High Degree Of Ionization Research Articles

Sputtering of fast meteoroids’ surface

Sputtering effect was proposed as an explanation of high altitude ionization and luminosity, which are not explained by the classical ablation theory. Fast sputtered particles may create luminous area at the altitudes above the altitude of intensive evaporation. We consider the air-meteoroid interaction by the Monte-Carlo type physical model, which allows us to describe the sputtering of meteoroid surface under impacts of incoming air particles. At the altitude 150 km fast particles carry out about 10–20% of incoming flux energy for high velocity meteors. There are also reflected particles, but the most part of total particle outcome is formed by the particles of the meteoroid material. Presence of fast particles possibly explains a large size of meteors in diffuse stage at high altitudes (above 130 km). The sputtering is negligible in the case of meteor velocities below 30 km/s. Sputtered and reflected particles have relatively high ionization degree, which is larger than ionization degree of surrounding atmosphere. We estimated oxygen radiation, which occurs due to the interaction of sputtered particles with surrounding atmosphere, and compared it with observations.

About the EDF formation in a capacitively coupled argon plasma

The formation of the electron distribution function (EDF) in the bulk plasma of a capacitively coupled radio-frequency (rf) discharge in argon generated in the plasma-chemical reactor PULVA-INP is investigated experimentally and theoretically. Measurements of the EDF and internal plasma parameters were performed by means of a Langmuir probe at pressures of 0.5–100 Pa and discharge powers of 5–100 W. The observed EDFs have revealed a two-temperature behaviour at low pressures and evolved into a Maxwellian distribution at high gas pressures and large discharge powers. Theoretical determination of the EDF is based on the numerical solution of the Boltzmann kinetic equation in the local and non-local approaches under experimental conditions. The model includes elastic and inelastic electron–atom collisions and electron–electron interactions. Low electron temperatures and relatively high ionization degrees are the features of the PULVA-INP rf discharge. This leads to significant influence of the electron–electron collisions on the EDF formation. The modelled and measured distributions show good agreement in a wide range of discharge parameters, except for a range of low gas pressures, where the stochastic electron heating is intense. Additionally, mechanisms of the EDF formation in the dc and rf discharge were compared under similar discharge conditions.

Dielectric function and electron transport in collisional plasma

A procedure is proposed for finding a solution to the linearized kinetic equation with the Landau collision integral included for charged particles in a plasma with a high degree of ionization. This procedure is used to obtain an expression for dielectric permittivity tensor for a collisional plasma over the entire range of frequencies and wave numbers as well as the collisionality parameter. This is transformed to the known expressions in the corresponding asymptotic strongly collisional and collisionless limits. Nonlocal linear transport equations for small perturbations are also formulated for arbitrary relations between the characteristic space, time and collision scales of the plasma

Investigation of pyroelectric electron emission from monodomain lithium niobate single crystals

The behaviors of thermally stimulated electron emission from pyroelectric monodomain lithium niobate single crystal (LiNbO 3) were investigated by utilizing a Si p–n junction photodiode as electron detector and a receptive electron beam resist (E-beam resist) as electron collector. In high vacuum (10 −6 Torr), the pyroelectric electron emission (PEE) was found to depend on the exposed emitting polar crystal surface (+ Z face or − Z face) and was significantly influenced by the emitter-electron receiver gap distances. Thus, the PEE from + Z face was detected during heating and was activated, in small gaps (<2 mm), by field emission effect on which was superposed an intense field ionization effect that primed intermittent runway ionizations (plasma breakdown into a glow discharge). In large gaps (>2 mm) the emission was simply mastered by field emission effect. Whereas, The PEE from − Z face was detected during cooling and was solely due to the field ionization effect. Therewith, for small gaps (<2 mm) the emission was governed by intermittent runway ionization ignitions resulting from a high ionization degree leading to dense plasma formation, and for large gaps (>2 mm) PEE was governed by field ionization generating a soft and continuous plasma ambient atmosphere. Significant decrease of electron emission current was observed from + Z face after successive thermal cycles. A fast and fully emission recovery was established after a brief exposure of crystal to a poor air vacuum of 10 −1 Torr.

