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High-frequency plasma jets driven by voltages in the frequency range of 6-60MHz are developed. A long plasma jet, 40mm in length, is successfully produced by using a pair of ring electrodes outside a quartz tube. The electrode pair consists of a wide power electrode and a narrow ground electrode that is positioned at the head of the tube. The ratio of the length of the ground electrode to the length of the power electrode must be small in order to produce long plasma jets. The highfrequency plasma jet is operated in a non-thermal-equilibrium state at a gas temperature of around 60°C. Operation at the very-high-frequency of 60MHz leads to a lower discharge voltage and lower electron energy compared to lower frequencies of 6 and 13.56MHz. The ability of the very-highfrequency (60 MHz) plasma jet to produce reactive oxygen and nitrogen species in water is also investigated. High H2O2 and NO3- concentrations of more than 1mmol/l are realized by irradiating 3ml of deionized water with the plasma for a short period of 2min. [ABSTRACT FROM AUTHOR]

The electron power absorption dynamics and plasma uniformity in low pressure capacitively coupled RF discharges with structured electrodes are investigated by graphics processing unit-based 2d3v particle-in-cell/Monte Carlo simulations in argon gas. In the presence of planar electrodes, the plasma is radially nonuniform due to strong electron density peaks close to the reactor sidewall, which are caused by edge effects that locally enhance the electron power absorption and ionization. Such a local enhancement of these characteristics can also be achieved in a controllable manner by using a single ring-shaped rectangular trench embedded in the powered electrode close to the reactor center. This effect is understood by analyzing the trajectories of selected electrons as well as the time evolution of their energy and velocity inside and above such trenches. Electrons are found to gain high energies inside the trench by bouncing between the sheaths at the trench walls during the sheath expansion phase. Combined with the cross-firing of energetic electrons at the trench orifice, this leads to high local ionization rates. Using these trench effects, the plasma uniformity above the wafer placed on a planar powered electrode can be remarkably improved by including multiple trenches in the opposing grounded electrode, which enhance the ionization and plasma density at their respective radial positions. Meanwhile, the ion flux-energy distribution function at the wafer is found to be almost unaffected. [ABSTRACT FROM AUTHOR]

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]

A comparative study of electrical breakdown properties of deionized water (H2O) and heavy water (D2O) is presented with two different electrode materials (stainless steel (SS) and brass) and polarity (positive and negative) combinations. The pulsed (~a few tens of nanoseconds) discharges are conducted by applying high voltage (~a few hundred kV) pulse between two hemisphere electrodes of the same material, spaced 3 mm apart, at room temperature (~26-28 °C) with the help of Tesla based pulse generator. It is observed that breakdown occurred in heavy water at lesser voltage and in short duration compared to deionized water irrespective of the electrode material and applied voltage polarity chosen. SS electrodes are seen to perform better in terms of the voltage withstanding capacity of the liquid dielectric as compared to brass electrodes. Further, discharges with negative polarity are found to give slightly enhanced discharge breakdown voltage when compared with those with positive polarity. The observations corroborate well with conductivity measurements carried out on original and post-treated liquid samples. An interpretation of the observations is attempted using Fourier transform infrared measurements on original and post-treated liquids as well as in situ emission spectra studies. A yet another important observation from the emission spectra has been that even short (nanosecond) duration discharges result in the formation of a considerable amount of ions injected into the liquid from the electrodes in a similar manner as reported for long (microseconds) discharges. The experimental observations show that deionised water is better suited for high voltage applications and also offer a comparison of the discharge behaviour with different electrodes and polarities. [ABSTRACT FROM AUTHOR]

Streaming currents were measured in silica slit-like nanochannels with integrated electrodes using a pulsed flow of deionized water. The analysis of the transient streaming current measurements in nanochannels shows that streaming currents are proportional to the surface charge density σ and that the effective reduction of nanochannel height by immobilized biomolecules needs to be taken into account. The σ of silica nanochannels was measured after performing sequential chemical surface modification steps. The nanochannel surface was first altered with positively charged polylysine and then with non-charged polyethylene glycol showing that nanochannels can sense the charge and size of surface-immobilized molecules. [ABSTRACT FROM AUTHOR]