On phenomena in ionized gases
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- Acknowledgements
- Pulsed electron beams for thin film deposition
- Electron/molecular-cation collisions in cold plasmas: super-excited states at "zero" energy
- Simulation of glow discharge electrolysis for material processing in liquid
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2. Main results Stationary and time-dependent experiments with different binary metal-oxides placed either directly in contact with plasma or after the active plasma zone demonstrated that the metal-oxides could act both as NO x adsorbents and oxidation catalysts. With the catalyst directly in contact with the plasma, the back-reaction in gas phase remained important but the reaction balance was shifted towards the production of NO 2 . The time-dependent changes of the NO x concentrations suggested that the surface
processes involved both the
adsorption/disproportionation reactions of NO 2 [5] and reactions with plasma produced oxygen species. The importance of the latter process was also emphasised by the production of NO 2 on the catalyst surfaces previously treated by oxygen discharge. The back-reaction can be avoided when the plasma is used indirectly for the production of ozone which then reacts with NO x . In this configuration the catalyst enhanced considerably the oxidation of NO 2 to N 2 O 5 [3]. The surface processes involved the decomposition of O 3 to surface bound oxygen species which then aided the oxidation of NO 2 to NO 3 . Subsequent formation of N 2 O 5 on the surface resulted also in the increased NO x adsorption ability of tested metal-oxides.
The study was partially financed by Estonian Research Council (Grant nr. 585).
[1] K. Skalska, J.S. Miller, S. Ledakowicz, Sci. Total. Environ. 408 (2010) 3976. [2] I. Jõgi, E. Levoll, J. Raud, Chem. Eng. J. 301 (2016) 149. [3] I Jõgi, K. Erme, J. Raud, M. Laan, Fuel 173 (2016) 45. [4] I. Jõgi, E. Levoll, J. Raud, Catal. Lett. 147 (2017) 566. [5] L. Sivachandiran, F. Thevenet, P. Gravejat, A. Rousseau, Appl. Catal. B: Environ. 142 (2013) 196.
Topic number 17 32
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Pulsed electron beams for thin film deposition
M. Nistor P
P National Institute for Lasers, Plasma and Radiation Physics (NILPRP), Plasma Physics and Nuclear Fusion Laboratory, L22, P.O. Box MG-36, 7712 Magurele-Bucharest, Romania
In this work we present results on pulsed electron beams produced in a channel-spark discharge used for thin film deposition. The measured electron beam energy distribution is polyenergetic, having a high-energy electron component at the beginning of the applied high voltage fall and a dominant contribution of lower energy electrons increasing towards later times of the voltage fall. In situ diagnostics of ablation plasma produced in PED by fast imaging, optical emission spectroscopy and Langmuir probes showed that the kinetic energy of the species emitted by the target was roughly in the 10 to 60 eV range. These investigations led to the growth of high quality oxide thin films by the precise control of the PED parameters.
The discovery of the “pseudospark” gas discharge in 1979 by J. Christiansen and C. Schultheiss [1] has paved the way for many studies on pulsed electron beams and their application in pulsed-power switching, extreme ultraviolet sources for lithography, compact X-ray
sources, microthrusters, high power microwave generation, etc. These pulsed electron beams are produced in low pressure gas discharges (10 -3 -10
-1 mbar) for applied voltages up to tens of kV. A pulsed electron beam, which propagates in a self-focused way due to the space-charge neutralization, has
typical parameters: currents of tens - hundreds of A, pulse widths of tens - hundreds of ns, and energies up to tens of keV. The channel-spark discharge [2] has been derived from the pseudospark one by replacing the floating electrodes from multigap pseudospark geometry with a dielectric tube, leading to a stable electron source for a low cost thin film deposition method: the pulsed electron beam deposition (PED). It has common features with pulsed laser deposition, i.e. the pulsed nature of process, the very anisotropic character of the ablation plume and the high energy of species, but uses a pulsed electron beam instead of a laser beam for ablating a target. Due to the specific electron-matter interaction, the range of materials that could be ablated