Numerical Simulation on Expansion Process of Ablation Plasma Induced by Intense Pulsed Ion Beam

We present a one-dimensional time-dependent numerical model for the expansion process of ablation plasma induced by intense pulsed ion beam （IPIB）. The evolutions of density, velocity, temperature, and pressure of the ablation plasma of the aluminium target are obtained. The numerical results are well in agreement with the relative experimental data. It is shown that the expansion process of ablation plasma induced by IPIB includes strongly nonlinear effects and that shock waves appear during the propagation of the ablation plasma.     

Hydrocarbon film growth by energetic CH3 molecule impact on SiC (0 0 1) surface

Classic molecular dynamics (MD) calculations were performed to investigate the deposition of thin hydrocarbon film. SiC (1 0 0) surfaces were bombarded with energetic CH₃ molecules at impact energies ranging from 50 to 150 eV. The simulated results show that the deposition yield of H atoms decreases with increasing incident energy, which is in good agreement with experiments. During the initial stages, with breaking Si-C bonds in SiC by CH₃ impacting, H atoms preferentially reacts with resulting Si to form Si-H bond. The C/H ratio in the grown films increases with increasing incident energy. In the grown films, CH species are dominant. For 50 eV, H-Csp3 bond is dominant. With increasing energy to 200 eV, the atomic density of H-Csp2 bond increases.     

Etching of SiC by energetic F2: Molecular dynamics simulation

Molecular dynamics (MD) simulations were performed to investigate F₂ continuously bombarding silicon carbide (SiC) surfaces with energies in the range of 50-200 eV at normal incidence and room temperature. The Tersoff-Brenner form potential was used. The simulation results show that the uptake of F atoms, the etch yields of C and Si from the initial substrate, and the surface structure profile are sensitive to the incident energy. Like occurrence in Si etching, steady-state etching is observed and an F-containing reaction layer is formed through which Si and C atoms are removed. A carbon-rich surface layer after bombarding by F₂ is observed which is in good agreement with experiments. In the reaction layer, SiF in SiF₂ species are dominant; with increasing incident energy, the total fraction of SiF and SiF₂ increases, while the amount of SiF₃ and SiF₄ decreases. Finally, etching mechanisms are discussed.     

Molecular dynamics simulation of deposition and etching of Si bombarding by energetic SiF

In this study, SiF interaction with amorphous Si surface at normal incidence was investigated using molecular dynamics simulation at 300 and 600 K. The incident energies of 50, 100 and 200 eV were used. The results show that the deposition rate is not sensitive to the incident energy, while with increasing the surface temperature, the deposition rate decreases. The etch yield is sensitive to the incident energy and the surface temperature. The etch yield increases with increasing incident energy and temperature. After bombarding, a Si_xF_y interfacial layer is formed. The interfacial layer thickness increases with increasing incident energy mainly through enhanced penetration of the silicon lattice. In the interfacial layer, for SiF_x (x = 1-3) species, SiF is dominant and only little SiF₃ is present. At the outmost and innermost of the interfacial layer, SiF species is dominant. Most of SiF₃ species is concentrated above the initial surface.     

Plasma polymerization of styrene with carbon dioxide under glow discharge conditions

Plasma polymerization gains increasing interest for the deposition of films with functional properties suitable for a wide range of modern applications on account of its advantageous features. In this study, carbon dioxide (CO₂) was chosen as carrier gas at flow rates of 30 and 60 sccm, respectively and styrene vapor was used as the monomer to prepare polystyrene films on glass substrates. The structure and composition of the plasma polymerized films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and compared with the film prepared by conventional thermal polymerization. The morphology information of the films was provided by optical microscopy. XPS and FT-IR results reveal that chemical composition of the plasma polymerized films is different from that of the thermal polymerized film and that oxygen content in the plasma polymerized films increases with the flow rate of CO₂. Furthermore, the presence of oxygen-containing groups on the surface of plasma polymerized polystyrene films is confirmed. It is also found that the composition and morphology of the plasma polymerized films are controlled by the flow rate of CO₂.     

Improvement of hydrophobic properties of silk and cotton by hexafluoropropene plasma treatment

Plasma surface-treatment of silk and cotton fabrics were carried out in a hexafluoropropene (C₃F₆) atmosphere under different experimental conditions. Analysis of the treated fibers by X-ray photoelectron spectroscopy (XPS) indicated about 50 at% fluorine atoms were incorporated in the surface structure of two fibers and confirmed the presence of -CF, -CF₂, -CF₃ groups on the surface. After water-washing and alcohol-extraction, though partial loss of fluorine from the surface has been observed, contact angle and wet-out time measurements on the fibers still show much improved hydrophobic properties. The other properties of the treated fabrics, such as water vapor permeability and tensile strength were also evaluated.     

Study of plasma—solid interaction in electronegative gas mixtures

Low-temperature reactive plasmas employing electronegative gases are often used in modern technologies. Negative ions in such plasmas affect the transport of charged species and in this way influence the processes in the boundary layer between plasma and surface of metal substrate or probe. The contribution presents results of the computer experiment describing the interaction of electronegative plasma with immersed substrates. The method of solution was the particle simulation technique and several approximations were used; the most important was the simplified geometry of substrates. The simulation is based on experimental data obtained in a dc glow discharge in mixtures of oxygen with rare gases. This work is a part of the research plan MSM0021620834 that is financed by the Ministry of Education of Czech Republic.     

