High Degree Of Ionization Research Articles

The construction of anhydride-modified silica nanoparticles (AMSNPs) strengthened wormlike micelles based on strong electrostatic and hydrogen bonding interactions

To further investigate the interaction between surface-modified nanoparticles and wormlike micelles (WLMs) and their rheological response, a newly kind of anhydride-modified silica nanoparticles (AMSNPs) was modified by succinic anhydride. A quaternary ammonium surfactant with the headgroup modified by two hydroxyethyl groups N-cetyl-N,N-di(2-hydroxyethyl)methylammonium bromide (CDHAB) was synthesized in this work. The transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS) were used to characterize AMSNPs. The formation of WLMs by CDHAB and sodium salicylate (NaSal) was observed by cryogenic transmission electron microscopy (cryo-TEM). With the addition of nanoparticles, rheological properties of WLM solution get enhancement remarkably. Furthermore, compared with the aid of normal silica nanoparticles (SNPs), WLMs with AMSNPs show higher viscosity and better viscoelasticity. This can be attributed to the high ionization degree of AMSNPs in the nanofluid and stronger electrostatic attraction and extra hydrogen bonding interaction between functional groups of AMSNPs and CDHAB, leading to more micelle-nanoparticle junctions and longer micelles. This work can give further view and knowledge of interaction between functional groups of modified nanoparticles and special surfactants of WLMs.

Interaction of a plane shock wave with an area of ionization instability of discharge plasma in air

The conducted study is devoted to the research area of control of high speed flows and shock-wave configurations. Experimental and numerical results on the interaction of a plane shock wave (M = 5–6) with the area formed by ionization instability in gas discharge plasma at a pressure of 3–7 Torr and gas-discharge current of 100–400 mA are presented. The region of ionization instability in plasma of high degree of ionization and non-equilibrium (gas temperature T ∼ 300–600 K, electron temperature Te∼5⋅103 K) has been obtained experimentally in air. This instability is characterized by spherical strata of changing shape. Two types of a shape of the ionization instability have been obtained: large-scale type and small-scale type. Also, the transitional type from large-scaled strata to low-scaled ones has been obtained. The influence of the ionization instability was established to cause the distortion of an initially plane shock wave up the complete disappearance of its front. Numerical modeling the interaction of the initially plane shock wave with ionization-unstable plasma using the Euler system of equations has been conducted. The area formed by ionization unstable plasma was modeled via a set of thermal layers with varying densities (and temperatures). Changing the physical–chemical properties of the gas medium was taken into account varying the ratio of specific heats. Layered structures with wavy shock-wave and contact discontinuity fronts have been observed. The multiple generations of shear layer instabilities and the Richtmyer–Meshkov instabilities have been obtained as the result of the interaction of a shock wave with thermal strata. It has confirmed that the shapes of the both discontinuities change acquiring an unstable character. Examples of the flow modes with the disappearance of the shock wave front causing by the origination of a structure with cellular order of shear layer instabilities have been presented. A good agreement at the qualitative level with the experimental Schlieren images has been demonstrated.

Розвиток технології вакуумного йонно-плазмового напилення та напрями її вдосконалення

Проаналізовано існуючі способи нанесення вакуумних покриттів. Обґрунтовано переваги методу вакуумного йонно-плазмового напилення покриттів в умовах йонного бомбардування (метод КІБ), порівняно з іншими. Наведено класифікацію катодних плям (КП) та їхній вплив на величину ерозії катода. Встановлено залежності струму розряду, при якому починається поділ КП, і величин коефіцієнтів ерозії від матеріалу катода. Охарактеризовано структуру та фазовий склад плазмової дуги та їхній вплив на ступінь іонізації. Наведено відомості про типи магнітних фільтрів різноманітних конструкцій для зменшення у плазмовому потоці частки крапельної фази та макрочастинок. Розглянуто типи випаровувачів та їхню класифікацію залежно від способу утримання КП на поверхні випаровування катода та від впливу на КП з метою надання їй певної швидкості руху по визначеній траєкторії. Наведено вимоги до конструкції випаровувачів, розглянуто їхні основні типи. Проаналізовано результати дослідження трибологічних характеристик, залишкових напружень покриттів на підставі Ті, Zr, Mo, Al, Cr, W. Висвітлено принципи формування багатошарових покриттів. Охарактеризовано способи одержання наноструктурних покриттів. Зроблено висновок про необхідність звернути увагу на дослідження властивостей покриттів, які працюють в умовах одночасного впливу механічних навантажень і технологічних середовищ.