Influence of Si—OH groups on properties and avoidance for SiCOH films prepared by decamethylcyclopentasiloxane electron cyclotron resonance plasma

This paper investigates the effect of Si—OH groups on dielectric property and leakage current of the SiCOH low dielectric constant films deposited by decamethylcyclopentasioxane (D5) electron cyclotron resonance plasma. The results show that the increasing of Si—OH content in the films can lead to the increasing of dielectric constant k, decreasing of leakage current and rise in dielectric dispersion. The increasing of k value is the result of compensation of the decreasing of k value originated from cage by the strong polarization of Si—OH groups. The decreasing of leakage current at high Si—OH content is due to the low connecting probability p of networks because the networks break at the terminal Si—OH groups. In the case of high ionization degree of D5 plasma, more Si—OH groups break and form Si—O—Si linkages by chemical condensation occurring between proximal Si—OH groups. As a result, the k value of SiCOH films can be further reduced.

Effect of Si–OH group on characteristics of SiCOH films prepared by decamethylcyclopentasiloxane electron cyclotron resonance plasma

This paper investigates the effect of Si–OH group on dielectric property and leakage current of the SiCOH low dielectric constant films deposited by decamethylcyclopentasiloxane electron cyclotron resonance plasma. The results show that the increasing of Si–OH content in the films can lead to the increasing of dielectric constant k, decreasing of leakage current and stronger dielectric dispersion. Due to the strong polarization of Si–OH group, it leads to the increase of k value of the SiCOH films. The decreasing of leakage current at high Si–OH content is due to the low connecting probability p of networks because the networks break at the terminal Si–OH groups. At the case of high ionization degree of precursor, more Si–OH groups break and form Si–O–Si linkages by condensation chemistry occurring between proximal Si–OH groups. As a result, the k value of SiCOH films can be further reduced.

Enthalpy Changes upon Dilution and Ionization of Poly(l-glutamic acid) in Aqueous Solutions

The enthalpy changes accompanying the dilution and ionization of poly(L-glutamic acid) in water have been measured at 25 degrees C for two degrees of polymerization (DP = 115 and DP = 480) at various degrees of ionization, alpha, for a concentration range from about 0.2 to 0.002 monomol/L. The heat of dilution displays an unusual dependence on the degree of ionization, which is in sharp contrast to the behavior of other weak carboxylic polyelectrolytes, such as poly(acrylic acid). The exothermic heat effects observed at low values of alpha become endothermic for the region where the helix-coil transition is most pronounced, and for high degrees of ionization, they are exothermic again. Evidently, an endothermic heat effect, produced by an additional conformational transition in the dilution process, is superimposed on the exothermic enthalpy of dilution, and it overweighs the latter in the region of alpha where the conformational transition is prevailing. The calorimetric titration curve, which gives the dependence of the heat of ionization, deltaH(i), on alpha, has a maximum and is typical for poly(carboxylic acids) which undergo pH-induced conformational transition, such as poly(methacrylic acid). The values of deltaH(i) obtained at two polymer concentrations indicate that the enthalpy of ionization depends on the polypeptide concentration.

Optical emission spectroscopy investigation on SiCOH films deposition using decamethylcyclopentasiloxane electron cyclotron resonance plasma

This paper investigates the characterization of decamethylcyclopentasiloxane electron cyclotron resonance plasma at different ECR position and field distribution, which were used as a precursor to deposit SiCOH low dielectric constant films. An ECR position threshold for microwave energy couple is found. Before this ECR position threshold, the radicals show an unsaturated distribution. However, a saturation radical distribution can be obtained after the position threshold. According to the radical distribution, the possible chemical reactions in ECR discharge plasma are presented and the relationship between SiCOH films structure and the radical distribution is analyzed. The results show that at a high ionization degree of DMCPS, the fivefold Si–O rings break and form new threefold Si–O rings. Meanwhile, more Si–OH groups break and form Si–O–Si linkages by a condensation chemistry occurring between proximal Si–OH groups. This helps to reduce the k value of SiCOH films.

