Plasma basic concepts and nitrogen containing plasmas

Basic concepts related to plasmas are described as well as the typical characterization methods currently available. A brief overview about some plasma applications is given, but focusing on plasma used in material processing mainly devoted to the microelectronics industry. Finally, specific applications related to plasma-assisted MBE for nitrides and dilute nitrides are given, showing some interesting research works performed to that purpose, and giving the usual characterization techniques commonly used in such processes

Energy distributions of neutrals and ions in H2 low temperature plasmas: a study of fast H atoms

In this work we study by visible emission spectroscopy, energy resolved ion mass spectrometry and electric probes, H2 plasmas generated in low pressure hollow cathode glow discharges. The study allows the determination of the energy distributions of the different plasma constituents (ions, electrons and neutrals), which span five orders of magnitude. The rotational H2 temperature, assumed to be close to the translational one, scarcely exceeds the room temperature (0.03 eV); free electrons, responsible of primary ionizations and dissociations, display mean kinetic energies of 3-6 eV; whereas ions (H+, H2+, H3+) and a part of H atoms reach the highest energies (300 eV). Our present study focuses on the line-shape analysis of the H Balmer series emitted by the plasma, whose spectral profiles evince its remarkable deviation from thermal equilibrium, and on the dependence of these profiles with H2 pressure. The aim is to get a deeper understanding of the processes responsible of this behaviour. Three different Doppler broadenings are found in the atomic lines: the narrow peak, the plateau, and the far wings, with FWHM of ~ 0.3, 6 and up to 80 eV, respectively [1]. Besides, a directional and asymmetric behaviour in the line shifts up to some 300 eV is observed when ions are directed preferentially towards the observation window through a grounded grid. The narrow line peak can be explained by direct electron impact excitation of the free H atoms and by Frank-Condon transitions to Rydberg levels. The plateau is also explained by electronic excitations, in this case to pre-dissociative levels and levels giving rise to dissociative ionization. Their effectiveness depends primarily on electron temperature. In contrast, the far wings are assumed to be mainly due to charge transfer processes and dissociative reactions of H2 with the H+, H2+ and H3+ ions accelerated in the plasma sheath. The latter processes depend strongly on collision frequency and increase appreciably with pressure. The ion energy distributions obtained by mass spectrometry [2, 3] and the electron temperatures measured with the electric probe support the validity of the proposed mechanisms.Peer Reviewe

From carbon nanostructures to new photoluminescence sources: an overview of new perspectives and emerging applications of low pressure PECVD

13 pages, 9 figures.Low-pressure, plasma-enhanced (PE)CVD is a powerful and versatile technique that has been used for thin-film deposition and surface treatment since the early 1960s. However, it is only recently that it has been used in applications other than the different stages of microelectronic circuit fabrication. Now, PECVD is being used in emerging applications due to new materials and process requirements in a wide variety of areas, such as biomedical applications, solar cells, fuel cell development, fusion research, or the synthesis of silicon nanocrystals showing efficient photoluminescence, useful for future solid-state light sources. These new scenarios have stimulated further development of novel PECVD diagnostic techniques, together with fundamental experimental and theoretical studies aimed at a better understanding of some of the basic processes underlying the plasma/surface interaction. This paper gives an overview of some new research areas where PECVD is finding promising applications.FJGV acknowledges partial financial support from CSIC-CAM (Project No. 200550M016 and 200650M016) and MEC (Projects No. MAT2006-13006-C02-01 and ENE2006-14577-C04-03), VJH and IT acknowledge funding from MEC (Projects No. FTN-2003-08228-C03-03, FIS2004-00456 and ENE2006-14577-C04-03).Peer reviewe

Neutral and ion kinetics in glow discharges of H2/O2 mixtures. Diagnostics and modelling

A combined diagnostics and modelling of low pressure H2/O2 plasmas at different pressures and mixture ratios, generated in a low pressure hollow cathode DC reactor, is presented. Neutral and ion distributions are measured by mass spectrometry. Langmuir probes provide charge densities and electron temperatures. As expected, apart from the precursors, H2O is detected in considerable amounts and H3O+ is a major ion for H-rich mixtures. A zero order kinetic model is used to explain the experimental results. H2O is produced via plasma-surface interactions in a multistep process. The ion distributions are determined in each case by a balance between the relative weights of electron impact processes and proton transfer chemistry.N

Neutral and ion kinetics in glow discharges of H2 / O2 mixtures. Diagnostics and modelling