Structure and stress of Cu films prepared by high power pulsed magnetron sputtering

Owing to its high ionization degree, high power pulsed magnetron sputtering (HPPMS) has proven advantageous for Cu film growth. In this study, Cu films with different thicknesses deposited by HPPMS at different peak powers were prepared. Moreover, a titanium (Ti) interlayer was used to improve the Cu (111) out-of-plane preferred orientation and adhesion. The films prepared at high peak power exhibited high tensile stress, large grain size, and low electrical resistivity. Thicker Cu films exhibited lower stress and larger grain size, resulting in better electrical conductivity and adhesion. At the same time, a Ti interlayer with (002) preferred orientation could greatly improve the (111) out-of-plane preferred orientation and adhesion of the Cu film.

Strong Enhancement of Electron–Ion Recombination Owing to Free–Bound and Bound–Bound Resonance Transitions

The effect of free–bound and bound–bound resonance nonadiabatic transitions of an electron on electron–ion recombination rates in the plasma of a Ne/Xe and Ar/Xe inert gas mixture has been studied. A kinetic model of recombination has been proposed including energy relaxation in collisions with electrons, resonant electron capture to Rydberg states through three-body collisions of Xe+ ions with Ne or Ar atoms and dissociative recombination of NeXe+ or ArXe+ ions, and n → n' resonance transitions. It has been shown that effective resonance processes occurring in quasimolecular systems sharply increase both the recombination coefficient and the effect of collisions with neutral particles even at quite high degrees of ionization of the plasma.

Dual-pulse laser ignition model

A two-dimensional mathematical model of dual-pulse laser ignition that self-consistently integrates Navier-Stokes, translational and vibrational energy, and neutral and charged species equations has been presented. The results showed that the ignition kernel dynamics depends on the shape and initial energy distribution in the energy spot created by the first ultraviolet laser pulse. The results also suggest that the ignition delay time and the flame kernel development depend on the laser intensity, vibrational-nonequilibrium, and initial electron number density. For the high initial degree of ionization, we have obtained ignition of the lean methane–air mixture with the equivalence ratio of 0.6. Vibrational-nonequilibrium taken into account by the Landau-Teller model leads to the slower ignition kernel growth and the significant increase in the ignition delay time. For the case modeled, a change in the overlap of the second laser with the focal point of the first laser pulse leads to the early split up of the kernel and the flame extinguishment.

Anisotropy in multiple ionisation of CO by ion collisions at intermediate interaction strengths

Multiple ionisation of the CO molecule following the impact of 100–700 keV He2+ ions was studied. Fragments arising from the dissociation of were recorded using the coincidence momentum imaging technique. By measuring the angular distribution of the fragment ions in coincidence, and applying the axial recoil approximation, the angle between the axis of the molecule and the direction of the projectile was determined. Strong anisotropy was observed for high degree of ionisation. The dependence of the anisotropy on the interaction strength and the projectile energy was studied and the results were compared with the predicted values in the literature for diatomic molecules. Furthermore, an asymmetry in the angular distribution owing to the heteronuclear nature of the molecule was observed and quantified, showing that the anisotropy is not entirely a geometric effect as has been presented in earlier works.