Efficient absorption and intense soft X-ray emission from gas cluster plasmas irradiated by 25-ps laser pulses

A highly efficient absorption is observed in multipicosecond laser pulse irradiation of argon and nitrogen gas cluster targets at moderate intensities of /spl sim/10/sup 15/ W/cm/sup 2/ using a 1.5 J/25 ps Nd : phosphate glass laser (/spl lambda/=1.054 /spl mu/m). Measurements of laser light absorption, side scattering, and extreme-ultraviolet (XUV) emission spectrum are performed for argon and nitrogen gases puffed through sonic or hypersonic nozzles in the pressure range from 10 to 60 bar. High values of 80%-85% of laser light absorption have been measured in both nitrogen and argon gas cluster plasmas. The X-ray line emission from argon plasma was /spl sim/ 30-40 times stronger than that from the nitrogen plasma, which is related to the formation of larger sized clusters in argon. The very high laser light absorption observed in these multipicosecond laser pulse irradiation experiments may be understood to be occurring due to intense heating of the near solid density clusters in the initial part of the laser pulse creating a plasma of a high degree of ionization, which continues to absorb the rest of the laser pulse energy through collisional processes during its expansion to subcritical densities.

PEGylation and aqueous solution behaviour of pH responsive poly( l-lysine iso-phthalamide)

The effect of PEGylation on the aqueous solution properties of a pH responsive pseudopeptide, poly( l-lysine iso-phthalamide), has been investigated using UV and fluorescence spectroscopy, 1H NMR spectroscopy and dynamic light scattering. It was demonstrated that the level of PEGylation had a critical effect on the pH response of the parent polymer. When the degree of PEGylation was less than 23.4 wt% the modified polymer exhibited a transition from an expanded structure at high degrees of ionization to a compact hydrophobically stabilised structure at low degrees of ionization. The specific pH at which the conformational transition occurred was dependent on the degree of PEGylation. At levels of PEGylation in excess of 25.6 wt% the polymer no longer displayed this pH dependent conformation and existed in a micellar form (100–200 nm) over the whole range of ionization. Both linear and micellar forms of the pseudopeptide have applications in drug delivery.

Synthesis of diamond coatings on tungsten carbide with photon plasmatron

In this paper, recent results on the synthesis of diamond coatings on cemented tungsten carbide substrates (WC–Co) with photon plasmatron are presented. This new plasma-CVD method for high-rate diamond synthesis in the open-air atmosphere has been described in a previous paper [S. Metev, H. Brecht, J. Schwarz, G. Sepold, New technology for high-rate synthesis of PC-diamond coatings in air with photon plasmatron, Diamond and Rel. Materials, 11 (2002), p. 472]. In the course of the work, the influence of the outstanding plasma parameters and deposition conditions (plasma temperature 15.000–20.000 °C, high ionization degree, operating pressure ≥1 atm, deposition rates of 12 up to 60 μm/h) on the film properties have been investigated. Special emphasis has been laid out on the influence of the composition and the properties of the substrate material. The latter varied concerning the WC–Co ratio, grain size and surface roughness. The presence of the binder phase Co is a well-known handicap for the deposition of adhesive diamond coatings. Therefore, selected pretreatment methods (grinding, etching, ultrasonic baths, seeding) in combination with the specific deposition conditions have been used to optimize the film properties. Effects of the substrate pretreatment and the film properties have been characterized by analytical methods, including SEM, EDX, RAMAN, Profilometer and scratch testing.

Ionization kinetics in a supersonic xenon plasma flow entering electric field

We have studied xenon plasma moving in a supersonic diffuser in external electric and magnetic fields. The main physical parameters of the plasma (electron temperature and density) were determined using specially developed methods based on the theory of continuous optical emission from inert gas atoms. These experimental data are compared to the results of theoretical calculations. Based on an analysis of the results of spectroscopic measurements, a mechanism of plasma ionization is established which is capable of maintaining a high degree of ionization in the supersonic xenon plasma flow.