London, United Kingdom, 14–17 April 2014; http://plasma14.iopconfs.org/homeLow pressure plasmas in electrical discharges with H2 and O2 are of interest in a variety of fields. In astrochemistry, the formation of H2O and H3O+ is of great relevance as they can be detected in interstellar environments. In fusion research, discharge cleaning is used to eliminate the residual molecules in a vacuum vessel, of which oxygen and water are major components. In this work, we present a study of the chemistry of neutral and ionic species in H2/O2 plasmas based on the experimental diagnostics and kinetic modelling of hollow cathode discharges at different pressures and mixture proportions. Neutral and ion distributions are measured by mass spectrometry, and Langmuir probes provide charge densities and electron temperatures. As expected, apart from the precursors, H2O is detected in considerable amounts. Concerning the charged species, pure hydrogen and oxygen ions are detected together with mixed ones. With increasing pressure, the ion distributions are dominated by H3O+ for mixtures with H2 concentrations higher than ~ 30%, in contrast, the protonated species O2H+ is hardly formed. A zero order kinetic model is used to explain the experimental results. H2O is produced via plasma-surface interactions in a multistep process. The ion distributions are determined in each case by a balance between the relative weights of electron impact processes and proton transfer chemistry. The relevance of negative ions in the plasma chemistry is also studied.Peer Reviewe

Chemistry in glow discharges of H2/O2 mixtures. Diagnostics and modelling

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An infrared study of solid glycine in environments of astrophysical relevance

9 p.: gráf.The conversion from neutral to zwitterionic glycine is studied using infrared spectroscopy from the point of view of the interactions of this molecule with polar (water) and non-polar (CO2, CH4)surroundings. Such environments could be found on astronomical or astrophysical matter.The samples are prepared by vapour-deposition on a cold substrate (25 K), and then heated up to sublimation temperatures of the co-deposited species. At 25 K, the neutral species is favoured over the zwitterionic form in non-polar environments, whereas for pure glycine, or in glycine/water mixtures, the dominant species is the latter. The conversion is easily followed by the weakening of two infrared bands in the mid-IR region, associated to the neutral structure. Theoretical calculations are performed on crystalline glycine and on molecular glycine, both isolated and surrounded by water. Spectra predicted from these calculations are in reasonable agreement with the experimental spectra, and provide a basis to the assignments. Different spectral features are suggested as probes for the presence of glycine in astrophysical media, depending on its form (neutral or zwitterionic), their temperature and composition. © the Owner Societies 2011Funding from the Spanish Ministry of Education, Projects FIS2007-61686 and FIS2010-16455.Financial support from Ministerio de Ciencia e Innovación, ‘‘Ramón y Cajal’’ program and CSIC, JAE-Doc ProgramPeer reviewe

Chemistry in glow discharges of H2/O2 mixtures. Diagnostics and modelling

Peer Reviewe

The High Resolution Infrared Spectrum of HCl+

The chloroniumyl cation, HCl+, has been recently identified in space from Herschel’s spectra. A joint analysis of extensive vis-UV spectroscopy emission data together with a few high-resolution and high-accuracy millimiter-wave data provided the necessary rest frequencies to support the astronomical identification. Nevertheless, the analysis did not include any infrared (IR) vibration-rotation data. Furthermore, with the end of the Herschel mission, infrared observations from the ground may be one of the few available means to further study this ion in space. In this work, we provide a set of accurate rovibrational transition wavenumbers as well as a new and improved global fit of vis-UV, IR and millimiter-wave spectroscopy laboratory data, that will aid in future studies of this molecule.Peer reviewe

High energy electron irradiation of interstellar carbonaceous dust analogs: Cosmic ray effects on the carriers of the 3.4 μm absorption band

9 págs; 5 figs.; 6 tabs.The effects of cosmic rays on the carriers of the interstellar 3.4 μm absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH3 and CH2 in carbonaceous dust. It is widely observed in the diffuse interstellar medium, but disappears in dense clouds. Destruction of CH3 and CH2 by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, cules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron the 3.4 μm band carriers lie in the 108 yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3×107 yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds.This work has been funded by the MINECO of Spain under grant FIS2013-48087-C2-1P, by the MICINN of Spain under grant CDS2009-00038, and by the European project ERC-2013-Syg 610256. G.M. acknowledges MINECO PhD grant BES-2014-069355.Peer reviewe