High Ion Density Research Articles

Langmuir Probe Method for Precise Evaluation of the Negative‐Ion Density in Electronegative Gas Discharge Magnetized Plasma

AbstractThe paper reports results from Langmuir probe current‐voltage (IV) characteristic measurements in argon and oxygen low‐gas‐pressure magnetized plasma. The plasma was produced in a stainless steel discharge tube with length 1.5 m and diameter 0.17 m with a hot filaments cathode. The wall of the discharge tube was grounded. An axial magnetic field B was created by a solenoid. A platinum cylindrical Langmuir probe with radius R = 5· 10−5 m and length L = 5· 10−3 m was placed axially and radially at the center of the discharge tube in order to perform measurements along and across the magnetic field.Using the second derivatives of the measured IV probe characteristics, the EEDF in argon and oxygen was evaluated. The derivatives were taken numerically. Measurements in an argon (i.e., in the absence of negative ions) were performed to obtain results for comparison with the measurements in an oxygen gas discharge, where a high density of negative ions is expected.In the measurements of the second derivatives of the IV characteristics with the probe parallel to the magnetic field in oxygen, a peak appears close to the plasma potential due to the registration of negative ions. In the same time, the electron part of the second derivative was substantially suppressed relatively to the case with the probe oriented perpendicular to the magnetic field. Thus using the appropriate orientation of the probe and a low magnetic field, when the electron part of the second derivative is suppressed, since the negative ion part is not affected by the low magnetic field applied, we can evaluate precisely the negative ion density.The results from the plasma parameters evaluation (plasma potential, electron and negative ion densities and electron temperatures) are presented and discussed (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Steep plasma depletion in dayside polar cap during a CME‐driven magnetic storm

A series of steep plasma depletions was observed in the dayside polar cap during an interval of highly enhanced electron density on 14 October 2000 through EISCAT Svalbard Radar (ESR) field‐aligned measurements and northward‐directed low‐elevation measurements. Each depletion started with a steep dropoff to as low as 1011 m− 3 from the enhanced level of ∼3 × 1012 m−3 at F2 region altitudes, and it continued for 10–15 min before returning to the enhanced level. These depletions moved poleward at a speed consistent with the observed ion drift velocity. DMSP spacecraft observations over an extended period of time which includes the interval of these events indicate that a region of high ion densities extended into the polar cap from the equatorward side of the cusp, i.e., a tongue of ionization existed, and that the ion densities were very low on its prenoon side. Solar wind observations show that a sharp change from IMF By > 0 to By < 0 is associated with each appearance of the ESR electron density dropoff. From this unprecedented clear correlation we present a specific scenario: the series of plasma density depletions observed using the ESR is a result of the poleward drift of the undulating boundary of the tongue of ionization; this undulation is created in the cusp roughly 20 min before the ESR observation by the azimuthal intrusion, in response to the rapid prenoon shift of the footprint of the reconnection line, of the low‐density plasmas originating in the morning sector.

The Structure and Bonding State for Fullerene-Like Carbon Nitride Films with High Hardness Formed by Electron Cyclotron Resonance Plasma Sputtering

We studied pure carbon films and carbon nitride (CN) films by using electron cyclotron resonance (ECR) sputtering. The main feature of this method is high density ion irradiation during deposition, which enables the pure carbon films to have fullerene-like (FL) structures without nitrogen incorporation. Furthermore, without substrate heating, the ECR sputtered CN films exhibited an enhanced FL microstructure and hardness comparable to that of diamond at intermediate nitrogen concentration. This microstructure consisted of bent and cross-linked graphene sheets where layered areas remarkably decreased due to increased sp3 bonding. Under high nitrogen concentration conditions, the CN films demonstrated extremely low hardness because nitrile bonding not only decreased the covalent-bonded two-dimensional hexagonal network but also annihilated the bonding there. By evaluating lattice images obtained by transmission electron microscopy and the bonding state measured by X-ray photoelectron spectroscopy, we classified the ECR sputtered CN films and offered phase diagram and structure zone diagram.

Bit Patterned Structure Fabricated by Kr$^{+}$ Ion Irradiation onto MnBiCu Films

Mn54Bi24Cu21 (15 nm) films with a perpendicular anisotropy were prepared by annealing the sputtered MnCu/Bi multilayer at a temperature of 350 °C. The MnBiCu film had a rather flat surface of Ra = 1.1 nm, and uniform maze domain was observed before the ion irradiation. The magnetization and coercivity of the MnBiCu film were confirmed to disappear after a low Kr+ ion dose of 5 ×1013 ions/cm2. Bit patterned media (BPM) using the MnBiCu (15 nm) films were fabricated by 30 kV Kr+ ion irradiation through electron beam lithography-made resist masks. The surface of the ion-irradiation BPM was almost identical to that of the as-annealed film. The magnetization processes of the bit patterned media were investigated by magnetic force microscope observations after application of the magnetic field. The patterned MnBiCu bits with a size ranging from 500 × 500 nm to 300 × 300 nm have a multidomain state and their magnetization reversals undergo nucleations of the reversed domain and wall propagation. By decreasing the bit size of the patterned MnBiCu, the average switching field Hsf of the bits was increased. This means that the exchange coupling between the patterned bits and the bit edge damage were negligibly small, and shows the possibility of high density ion irradiated planar bit patterned media.