Electron capture dissociation distinguishes a single d-amino acid in a protein and probes the tertiary structure

First results are reported on the application of ECD in analysis of 2+ and 3+ ions of stereoisomers of Trp-cage (NLYIQWLKDGGPSSGRPPPS), the smallest and fastest-folding protein, which exhibits a tightly folded tertiary structure in solution. The chiral recognition based on the ratios of the abundances of z 18 and z 19 fragments in ECD of 2+ ions was excellent even for a single amino acid (Tyr) D-substitution ( R chiral = 8.6). The chiral effect decreased with an increase of temperature at the electrospray ion source, as well as at a higher degree of ionization, 3+ ions ( R chiral = 1.5). A general approach is suggested for charge localization in n+ ions by analysis of ECD mass spectra of ( n + 1)+ ions. Application of this approach to 3+ Trp-cage ions revealed the protonation probability order in 2+ ions: Arg 16 ≫ Gln 5 >≈ N-terminus. The ECD results for native form of the 2+ ions favor the preservation of the solution-phase tertiary structure, and chiral recognition through the interaction between the charges and the neutral bond network. Conversely, ECD of 3+ ions supports the dominance of ionic hydrogen bonding which determines a different gas-phase structure than found in solution. Vibrational activation of 2+ ions indicated greater stability of the native form, but the fragmentation patterns did not provide stereoisomer differentiation, thus underlying the special position of ECD among other MS/MS fragmentation techniques. Further ECD studies should yield more structural information as well as quantitative single-amino acid d/l content measurements in proteins.

Pulsed Plasmas For Sputtering Applications

Pulsed plasmas for sputtering applications have increased in popularity in the past few years. Recently, a new pulsed plasma technique has been introduced to the sputtering world. High power pulsed magnetron sputtering (HPPMS) applies a very large power pulse (up to several megawatts) to the target in a short period of time, which results in a high degree of ionisation of the sputtered species. The ionised species can be used to improve the structure and properties of the deposited film. An experimental power supply was designed and built to learn more about HPPMS. It can produce pulses with peak powers of ≤3 MW with a pulse width of 100–150 μs. The repetition rate for the pulse is from single shot to 500 Hz, and the average delivered power is ≤20 kW. Evidence of the ionisation of the sputtered species is shown with time resolved optical spectroscopy of the plasma. The degree of ionisation is a function of the power. Deposition of very thin, very high density (2.7 g cm3) carbon films by HPPMS is reported. An enabling feature of the power supply is that it can detect and suppress arcs. In addition, the pulsing power supply circuitry prevents the initiation of the arc state in normal operation. At the beginning of the pulse, it transitions directly from the glow to the highly ionised state without accessing the arc regime. SE/500

Ion flows from a beam-plasma discharge

The results of measurements of the energy distribution function of ions escaping from a beam-plasma discharge are compared with the data from probe measurements in the discharge region. It is shown that, on the discharge axis, there is a region with a higher degree of ionization, whose position depends on the external parameters, in particular, on the gas pressure. The mean energy of the ions that leave the plasma from the outside of this region is determined by the potential of the plasma column. Inside the region with a higher degree of ionization, there is an additional mechanism for ion acceleration; as a result, the energy of the ions that leave the plasma from this region is higher than the energy of the electrostatically accelerated ions by a factor of 1.5 to 5. The results obtained show promise for creating a plasma-processing reactor with controlled ion parameters for the purposes of treating materials for microelectronics.

The Effect of Point Defects on the Activation Processes in Semiinsulating GaAs Irradiated by Si28Ions

The layered concentration, concentration profile, and mobility of electrons in the Si28 ion-implanted layers (IIL) of semiinsulating GaAs are investigated. The specific resistance of the latter is also studied upon radiation annealing (RA) in the temperature range 590–800 °C using electron energies higher than the threshold energy of defect formation. The IIL are shown to form during RA at much lower temperatures. The layers exhibit high electrical activation of Si28 ions, with the electron-concentration profile corresponding to the calculated one, and a low concentration of residual defects limiting the electron mobility. The radiation annealing increases the resistance of semiinsulating GaAs. The calculations show that these effects are due to the Frenkel pairs (FP) generated by radiation. A high degree of ionization of GaAs atoms significantly reduces energies of potential barriers of diffusion, FP recombination, and electrical impurity activation.

Swelling pressure induced phase-volume transition in hybrid biopolymer gels caused by unfolding of folded crosslinks: a model.

