Optical and mass spectroscopy measurements of Ar/CH4/H2 microwave plasma for nano-crystalline diamond film deposition

Zhou, Hang; Watanabe, Jun; Miyake, Masato; Oginö, Kazuhíde; Nagatsu, Masaaki; Zhan, Reggie

doi:10.1016/j.diamond.2006.11.074

Cited by 44 publications

(18 citation statements)

References 17 publications

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“…As listed in Table 1, the input power for He, Ar-H2, and Ar-N2 is clearly higher than that for Ar because of the higher enthalpy for He, H2, and N2, even though the average gas temperature is always controlled to be 3500 K. Hence, the addition of high-enthalpy gas indicates an environment Recent research suggests that the C 2 radicals are the main precursor species of graphene flakes [21,25,28]. In the Ar-H 2 atmosphere, the formed C 2 radicals can be consumed due to the formation of hydrocarbons by collision with the hydrogen molecules through the reaction [73,74]: C 2 + H 2 → C 2 H + H, so the synthesis rate of graphene flakes decreases. Similarly, the presence of N 2 in plasma favors the formation of cyanides due to the interaction of nitrogen molecules with C 2 radicals through the reaction [75,76]: C 2 + N 2 → CN + CN.…”

Section: Discussionmentioning

confidence: 99%

Effects of Buffer Gases on Graphene Flakes Synthesis in Thermal Plasma Process at Atmospheric Pressure

et al. 2020

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A thermal plasma process at atmospheric pressure is an attractive method for continuous synthesis of graphene flakes. In this paper, a magnetically rotating arc plasma system is employed to investigate the effects of buffer gases on graphene flakes synthesis in a thermal plasma process. Carbon nanomaterials are prepared in Ar, He, Ar-H2, and Ar-N2 via propane decomposition, and the product characterization is performed by transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the Brunauer–Emmett–Teller (BET) method. Results show that spherical particles, semi-graphitic particles, and graphene flakes coexist in products under an Ar atmosphere. Under an He atmosphere, all products are graphene flakes. Graphene flakes with fewer layers, higher crystallinity, and a larger BET surface area are prepared in Ar-H2 and Ar-N2. Preliminary analysis reveals that a high-energy environment and abundant H atoms can suppress the formation of curved or closed structures, which leads to the production of graphene flakes with high crystallinity. Furthermore, nitrogen-doped graphene flakes with 1–4 layers are successfully synthesized with the addition of N2, which indicates the thermal plasma process also has great potential for the synthesis of nitrogen-doped graphene flakes due to its continuous manner, cheap raw materials, and adjustable nitrogen-doped content.

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Section: Discussionmentioning

confidence: 99%

Effects of Buffer Gases on Graphene Flakes Synthesis in Thermal Plasma Process at Atmospheric Pressure

et al. 2020

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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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“…34 So, the C 2 species form hydrocarbon that then flows out of the reaction zone without producing any allotropes of carbon. 26,29 The PR of collected powder is $1 and 16 mg/min at 600 and 700 mbar, respectively, betokening that the saturation ratio is high enough to favor particle nucleation due to higher rT caused by enhanced collisions with an increase in pressure. Thus, the decrease in C 2 density with an increasing pressure is associated with conversion from gaseous to condensed phase.…”

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confidence: 99%

“…X 2 PÞ and H 2 . 25,26 The formation of C 2 , C 3 , and CH radicals indicates that electron impact and the dehydrogenation processes are responsible for the dissociation of CH 4 due to the presence of both electrons and atomic hydrogens in the plasma. 25 The C 2 transitions observed in the Ar/ H 2 /CH 4 plasma arise due to the energy transfer from Ar* to C 2 H 2 and/or C 2 H formed during the dissociation of CH 4 .…”

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confidence: 99%

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Methane dissociation process in inductively coupled Ar/H2/CH4 plasma for graphene nano-flakes production

Mohanta

Lanfant

Asfaha

et al. 2017

Applied Physics Letters

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The role of hydrogen and methane dissociation process in induction plasma synthesis of graphene nano-flakes (GNF) is studied by the optical emission spectroscopy of Ar/H2/CH4 plasma. The condensation of C2 species formed due to methane decomposition produces GNF, which depends on pressure. Electron impact and dehydrogenation processes dissociate methane, which promotes and hinders the GNF production, respectively. The effect of hydrogen is insignificant on quality, size and morphology of the GNF. The CH4 flow rate has no influence on particle temperature but has effect on cooling rate at the point of nucleation and, therefore, on production rate and thickness of GNF.

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Optical and mass spectroscopy measurements of Ar/CH4/H2 microwave plasma for nano-crystalline diamond film deposition

Cited by 44 publications

References 17 publications

Effects of Buffer Gases on Graphene Flakes Synthesis in Thermal Plasma Process at Atmospheric Pressure

Effects of Buffer Gases on Graphene Flakes Synthesis in Thermal Plasma Process at Atmospheric Pressure

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

Methane dissociation process in inductively coupled Ar/H2/CH4 plasma for graphene nano-flakes production

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