Effects of secondary electron emission from a floating surface on the plasma sheath

The paper describes the region between a Maxwellian plasma source and a floating surface by a 1D-3 V fully kinetic, electrostatic particle simulation. The electric field is self-consistently computed from the Poisson equation. The secondary electron emission is modelled by considering an expression for the secondary emission coefficient dependent on the primary electron energy and surface materials and a realistic secondary electron distribution function is introduced at the collector surface. The model is able to simulate the space-charge-limited conditions as well as the positively charged wall cases.     

Computational study of plasma-solid interaction in mixtures of oxygen with rare gases

The computer experiment describing the interaction of electronegative plasma with immersed substrates is presented and results of modelling are discussed. The main attention is devoted to the sheath region and to the influence of plasma parameters on its formation. The used computational method is the self-consistent particle modelling. The input parameters for modelling were derived both by the measurement in mixtures of oxygen with rare gases and by the simulation of oxygen plasma by the macroscopic kinetic approach.     

Multidimensional fluid-particle modelling technique in low-temperature argon plasma at low pressure

In the contribution there is presented a new computer modelling technique, which can be used in multidimensional computer simulations of plasma at low pressure. The technique is based on the fluid-particle approach and can be used in the study of the range of physical phenomena, e.g. plasma behaviour in the vicinity of substrates, probe diagnostics, plasma technology, etc. The computer model is useable for the solution of three-dimensional problems and it minimizes the restrictions arising in complicated model geometry. The algorithm has been tested during the study of plasma sheath formation in the vicinity of probes with various geometries immersed into low-temperature argon plasma. Some results of these simulations are presented in the last section.     

Heating of polymer substrate by discharge plasma in radiofrequency magnetron sputtering deposition

The substrate used for the thin film deposition in a radiofrequency magnetron sputtering deposition system is heated by the deposition plasma. This may change drastically the surface properties of the polymer substrates. Deposition of titanium dioxide thin films on polymethyl methacrylate and polycarbonate substrates resulted in buckling of the substrate surfaces. This effect was evaluated by analysis of atomic force microscopy topography images of the deposited films. The amount of energy received by the substrate surface during the film deposition was determined by a thermal probe. Then, the results of the thermal probe measurements were used to compute the surface temperature of the polymer substrate. The computation revealed that the substrate surface temperature depends on the substrate thickness, discharge power and substrate holder temperature. For the case of the TiO₂ film depositions in the radiofrequency magnetron plasma, the computation indicated substrate surface temperature values under the polymer melting temperature. Therefore, the buckling of polymer substrate surface in the deposition plasma may not be regarded as a temperature driven surface instability, but more as an effect of argon ion bombardment.     

XPS study of oxygen plasma activated PET

A study on oxygen plasma functionalization of polyethyleneterephthalate (PET) is presented. Samples were exposed to a weakly ionized, highly dissociated RF oxygen plasma with an electron temperature of 5 eV, a density of positive ions of 8×10¹⁵ m⁻³ and a density of neutral oxygen atoms of 4×10²¹ m⁻³. The oxygen pressure was 75 Pa and the discharge power was 200 W. The wettability of plasma-modified samples was determined by measuring the contact angle of a water drop, while the appearance of the functional groups on the sample surface was determined by using a high-resolution X-ray photoelectron spectrometer (XPS). Already in the order of seconds of the plasma treatment the samples were covered by the surface functional groups. These results were explained by the high flux of oxygen atoms onto the sample surface. The stability of functional groups on the plasma-modified PET surface stored in a dry plastic box was monitored by using XPS as a function of the ageing time. After 1 day of ageing, the concentration of newly formed functional groups decreased by about 15%.     

Techniques for computational study of plasma-solid interaction at higher pressures

Several techniques of computational physics used in low-temperature plasma simulations at higher pressures are presented in our contribution. The first approach is called fluid modelling, the second one hybrid modelling and the third technique—particle modelling presented here is realized as a part of hybrid model. There are several techniques applicable in computational plasma physics but some of these methods have explicit limitation. For example, time consumption of standard particle-in-cell Monte Carlo (PIC-MC) particle simulation is increased profoundly with increasing pressure of plasma. Hence, we have used the fluid and hybrid modelling. Hybrid model consists of two parts—particle model, simulating fast electrons while fluid model simulates slow electrons and positive argon ions. In particle model, the positions and velocities of fast electrons are calculated by means of deterministic Verlet algorithm while the collision processes are treated by the stochastic way. For solution of fluid equations, the Scharfetter-Gummel exponential scheme was used. Typical results of our calculations are electric field distribution, fluxes and collision rates of charged particles near the planar probe.     