A thermodynamic model is proposed describing swelling changes and swelling transitions of hybrid gels in which domains of folded chains are chemically built in as cross-links. These folded domains can be unfolded to random coils by osmotic forces produced by the synthetic gel matrix. Uncoiling takes place if the osmotic force acting on the cross-links exceeds the critical value. By unfolding, a new interacting surface is exposed to interactions and affects the swelling pressure. The chains of the folded domains may have ionized groups. The model is based on mean-field statistical-thermodynamic treatment of swelling of polyelectrolyte gels with finite extensibility of network chains. This study is related to hybrid hydrogels with built in protein motifs. A continuous change in external variables increasing the degree of swelling of the hydrogel brings about an abrupt increase in volume (transition) of the gel. The position and magnitude of the transition depend on structural parameters of the hybrid gel, such as fraction of the folded domains in the gel, degree of ionization of chains in the domain, presence of additional chemical cross-links, or degree of dilution at gel formation. Two options for reversibility of the changes are considered: (a) unfolding is irreversible and deswelling proceeds along other curve than swelling and (b) swelling is reversible when the osmotic force decrease below the critical value. In the latter case, swelling changes are described by a closed loop with two transitions. Under certain conditions (high dilution at network formation and sufficiently high degree of ionization of chains of the folded domains), a transition appears known as the collapse transition induced by balance of hydrophobic and hydrophillic interactions. This collapse transition induces the folding transition by which the folded domains are reformed.

Orientation dependence of N2 and O2 multiple ionization in slow and fast collisions with highly charged Xe-ions

The influence of the molecular orientation on the multiple ionization of N2 and O2 was studied in collisions with highly charged Xe-ions at velocities of 0.2–0.3 and ≈15 a.u. The applied technique is based on a position- and time-sensitive multi-particle detector which allows to determine the ionization cross-section as a function of the orientation of the molecular axis. At lower collision energies, e.g. in collisions with 360 keV Xe18+, no anisotropy was found, whereas in collisions with 770 MeV Xe18+ significant orientation effects appear at higher degrees of ionization.

Plasma deposition of boron films with high growth rate and efficiency using carborane

The injection of carborane (C 2B 10H 12) on the PISCES-B linear plasma device has been used to produce boron containing films on various target species. Film growth rates achieved are extremely high (up to 30 nm/s) compared to those typically found for glow discharges (∼0.01 nm/s). For low- Z target materials (C and Al) the film production is highly efficient, with the boron film growth rate comparable to the incident ion flux and the injection rate of boron atoms. The boron to carbon ratio is 3.0–3.6 for these films. Similarly high growth rates (∼10 nm/s) are obtained with high- Z target (W), but with lower deposition efficiency and higher B/C film ratio. The high film growth rate/efficiency are apparently linked to the high degree of carborane ionization and dissociation caused by the ∼40 eV PISCES-B plasma, compared with T<1 eV plasmas of glow discharges. This technique opens the possibility of continuously producing protective B films in thermonuclear devices where net erosion rates approach 10 nm/s.

1–2.5 μm spectra of jets from young stars: Strong $\ion{Fe}{ii}$ emission in HH111, HH240-241 and HH120

As part of a 1-2.5m spectroscopic survey of jets and molecular outflows, we present the spectra of three Herbig Haro chains (HH111, HH240/241, HH120) characterized by strong emission from several Feii transitions originating from the first 13 fine structure levels. Such emission is correlated with optical Sii emission and appears to decrease moving away from the driving source. From the analysis of the Feii lines we have derived electron densities values in the range 3 10 3 - 2 10 4 cm 3 , which are systematically larger than those inferred from optical Sii line ratios. We suggest that Feii lines, having critical densities higher than the optical Sii transitions, trace either regions of the post-shock cooling layers with higher compression, or a section of the jet axis at a higher degree of ionization. Strong H2 emission lines are also detected along the three flows and their analysis indicates that a combination of dierent shocks can be responsible for their excitation in the dierent objects. Consequently the Feii line emission, which requires the presence of fast dissociative shocks, is completely independent from the excitation mechanism giving rise to the molecular emission. In addition to the Feii and H2 lines, emission from other species such as Ci ,S ii ,N i as well as recombination lines from the Paschen series are detected and have been used as a reference to infer the gas-phase iron abundance in the observed HH objects. We estimate a grain destruction eciency of about 30-60%: the highest value is found for HH240A, which also shows the highest degree of excitation among the observed objects.