has been extended to those that are transparent to laser wavelengths. The knowledge of the electron beam energy distribution of the pulsed electron beams used in PED method plays a key role for an efficient ablation of the target surface and thus to the deposition of thin films. Experimental methods have been employed to determine electron beam energy distribution: self-biasing Faraday cup and X-ray radiation at the interaction of the electron beam with a target. Our measurements showed that in the channel-spark discharge the electron beam energy distribution is polyenergetic, spreading from hundreds of eV to the energy eU, where U is the applied high voltage and e is the electron charge. This distribution has a high-energy electron component (more than a few keV) at the beginning of the applied high voltage fall (U) and a dominant contribution of lower energy electrons increasing towards later times of the voltage fall. For U=16 kV, the voltage fall lasts 210 ns and the total beam current has a maximum value of 750 A, from which a current with a maximum value of 400A and pulse width of about 110 ns is carried by electrons having energy higher than 1.84 keV [3]. Tailoring the electron energy distribution function by variation of the discharge parameters has influenced the quality of grown thin films by PED. In situ diagnostics of ablation plasma produced in PED by fast imaging, optical emission spectroscopy and Langmuir probes demonstrated that the kinetic energy of the species emitted by the target was roughly in the 10 to 60 eV range, leading to high surface mobility for these species. As a result, growth of stoichiometric and crystalline oxide thin films, even epitaxial films at relatively low temperatures, has been obtained. The tuning of the physical properties of thin films was possible by the precise control of PED growth conditions [4]. [1] J. Christiansen, C. Schultheiss, Z. Phys. A 290 (1979) 35 [2] G Müller, M. Konijnenberg, G. Krafft, C. Schultheiss, Science and Technology of Thin Film, World Scientific Publ. (1995) 89. [3] M. Nistor, N.B. Mandache, J. Perrière, J. Phys. D: Appl. Phys. 41 (2008) 165205. [4] M. Nistor, L. Mihut, E. Millon, C. Cachoncinlle, C. Hebert, J. Perrière, RSC Adv. 6 (2016) 41465. Topic number 8 33
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Electron/molecular-cation collisions in cold plasmas: super-excited states at "zero" energy
J. Zs. Mezei 1,2,3,4 , F. Colboc 1 , Y. Moulane 1,5,6, , N. Pop
1,7 , S. Niyonzima 1,8 , M. D. Epée Epée 1,9 , O. Motapon 1,9,10 , D. A. Little 11 , F. Iacob 12 , R. Boata 13 , V. Laporta 1,11,14 , R. Celiberto 14,15 ,
K. Chakrabarti 1,16
, E. Jehin 6 , Z. Benkhaldoun 5 , K. Hassouni 2 , D. Benredjem 3 , A. Faure 17 ,
A. Bultel 18 , J. Tennyson 11 , I. F. Schneider 1,3
P 1 Laboratoire Ondes et Milieux Complexes, CNRS, Université du Havre, Le Havre, France 2 Laboratoire des Sciences des Procédés et des Matériaux, CNRS, Université Paris 13, Villetaneuse, France 3 Laboratoire Aimé Cotton, CNRS, ENS Cachan and Université Paris-Sud, Orsay, France 4 Instititute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, Hungary 5 Oukaimeden Observatory, High Energy Physics & Astrophysics Lab., Cadi Ayyad Univ., Marrakech, Morocco
Institut d'Astrophysique et de Géophysique, Liège, Belgium 7 Department of Physical Foundations of Engineering, Politehnica University Timișoara, Timișoara, Romania 8 Département de Physique, Université du Burundi, Bujumbura, Burundi 9 Department of Physics, Faculty of Sciences, University of Douala, Douala, Cameroon 10 University of Maroua, Faculty of Science, Maroua, Cameroon 11 Department of Physics and Astronomy, University College London, United Kingdom
Physics Faculty, West University of Timișoara, Timișoara, Romania 13 Astronomical Institute of the Romanian Academy, Timisoara Astronomical Observatory, Timișoara, Romania 14 Istituto di Nanotecnologia, CNR, Bari, Italy 15 Dipartimento di Ingegneria Civile, Ambientale, del Territorio, Edile e di Chimica, Politecnico di Bari, Italy 16 Department of Mathematics, Scottish Church College, Calcutta, India 17 Université de Grenoble Alpes, CNRS, Inst. de Planétologie et d’Astrophysique de Grenoble, Grenoble, France 18 Laboratoire CORIA, CNRS, Université de Rouen, Saint Etienne de Rouvray, France We will discuss the role of excited states in cold ionized media, as resonances in reactive collisions, and as initial states of the target in non-equilibrium regime.
