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Particle-in-cell/Monte Carlo collision (PIC/MCC) simulations are performed to investigate the asymmetric secondary electron emission (SEE) effects when electrons strike two different material electrodes in low pressure capacitively coupled plasmas (CCPs). To describe the electron-surface interactions, a realistic model, considering the primary electron impact energy and angle, as well as the corresponding surface property-dependent secondary electron yields, is employed in PIC/MCC simulations. In this model, three kinds of electrons emitted from the surface are considered: (i) elastically reflected electrons, (ii) inelastically backscattered electrons, and (iii) electron induced secondary electrons (SEs, i.e., δ-electrons). Here, we examined the effects of electron-surface interactions on the ionization dynamics and plasma characteristics of an argon discharge. The discharge is driven by a voltage source of 13.56 MHz with amplitudes in the range of 200–2000 V. The grounded electrode material is copper (Cu) for all cases, while the powered electrode material is either Cu or silicon dioxide (SiO2). The simulations reveal that the electron impact-induced SEE is an essential process at low pressures, especially at high voltages. Different electrode materials result in an asymmetric response of SEE. Depending on the instantaneous local sheath potential and the phase of the SEE, these SEs either are reflected by the opposite sheath or strike the electrode surface, where they can induce δ-electrons upon their residual energies. It is shown that highly energetic δ-electrons contribute significantly to the ionization rate and a self-bias forms when the powered electrode material is assumed to be made of SiO2. Complex dynamics is observed due to the multiple electron-surface interaction processes and asymmetric yields of SEs in CCPs. [ABSTRACT FROM AUTHOR]

Liquid-cathode discharge at atmospheric pressure has been excited by a direct current voltage above the surfaces of deionized and tap water. Gap voltage decreases with increasing discharge current, which suggests that the discharges above both the liquids belong to a normal glow regime. For a given discharge current, gap and power voltages of the discharge above deionized water are higher than those above tap water. The optical spectrum obtained from the water surface reveals that there are abundant active species related to oxygen, nitrogen, and water vapor, which leads to changes in the pH value, conductivity, and concentrations of NO 3 − , NO 2 − , and H2O2 in liquid. Therefore, these parameters are investigated in the two liquids as functions of discharge current and plasma activation time. For both of them, the results show that the pH value decreases, while conductivity increment and concentrations of NO 3 − , NO 2 − , and H2O2 increase with increasing discharge current or activation time. Compared to activated tap water, deionized water has a lower pH value, while higher conductivity increment and concentrations of NO 3 − , NO 2 − , and H2O2 are observed after the same activation time and discharge current. Finally, these parameters are compared for different salt types and salt concentrations after plasma activation. [ABSTRACT FROM AUTHOR]

Interest in plasma-liquid interaction phenomena has grown in recent years due to applications in plasma medicine, water purification, and plasma-hydrocarbon reforming. The plasma in contact with liquid is generated, for example, using the plasma jets or streamer discharges. The interaction between the streamer and water can cause both physical and chemical modifications of the liquid. In this paper, the interaction between an anode-directed streamer and the de-ionized water is studied using one-dimensional particle-in-cell Monte Carlo collisions model. In this model, plasma species in both gas and liquid phase are considered as the macro-particles. We find that the penetration of the streamer head into the liquid causes ionization of water molecules by electron impact, a process which is usually ignored in the fluid models. The main charge carriers in the liquid phase are negative water ions which agree with earlier experimental and computational modeling studies. Additionally, we observe an ion-rich sheath in the vicinity of the water surface on the gas side. [ABSTRACT FROM AUTHOR]