Molecular processes in CH4H2 plasmas diluted with rare gases: reactions of X∗ atoms and X+ ions (X  Ne and Ar) with methane molecules

Tosi, Paolo; Bassi, Davide; Brunetti, Brunetto Giovanni; Vecchiocattivi, Franco

doi:10.1016/0168-1176(95)04267-o

Cited by 21 publications

(12 citation statements)

References 36 publications

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“…One variable that has engendered much interest is the fraction of rare gas (e.g., argon) in the process gas mixture. [4][5][6][7][8][9] Small amounts of argon were added to the process gas mixtures used in many early MW-PECVD studies to help initiate and/or stabilize the plasma and/or to enable actinometry measurements. 10,11 The C/H ratio in the process gas mixture can have a profound effect on the morphology of the asgrown diamond: increasing the C/H ratio by, for example, increasing the CH 4 fraction leads to a reduction in average grain size [e.g., from microcrystalline diamond (MCD) to nanocrystalline diamond (NCD)].…”

Section: Introductionmentioning

confidence: 99%

Combined experimental and modeling studies of microwave activated CH4/H2/Ar plasmas for microcrystalline, nanocrystalline, and ultrananocrystalline diamond deposition

Richley

Fox

Ashfold

et al. 2011

Journal of Applied Physics

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A comprehensive study of microwave (MW) activated CH 4 /H 2 /Ar plasmas used for diamond chemical vapor deposition is reported, focusing particularly on the effects of gross variations in the H 2 /Ar ratio in the input gas mixture (from H 2 /Ar mole fraction ratios of > 10:1, through to $1:99). Absolute column densities of C 2 (a) and CH(X) radicals and of H(n ¼ 2) atoms have been determined by cavity ringdown spectroscopy, as functions of height (z) above a substrate and of process conditions (CH 4 , H 2 , and Ar input mole fractions, total pressure, p, and input microwave power, P). Optical emission spectroscopy has also been used to explore the relative densities of electronically excited H atoms, and CH, C 2 , and C 3 radicals, as functions of these same process conditions. These experimental data are complemented by extensive 2D (r, z) modeling of the plasma chemistry, which provides a quantitative rationale for all of the experimental observations. Progressive replacement of H 2 by Ar (at constant p and P) leads to an expanded plasma volume. Under H 2-rich conditions, > 90% of the input MW power is absorbed through rovibrational excitation of H 2. Reducing the H 2 content (as in an Ar-rich plasma) leads to a reduction in the absorbed power density; the plasma necessarily expands in order to accommodate a given input power. The average power density in an Ar-rich plasma is much lower than that in an H 2-rich plasma operating at the same p and P. Progressive replacement of H 2 by Ar is shown also to result in an increased electron temperature, an increased [H]/[H 2 ] number density ratio, but little change in the maximum gas temperature in the plasma core (which is consistently $3000 K). Given the increased [H]/[H 2 ] ratio, the fast H-shifting (C y H x þ H $ C y H xÀ1 þ H 2 ; y ¼ 1À3) reactions ensure that the core of Ar-rich plasma contains much higher relative abundances of "product" species like C atoms, and C 2, and C 3 radicals. The effects of Ar dilution on the absorbed power dissipation pathways and the various species concentrations just above the growing diamond film are also investigated and discussed. V

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Section: Introductionmentioning

confidence: 99%

Combined experimental and modeling studies of microwave activated CH4/H2/Ar plasmas for microcrystalline, nanocrystalline, and ultrananocrystalline diamond deposition

Richley

Fox

Ashfold

et al. 2011

Journal of Applied Physics

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“…Many measurements have been performed for reactions of CH 4 with rare gas cations (such as He + , Ar + , and Ne + ) (Chatham et al 1983;Tosi et al 1995). In all these experiments only BRs for the production of charged fragments have been measured.…”