Dissociative recombination (DR) [1,2]: AB + (N i + ,v i + )+e - →AB*,AB**→A+B, (1) the major recombination process in low pressure ionized gases, is often notably fast at “zero” (i.e. low) energy of the incident electrons, since it occurs via super-excited molecular states singly- (AB*) or doubly- (AB**) excited, embedded in the ionization continuum of the target ion. This process is competed by ro-vibrational and dissociative excitation: AB +
i + ,v i + )+e - →AB*,AB**→AB + (N
+ ,v f + )+e
- , (2)
→A+B + +e - . (3) The use of the Multichannel Quantum Defect Theory [3] resulted in accurate state-to-state cross sections and rate coefficients, displaying a resonant character and a strong dependence on the target state. These features are particularly important for the collisional-radiative modeling of the cold ionized gases – Fig. 1 - in various environments - interstellar space, comets, planetary ionospheres, shock-waves in the entries of spacecrafts, ionic propulsion devices, industrial and edge fusion plasmas - and containing various cations - H 2 + , BeH
+ , BF
+ [2,4],
N 2 + [5], CO + [6], SH + , ArH
+ , H
3 + [7], BF 2 + , etc.
Fig.1. Maxwell rate coefficients for the Dissociative Recombination (DR) of H 2 +
vibrational temperature of the ions.
References [1] I. F. Schneider, O. Dulieu, J. Robert, Proc. of DR2013: The 9 th Int. Conf. on Dissociative Recombination: Theory, Experiment and Applications, Paris, July 7-12, 2013, EPJ Web of Conferences 84 (2015). [2] N. Pop et al, poster contribution to this conference. [3] O. Motapon et al, Phys. Rev. A 90 (2014) 012706. [4] V. Laporta et al, Pl. Phys. Contr. Fusion 59 (2017) 045008. [5] D. A. Little et al, Phys. Rev. A 90 (2014) 052705. [6] J. Zs. Mezei et al., Pl. Sour. Sci. Tech. 24 (2015) 035005. [7] I. F. Schneider et al, Phys. Rev. A 86 (2012) 062706. 34
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Simultaneous vacuum UV and broadband UV-NIR plasma spectroscopy for LIBS improvement
P. Veis
P 1 P , U J. Kristof UP 1, 2
P
P 1 P Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynská dolina F2, Bratislava 842 48 Slovakia P 2
Graduate School of Science and Technology, Shizuoka University, Johoku, Hamamatsu, 432-8561 Japan
LIBS (Laser Induced Breakdown Spectroscopy) of light elements was investigated. As a spectrum of some light elements has not enough emission lines in UV-NIR range, such as B, C, P and S, determination of the electron temperature from Saha-Boltzmann plot is very difficult or impossible. Our aim, improvement of the precision of the electron temperature determination by broadening of emission of UV-NIR range up to VUV range allowed observing more emission lines and very often neutral, single ionized and also double ionized. Precision of the electron temperature of other elements such as Si, Ge, Zn was also studied. Ions abundance evolution of the elements allowed us to find the best experimental conditions for generation of the double ionized ions in LIBS plasma.
1. Introduction LIBS is an analytical method, which determines elemental composition of materials based on atomic emission of spark created by a laser beam focused on the surface. For light elements as B, C, P and S important characteristic spectral lines are few and appear in VUV range only [1]. Including VUV, in addition to conventional UV-NIR range yields in more reliable data set for Saha-Boltzmann (S-B) plot, which helps to quantify light elements more precisely using calibration free LIBS. Heavy elements, such as tungsten have plenty lines in UV-NIR, but their overlap makes the S-B unprecise. Therefore the detection of double ionized W III lines in VUV proves to be advantageous [2].
2. Experiment 2.1. Experimental Set-up
LIBS measurements were realized under low pressure (1330 Pa) He and Ar atmosphere for various delays after the laser pulse to ensure narrow emission lines and observation of all three ionization degrees (neutral - double ionised). Plasma was generated by Nd:YAG laser (Quantel) operating at 266 nm (4-th harmonic) - see Figure 1.