Differential pumping requirements for the light-ion helicon source and heating systems of Proto-MPEX

The physics of electron and ion heating of high-density deuterium helicon plasmas (>3 × 1019 m−3) in the Proto-Material Plasma Exposure Experiment linear device are under investigation. Theoretical estimates indicate that for efficient heating, discharges with very low neutral gas content (≪0.1 Pa) in the heating sections are required to minimize collisional losses and charge exchange interactions with neutrals. However, this requirement is typically not compatible with the neutral gas pressures (1–2 Pa) commonly used in high-density, light-ion helicon sources. To satisfy these competing requirements, differential pumping techniques are needed. In this paper, results are presented that demonstrate the production of high-density discharges (2–6 ×1019 m−3) with very low neutral gas content (<0.01 Pa) and high degree of ionization (>75%) in the heating sections. Results indicate that the best fueling location is upstream of the plasma source. We elaborate on the key aspects that must be considered to produce these discharges: (1) fueling location, radio-frequency pulse length, and magnetic field configuration, (2) flow rate and timing of the gas injection, and (3) use of conductance-limiting elements.

Enhanced extraction efficiency of the sputtered material from a magnetically assisted high power impulse hollow cathode

The high power impulse hollow cathode sputtering (HiPIHCS) technique was pioneered by researchers attempting to combine the high ionization degree of sputtered species in a high power impulse magnetron sputtering discharge with the highly energetic electrons from a hollow cathode (HC) in order to obtain high-density and high-energy fluxes of sputtered metal species. Hence, this novel technique may open new horizons in surface engineering, offering the ability to control, enhance and tailor coating properties by using additional electric and/or magnetic fields. However, there are still many issues to be solved, including the ionization degree of the sputtered material and the deposition rate, as well as the extraction efficiency. This work reports on the improvement of the extraction efficiency of the sputtered material in an HiPIHCS process when an external magnetic field is applied. The HiPIHCS discharge was operated with ultra-short pulses (5 μs) of high voltage (600–800 V) applied directly on the HC. The obtained experimental results show that the extraction efficiency of both neutral and ionized sputtered material increases at least by a factor of two when an external magnetic field of only 15 mT is applied in the HC discharge region.

Theoretical investigation of supersonic flow control by nonthermal DC discharge

This work describes a theoretical study on shock wave modification by the electrical discharge generated with a DC voltage. Weakly ionized and high-density assumptions for nonthermal plasma were examined to demonstrate heat and momentum transfer contributions in supersonic flow control. The momentum equation for the plasma electrons and ions was considered to evaluate the changes in the incident flow velocity by the plasma. The change in the incident flow temperature was studied by applying source terms arising from a weakly ionized and high-density plasma to the energy equation. It was concluded that the momentum transfer from a nonthermal plasma into the incoming supersonic flow was responsible for the increasing shock wave angle. On the other hand, a nonthermal plasma with a remarkably high ionization degree increases the incident flow temperature drastically, while a weakly ionized plasma has a negligible effect on flow temperature. Our numerical results show that the electric field distribution has a significant role in the plasma flow control mechanisms, suggesting a new tailoring parameter via cathode geometry. The results of this work are in good agreement with respective experimental validation data and can be used in plasma-based shock wave control apparatus.

Influence of inlet ionization degree on performance of seed‐free MHD generator

AbstractPower generating characteristics of seed‐free linear shaped Faraday type and disk shaped Hall type MHD generators are examined by two‐dimensional numerical simulation with changing the inlet ionization degree. A liner shaped Faraday type generator can get stable and high power output at high inlet ionization degree. The net enthalpy extraction ratio, however, is reduced owing to the increase in the required pre‐ionization power. At low inlet ionization degree, on the other hand, ionization instability occurs and the enthalpy extraction ratio decreases. A disk shaped Hall type generator can get high net enthalpy extraction ratio even at low inlet ionization degree under a low pre‐ionization power. The net enthalpy extraction ratio decreases for an excessive inlet ionization degree because of a strong MHD interaction.

Curvature dependence of the effect of ionic functionalization on the attraction among nanoparticles in dispersion.