Reconnection Rate in Collisionless Magnetic Reconnection under Open Boundary Conditions

Collisionless magnetic reconnection is studied by using two-dimensional Darwin particle-in-cell simulations with different types of open boundary conditions. The simulation results indicate that reeonneetion rates are strongly dependent on the imposed boundary conditions of the magnetic field Bx in the inward side. Under the zerogradient Bx boundary condition, the reconnection rate quickly decreases after reaching its maximum and no steady-state is found. Under both electromagnetic and magnetosonie boundary conditions, the system can reach a quasi-steady state. However, the reconnection rate Er ≈ 0.08 under the electromagnetic boundary condition is weaker than Er ≈ 0.13 under the magnetosonic boundary condition.     

Effects of Ion-to-Electron Mass Ratio on Electron Dynamics in Collisionless Magnetic Reconnection

A 2 1/2-dimensional electromagnetic particle-in-cell （PIC） simulation code is used to investigate electron behaviour in collisionless magnetic reconnectfon. The results show that the ion/electron mass ratio （mi/me） almost has no impact on the reconnection rate, however it can significantly affect electron behaviour in the diffusion region. For the case with larger mass ratio, the width of electron current sheet becomes smaller and the outflow region along the separatrix is smaller, hence the peak of the electron outflow speed is essentially larger. Density cavities and the parallel electric field E// along the separatrix can be found in the case with larger mass ratio, which may have significant influences on the acceleration and heating of the electrons near the X point.     

（Ti,Al）N Film on Normalized T8 Carbon Tool Steel Prepared by Pulsed High Energy Density Plasma Technique

Under optimized operating parameters, a hard and wear resistant （Ti,Al）N film is prepared on a normalized T8 carbon tool steel substrate by using pulsed high energy density plasma technique. Microstructure and composition of the film are analysed by x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy and scanning electron microscopy. Hardness profile and tribological properties of the film are tested with nano- indenter and ring-on-ring wear tester, respectively. The tested results show that the microstructure of the film is dense ahd uniform and is mainly composed of （Ti,Al）N and A1N hard phases. A wide transition interface exists between the film and the normalized T8 carbon tool steel substrate. Thickness of the film is about lO00nm and mean hardness value of the film is about 26 GPa. Under dry sliding wear test conditions, relative wear resistance of the （Ti, Al）N film is approximately 9 times higher than that of the hardened T8 carbon tool steel reference sample. Meanwhile, the （Ti,Al）N film has low and stable friction coefficient compared with the hardened T8 carbon tool steel reference sample.     

Optimization of plasma parameters for high rate deposition of titanium nitride films as protective coating on bell-metal by reactive sputtering in cylindrical magnetron device

Nano-structured titanium nitride (TiN) thin film coating is deposited by reactive sputtering in cylindrical magnetron device in argon and nitrogen gas mixtures at low temperature. This method of deposition using DC cylindrical magnetron configuration provides high uniform yield of film coating over large substrate area of different shapes desirous for various technological applications. The influence of nitrogen gas on the properties of TiN thin film as suitable surface protective coating on bell-metal has been studied. Structural morphological study of the deposited thin film carried out by employing X-ray diffraction exhibits a strong (2 0 0) lattice texture corresponding to TiN in single phase. The surface morphology of the film coating is studied using scanning electron microscope and atomic force microscope techniques. The optimized condition for the deposition of good quality TiN film coating is found to be at Ar:N₂ gas partial pressure ratio of 1:1. This coating of TiN serves a dual purpose of providing an anti-corrosive and hard protective layer over the bell-metal surface which is used for various commercial applications. The TiN film's radiant golden colour at proper deposition condition makes it a very suitable candidate for decorative applications.     

In situ characterisation of thin-film formation in molecular low-temperature plasmas

Thin films can be formed in low-temperature plasma in two ways: as a result of material modification usually in a discharge of non-organic gas and in the course of a deposition process in a discharge of organic vapour. Thin-film formation requires in situ control of plasma processing in order to get information on the growth mechanisms and control the deposition process. Here are shown some effective in situ techniques of thin-film characterisation: various kinds of infrared spectroscopy (infrared reflection absorption spectroscopy, attenuated total reflection spectroscopy, etc.), ellipsometry and microgravimetry. We discuss the application of these methods to polymer modification as well as plasma polymerisation. The applied techniques give very good spatial resolution, up to a few nm. The limitations of method or equipment on time resolution can be compensated by the appropriate experimental arrangement. Received: 4 October 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001     

Surface modification of γ-TiAl alloys by acetylene plasma deposition

Surfaces of two γ-TiAl alloys, Ti-47 at% Al-2at% Nb-2 at% Cr (MJ12) and Ti-47 at% Al-2 at% Nb-2 at% Mn + 0.8 at% TiB₂ (MJ47), have been modified by acetylene plasma deposition at bias voltages of −4, −5 and −6 kV for 3.6 × 10³ s (1 h) and 1.44 × 10⁴ s (4 h). Knoop hardness (HK) of the alloys is increased with the increase of bias voltage and prolonged time for the deposition. HK of MJ12 and MJ47 deposited at −6 kV for 1.44 × 10⁴ s is, respectively, 3.36 and 3.32 times as hard as the untreated alloys. SEM and AFM analyses show that the deposited alloys compose of a number of nano-dots which reflect their surface properties. The phases analyzed by XRD are in accord with the elements analyzed by EDX.     

