Influence of non-axial magnetic field in a 3D3V Particle-In-Cell plasma model

In this article we report on results obtained using a newly developed self-consistent fully 3D Particle-In-Cell code for modelling of plasma-solid interaction.The model presented here involves a hollow cylindrical chamber opened to the plasma, with a thin cylindrical guard at the inlet and a strong external magnetic field limiting access of charged particles to the cylindrical wall. This model layout might provide more insight into processes taking place during magnetron deposition of thin films onto porous media. It is also a basis for probe diagnostics in fusion plasma research.The magnetic field is either parallel or slightly inclined with respect to the cylindrical axis. The results presented are axial and azimuthal ion current densities and cumulative distribution functions of ions impinging on the cylindrical surface for several angles of magnetic field inclination. They confirm the importance of proper alignment with magnetic field in certain geometries.Efficiency and possibilities of further extensions to the 3D model are also briefly discussed.     

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.     

Magnetic field effect on electron emission from plasma

The influence of external magnetic field on the significant parameters of electrons from laser induced plasma (LIP) is investigated. A Q-switched Nd:YAG laser (1064 nm, 9-14 ns, 10 mJ, 1.1 MW) is focused on annealed, 4N pure (99.99%) Silver target (2 × 2 × 0.2 cm³) for production of plasma under vacuum ∼10⁻³ torr. Temperature, density and energy measurements for electrons were made by self fabricated Langmuir probe both in the absence and presence of external magnetic field (∼1.2 T) at different positions. The signals are recorded on 200 MHz UTT 2202 digital storage oscilloscope. The results thus obtained reveal decrease in electron temperature, energy and density in presence of external magnetic field. Confinement of plasma is also observed.     

Effects of surface track potential on secondary electron emission and surface stopping power

In ion-surface scattering a positive surface track potential is induced on the surface behind the projectile due to ionizing collisions. The surface track potential is expected to affect secondary electron emission as well as the energy loss process of the projectile ions. We measure secondary electron yield induced by 0.5 MeV/u H⁺, He²⁺, Li²⁺ and B³⁺ ions during grazing angle scattering at a KCl(0 0 1) surface. The position-dependent secondary electron production rate was derived from the observed secondary electron yield. The secondary electron production rate is normalized by the mean square charge of the reflected ions. The normalized rate decreases with Z₁ suggesting that the surface track potential recapture the secondary electrons. We also measure the energy losses of 0.5 MeV/u H⁺, He²⁺, Li²⁺, B³⁺ and C⁴⁺ ions during grazing angle scattering at a KCl(0 0 1) surface. The observed result suggests that the surface stopping power is reduced by the surface track potential.     

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.     

Molecular pumping properties of the LHC arc beam pipe and effective secondary electron emission from Cu surface with artificial roughness

A simplified 2D method of angular coefficients is applied to calculations of the molecular pumping properties of complex vacuum systems. An optimization of geometry for the cold LHC beam vacuum chamber with electron shields is performed.An additional interesting application of the angular coefficients method is the estimation of the effective secondary electron emission from surface with artificial roughness. This method allows to take into account re-reflection of electrons using experimental data of the secondary electron energy distributions and surface reflectivity. The suppression efficiency of the secondary electron emission from Cu as a function of roughness parameter is presented. This result is a good input for designing future accelerators and storage rings with potential electron-cloud problems.     

Peculiarities of field electron emission from submicron protrusions on a rough InSb surface

Technical Physics Letters - Mechanisms of field-electron emission (FEE) from submicron protrusions on a rough InSb surface have been studied. It is established that the FEE current is...     

A study on the secondary electron emission from Na-ion-doped MgO films in relation to the discharge characteristics of plasma display panels

Using a sol-gel precursor, Na-ion-doped MgO was prepared and applied to alternative current plasma display panels (ac-PDP). The cathodoluminescence spectra showed that the F⁺ center was increased as the concentration of Na⁺ was increased. Numerous pores were found on the printed MgO surface and seemed to give higher memory margin of ac-PDP compared to an electron beam-evaporated MgO film. All doped MgO showed higher secondary electron emission than printed pure MgO, likely owing to the O defect states of MgO. In addition, this result indicated the operational memory margin of the ac-PDP was directly proportional to the grade of surface charging.     

Investigation of some characteristics of electron emission from the surface of a PLZT ferroelectric

Results are presented of an investigation of some characteristics of electron emission from the surface of a PLZT ferroelectric (TsTSL in Russian) when a pulsed voltage is applied to the sample. It is shown that the emitted charge is compensated by migration of electric charge through the bulk of the ferroelectric. The energies of the emitted electrons were estimated for a specific ferroelectric sample, and it was shown that the residual gas pressure influences the emitted charge. The results were obtained using a new method for direct measurement of the average pulsed currents in the electrode circuits of the solid-state ferroelectric sample and in the collector circuit. Pis’ma Zh. Tekh. Fiz. 24, 19–22 (December 12, 1998)     

