Song Yuan-Hong

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.

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.

Frequency Matching Effects on Characteristics of Bulk Plasmas and Sheaths for Dual-Frequency Capacitively Coupled Argon Discharges: One-Dimensional Fluid Simulation

A one-dimensional fluid model is proposed to simulate the dual-frequency capacitively coupled plasma for Ar discharges. The influences of the low frequency on the plasma density, electron temperature, sheath voltage drop, and ion energy distribution at the powered electrode are investigated. The decoupling effect of the two radio-frequency sources on the plasma parameters, especially in the sheath region, is discussed in detail.

Kinetic Study on Channelling of Protons in Metallic Carbon Nanotubes

Based on the kinetic model and the dielectric response theory, a theoretical model is put forward to describe the transport of protons along nanotube axes. With the introduction of electron band structure for different nanotubes like zigzag and armchair nanotubes of metallic properties, the collective excitation of electrons on the cylinders induced by the incident ions is studied, showing several distinct peaks in the curves of the energy loss function. Furthermore, the stopping power and the self-energy are calculated as functions of ion velocities, especially taking into account the influence of damping coefficients. It is conceivable from the results that, in the kinetic formulation, plasmon excitation plays a major role in the stopping. And as the damping increases, the peaks of the stopping power shift to the lower velocities, with the broadening of the plasmon resonance.

Monte Carlo simulation of ion transport process in ECR microwave plasma with negative bias

In the presence of the external magnetic field, Monte Carlo method has been used to simulate a complete course, in which the ions pass through the neutral region, the sheath region and finally are absorbed by the workpiece surface with negative bias in Electron Cyclotron Resonance microwave plasma. The charge exchange and elastic scattering collisions between ions and neutrals are taken into account. The distributions of the ion energy and angle at the workpiece surface are obtained. It is found that under the same neutral gas pressure the lesser the distance from the target, the more the high-energy ions and smaller the scattering angle, and most of the ions are almost vertically incident on the target. As the neutral gas pressure increases, the number of high-energy ions at the target decreases and the number of low-energy ions increases. At the same time, numerical results show that with increasing magnetic mirror ratio, the number of high-energy ions striking the target increases and the scattering angle decreases obviously. The effect of secondary electrons on the sheath potential cannot be neglected.

Hybrid Simulation of Duty Cycle Influences on Pulse Modulated RF SiH4/Ar Discharge

A one-dimensional fluid/Monte-Carlo (MC) hybrid model is developed to describe capacitively coupled SiH4/Ar discharge, in which the lower electrode is applied by a RF source and pulse modulated by a square-wave, to investigate the modulation effects of the pulse duty cycle on the discharge mechanism. An electron Monte Carlo simulation is used to calculate the electron energy distribution as a function of position and time phase. Rate coefficients in chemical reactions can then be obtained and transferred to the fluid model for the calculation of electron temperature and densities of different species, such as electrons, ions, and radicals. The simulation results show that, the electron energy distribution f() is modulated evidently within a pulse cycle, with its tail extending to higher energies during the power-on period, while shrinking back promptly in the afterglow period. Thus, the rate coefficients could be controlled during the discharge, resulting in modulation of the species composition on the substrate compared with continuous excitation. Meanwhile, more negative ions, like SiH−3 and SiH−2, may escape to the electrodes owing to the collapse of ambipolar electric fields, which is beneficial to films deposition. Pulse modulation is thus expected to provide additional methods to customize the plasma densities and components.

Effects of Fast-Ion Injection on a Magnetized Sheath near a Floating Wall

A fully kinetic particle-in-cell/Monte Carlo model is employed to self-consistently study the effects of fast-ion injection on sheath potential and electric field profile in collisional magnetized plasma with a floating absorbing wall. The influences of the fast-ion injection velocity and density, the magnetic field and angle θ0 formed by the magnetic field and the x-axis on the sheath potential and electric field are discussed in detail. Numerical results show that increasing fast-ion injection density or decreasing injection velocity can enhance the potential drop and electric field in the sheath. Also, increasing the magnetic field strength can weaken the loss of charged particles to the wall and thus decrease the potential and electric field in the sheath. The time evolution of ion flux and velocity distribution on the wall is found to be significantly affected by the magnetic field.

The effects of process conditions on the plasma characteristic in radio-frequency capacitively coupled SiH4/NH3/N2 plasmas: Two-dimensional simulations

A two-dimensional (2D) fluid model is presented to study the behavior of silicon plasma mixed with SiH4, N2, and NH3 in a radio-frequency capacitively coupled plasma (CCP) reactor. The plasma-wall interaction (including the deposition) is modeled by using surface reaction coefficients. In the present paper we try to identify, by numerical simulations, the effect of variations of the process parameters on the plasma properties. It is found from our simulations that by increasing the gas pressure and the discharge gap, the electron density profile shape changes continuously from an edge-high to a center-high, thus the thin films become more uniform. Moreover, as the N2/NH3 ratio increases from 6/13 to 10/9, the hydrogen content can be significantly decreased, without decreasing the electron density significantly.

One-Dimensional Fluid Model of Pulse Modulated Radio-Frequency SiH4/N2/O2 Discharge

Driven by pulse modulated radio-frequency source, the behavior of SiH4/N2/O2 plasma in capacitively coupled discharge are studied by using a one-dimensional fluid model. Totally, 48 different species (electrons, ions, neutrals, radicals and excited species) are involved in this simulation. Time evolution of the particle densities and electron temperature with different duty cycles are obtained, as well as the electronegativity nSiH−3/ne of the main negative ion (SiH−3). The results show that, by reducing the duty cycle, higher electron temperature and particle density can be achieved for the same average dissipated power, and the ion energy can also be effectively reduced, which will offer evident improvement in plasma deposition processes compared with the case of continuous wave discharge.

One-Dimensional Fluid Model for Dust Particles in Dual-Frequency Capacitively Coupled Silane Discharges

A self-consistent fluid model, which incorporates density and flux balances of electrons, ions, neutrals and nanoparticles, electron energy balance, and Poissons equation, is employed to investigate the capacitively coupled silane discharge modulated by dual-frequency electric sources. In this discharge process, nanoparticles are formed by a successive chemical reactions of anion with silane. The density distributions of the precursors in the dust particle formation are put forward, and the charging, transport and growth of nanoparticles are simulated. In this work, we focus our main attention on the influences of the high-frequency and low-frequency voltage on nanoparticle densities, nanoparticle charge distributions in both the bulk plasma and sheath region.