Solubilization of nanoparticles facilitates nanomaterial processing and enables new applications. An effective method to improve dispersibility in water is provided by ionic functionalization. We explore how the necessary extent of functionalization depends on the particle geometry. Using molecular dynamics/umbrella sampling simulations, we determine the effect of the solute curvature on solvent-averaged interactions among ionizing graphitic nanoparticles in aqueous dispersion. We tune the hydrophilicity of molecular-brush coated fullerenes, carbon nanotubes, and graphane platelets by gradually replacing a fraction of the methyl end groups of the alkyl coating by the ionizing -COOK or -NH3Cl groups. To assess the change in nanoparticles' dispersibility in water, we determine the potential-of-mean-force profiles at varied degrees of ionization. When the coating comprises only propyl groups, the attraction between the hydrophobic particles intensifies from spherical to cylindrical to planar geometry. This is explained by the increasing fraction of surface groups that can be brought into contact and the reduced access to water molecules, both following the above sequence. When ionic groups are added, however, the dispersibility increases in the opposite order, with the biggest effect in the planar geometry and the smallest in the spherical geometry. These results highlight the important role of geometry in nanoparticle solubilization by ionic functionalities, with about twice higher threshold surface charge necessary to stabilize a dispersion of spherical than planar particles. At 25%-50% ionization, the potential of mean force reaches a plateau because of the counterion condensation and saturated brush hydration. Moreover, the increase in the fraction of ionic groups can weaken the repulsion through counterion correlations between adjacent nanoparticles. High degrees of ionization and concomitant ionic screening gradually reduce the differences among surface interactions in distinct geometries until an essentially curvature-independent dispersion environment is created. Insights into tuning nanoparticle interactions can guide the synthesis of a broad class of nonpolar nanoparticles, where solubility is achieved by ionic functionalization.

Relationship between the Polymeric Ionization Degree and Powder and Surface Properties in Materials Derived from Poly(maleic anhydride-alt-octadecene).

Polymeric materials derived from poly(maleic anhydride-alt-octadecene)—here referred as PAM-18—have shown interesting properties that make them potential pharmaceutical excipients. In this work, eight polymers derived from PAM-18 were obtained using NaOH and KOH at 1:1; 1:0.75, 1:0.5, and 1:0.25 molar ratios. The resulting products were labeled as PAM-18Na and PAM-18K, respectively. Each polymer was purified by ultrafiltration/lyophilization, and the ionization degree was determined by potentiometric studies, which was related to the zeta potential. The structural characterization was performed using the Fourier transform infrared (FT-IR) espectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) techniques. The physical characterization was carried out by SEM, particle analysis, and humidity loss and gain studies; the surface studies were performed by the sessile drop method. PAM-18Na had ionization degrees of 95%, 63%, 39% and 22%, whereas those for PAM-18K were 99%, 52%, 35% and 20%, respectively. The results also showed that for higher inorganic base amounts used, the polymeric materials obtained possess high ionization degrees, which could form polymeric solutions or hetero-dispersed systems. Likewise, it was observed that for higher proportions of carboxylate groups in the polymeric structure, the capability to retain water is increased and, only can be eliminated by drying at temperatures greater than 160 °C. On the other hand, the modification of PAM-18 to its ionized forms led to the formation of powder materials with low flowability and surfaces that ranged from very hydrophobic to slightly wettable.

Search for Variability in Young Planetary Nebulae

Data from long-term spectral observations of two young planetary nebulae are presented. A significant enhancement of the radiation fluxes in all emission lines and a higher degree of ionization of the gas are detected in the spectrum of M1-46. The opposite effect is observed in the spectrum of M1-65. Over 10 years (2005-2015) the radiative fluxes in the emission lines fell by a factor of 2-3, after which they began to increase. The cause of the observed variability may be a change in the temperature of the central star or a change in the inhomogeneous structure of the nebula through which the ionizing radiation passes.

