Distinct nonequilibrium plasma chemistry of C2 affecting the synthesis of nanodiamond thin films from C2H2 (1%)/H2/Ar-rich plasmas

6 pages, 5 figures, 6 tables.We show that the concentrations of the species C2 (X 1Σg+), C2 (a 3Πu), and C2H exhibit a significant increase when the argon content grows up to 95% in medium pressure (0.75 Torr) radio frequency (rf) (13.56 MHz) produced C2H2 (1%)/H2/Ar plasmas of interest for the synthesis of nanodiamond thin films within plasma enhanced chemical vapor deposition devices. In contrast, the concentrations of CH3 and C2H2 remain practically constant. The latter results have been obtained with an improved quasianalytic space–time-averaged kinetic model that, in addition, has allowed us to identify and quantify the relative importance of the different underlying mechanisms driving the nonequilibrium plasma chemistry of C2. The results presented here are in agreement with recent experimental results from rf CH4/H2/Ar-rich plasmas and suggest that the growth of nanodiamond thin films from hydrocarbon/Ar-rich plasmas is very sensitive to the contribution of C2 and C2H species from the plasma.This work was partially funded by CICYT (Spain) under a Ramón y Cajal project and under Project No. TIC2002- 03235. One of the authors (F.J.G.V.) acknowledges a Ramón y Cajal contract from the Spanish Ministry of Science and Technology (MCYT). One of the authors (J.M.A.) acknowledges partial support from CICYT (Spain) under Project No. MAT 2002-04085-C02-02.Peer reviewe

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

A one-dimensional self-consistent model has been developed to study the chemical and thermal effects of a single sprite streamer in the Earth's mesosphere. We have used sprite streamer profiles with three different driving current durations (5 ms, 50 ms, and 100 ms) between 50 and 80 km of altitude and considering a kinetic scheme of air with more than 90 chemical species. Our model predicts strong increases in practically all the concentrations of the species studied at the moment of the streamer head passage. Moreover, their densities remain high during the streamer afterglow phase. The concentration of electrons can reach values of up to 10 cm in the three cases analyzed. The model also predicts an important enhancement, of several orders of magnitude above ambient values, of nitrogen oxides and several metastables species. On the other hand, we found that the 4.26 μm IR emission brightness of CO can reach 10 GR at low altitudes (< 65 km) for the cases of intermediate (50 ms) and long (100 ms) driving currents. These results suggest the possibility of detecting sprite IR emissions from space with the appropriate instrumentation. Finally, we found that the thermal impact of sprites in the Earth's mesosphere is proportional to the driving current duration. This produces variations of more than 40 K (in the extreme case of a 100 ms driving current) at low altitudes (< 55 km) and at about 10 s after the streamer head. Key Points Chemical and thermal impacts of sprites in the mesosphere are calculated The calculated concentration of electrons exhibits a significant enhancement The model predicts an increase in the gas temperature at low altitudes.©2016. American Geophysical Union. All Rights Reserved.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-2011-07801Peer Reviewe

Upper D region chemical kinetic modeling of LORE relaxation times

The recovery times of upper D region electron density elevations, caused by lightning-induced electromagnetic pulses (EMP), are modeled. The work was motivated from the need to understand a recently identified narrowband VLF perturbation named LOREs, an acronym for LOng Recovery Early VLF events. LOREs associate with long-living electron density perturbations in the upper D region ionosphere; they are generated by strong EMP radiated from large peak current intensities of +/- CG (cloud to ground) lightning discharges, known also to be capable of producing elves. Relaxation model scenarios are considered first for a weak enhancement in electron density and then for a much stronger one caused by an intense lightning EMP acting as an impulsive ionization source. The full nonequilibrium kinetic modeling of the perturbed mesosphere in the 76 to 92 km range during LORE-occurring conditions predicts that the electron density relaxation time is controlled by electron attachment at lower altitudes, whereas above 79 km attachment is balanced totally by associative electron detachment so that electron loss at these higher altitudes is controlled mainly by electron recombination with hydrated positive clusters H+(H2O)(n) and secondarily by dissociative recombination with NO+ ions, a process which gradually dominates at altitudes > 88 km. The calculated recovery times agree fairly well with LORE observations. In addition, a simplified (quasi-analytic) model build for the key charged species and chemical reactions is applied, which arrives at similar results with those of the full kinetic model. Finally, the modeled recovery estimates for lower altitudes, that is < 79 km, are in good agreement with the observed short recovery times of typical early VLF events, which are known to be associated with sprites.This work was supported by the Spanish Ministry of Science and Innovation, MINECO under projects ESP2013-48032-C5-5-R, FIS2014-61774-EXP, and ESP2015-69909-C5-2-R, and by the EU through the FEDER program. A.L. acknowledges support by a Ramon y Cajal contract, code RYC-2011-07801.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