Numerical analysis of ion-implantation in target with a rectangular groove

Ion dynamics of pulsed plasma sheath during the plasma source ion-implantation (PSII) affects the resultant surface properties and structures. In this work, a two-dimensional fluid model is applied to the problem of computing ion dynamics in the sheath of a target with a rectangular groove. The evolution of sheath edge, x and y components of ion velocity on the target surface are simulated to describe the physics of sheath in PSII.     

Influence of additional magnetic field on plasma parameters in magnetron sputtering

With three additional magnetic rings being assembled outside the discharge room and connected with the magnetic field of the conventional unbalanced magnetron sputtering, a closed magnetic field configuration distribution had been formed in the whole discharge room and which can confine discharge plasma more effectively. The spatial distribution of the newly designed magnetic field configuration was simulated using the ANSYS software. Plasma potential, electron temperature, electron density and ion density in the discharge plasma were diagnosed by Langmuir probe and the optical emission line intensity ratios of Ar⁺/Ar and Cu⁺/Cu were studied by optical emission spectroscopy. The structure and morphology of the Cu films are measured by scanning electron microscopy. A comparative study of the new magnetic field configuration with the conventional unbalanced magnetic field configuration was conducted. The results showed that the application of the additional magnetic field can increase the plasma density, enhance the ionization degree of the sputtered Cu and decrease the plasma potential effectively. The characteristics of the deposited Cu film were also influenced by the new magnetic field configuration greatly.     

Molecular dynamics simulations of CF3 etching of SiC

Molecular dynamics simulations were performed to investigate CF₃ continuously bombarding SiC surfaces with energies of 100, 150 and 200 eV at normal incidence and room temperature. The simulated results show that the etching rates of Si and C atoms increase linearly with the incident energy. The etch rate of Si atoms is much more than that of C atoms. A carbon-rich surface layer is observed which is in good agreement with experiments. Under bombarding by CF₃, an F-containing reaction layer is formed through which Si and C atoms are removed. In reaction layer, SiF and CF species are dominant. The formation mechanisms of ejected products are discussed. In etching products, SiF₃ is dominant. It is found that etching of C atoms in SiC is controlled by physical sputtering, while etching of Si atoms in SiC is controlled by chemical sputtering.     

Effect of pressure on plasma sheath in a magnetic field

The effects of collisions on plasma sheath in an external magnetic field have been investigated by considering the collisions between ions and neutral gas atoms. The ion fluid equations containing an external magnetic field and the collisions are solved numerically to study the ion dynamics under various pressures.     

Dynamics of the magnetic field transport in a plasma opening switch

It is shown that the process of magnetic field penetration into the plasma bridge in a plasma opening switch is determined by the field diffusion near the magnetic piston, followed by the convective transport of magnetic field in the bridge. This transport is due to the field being “frozen in” to the flow of plasma behind the front of a shock wave, which is formed in the plasma accelerated by the magnetic field pressure.     

3He superfluid phases in a magnetic field

A Green's function approach is used to derive an approximate expression for the grand potential in the presence of a magnetic field. This approximation is used to derive a relation between the A₁, A, and B phases as functions of temperature and magnetic field strength. Where the approximation is quantitatively valid, comparison with experiment is made, as a result of which a value for the gap rather less than the BCS value is derived. A value for the difference between the Balian-Werthamer and Anderson-Brinkman-Morel terms in the grand potential to sixth order in the gap function at the polycritical pressure is also found.     

