Wang Younian

Surface Modification of Polyethylene (PE) Films Using Dielectric Barrier Discharge Plasma at Atmospheric Pressure

Modification of the surface properties of polyethylene (PE) films is studied using air dielectric barrier discharge at atmospheric pressure. The treated samples are examined by water contact angle measurements, Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). With the increase in treating time, the water contact angle changes from 93.2° before treatment to a minimum of 53.3° after a treatment for 50 s. Both ATR and XPS results show some oxidized species are introduced into the sample surface by the plasma treatment and the tendency of the water contact angle with the treating time is the same as that of oxygen concentration on the treated sample surface. SEM result shows the surface roughness of PE samples increases with the treatment time increasing.

Comparison of Yeast Inactivation Treated in He, Air and N2 DBD Plasma

In this paper, the mechanism of yeast inactivation in low temperature atmospheric pressure helium, nitrogen and air plasmas generated by dielectric barrier discharge is analysed and compared. The results show that all the three gas plasmas have a high germicidal efficiency. The morphology of the yeast is observed by scanning electron microscopy, which reveals that the yeast treated in helium plasma is ruptured completely but there are only some flaws on the cell walls in the nitrogen and air plasma treated samples. Also, the flaws on the cell walls treated by air plasma are more significant than that by nitrogen treatment. Simultaneously, the pH values of the samples after 5 min nitrogen and air plasma treatment have no remarkable change either, while the sample treated with helium plasma descends below 4.0, which is beyond the optimum one for the yeasts living environment. The difference in pH values may be caused by the treatment effect and the degree of the cells rupture when the gas discharge plasma treatment is applied.

Interactions of a Charged Particle with Parallel Two-Dimensional Quantum Electron Gases

By using the linearized quantum hydrodynamic (QHD) theory, electronic excitations induced by a charged particle moving between or over two parallel two-dimensional quantum electron gases (2DQEG) are investigated. The calculation shows that the influence of the quantum effects on the interaction process should be taken into account. Including the quantum statistical and quantum diffraction effects, the general expressions of the induced potential and the stopping power are obtained. Our simulation results indicate that a V-shaped oscillatory wake potential exists in the electron gases during the test charge intrusion. Meanwhile, double peaks will occur in the stopping power when the distance of two surfaces is smaller and the test charge gets closer to any one of the two sheets.

Nonlinear Plasma Dynamics in Electron Heating of Asymmetric Capacitive Discharges with a Fluid Sheath Model

A fluid radio-frequency (rf) sheath model coupled to an equivalent circuit method is adopted to describe the nonlinear series resonance effects due to nonlinear interaction of plasma bulk and sheath in asymmetric capacitive discharges. With the fluid sheath model, we can determine self-consistently the relationship between the instantaneous potential drop across the rf sheath and the instantaneous sheath thickness. The numerical results demonstrate that the self-excitation of the plasma series resonance significantly enhances both ohmic heating and stochastic heating. Also, we observe that the effects of nonlinear series resonance increases the total power dissipation by factors of 2–5 for low pressure capacitive plasmas. Furthermore, we find that the largest harmonic is about 13 for the plasma current.

The Study of Active Atoms in High-Voltage Pulsed Coronal Discharge by Optical Diagnostics

In this study, the emission spectra of active atoms O (3p5P → 3s5S20 777.4 nm), Hα (3P → 2S 656.3 nm) and N (3p4P → 3s4S0 742.3 nm, 744.2 nm, 746.8 nm) produced by the positive high-voltage pulsed corona discharge (HVPCD) of N2 and H2O mixture in a needle-plate reactor have successfully been recorded against a severe electromagnetic interference coming from the HVPCD at one atmosphere. The effects of the peak voltage, the repetition rate of pulsed discharge and the flow rate of oxygen on the production of those active atoms are investigated. It is found that when the peak voltage and the repetition rate of the pulsed discharge are increased, the emission intensities of those active atoms rise correspondingly. And the emission intensities of O (3p5P → 3s5S20 777.4 nm), Hα (3P → 2S 656.3 nm) and N (3p4P → 3s4S0 742.3 nm, 744.2 nm, 746.8 nm) increase with the flow rate of oxygen (from 0 to 25 ml/min) and achieve a maximum value at a flow rate of 25 ml/min. When the flow rate of oxygen is increased further, the emission intensities of those atoms visibly decrease correspondingly. The main physicochemical processes of interaction involved between electrons, neutrals and ions are also discussed.

