic University of Chile, Santiago, Region Metropolitana de Santiago, Chile

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Publications (11)12.25 Total impact

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    ABSTRACT: We have performed an experimental investigation of the potential use of intense plasma jets produced in a repetitive pulsed capillary discharge (PCD) operating in methane gas, to irradiate Si (1 0 0) substrates. The surface modifications induced by the plasma jet using two different material inserts at the capillary end, graphite and titanium, are characterized using standard surface science diagnostic tools, such as scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and Raman spectroscopy (RS). It has been found that the application of methane plasma jet results in the formation of sub-micron size carbon structures. It is observed that the resulting plasma irradiated surface morphologies are different, depending on the different material inserts used at the capillary end, at otherwise identical operational conditions. To investigate the species responsible for the observed surface changes in different material inserts to the capillary, optical-emission spectroscopy (OES) was recorded using a 300–1000 nm spectrometer. The OES results show the presence of H, CH and C2 Swan band in the discharge plasma, which play a significant role in the formation of the carbon structures.
    Applied Surface Science 01/2009; · 2.54 Impact Factor
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    ABSTRACT: Ion current and electron temperature are measured using electrostatic probes in a dc, nonfiltered vacuum arc operated with argon and nitrogen as filling gases in the pressure range 0.001–1 mbar. It is found that the measured ion current for argon is between two and six times larger than for nitrogen, for similar operating conditions. Also, the electron temperature is smaller for Ar. These differences can be satisfactorily explained with a simple one-dimensional model, which includes the most relevant elastic and inelastic processes that take place in the interelectrodic plasma: elastic scattering of metallic ions by neutral gas, charge exchange, electron impact ionization of gas, dissociative recombination of gas ions, and conversion of atomic ions into molecular ions. The observed differences between nitrogen and argon are attributed to the low rate of conversion of atomic argon into molecular argon, that makes inoperative the channel of dissociative recombination for this gas, together with the higher ionization rate of argon.
    Journal of Applied Physics 09/2004; 96(6):3077-3083. · 2.21 Impact Factor
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    ABSTRACT: The behavior of some selected visible spectral lines emitted in the interelectrode space of a Copper vacuum arc operated with background gases (mainly Oxygen gas) is determined in terms of the gas filling pressure value. It is found that the behavior of these Cu I and Cu II lines with the gas pressure value is essentially the opposite: after an intensity "plateau" at low-pressure values, the CuI line intensity grows, while the corresponding Cu II intensity decreases. On the other hand, no transitions corresponding to Cu III were registered within the spectral range investigated (340 to 600 nm). The measured line intensities are compared with the particle densities calculated with a one-dimensional model, which includes four metallic species (having no inner structure) with different charge state, and takes into account ion slowing down by elastic scattering with neutrals, radial diffusion loses to the chamber wall, charge-exchange processes with neutrals and ionization (or recombination) of the gas molecules (or gaseous ions) by electron impact. It is inferred that the population of an excited level responsible for a given emission line is much smaller (of the order of 10<sup>3</sup>-10<sup>4</sup> cm<sup>-3</sup>) than those expected for the fundamental levels of the particles. The explanation for the observed behavior of these spectral lines with the pressure value rests on the local generation of excited states from lower lying levels by electron impact, but admitting the presence of a certain amount of metal vapor (generated by microdroplet evaporation in the vicinities of the cathode surface) in the interelectrode region
    IEEE Transactions on Plasma Science 03/2002; · 0.87 Impact Factor
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    ABSTRACT: The ion kinetic energy spectrum in a pulsed vacuum arc is presented. The arc current lasts for 35 ms (HAFW), having a peak value of 500 A. A retarding field analyzer system, (consisting in an aperture plate, a charge selecting grid and an energy analyzer collector electrode) and Langmuir probes are employed. The plasma density inside the retarding field analyzer is obtained, and it is shown that the spatial charge between the grid-collector region has some influence on the low energy part of the ion spectrum.
    04/2001;
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    ABSTRACT: The ion kinetic energy and ion density was determined for the plasma generated in the outer region of the arc channel in a pulsed low-pressure cathodic arc. The device was operated with N<sub>2</sub> gas and with a Ti cathode within the pressure range 10<sup>-2</sup>-150 Pa, with a peak current of 520 A. A retarding field analyzer, a spherical Langmuir probe, and a calorimetric system were employed. The resulting kinetic energy for both Ti<sup>+</sup> and Ti<sup>++</sup> ions was 40±3 eV at the cathode spots. The obtained values for the ion density are in agreement with those predicted by hydrodynamic models with spherical symmetry if the ion current penetrating into the outer region is taken as 10% of the total discharge current. It was also found that the ion density increases (and the ion kinetic energy decreases) with the filling pressure, a fact that can be attributed to an ion slowing by elastic collisions with neutrals. This behavior cannot be explained with the presence of a shock wave separating a plasma region from an unperturbed neutral gas region
