Inside Cover Picture: Plasma Process. Polym. 11/2019

Sun, Guangyu; Li, Han‐Wei; Sun, Anbang; Li, Yuan; Song, Bai‐Peng; Mu, Hai‐Bao; Li, Xiaoran; Zhang, Guanjun

doi:10.1002/ppap.201970024

Cited by 5 publications

(6 citation statements)

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“…Electron-induced secondary electron emission (ESEE) on the dielectric, ion-induced secondary electron emission (ISEE) on the metallic electrode, metal sputtering due to incident ions, ionization/electron-neutral collisions, outgassing and the relativistic effects of fast electrons are included in the simulation with similar algorithms in previous studies [17,18,43]. The data for the collision cross-section are imported from an existing database similar to our related works on plasma simulation [49,50]. A schematic of the simulation code is given in figure 1(d).…”

Section: Methodsmentioning

confidence: 99%

Estimation of surface flashover threshold in a vacuum II: flashover phase transition

Sun¹,

Guo²,

Li³

et al. 2019

J. Phys. D: Appl. Phys.

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Surface discharge in a vacuum occurs under an intense external field, also called a flashover. The flashover threshold over which the surface flashover occurs is of vital importance in the vacuum-solid interface. It is widely assumed that the flashover is initiated by a single surface multipactor and develops as a plasma discharge along a dielectric surface, namely the secondary electron emission avalanche (SEEA). Yet the SEEA model is not versatile for all practical vacuum-solid interfaces and there remain experiment results contradicting the theory predictions without a resolute answer. Here we further expand on previous theories and consider the conventional SEEA model under arbitrary field distributions. The example of a conical insulator is then given to test the validity of the SEEA model under an arbitrary field. It is found that the obtained flashover threshold is only consistent with the experiment at low cone angles where the field near the cathode triple junction is strong, while remarkable discrepancies appear when the anode field is significantly enhanced. The discrepancies can be understood if a different discharge model, i.e. an anode-initiated flashover (AIF) is included. Both particle-in-cell simulation and optical diagnostics are employed to visualize this unique discharge, which are then formalized on theoretical grounds to elucidate the early stage of the AIF. The transition between two flashover phases is then clarified. The plasma-surface interaction and sheath dynamics during the discharge are analyzed theoretically, showing distinct sheath evolutions in two flashover models. Additionally, a new factor reflecting field distortion is introduced to estimate the discharge threshold under an SEEA framework.

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Section: Methodsmentioning

confidence: 99%

Estimation of surface flashover threshold in a vacuum II: flashover phase transition

Sun¹,

Guo²,

Li³

et al. 2019

J. Phys. D: Appl. Phys.

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show abstract

“…Approaches like this are very convenient in simulation code to determine sheath edge location [12]. A similar criterion also using the non-neutrality sets the sheath edge at the location where (n i − n e )/n i = δ [10,62,63]. In theoretical analyses, the oscillating 'step function' electron density profile is commonly used [44,64,65].…”

Section: Simulation Resultsmentioning

confidence: 99%

“…In previous works, it has been confirmed experimentally that the secondary electron emission (SEE) can significantly modify important plasma parameters, such as the temperature, density, and particle/power balance [5,6]. Previous theoretical studies indicate that the SEE significantly modifies the plasma discharge characteristics [8,9]; these works also express the RF sheath as a function of the source amplitude and the SEE coefficient, giving quantitative current-voltage characteristic, sheath capacitance and conductance in the presence of boundary electron emission [10,11]. In addition to experimental and theoretical approaches, numerical simulations provide further insight into the physical details of PSI in CCP discharges.…”

Section: Introductionmentioning

confidence: 93%

Unveiling the role of dielectric trap states on capacitively coupled radio-frequency plasma discharge: dynamic charging behaviors

Zhang¹,

Sun²,

Volčokas³

et al. 2021

Plasma Sources Sci. Technol.