Wake Effects in Ion Transport through Carbon Nanotubes

A semiclassical kinetic model is explored to investigate the wake effects in the transport of charged particles through single-walled (SWCNT) and double-walled (2WCNTs) carbon nanotubes, with the introduction of electron band structure effect. The analytical expressions of the induced electron density at nanotube surface and the induced potential around the nanotube walls are obtained. The simulation results indicate that a bell-like distribution appears for the induced electron density when the incident particle speed is below a threshold value, otherwise wake-like oscillation can be seen behind the particle in the axial distribution. Dependencies of the amplitude and frequency of oscillations on the incident particle speed are also discussed. Meanwhile, we notice that the valence electrons on the outer wall of 2WCNTs tend to be easily excited by the polarized electrons on the inner wall, compared with that by the incident particle without the inner wall in SWCNTs. Finally, the induced potential trailing the incident particle also exhibits remarkable oscillations, not only along the axial direction but also in the lateral region, with evident extrema at the nanotube walls.

Numerical study of ion energy and angular distributions in dual‐frequency capacitively coupled CF4 plasmas

A one‐dimensional hybrid model is presented in the paper to study the characteristics of ion energy and angular distributions on the rf‐biased electrode in dual frequency capacitively coupled CF4 discharges. The hybrid model includes two parts: a fluid module and a Monte Carlo (MC) module. The fluid module determines the spatiotemporal evolutions of bulk plasma, and the MC module describes the ion‐neutral collisions to predict the ion energy and angular distributions on rf‐biased electrode. The discussion of this paper focuses on the influence of pressure, voltage, amplitude, and frequencies of the low frequency source on ion energy distributions (IEDs) and ion angular distributions (IADs) of CF3+ and F+ ions. For the CF3+ ions, the IEDs appear to have multiple‐peak structures in the dual frequency capacitively coupled rf discharge, and the IADs have a significant peak at a small angle. With the increase of pressure, the maximum energy in IEDs decreases, and the IADs spread to a large angle region. With t...

Feature Profile Evolution During Etching of SiO2 in Radio-Frequency or Direct-Current Plasmas

We have developed a plasma etching simulator to investigate the evolution of pattern profiles in SiO2 material under different plasma conditions. This model focuses on energy and angular dependent etching yield (physical sputtering in this paper), neutral and ion angular distributions, and reflection of ions or neutrals on the surface of a photoresist or SiO2. The effect of positive charge accumulation on the surface of insulated mask or SiO2 is studied and the charge accumulation contributes to a deflection of ion trajectory. The wafer profile evolution has been simulated using a cellular-automata-like method under radio-frequency (RF) bias and direct-current (DC) bias, respectively. On the basis of the critical role of angular distribution of ions or neutrals, the wafer profile evolution has been simulated for different variances of angles. Observed microtrenching has been well reproduced in the simulator. The ratio of neutrals to ions has been considered and the result shows that because the neutrals are not accelerated by an electric field, their energy is much lower compared with ions, so they are easily reflected on the surface of SiO2, which makes the trench shallower.

Spatial variation behaviors of argon inductively coupled plasma during discharge mode transition

A Langmuir probe and an ICCD are employed to study the discharge mode transition in Ar inductively coupled plasma. Electron density and plasma emission intensity are measured during the E (capacitive discharge) to H (inductive discharge) mode transitions at different pressures. It is found that plasma exists with a low electron density and a weak emission intensity in the E mode, while it has a high electron density and a strong emission intensity in the H mode. Meanwhile, the plasma emission intensity spatial (2D image) profile is symmetrical in the H mode, but the 2D image is an asymmetric profile in the E mode. Moreover, the electron density and emission intensity jump up discontinuously at high pressure, but increase almost continuously at the E to H mode transition under low pressure.

Comparison of 2D Hybrid Simulational and Experimental Results for Dual-Frequency Capacitively Coupled Argon Plasmas

A two-dimensional hybrid simulation scheme is proposed to study the characteristics of dual-frequency (DF) capacitively coupled plasma (CCP) discharge based on the geometry of real device. Given the experimental parameters for argon plasma, the output from the fluid module such as ion density, number flux, electron temperature and the Monte-Carlo collision (MCC) results of ion energy distribution function (IEDF) as well as electron energy distribution function (EEDF) are obtained and discussed in detail. A novel complete floating double probe is designed to measure both density and temperature of electron and a quadrupole mass spectrometer is also equipped for IEDF investigations. The measurements on the density of bulk plasma, electron temperature and IEDF agree well, qualitatively, with the simulated results. A comparison with experimental results indicates that, since the structure of real device is taken into account, this model is capable of describing the global dynamic characteristics occurred in DF-CCP and presenting more reliable results than the model with an ideal chamber structure.