A parameterization of long-continuing-current (LCC) lightning in the lightning submodel LNOX (version 3.0) of the Modular Earth Submodel System (MESSy, version 2.54)

Lightning flashes can produce a discharge in which a continuing electrical current flows for more than 40 ms. Such flashes are proposed to be the main precursors of lightning-ignited wildfires and also to trigger sprite charges in the mesosphere. However, lightning parameterizations implemented in global atmospheric models do not include information about the continuing electrical current of lashes. The continuing current of lightning flashes cannot be detected by conventional lightning location systems. Instead, these so-called long-continuing-current (LCC) flashes are commonly observed by extremely low-frequency (ELF) sensors and by optical instruments located in space. Reports of LCC lightning flashes tend to occur in winter and oceanic thunderstorms, which suggests a connection between weak convection and the occurrence of this type of discharge

Variation of lightning-ignited wildfire patterns under climate change

Lightning is the main precursor of natural wildfires and Long-Continuing-Current (LCC) lightning flashes are proposed to be the main igniters of lightning-ignited wildfires (LIW). Previous studies predict a change of the global occurrence rate and spatial pattern of total lightning. Nevertheless, the sensitivity of lightning-ignited wildfire occurrence to climate change is uncertain. Here, we investigate space-based measurements of LCC lightning associated with lightning ignitions and present LCC lightning projections under the Representative Concentration Pathway RCP6.0 for the 2090s by applying a recent LCC lightning parameterization based on the updraft strength in thunderstorms. We find a 41% global increase of the LCC lightning flash rate. Increases are largest in South America, the western coast of North America, Central America, Australia, Southern and Eastern Asia, and Europe, while only regional variations are found in northern polar forests, where fire risk can affect permafrost soil carbon release. These results show that lightning schemes including LCC lightning are needed to project the occurrence of lightning-ignited wildfires under climate chang

Coupling between atmospheric layers in gaseous giant planets due to lightning-generated electromagnetic pulses

©2014. American Geophysical Union. All Rights Reserved. Atmospheric electricity has been detected in all gaseous giants of our solar system and is therefore likely present also in extrasolar planets. Building upon measurements from Saturn and Jupiter, we investigate how the electromagnetic pulse emitted by a lightning stroke affects upper layers of a gaseous giant. This effect is probably significantly stronger than that on Earth. We find that electrically active storms may create a localized but long-lasting layer of enhanced ionization of up to 103 cm-3 free electrons below the ionosphere, thus extending the ionosphere downward. We also estimate that the electromagnetic pulse transports 107 J to 1010 J toward the ionosphere. There emissions of light of up to 108 J would create a transient luminous event analogous to a terrestrial >elve.> Key Points The EMP from lightning has a stronger effect in gaseous planets than on EarthThe EMP creates ionization and light upper atmosphere of Saturn and JupiterLight emitted by the EMP is one tenth of the light from the lightning strokeThis 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. D. D. and Y.Y. were supported by the Israeli Ministry of Science, scholarship in Memory of Col. Ilan Ramon and by the Israeli Science Foundation grant 117/09.Peer Reviewe

GRASSP: a spectrograph for the study of transient luminous events

We present the main parameters, design features, and optical characterization of the Granada Sprite Spectrograph and Polarimeter (GRASSP), a ground- based spectrographic system intended for the analysis of the spectroscopic signature of transient luminous events (TLEs) occurring in the mesosphere of the Earth. It has been designed to measure the spectra of the light emitted from TLEs with a mean spectral resolution of 0.235 nm and 0.07 nm/px dispersion in the wavelength range between 700 and 800 nm. (C) 2016 Optical Society of AmericaSpanish Ministry of Science and Innovation, Ministerio de Economia y Competitividad (MINECO) (ESP2013-48032-C5-5-R, ESP2015-69909-C5-2-R, FIS2014-61774-EXP); European Union FEDER Program; Ramon y Cajal Contract (RYC-2011-07801).Peer reviewe

Submicrosecond Spectroscopy of Lightning-Like Discharges: Exploring New Time Regimes

Abstract Submicrosecond (0.476 μs per frame with an exposure time of 160 ns) high-resolution (0.38 nm) time-resolved spectra of laboratory-produced lightning-like electrical discharges have been recorded for the first time within the visible spectral range (645–665 nm). The spectra were recorded with the GrAnada LIghtning Ultrafast Spectrograph (GALIUS), a high-speed imaging spectrograph recently developed for lightning research in the IAA-CSIC. Unprecedented spectral time dynamics are explored for meter long laboratory electrical discharges produced with a 2.0 MV Marx generator. The maximum electron density and gas temperature measured in a timescale of ≤0.50 μs (160 ns) were, respectively, ≃1018 cm−3 and ≃32,000 K. Overpressure in the lightning-like plasma channel, black-body dynamics, and self-absorption in spectral lines were investigated