Temperature-dependent ion chemistry in nanosecond discharge plasma-assisted CH4 oxidation

Abstract Ion chemistry with temperature evolution in weakly ionized plasma is important in plasma-assisted combustion and plasma-assisted catalysis, fuel reforming, and material synthesis due to its contribution to plasma generation and state transition. In this study, the kinetic roles of ionic reactions in nanosecond discharge (NSD) plasma-assisted temperature-dependent decomposition and oxidation of methane are investigated by integrated studies of experimental measurements and mathematical simulations. A detailed plasma chemistry mechanism governing the decomposition and oxidation processes in a He/CH4/O2 combustible mixture is proposed and studied by including a set of electron impact reactions, reactions involving excited species, and ionic reactions. A zero-dimensional model incorporating the plasma kinetics solver ZDPlasKin and the combustion chemical kinetics solver CHEMKIN is used to calculate the time evolution of the ion density. Uncertainty analysis of ionic reactions on key species generation is conducted by using different referenced data, and insignificant sensitivity is found. The numerical model is consistent with experimental data for methane consumption and generation of major species including CO, CO2, and H2. By modeling the temporal evolution of key ions, it is observed that O2+ presents the largest concentration in the discharge stage, followed by CH4+, CH3+, and CH2+, which is in accordance with the traditional ion chemistry in hydrocarbon flames and agrees well with molecular-beam mass spectrometer investigations. The path flux shows that the concentrations of key species, including electrons, O, OH, H, O(1D), O2(a1Δg), O2+, CH3+, and CH4+, change within 1–2 orders of magnitude and that the transition from a homogeneous state to a contracted/constricted state does not occur. The path flux and sensitivity analysis reveal the significant roles of cations in the stimulation of active radical generation, including CH, O, OH, and O(1D), thus accelerating methane oxidation. This work provides a deep insight into the ion chemistry of temperature-dependent plasma-assisted CH4 oxidation.

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Mechanism of Dry Etching of Silicon Dioxide: a Case of Direct Reactive Ion Etching

MRS Proceedings ◽

10.1557/proc-38-157 ◽

1984 ◽

Vol 38 ◽

Cited By ~ 2

Author(s):

Ch. Steinbruchel ◽

H. W. Lehmann ◽

K. Frick

Keyword(s):

Ion Beam ◽

Reactive Ion Etching ◽

Plasma Chemistry ◽

Experimental Conditions ◽

Ion Etching ◽

Ion Density ◽

Ion Beam Etching ◽

Plasma Species ◽

Parallel Plate Reactor ◽

Sputter Etching

AbstractReactive sputter etching of SiO2 with CHF3-O2 plasmas has been investigated in a parallel plate reactor by combining etch rate measurements with concurrent determination of ion densities (using a Langmuir probe) and the composition of neutral plasma species (using a mass spectrometer). Etch rates are found to follow the ion density and to be fairly independent of the plasma chemistry under most experimental conditions. Moreover, a comparison of reactive sputter etching and reactive ion beam etching of SiO2 with CHF3 and CF4 shows that etch yields per incoming ion are essentially independent of the flux of neutral radicals to the substrate. This strongly suggests as the dominant etch mechanism for SiO2 direct reactive ion etching, where ions themselves are the main reactants in the etch reaction. Measured values of etch yields are consistent with this picture.

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Mechanism of Aqueous Carbon Dioxide Reduction by the Solvated Electron

10.26434/chemrxiv.12674339 ◽

2020 ◽

Author(s):

Vladimir Rybkin

Keyword(s):

Carbon Dioxide ◽

Electron Transfer ◽

Plasma Chemistry ◽

Reorganization Energy ◽

Carbon Dioxide Reduction ◽

Solvated Electron ◽

Intermediate Transformation ◽

Proton Coupled Electron Transfer ◽

Key Species ◽

Proton Migration

Aqueous solvated electron, eaq, a key species in radiation and plasma chemistry, can effciently reduce CO2 in a potential green chemistry application. Here, the mechanism of this reaction is unravelled by condensed-phase Born-Oppenheimer molecular dynamics based on the correlated wave function and accurate DFT approximation. We introduce and apply the holistic protocol for solvated electron's reactions encompassing all relevant reaction stages starting from diffusion. The carbon dioxide reduction proceeds via a cavity intermediate, which is separated from the product, CO2-, by an energy barrier due to the bending of CO2 and the corresponding solvent reorganization energy. The formation of the intermediate is caused by solvated electron's diffusion, whereas the intermediate transformation to CO2- is triggered by solvent fluctuations. This picture of activation-controlled eaq reaction is very different from both rapid barrierless electron transfer, and proton-coupled electron transfer, where key transformations are caused by proton migration.