Optical and mechanical properties of alumina films fabricated on Kapton polymer by plasma immersion ion implantation and deposition using different biases

Alumina films are fabricated on Kapton polymer by aluminum plasma immersion ion implantation and deposition in an oxidizing ambient and the effects of the bias voltage on the film properties are investigated. Rutherford backscattering spectrometry (RBS) reveals successful deposition of alumina films on the polymer surface and that the O to Al ratio is higher than that of stoichiometric Al₂O₃. The thickness of the modified layers decreases from 200 to 120 nm when the bias voltage is increased from 5 to 20 kV. Our results indicate that higher bombardment energy may lead to higher crack resistance and better film adhesion. However, a higher sample bias degrades the optical properties of the films as indicated by the higher absorbance and lower energy band gap. Therefore, the processing voltage must be optimized to yield a protective layer with the appropriate thickness, superior optical properties, as well as high crack resistance.     

Nonlinear Evolution of Lower-Hybrid Drift Instability in Harris Current Sheet

We perform 2.5-dimensional particle-in-cell simulations to investigate the nonlinear evolution of the lower hybrid drift instability (LHDI) in Harris current sheet. Due to the drift motion of electrons in the electric field of the excited low hybrid drift (LHD) waves, the electrons accumulate at the outer layer, and therefore there is net positive charge at the inner edge of the current sheet. This redistribution of charge can create an electrostatic field along the z direction, which then modifies the motions of the electrons along the y direction by E×B drift. This effect strongly changes the structure of the current sheet.     

用于材料表面改性的多功能等离子体浸没离子注入装置

详细叙述了新近研制的多功能等离子体浸没离子注入（ＰⅢ）装置，在装置设计中，考虑了等离子体产生手段、高压脉冲电源和真空抽气系统多项功能要求，把离子注入、涂敷和溅射沉积结合起来，该已实现了多种气体等离子体注入、气－固离子混合与注入、金属等离子体沉积与注入、离子束混合与离子束增强沉积等，以满足不同材料制成的不同零件对多种表面处理工艺的需要，初步应用结果证明，该装置对于改进４５号钢、Ｔｉ－６Ａｌ０－４Ｖ和     

Simulation and Experimental Research of a Novel Vircator

A new configuration of an axially-extracted vircator with three resonant cavities is put forward and optimized by simulation with the PIC code. The output power of over 1 GW is obtained at around 4.1 GHz in the experiment, in agreement well with the PIC simulation results. The beam to wave power conversion efficiency is more than 6.6%.     

The Formation of Helium Bubbles in Silicon Surface Layers via Plasma Immersion Ion Implantation

The surface layers of single-crystal silicon Si(001) substrates subjected to plasma-immersion implantation with 2- and 5-keV helium ions to a dose of 5 × 10¹⁷ cm^–2 were probed via grazing incidence small-angle X-ray scattering and transmission electron microscopy. A surface layer formed by helium ions was found to possess a multilayer structure, wherein the upper layer is amorphous silicon, being on top of a sublayer with helium bubbles and a sublayer with a disturbed crystal structure. The in-depth electron density distribution, as well as the concentration and pore-size distribution, were established. The average pore sizes of bubbles at the above implantation energies are 4 nm and 8 nm, respectively.     

Experimental Investigation on Low Magnetic Field Operation of an Overmoded Slow-Wave High-Power Microwave Generator

The experimental results of an overmoded slow-wave high-power microwave generator operated at low magnetic field are presented. The feasibility of low magnetic field operation is investigated both theoretically and experimentally based on the characteristics of the overmoded slow-wave device. The experiments were carried out at the Spark-2 accelerator. Under the condition of guiding magnetic field strength of 0.55 T, diode voltage of 4 74 k V,and beam current of 5.2kA, a microwave was generated with power of 510 MW, mode of TM01, and frequency of 9.54 GHz. The relative half-width of the frequency spectrum is less than 1%, and the beam-to-microwave efficiency is about 21% in our experiments.     

Effect of electron emission and potential perturbations of a hot filament in high voltage pulsed glow discharge

The high voltage dc pulsed glow discharge can be ignited earlier by putting an electron emitting filament in the plasma chamber. The electrons emitted from the filament act as a seed and can cause earlier ignition. The potential of the hot filament shows some periodic positive perturbations (electron loss signals) when it is kept floating in the plasma chamber. It is observed that the positive perturbations disappear as potential difference between the plasma and the filament is made smaller by directly connecting the filament to the grounded chamber.