    IEEE Transactions on Plasma Science 09/2000; · 0.87 Impact Factor
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    ABSTRACT: The paper presents results of studies of the fast ion emission from two plasma facilities: PF-1000 and PF-II. The measurements were carried out mainly with solid-state nuclear track detectors (SSNTDs). To register ion mass- and energy-spectra, obtained when primary ion beams are deflected by magnetic and electric fields of a Thomson-type spectrometer, the SSNTDs plates were installed inside the analyzer. To measure ion angular distributions the SSNTDs were located within the main discharge chamber, at different angles to the electrode axis. The SSNTDs were also applied to register ion beam images formed within an ion pinhole camera, and to determine a spatial location of the fast ion sources.
    Radiation Measurements 01/1999; 31:185-190. · 0.86 Impact Factor
  • H Kelly, A Marquez
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    ABSTRACT: The influence of multiple scattering of ions in the derivation of the ion spectrum from a Thomson ion spectrometer in a plasma focus discharge is analysed. It is found that the corrections introduced in the ion spectrum by this process change the spectral law with respect to the ion energy and the total number of ions inferred from a Thomson spectrometer register.
    Measurement Science and Technology 12/1998; 6(4):400. · 1.44 Impact Factor
  • H. Kelly, A. Marquez, F.O. Minotti
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    ABSTRACT: A stationary fluid model with spherical symmetry is presented to describe the interaction between metallic plasma ions with neutral gas in the outer region of a multicathode spot vacuum are operated with a neutral background gas. It is found that the neutrals penetrate into the metallic plasma with density values smaller than the initial gas density values, but higher than the metallic ion densities. The neutrals are also strongly heated during the transient expansion stage of the metallic plasma. As a consequence, the ion kinetic energy is gradually delivered to the neutral gas so that the mean free path for ion-neutral elastic collisions is larger than the visible plasma ball radius which surrounds the arc
    IEEE Transactions on Plasma Science 09/1998; · 0.87 Impact Factor
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    ABSTRACT: The energy distribution and flux of fast nitrogen particles generated in a Mather-type plasma focus device operating at 0.4 Torr of N<sub>2</sub> pressure is reported. A Faraday cup operating in the secondary electron emission mode was employed. To determine the total number of beam particles, multiple scattering of the ions was taken into account. It has been possible to register the ion energy up to a lower kinetic energy threshold of &ap;50 keV, which is a value much lower than that obtained with a Thomson spectrometer in a previous work
    IEEE Transactions on Plasma Science 03/1998; · 0.87 Impact Factor
  • H. Kelly, A. Lepone, A. Marquez
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    ABSTRACT: The nitrogen ion spectrum generated from a low energy Mather-type Plasma Focus device is reported. The main species of ions present are N <sup>+1</sup>, N<sup>+2</sup>, and N<sup>+3</sup>. It is found that its relative concentrations at a distance of several cm from the ion source are in agreement with those predicted for an equilibrium charge-state of the beam, and hence the spectrum of the neutral nitrogen is also derived. By taking into account the lateral spread of the beam due to multiple elastic scattering with the background gas, the derivation of absolute values for the total ion spectrum within the investigated energy range (>170 keV), the total number and total energy of the fast particles has been obtained
    IEEE Transactions on Plasma Science 07/1997; · 0.87 Impact Factor
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    ABSTRACT: The paper reports on the analysis of responses of CN-type films and CR39-plastic nuclear track detectors (NTDs) to fast deutrons and nitrogen ions emitted from high-current Plasma-Focus (PF) facilities, as operated at SINS and INFIP. In order to separate the deutrons and nitrogen ions of different energy, the use was made of a Thomson-type mass-spectrometer adapted to measurements within dense plasma streams. Deutron and ion parabolaen were registered the CN-80 and CN-LR115 films as well as with the CR39 plastic NTDs, which were undergone routine etching procedures. On the basisof known characteristics of the spectrometer applied energy- and mass-scales for the obtained ion paraboale were determined. Using an optical microscope, a detailed analysis of track dimensions was performed in chosen points along the registered parabolae, and the calibration diagrams (i.e. a track diameter for the chosen ion energy and different etching times) were determined. Results of the calibration procedure, after comparing with other calibration data obtained with conventional particle accelerators, may be applicable for measurements of fast deutrons (i.g., in nuclear fusion experiments) and energetic nitrogen ions (i.g., in some plasma- and ion-facilities used for technological applications).
    Radiation Measurements 01/1997; · 0.86 Impact Factor

Publication Stats

69 Citations
12.25 Total Impact Points

Institutions

  • 2009
    • Pontifical Catholic University of Chile
      • Departamento de Física
      Santiago, Region Metropolitana de Santiago, Chile
  • 1997–2009
    • University of Buenos Aires
      • • Department of Physics (FI)
      • • Department of Physics (FCEN)
      Buenos Aires, Buenos Aires F.D., Argentina