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Computational Modeling of Homogeneous Nucleation and Particle Growth During Chemical Vapor Deposition of Silicon Films from Silane Plasmas

MRS Proceedings ◽

10.1557/proc-715-a19.2 ◽

2002 ◽

Vol 715 ◽

Author(s):

S Warthesen ◽

U Bhandarkar ◽

S Girshick ◽

U Kortshagen

Keyword(s):

Plasma Chemistry ◽

Chemical Vapor ◽

Electron Attachment ◽

Particle Growth ◽

Nucleation And Growth ◽

Gas Temperature ◽

New Materials ◽

Temperature Dependent ◽

Excited Species ◽

Simulation Results

AbstractWe have been developing a model to study the nucleation and growth of particles in silane plasmas. Presently we are experimenting with parameters that could potentially be important. It has been found that an increase in the heavy species gas temperature leads to a delay in the nucleation of particles in low pressure silane plasmas. This effect could be useful in tailoring processes for the manufacture of new materials such as polymorphous silicon. We have made an effort to study this effect using a plasma chemistry model. The model includes gas temperature dependent electron attachment and vibrational relaxation of excited species with a view to study their importance in relation to the gas temperature. Preliminary simulation results predict that these two processes do not contribute substantially to slowing the nucleation process when the gas temperature is increased. Extra efforts must be made to study this potentially important effect.

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Plasma Chemical Aspects of Magnetron Ion Etching with CF4/O2 and CF4/H2

MRS Proceedings ◽

10.1557/proc-98-217 ◽

1987 ◽

Vol 98 ◽

Author(s):

A. A. Bright ◽

S. Kaushik ◽

G. S. Oehrlein

Keyword(s):

Semiconductor Manufacturing ◽

Plasma Chemistry ◽

Operating Pressure ◽

Plasma Chemical ◽

Ion Etching ◽

Ion Density ◽

Atom Concentration ◽

Manufacturing Applications ◽

Etching System ◽

Ionization Rates

ABSTRACTMagnetron plasmas are of great current interest for semiconductor manufacturing applications because of their high ion density and low operating pressure. We have studied the properties of a magnetron ion etching system using CF4, CF4/O2, and CF4/H2 with respect to the plasma chemistry and the interaction of the plasma with the etched substrate. The higher dissociation and ionization rates lead to significant changes in the species present in the plasma as compared to a conventional reactive ion etching (RIE) plasma. The F atom concentration in a CF4 magnetron plasma is much higher than in a RIE plasma. The addition of O2 leads to only a small further enhancement and produces a decrease in the Si etch rate. Addition of H2 suppresses the F atom concentration slightly, produces very little C-F polymer, and does not lead to highly selective etching of SiO2 over Si. The highly dissociated species in the magnetron plasma produce less C-F polymer, both on the wafer and on the chamber walls, relative to RIE.

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Mechanism of Aqueous Carbon Dioxide Reduction by the Solvated Electron

10.26434/chemrxiv.12674339.v1 ◽

2020 ◽

Author(s):

Vladimir Rybkin

Keyword(s):

Carbon Dioxide ◽

Electron Transfer ◽

Plasma Chemistry ◽

Reorganization Energy ◽

Carbon Dioxide Reduction ◽

Solvated Electron ◽

Intermediate Transformation ◽

Proton Coupled Electron Transfer ◽

Key Species ◽

Proton Migration

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(111) Monocrystalline Nickel Films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100095819 ◽

1972 ◽

Vol 30 ◽

pp. 512-513

Author(s):

T.E. Pratt ◽

R.W. Vook

Keyword(s):

Film Thickness ◽

Deposition Rate ◽

Room Temperature ◽

Narrow Range ◽

High Vacuum ◽

Residual Pressure ◽

Temperature Dependent ◽

Deposition Parameters ◽

Transmission Electron ◽

Substrate Temperatures

(111) oriented thin monocrystalline Ni films have been prepared by vacuum evaporation and examined by transmission electron microscopy and electron diffraction. In high vacuum, at room temperature, a layer of NaCl was first evaporated onto a freshly air-cleaved muscovite substrate clamped to a copper block with attached heater and thermocouple. Then, at various substrate temperatures, with other parameters held within a narrow range, Ni was evaporated from a tungsten filament. It had been shown previously that similar procedures would yield monocrystalline films of CU, Ag, and Au.For the films examined with respect to temperature dependent effects, typical deposition parameters were: Ni film thickness, 500-800 A; Ni deposition rate, 10 A/sec.; residual pressure, 10-6 torr; NaCl film thickness, 250 A; and NaCl deposition rate, 10 A/sec. Some additional evaporations involved higher deposition rates and lower film thicknesses.Monocrystalline films were obtained with substrate temperatures above 500° C. Below 450° C, the films were polycrystalline with a strong (111) preferred orientation.

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