Section: Charge Exchange Reactionsmentioning

confidence: 99%

Breakdown curves of CH₂⁽⁺⁾, CH₃⁽⁺⁾, and CH₄⁽⁺⁾ molecules

Chabot

IdBarkach

Béroff

et al. 2020

A&A

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Aims. The aim of this work is to provide semi-empirical branching ratios (BRs) for the kinetic databases used in astrochemistry, such as the KInetic Database for Astrochemistry (KIDA). Our work focuses on the CHy(+) species (y = 2–4) excited by cosmic rays (CR), electrons, and photons (UV), or the intermediate excited complexes CHy(+) resulting from chemical reactions. It also intends to test the sensitivity of benchmark calculations to those new physical inputs in cold quiescent clouds and in photo-dissociation regions (PDRs). Methods. We constructed semi-empirical breakdown curves (BDCs) based on the collision of CHy+ (y = 2–4) projectiles of constant velocity (250 keV uma−1) with He atoms as explained in a previous paper, where BRs for UV, CR, and electronic processing were also derived. The same BDCs were applied to predict BRs for chemical reactions (bi-molecular neutral and ionic reactions, charge exchange). The effect of the new BRs on the chemical composition of cold dark clouds was tested using the time-dependent Nautilus gas-grain model. The same effect on the chemical composition of PDRs was tested using the Meudon PDR code. Results. Branching ratio predictions of the model are found to be in good agreement with available BR measurements for charge exchange reactions and the reaction between C and H3+. The chemistry for both cold clouds and PDRs is found to be not strongly affected by this update of BRs.

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“…For example, the rate constants for Penning ionization processes are of the same order of magnitude of gas phase bimolecular reactions of O͑ 1 D͒, Cl, or Br, which are known to be relevant in the atmospheric chemistry. 4,5 Other reactions exhibit rate constants that are at least one order of magnitude smaller. 5 The present paper deals with the collisional autoionization of N 2 O molecules by He * and Ne * metastable atoms, as studied by Penning ionization electron spectroscopy ͑PIES͒ and measurement of ionization cross sections, both as a function of the collision energy.…”

Section: Introductionmentioning

confidence: 99%

Penning ionization of N2O molecules by He(2S3,1) and Ne(P2,3) metastable atoms: A crossed beam study

Biondini

Brunetti

Candori

et al. 2005

The Journal of Chemical Physics

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The energetics of [Rg... N2O]* autoionizing collision complexes (where Rg=He or Ne) and their dynamical evolution have been studied in a crossed beam apparatus, respectively, by Penning ionization electron spectroscopy (PIES) and by mass spectrometry (MS) techniques in the thermal energy range. The PIES spectra, detected by an electron energy analyzer, were recorded for both complexes at four different collision energies. Such spectra allowed the determination of the energy shifts for Penning electron energy distributions, and the branching ratios for the population of different electronic states and for the vibrational population in the molecular nascent ions. For the [Ne...N2O]* collision complex it was found, by MS, that the autoionization leads to the formation of N2O+, NO+, O+, and NeN2O+ product ions whose total and partial cross sections were measured in the collision energy range between 0.03 and 0.2 eV. The results are analyzed exploiting current models for the Penning ionization process: the observed collision energy dependence in the PIES spectra as well as in the cross sections are correlated with the nature of the N2O molecule orbitals involved in the ionization and are discussed in term of the Rg-N2O interaction potentials, which are estimated by using a semiempirical method developed in our laboratory.

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Molecular processes in CH4H2 plasmas diluted with rare gases: reactions of X∗ atoms and X+ ions (X  Ne and Ar) with methane molecules

Cited by 21 publications

References 36 publications

Combined experimental and modeling studies of microwave activated CH4/H2/Ar plasmas for microcrystalline, nanocrystalline, and ultrananocrystalline diamond deposition

Combined experimental and modeling studies of microwave activated CH4/H2/Ar plasmas for microcrystalline, nanocrystalline, and ultrananocrystalline diamond deposition

Breakdown curves of CH₂⁽⁺⁾, CH₃⁽⁺⁾, and CH₄⁽⁺⁾ molecules

Penning ionization of N2O molecules by He(2S3,1) and Ne(P2,3) metastable atoms: A crossed beam study

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Molecular processes in CH4H2 plasmas diluted with rare gases: reactions of X∗ atoms and X+ ions (X  Ne and Ar) with methane molecules

Cited by 21 publications

References 36 publications

Combined experimental and modeling studies of microwave activated CH4/H2/Ar plasmas for microcrystalline, nanocrystalline, and ultrananocrystalline diamond deposition

Combined experimental and modeling studies of microwave activated CH4/H2/Ar plasmas for microcrystalline, nanocrystalline, and ultrananocrystalline diamond deposition

Breakdown curves of CH2(+), CH3(+), and CH4(+) molecules

Penning ionization of N2O molecules by He*(2S3,1) and Ne*(P2,3) metastable atoms: A crossed beam study

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Breakdown curves of CH₂⁽⁺⁾, CH₃⁽⁺⁾, and CH₄⁽⁺⁾ molecules

Penning ionization of N2O molecules by He(2S3,1) and Ne(P2,3) metastable atoms: A crossed beam study