轴向磁场对铌酸锂半波电压的影响

提出了平行与铌酸锂波导方向的轴向磁场对其半波电压产生影响的机理:加在电极上的电场对其中传播的偏振光产生线双折射,而磁场产生圆双折射,两者作用的结果是使得半波电压随磁场而变化。由此导出了半波电压随外界磁场变化的数学模型。仿真和实验结果表明,对于平均波长为1.30μm,20T的磁场,铌酸锂的半波电压可以减小了2.13%。     

Determination of plasma parameters with a probing magnetic field pulse

An experimental technique for the determination of electric conductivity and temperature of plasma is presented. The technique is based on comparing the signals that are produced by a pulsed magnetic field in the circuits of two probes located within the studied plasma and outside of it. The proposed technique for the measurement of plasma parameters was tested experimentally in the context of measuring the electric conductivity and temperature of plasma flux formed in cathode spots of a high-current pulsed vacuum arc with a magnesium cathode.     

Influence of a magnetic field on quartz crystal resonators

The magnetic sensitivity of quartz crystal resonators is a consequence of the ferromagnetic properties of the metal used as support for the vibrating plate. Various magneto-mechanic interactions can contribute to the overall sensitivity, the most important of which is shown to be the change in Young's modulus of the spring material submitted to a magnetic field, which in turn modifies the stress in the quartz plate and then induces a change in the crystal resonant frequency. The experimental setup and procedure are described and a large number of experimental results obtained with resonators of different technologies are presented and discussed. A comparison between the magnetic behavior of identical resonators mounted with different materials definitely proves the responsibility of the supports in the magnetic sensitivity of resonators and gives interesting information on its reduction     

Vortices in 3He-A in a weak magnetic field

The structure and the energy of vortices in rotating ³He-A are considered in the presence of a weak magnetic field. It is shown, using the logarithmic approximation for the free energy, that there will be a sequence of textural transitions when the magnetic field is increased. The transition from a nonsingular texture to a singular texture is studied in detail. It is shown that the l vector is almost uniform outside the cores of vortices. To verify these results, measurements by NMR and by ultrasound are suggested.This work has been financially supported by the Academy of Science of the USSR, by the Academy of Finland, and by the Committee of Scientific and Technical Cooperation between Finland and the USSR.     

Experiments on interferometric enhanced scattering in a plasma with a nonuniform magnetic field

Results are presented from the first experiments on interferometric enhanced scattering (IES) in a plasma in a nonuniform magnetic field. Measurements of the lower hybrid fluctuations of the plasma density by the IES and rf probe methods in an experimental geometry that models a tokamak configuration are found to be in satisfactory agreement. Pis’ma Zh. Tekh. Fiz. 24, 43–51 (October 26, 1998)     

Charge separation of plasma flow in curvilinear magnetic field

The energy spectra of ions occurring in various charged states in a flow of titanium plasma in a steady-state vacuum arc discharge have been studied. It is established that, during the motion of this flow through a plasma transport system based on a curvilinear magnetic field, ions with different charges are spatially separated. As a result, at the system output, ions with greater charges are concentrated in the inner part of the plasma flow, so that the average charge of ions in this region is higher than that in the outer part of the flow.     

Thermelectric power in ultrathin films ofA 3 II B 2 V semiconductors in the presence of a quantizing magnetic field

An attempt is made to study theoretically the thermoelectric power in ultrathin films ofA ₃ ^II B ₂ ^V semiconductors in the presence of a quantizing magnetic field by formulating a new magneto-dispersion law, within the framework ofk · p formalism incorporating the anisotropies in the band parameters. It is found, taking ultrathin films ofn-Cd₃P₂ as an example, that the same power decreases with increasing surface electron concentration and changes in an oscillatory manner with film thickness and quantizing magnetic field. In addition, the well-known results for parabolic energy bands have also obtained from our expressions as special cases.     

Influence of filament thickness, thermal process and magnetic field on misalignment angles in multifilament Bi2212 tapes

Misalignment angles in multifilament Bi2212 tapes have been studied by transport current density (J_c) measurements. Transversal misalignment angles depend on the filaments thickness due to the crystal growth along the Bi2212/silver interface. Therefore, the thinner the filaments, the higher the J_c.A dynamic thermal treatment improves grain alignment inside the tapes due to preferential crystal growth along the thermal gradient direction. Furthermore, melting in high magnetic field reduces the misalignment angle due to magnetic anisotropy effects. Therefore, good transport J_c performances can be expected for thicker multifilament Bi2212 tapes prepared using a combination of the dynamic process and melting in a high magnetic field.