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The influence of charge trap states in the dielectric boundary material on capacitively coupled radio-frequency (RF) plasma discharge is investigated with theory and particle-in-cell/Monte Carlo collision simulation. It is found that the trap states of the wall material manipulated discharge properties mainly through the varying ion-induced secondary electron emission (SEE) coefficient in response to dynamic surface charges accumulated within the solid boundary. A comprehensive SEE model considering surface charging is established first, which incorporates the valence band electron distribution, electron trap density, and charge trapping through Auger neutralization and de-excitation. Theoretical analysis is carried out to reveal the effects of trap states on sheath solution, stability, plasma density and temperature, particle and power balance, etc. The theoretical work is supported by simulation results, showing the reduction of the mean RF sheath potential as charging-dependent emission coefficient increases. As the gas pressure increases, a shift of the maximum ionization rate from the bulk plasma center to the plasma-sheath interface is observed, which is also influenced by the trap states of the electrode material where the shift happens at a lower pressure with traps considered. In addition, charge traps are proven to be helpful for creating asymmetric plasma discharges with geometrically symmetric structures; such an effect is more pronounced in γ-mode discharges.

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“…In earlier studies of ion-induced secondary electron (γ-electron) emission, a constant emission coefficient was usually set in the simulations due to a lack of data for the energyand material-dependent surface coefficients. Despite this, such studies reported strong effects of the γ-electron emission coefficients (the γ-coefficient) on the discharge operation mode [63][64][65][66][67][68]. When a low γ-coefficient was used in the simulations of argon discharges, the discharge was usually found to operate in the α-mode [69].…”

Section: Introductionmentioning

confidence: 99%

2D particle-in-cell simulations of geometrically asymmetric low-pressure capacitive RF plasmas driven by tailored voltage waveforms

Wang¹,

Hartmann²,

Song³

et al. 2021

Plasma Sources Sci. Technol.

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The effects of the simultaneous presence of two different types of plasma asymmetry, viz, geometric and electrical, on low-pressure capacitively coupled argon discharges are studied by 2D3V graphics-processing-unit-based particle-in-cell/Monte Carlo simulations. The geometric asymmetry originates from the different powered vs grounded electrode surface areas, while the electrical asymmetry is established by applying peaks/valleys and sawtooth-up/-down driving voltage waveforms. While in geometrically symmetric discharges, the {peaks ↔ valleys} and the {sawtooth-down ↔ sawtooth-up} switching of the waveforms is equivalent to exchanging the powered and grounded electrodes, this transformation is violated when the geometric symmetry is broken. Under such conditions, the plasma characteristics and the DC self-bias generation behave differently, compared to the geometrically symmetric case. This leads to different sheath dynamics and, therefore, strongly influences the electron power absorption dynamics. For identical peak-to-peak voltages, the plasma density obtained for such tailored voltage waveforms is found to be higher compared to the classical single-frequency waveform case. Reduced plasma densities are found in the valleys- and sawtooth-down waveform cases, compared to the peaks- and sawtooth-up waveforms. By including realistic energy and material-dependent secondary electron emission (SEE) coefficients in the simulations, the electron-induced SEE is found to be reduced in the valleys- and sawtooth-down waveform cases, which explains the behaviour of the plasma density. Using such tailored waveforms in geometrically asymmetric discharges is also found to lead to the formation of different charged particle energy distributions at the boundary surfaces, compared to those in geometrically symmetric plasma sources.

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Inside Cover Picture: Plasma Process. Polym. 11/2019

Cited by 5 publications

References 0 publications

Estimation of surface flashover threshold in a vacuum II: flashover phase transition

Estimation of surface flashover threshold in a vacuum II: flashover phase transition

Unveiling the role of dielectric trap states on capacitively coupled radio-frequency plasma discharge: dynamic charging behaviors

2D particle-in-cell simulations of geometrically asymmetric low-pressure capacitive RF plasmas driven by tailored voltage waveforms

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