Ion-induced secondary electron emission from MgO and Y2O3 thin films

We report a detailed study of the electron emission from MgO and Y₂O₃ induced by the impact of 0.1-1 keV Ar⁺ ions. The mechanisms of ion-induced secondary electron emission from oxides are far less understood because charging of the target surface during ion irradiation prohibits the precise measurement of electron yield. For this study, targets were prepared by depositing 20 nm thick films of MgO and Y₂O₃ on the semi-conducting SnO₂ substrate, which helps in charge neutralization. Additionally, a pulsed ion beam was used to further reduce the surface charging. It was found that the electron yield of both targets increases with energy of the ion. However, at a given ion energy the electron yield of Y₂O₃ was larger than MgO. Another important result of this study is that the electron emission from these large band gap insulators did not show any threshold effect, in contrast to the metal targets. It may be due to local reduction of the band gap through electron promotion processes. In addition, a Monte Carlo program was used to calculate the yield of secondary electrons excited by projectile ions, recoiling target atoms and electron cascades, and average escape depth of the secondary electrons emitted from the MgO and Y₂O₃ thin films.     

The formation of a multipeak relief on the surface on nanostructured nickel and field electron emission from it

Technical Physics Letters - Studies of the relief formed on the surface of nanostructured nickel with nonequilibrium grain boundaries formed upon ion-beam sputtering are presented. It has been...     

A zero-time detector of charged particles based on secondary electron emission from low density dielectrics

A detector of controllable secondary electron emission from a low density dielectric material is described in which the isochronous transport of secondary electrons to microchannel plates is done by means of an electrostatic mirror. The time resolution for a time-of-flight system consisting of two identical detectors was 2τ ? 0.25 ns at the level of 100% detection efficiency for 4.5 – 7.5 MeV α-particles.     

Effects of annealing temperature on the structure and photoluminescence properties of ZnO films

Zinc oxide (ZnO) films with c-orientation were deposited on Si (1 1 1) substrates at room temperature (RT) by RF-magnetron sputtering. Violet (394 and 412 nm) and green (560 and 588 nm) photoluminescence (PL) were observed from the as-deposited and annealed samples. The PL intensity was increasing with increasing annealing temperature (T_a). The 412 nm violet peak shifted from 412 to 407 nm and the 394 nm violet peak shifted from 394 to 399 nm on increasing the temperature from 500 to 900 °C, whereas no shift in PL green peaks was observed over the whole range of temperature examined. The 412 nm violet luminescence is ascribed to radiative defects related to the interface traps existing at grain boundaries. With the increase of T_a, the stress in the films changed from compressive to tensile, which is believed to have resulted in the observed 412 nm violet emission peak shifts from 412-407 nm. The 394 nm violet luminescence observed is attributed to free excitonic emission, and the increase of the crystal size may result in the 394 nm violet emission peak shifts from 394 to 399 nm. The other two PL bands located at 560 and 588 nm are attributed to oxygen deficiency.     

Effect of secondary electron emission on charge of drops of metal melts in electron flow

The process of charging of drops of metal melts in an electron flow up to the Rayleigh threshold is analyzed. It is shown that the selection of the energy spectrum of the electron flow used is primarily governed by secondary electron emission. Requirements for electron-flow parameters are formulated at which the efficient discharge of metal melt drops is implemented and no drop overheating occurs, which leads to their discharge due to thermoelectron emission.     

Equipment for investigating the secondary electron emission of effective emitter materials

A method of investigating secondary electron processes experimentally, and equipment which enables the total secondary electron emission coefficient σ and the inelastic reflection coefficient η to be measured, and also enables a television picture of the objects being investigated to be obtained with a qualitative estimate of σ of the surface of effective emitter specimens, are described. A special raster-generating apparatus, which forms part of a video-monitoring unit, is developed and constructed in the form of an actual model. Translated from Imzeritel'naya Tekhnika, No. 3, pp. 61–63, March, 1996.     

Effects of porous silicon morphology on ballistic electron emission

Porous silicon ballistic electron emission source with a structure of metal/porous silicon/Si/metal is obtained by anodization, rapid thermal oxidation, and sputtering. The microstructures of porous silicon layers are characterized by means of scanning electron microscope. The results show that disordered pores are formed at anodization current densities of 15 mA/cm2, 30 mA/cm2, and 45 mA/cm2 for 5 min, respectively. However, straight pores are formed at anodization current densities of 60 mA/cm2, and 75 mA/cm2 for 5 min, respectively. The electron emission characteristic of porous silicon ballistic electron emission sources is measured in vacuum. The results show that electrons emitted into the vacuum from the porous silicon samples with disordered pores. Under a bias condition, injected electrons from the substrate are accelerated by the strong electric field on the surfaces of the Si nanocrystallites in disordered pores, and then emitted into the vacuum through Pt film. However, no electron emission is observed in porous silicon samples with straight pores. It attributes to the lack of Si nanocrystallites in straight pores. So there is not accelerating tunnels enough for electrons. According to disordered or straight pores, we can estimate whether PS samples emit electrons or not.