Influence of ion-to-neutral flux ratio on the mechanical and tribological properties of TiN coatings deposited by HiPIMS

High power impulse magnetron sputtering (HiPIMS), due to its dense plasma and high ionization degree of sputtered material, enables to deposit high-quality thin films, with fully dense structure, low root mean square (RMS) surface roughness and superior hardness and wear properties. Operating the HiPIMS discharge with ultra-short pulses opens the possibility to control the degree of metal ionization and to tailor the microstructure of the growing film.In order to study the influence of ion-to-neutral flux ratio on the films microstructure, nanocrystalline titanium nitride (TiN) thin films were deposited on silicon substrates, at different degrees of metal ionization and reactive gas dissociation, by adjusting the HIPIMS pulse duration and operation mode (single- or multi-pulse). Energy resolved mass spectrometry and quartz crystal microbalance in combination with a two-gridded energy analyzer were used to determine the ion energy distributions, composition and fraction of ionized species in the substrate's vicinity. The properties of deposition flux were correlated to the topological, structural, mechanical and tribological properties (hardness, H, Young's modulus, E, adhesion/cohesion, kinetic coefficient of friction) of TiN thin films. Atomic force microscopy, X-ray diffraction, scanning electron microscopy, nanoindentation, scratch and tribological measurements were carried out in order to study the previously mentioned properties of deposited TiN thin films.According to the mass spectrometry results, the contribution of low and intermediate energetic parts (ions with energies below 20eV) to Ti+ ion energy distribution functions significantly increases during ultra-short and multi-pulse HiPIMS discharge. The highest ion flux fraction (up to 52%) was measured for the multi-pulse HiPIMS operation mode. The hardest coatings, with the highest H/E and H3/E2 ratios and lowest kinetic coefficient of friction were found to be the TiN thin films deposited by multi-pulse HiPIMS.

Noncontact measurement of substrate temperature by optical low-coherence interferometry in high-power pulsed magnetron sputtering

Substrate temperature is one of the important parameters that affect the quality of deposited films. The monitoring of the substrate temperature is an important technique of controlling the deposition process precisely. In this study, the Si substrate temperature in high-power pulse magnetron sputtering (HPPMS) was measured by a noncontact method based on optical low-coherence interferometry (LCI). The measurement was simultaneously performed using an LCI system and a thermocouple (TC) as a contact measurement method. The difference in measured value between the LCI system and the TC was about 7.4 °C. The reproducibilities of measurement for the LCI system and TC were ±0.7 and ±2.0 °C, respectively. The heat influx from the plasma to the substrate was estimated using the temporal variation of substrate temperature and increased from 19.7 to 160.0 mW/cm2 with increasing target applied voltage. The major factor for the enhancement of the heat influx would be charged species such as ions and electrons owing to the high ionization degree of sputtered metal particles in HPPMS.

Reduced atomic shadowing in HiPIMS: Role of the thermalized metal ions

In magnetron sputtering, the ability to tailor film properties depends primarily on the control of the flux of particles impinging on the growing film. Among deposition mechanisms, the shadowing effect leads to the formation of a rough surface and a porous, columnar microstructure. Re-sputtered species may be re-deposited in the valleys of the films surface and thereby contribute to a reduction of roughness and to fill the underdense regions. Both effects are non-local and they directly compete to shape the final properties of the deposited films. Additional control of the bombarding flux can be obtained by ionizing the sputtered flux, because ions can be controlled with respect to their energy and impinging direction, such as in High-Power Impulse Magnetron Sputtering (HiPIMS). In this work, the relation between ionization of the sputtered species and thin film properties is investigated in order to identify the mechanisms which effectively influence the shadowing effect in Deep Oscillation Magnetron Sputtering (DOMS), a variant of HiPIMS. The properties of two Cr films deposited using the same averaged target power by d.c. magnetron sputtering and DOMS have been compared. Additionally, the angle distribution of the Cr species impinging on the substrate was simulated using Monte Carlo-based programs while the energy distribution of the energetic particles bombarding the substrate was evaluated by energy-resolved mass analysis. It was found that the acceleration of the thermalized chromium ions at the substrate sheath in DOMS significantly reduces the high angle component of their impinging angle distribution and, thus, efficiently reduces atomic shadowing. Therefore, a high degree of ionization in HiPIMS results in almost shadowing effect-free film deposition and allows us to deposit dense and compact films without the need of high energy particle bombardment during growth.