Plasma emission was recorded simultaneously by two spectrometers: broadband UV-NIR echelle type spectrometer (230 nm – 950 nm, ME 5000, Andor) and VUV one (114-295 nm, McPherson), both equipped with iCCD camera (iStar, Andor).
2.2. Results Figure 2. VUV spectra 300 and 500 ns after laser pulse.
The UV-NIR spectra of sulphur doesn’t contains neutral S I lines. The VUV spectra allows to observe lines from different degree of ionisation, S I-III lines at 100 ns delay and S I-II lines at 500 ns delay (Figure 2). Clear line detection from three degree of ionisation (S I-III) allows us to determine electron temperature in the early state of the plasma plume (100 ns, Figure 3) and that leads to precise determination of sulphur concentration in a sample. LIBS of o ther elements (Si, Ge, Zn) was also studied.
Acknowledgement: This work has been supported by SRDA (No. APVV-15-0641).
3. References [1] J. Jašík, J. Heitz, J. D. Pedarning, P. Veis, Spectrochimica Acta Part B 64 (2009) 1128. [2] M. Pribula, J.Kristof, A. Hakola, P. Veis et al, Physica Scripta T167 (2016) 014045. 6 35
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Simulation of glow discharge electrolysis for material processing in liquid
F. Tochikubo P
P Department of Electrical and Electronic Engineering, Graduate School of Science and Engineering, Tokyo Metropolitan University, Tokyo, Japan P
In glow discharge electrolysis, the liquid-phase reactions are induced by electrons/ions irradiation of the liquid surface from the plasma. In this work, we carried out numerical simulation of glow discharge electrolysis, which consists of atmospheric-pressure dc glow discharge and electrolyte solution connected in series between parallel plate metal electrodes, based on fluid simulation. The calculated glow discharge facing the liquid is essentially the same as that generated between metal electrodes. In the liquid, electric double layer with approximately 10 nm width was reproduced in front of metal electrode while no electric double layer was observed at plasma-liquid interface. We found that the liquid-phase chemistry is strongly affected by the electron/positive ion irradiation of the liquid surface from the glow discharge, especially in the thin region from the liquid surface.
Atmospheric-pressure dc glow discharge with liquid electrode is applied for material processing such as metallic nanoparticles generation [1-2]. This system is considered as glow discharge electrolysis (GDE) at atmospheric pressure. In this system, the reactions in liquid are induced by the electrons/ions irradiation of the liquid surface from the liquid-phase thin layer at the plasma-liquid interface. Therefore, it is necessary to clarify the transport of charged and neutral species both in gas and liquid. In this work, we carried out one-dimensional numerical simulation of atmospheric-pressure GDE.
The simulation model for GDE is shown in Fig. 1. A glow discharge in atmospheric-pressure helium with 1 mm gas-gap is connected with NaCl solution with 1 mm depth in series. Both the glow discharge and the liquid regions were calculated based on fluid model using continuity equations for charged/neutral species coupled with Poisson equation. Boundary conditions at plasma-liquid interface is important to determine the characteristics of GDE. However, the information on the reactions at plasma-liquid interface is very limited, therefore, we assumed the following simple model: electron irradiation of the liquid surface from the plasma generates hydrated electrons: negative ion irradiation also generates hydrated electrons: any positive ion irradiation causes the generation of H + and OH through charge transfer collision: neutrals dissolve in the solution. 3. Simulation results The structure of atmospheric-pressure dc glow discharge is essentially the same as that calculated between two metal electrodes. Fig. 2 shows the ion distributions in liquid with glow discharge cathode. Very narrow negative charge layer with strong electric field is formed in the region of roughly 10 nm from metal anode. In front of the glow discharge cathode, we could not find the large difference in the concentrations between Na + and Cl - . The incident electrons become hydrated electrons in the liquid, and react with other species. In the present case, hydrated electrons generate OH - by the reaction with H 2 O.
Therefore, plenty of OH - is generated close to the liquid surface, and local pH becomes approximately 10. The hydrated electron works as reductant. For example, hydrated electrons reduce the metal ions such as Ag + to synthesize Ag nanoparticles in liquid. This work is partly supported by Grant-in-Aid for Scientific Research (B) from JSPS (No. 15H03584). Download 9.74 Mb. Do'stlaringiz bilan baham: 
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