Molecular Simulation of Oxygen Reactions with Realistic Carbon and Silica Surfaces at High Temperature

Schwartzentruber, Thomas E.; Poovathingal, Savio J.; Stern, Eric C.

doi:10.2514/6.2015-3567

Cited by 3 publications

(2 citation statements)

References 32 publications

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“…As such, we assume that, unlike recombination on a regular stable chemisorption site, recombination on a metastable chemisorption site has no energy barrier. This is in line with the work by Schwartzentruber et al [33], where atomic level Molecular Dynamics and Density Functional Theory calculations of oxygen-silica reactions show the main recombination mechanism (O + (Si − O − O)) to be non-activated (associated with no energy barrier). Models of Si metastable chemisorption site creation in hydrogenated amorphous silicon have been proposed by Powell et al [32], considering both light-induced and bias-stress-induced defect creation.…”

Section: Metastable Chemisorption Site Productionsupporting

confidence: 91%

Plasma-induced reversible surface modification and its impact on oxygen heterogeneous recombination

Afonso,

Vialetto,

Guerra

et al. 2023

J. Phys. D: Appl. Phys.

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A novel model is developed for atomic oxygen surface kinetics in silica-like walls, introducing a plasma-induced surface modification, which may impact intermediate pressure plasma reactors. The model is the first to reproduce experimental measurements in an oxygen glow discharge operating in the pressure range between 0.27 mbar (0.2 Torr) and 4 mbar (3 Torr), showing a decrease with pressure of the O recombination probability on Pyrex between 0.27 mbar and 1 mbar. The numerical simulations suggest that a modification is induced by the production and destruction of metastable chemisorption sites at the surface. As such, the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) recombination mechanisms take place involving not only physisorption (1) and stable chemisorption (2) sites, but also metastable chemisorption sites (3), produced by the impact of fast O2 ions and neutrals. The presence of metastable sites can be reversed by increasing the plasma pressure.

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Section: Metastable Chemisorption Site Productionsupporting

confidence: 91%

Plasma-induced reversible surface modification and its impact on oxygen heterogeneous recombination

Afonso,

Vialetto,

Guerra

et al. 2023

J. Phys. D: Appl. Phys.

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“…These DFT results will be reported in a separate paper. The regeneration mechanism for Si-O-Osites has also been studied by Schwartzentruber et al [61].…”

Section: Recombination Probability At Pressures Below 075 Torrmentioning

confidence: 92%

Oxygen (³P) atom recombination on a Pyrex surface in an O₂ plasma

Booth

Guaitella

Chatterjee

et al. 2019

Plasma Sources Sci. Technol.

258

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The recombination of O (3 P) atoms on the surface of a Pyrex tube containing a DC glow discharge in pure O 2 was studied over a wide range of pressure (0.2-10 Torr) and discharge current (10-40 mA) for two fixed surface temperatures (+50°C and +5°C). The recombination probability, , was deduced from the observed atom loss rate (dominated by surface recombination) determined by time-resolved optical emission actinometry in partially-modulated (amplitude ~15-17%) discharges. The value of  increased with discharge current at all pressures studied. As a function of pressure it passes through a minimum at ~0.75 Torr. At pressures above this minimum  is well-correlated with the gas temperature, T g , (determined from the rotational structure of the O 2 (b 1  g + ,v=0)  O 2 (X 3  g-,v=0) emission spectrum) which increases with pressure and current. The temperature of the atoms incident at the surface was deduced from a model, calibrated by measurements of the spatially-averaged gas temperature and validated by radial temperature profile measurements. The value of  follows an Arrhenius law depending on the incident atom temperature, with an activation energy in the range 0.13-0.16 eV. At the higher surface temperature the activation energy is the same, but the pre-exponential factor is smaller. Under conditions where the O flux to the surface is low  falls below this Arrhenius law. These results are well explained by an Eley-Rideal (ER) mechanism with incident O atoms recombining with both chemisorbed and more weakly bonded physisorbed atoms on the surface, with the kinetic energy of the incident atoms providing the energy to overcome the activation energy barrier. A phenomenological Eley-Rideal model is proposed that explains both the decrease in recombination probability with surface temperature as well as the deviations from the Arrhenius law when the O flux is low. At pressures below 0.75 Torr  increases significantly, and also increases strongly with the discharge current. We attribute this effect to incident ions and fast neutrals arriving with sufficient energy to clean or chemically modify the surface, generating new adsorption sites. Discharge modeling confirms that at pressures below ~0.3 Torr a noticeable fraction of the ions arriving at the surface have adequate kinetic energy to break surface chemical bonds (> 3-5 eV).

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Catalytic recombination assessment on carbon in dissociated shock tube flow

et al. 2021

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Molecular Simulation of Oxygen Reactions with Realistic Carbon and Silica Surfaces at High Temperature

Cited by 3 publications

References 32 publications

Plasma-induced reversible surface modification and its impact on oxygen heterogeneous recombination

Plasma-induced reversible surface modification and its impact on oxygen heterogeneous recombination

Oxygen (³P) atom recombination on a Pyrex surface in an O₂ plasma

Catalytic recombination assessment on carbon in dissociated shock tube flow

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Molecular Simulation of Oxygen Reactions with Realistic Carbon and Silica Surfaces at High Temperature

Cited by 3 publications

References 32 publications

Plasma-induced reversible surface modification and its impact on oxygen heterogeneous recombination

Plasma-induced reversible surface modification and its impact on oxygen heterogeneous recombination

Oxygen (3P) atom recombination on a Pyrex surface in an O2 plasma

Catalytic recombination assessment on carbon in dissociated shock tube flow

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Oxygen (³P) atom recombination on a Pyrex surface in an O₂ plasma