Dissociative ionization of the H2O molecule induced by medium-energy singly charged projectiles

We report on the fragmentation of the water molecule by $1$ MeV H$^{+}$, He$^{+}$ and 650 keV N$^{+}$ ion impact. The fragment-ion energy spectra were measured by an electrostatic spectrometer at different observation angles. The obtained double-differential fragmentation cross sections for N$^{+}$ is found to be more than an order of magnitude higher, than that for H$^{+}$. The relative ratios of the fragmentation channels are also different for the three projectiles. Additional fragmentation channels were observed in the spectra for He$^{+}$ and for N$^{+}$ impact, which are missing in the case of H$^{+}$. From the analysis of the kinetic energy of the fragments, the maximum observed degree of ionization was found to be $q\rm{_{max}}=3$, $4$, and $5$ for H${^+}$, He${^+}$ and N${^+}$ impact, respectively. Absolute multiple ionization cross sections have been determined. They are compared with the predictions of the classical trajectory Monte Carlo and continuum-distorted-wave eikonal-initial-state theories. At lower degrees of ionization, theories provide reasonable agreement with experiment. The systematic overestimation of the cross section by the theories towards higher degrees of ionization indicates the failure of the independent particle model.

Electric and magnetic fields synergistically enhancing high power impulse magnetron sputtering deposition of vanadium coatings

The high power impulse magnetron plasmas (HIPIMS) were employed as a novel deposition technique, which had the benefit of providing a high ionization degree. In contrast, due to the ion return effect, the deposition rate was relatively low compared to the conventional direct current. In this paper, the external electric field and external magnetic field enhanced simultaneously the HIPIMS ((E-MF)-HIPIMS) to achieve higher deposition rate of the coatings. The vanadium coatings were deposited by the (E-MF)-HIPIMS at equivalent average target powers. The substrate peak ion current density measured in the (E-MF)-HIPIMS mode was increased by a factor of 4 to the discovered current density for the HIPIMS conditions when the anode voltage was set to 70 V. The enhanced ion flux bombardment from the highly ionized (E-MF)-HIPIMS plasma led to the formation of a smoother surface and a denser structure. At the same average target power for the vanadium coatings depositions, the (E-MF)-HIPIMS exhibited higher deposition rates compared to the conventional HIPIMS by approximately 73%. The (E-MF)-HIPIMS sputtered vanadium coating exhibited significantly higher-sized film and substrate interface bonding strengths than compared to the HIPIMS by the Rockwell adhesion testing. In addition, the (E-MF)-HIPIMS sputtered vanadium coating exhibited an improved friction coefficient and improved corrosion resistance compared to the substrate and the HIPIMS sample. The improvement occurred due to the enhanced particle ionization and intense ion bombardment.

Influence of hollow anode position on the performance of a hall-effect thruster with double-peak magnetic field

A low-power Hall-effect thruster was designed with two permanent magnet rings. This Hall-effect thruster contains a symmetrical double-peak magnetic field with a gradient larger than that of conventional Hall-effect thrusters. The matching of the anode position with the magnetic field determines the performance of the thruster to a very large extent. This study investigates the laws and mechanisms that govern the front end of a U-shaped hollow anode at the inner magnetic separatrix, the outer magnetic separatrix, and the area between them and influence the discharge characteristics of the thruster. The study shows that with the increase of anode length, the ionization and acceleration zones are pushed down toward the channel outlet and even into the plume region. At the same operating point, both the thrust and the efficiency are the largest when the anode is placed between the inner and outer magnetic separatrices. When the anode is placed at the inner magnetic separatrix, both the thrust and the efficiency are small because of the heavy energy loss on the walls, despite the high degree of ionization. Finally, when the anode is at the outer magnetic separatrix, the performance of the Hall-effect thruster is the poorest because of the lower degree of ionization and larger divergence angle of the plume upon the shift of the ionization zone toward the plume region.