Reduced Contribution of Thermally-Labile Sugar Lesions to DNA Double-Strand Break Formation after Exposure to Neutrons

In cells exposed to ionizing radiation, double-strand breaks (DSBs) form within clustered damage sites from lesions disrupting the DNA sugar-phosphate backbone. It is commonly assumed that DSBs form promptly and are immediately detected and processed by the cellular DNA damage response apparatus. However, DSBs also form by delayed chemical conversion of thermally-labile sugar lesions (TLSL) to breaks. We recently reported that conversion of thermally-labile sugar lesions to breaks occurs in cells maintained at physiological temperatures. Here, we investigate the influence of radiation quality on the formation of thermally-labile sugar lesions dependent DSBs. We show that, although the yields of total DSBs are very similar after exposure to neutrons and X rays, the yields of thermally-labile sugar lesions dependent DSBs from neutrons are decreased in comparison to that from X rays. Thus, the yields of prompt DSBs for neutrons are greater than for X rays. Notably, after neutron irradiation the decreased yield of thermally-labile sugar lesion dependent DSBs is strongly cell line dependent, likely reflecting subtle differences in DNA organization. We propose that the higher ionization density of neutrons generates with higher probability prompt DSBs within ionization clusters and renders the ensuing chemical evolution of thermally-labile sugar lesions inconsequential to DNA integrity. Modification of thermally-labile sugar lesion evolution may define novel radiation protection strategies aiming at decreasing DSB formation by chemically preserving thermally-labile sugar lesions until other DSB contributing lesions within the clustered damage site are removed by non-DSB repair pathways.

Role of ion density in growth, transport, and morphology of nanoparticles generated in plasmas

Spatial distribution, growth, and morphology of the nanoparticle were investigated in the plasmas with relatively low and high ion densities. Our experimental results reveal that cauliflower-shaped amorphous nanoparticles are dominantly distributed throughout the entire plasma in the low ion density plasma while spherical crystalline particles are spread near the plasma edge in the high ion density plasma. Only agglomeration growth step of the nanoparticles was observed without molecular accretion growth step in the high density plasma. Based on the experimental and numerical results, the role of ion density in the growth mechanism and transport of the nanoparticles is discussed.

Accurate Description of Aqueous Carbonate Ions: An Effective Polarization Model Verified by Neutron Scattering

The carbonate ion plays a central role in the biochemical formation of the shells of aquatic life, which is an important path for carbon dioxide sequestration. Given the vital role of carbonate in this and other contexts, it is imperative to develop accurate models for such a high charge density ion. As a divalent ion, carbonate has a strong polarizing effect on surrounding water molecules. This raises the question whether it is possible to describe accurately such systems without including polarization. It has recently been suggested the lack of electronic polarization in nonpolarizable water models can be effectively compensated by introducing an electronic dielectric continuum, which is with respect to the forces between atoms equivalent to rescaling the ionic charges. Given how widely nonpolarizable models are used to model electrolyte solutions, establishing the experimental validity of this suggestion is imperative. Here, we examine a stringent test for such models: a comparison of the difference of the neutron scattering structure factors of K2CO3 vs KNO3 solutions and that predicted by molecular dynamics simulations for various models of the same systems. We compare standard nonpolarizable simulations in SPC/E water to analogous simulations with effective ion charges, as well as simulations in explicitly polarizable POL3 water (which, however, has only about half the experimental polarizability). It is found that the simulation with rescaled charges is in a very good agreement with the experimental data, which is significantly better than for the nonpolarizable simulation and even better than for the explicitly polarizable POL3 model.

High resolution and high density ion beam lithography employing HSQ resist

In the early stages of focused ion beam (FIB) development, ion beam lithography (IBL) employing organic resists showed potential advantages over electron beam lithography (EBL) (most notably less proximity effects and higher sensitivity [1,2]). However, EBL has always been more popular for various reasons (e.g., instrument capabilities, well known process technology, higher resolution, absence of potential shot noise effects, no unintended doping of the irradiated substrate area [3]). We will present and detail our results obtained with a gallium (Ga) liquid metal ion source (LMIS) nanofabrication system studying the resolution limits related to this kind of IBL. We will show that minimum feature sizes below 10nm and periodicity of 30nm are possible in a 6nm hydrogen silsesquioxane (HSQ) layer. Our experiments have revealed that the minimum reachable feature sizes are limited by a phenomenon called ''discontinued lines''[2,4]. Our results indicate that statistical dose fluctuations do not dominate this effect.

Acceleration of laser-driven ion bunch from double-layer thin foils

Generation of monoenergetic ion bunch from a double-layer thin-foil target irradiated by an intense linearly polarized laser pulse is investigated using two-dimensional particle-in-cell simulation. The protons in the front low-density hydrogen target layer accelerated by the space-charge field of the laser-driven hot electrons can penetrate through the high-Z high-mass and high-density ion layer, resulting in an energetic proton bunch. A part of the latter is further accelerated by the space-charge field of the hot electrons in the vacuum behind the high-Z ion layer. With this scheme, quasi-monoenergetic proton bunches can be produced using presently available laser pulses of moderate contrast and duration.

Energy dependence of the relative light output of YAlO3:Ce, Y2SiO5:Ce, and YPO4:Ce scintillators

The nonlinear dependence of the relative light output on the energy deposited in single-crystal scintillation materials YAlO3:Ce (YAP:Ce), Y2SiO5:Ce (YSO:Ce), and YPO4:Ce (YPO:Ce) has been studied. The investigations have been conducted under quasi-monochromatic X-ray excitation in the energy range of 9.5–100 keV. In addition to the standard technique for measuring the nonproportional scintillator response based on the dependence of the full-energy peak position on the energy of incident radiation, a method is proposed for measuring the light output by X-ray fluorescence peaks. Using this method for YAP:Ce, it is possible to investigate the nonlinear dependence of the light output on the photon energy in the energy range of 2–40 keV. Along with this method, the K-dip spectroscopy method has been proposed and tested by measuring the dependence of the relative light output on the electron energy in the range of 0.1–80.0 keV. The processes resulting in the loss of the scintillation material efficiency at a high ionization density are considered.

The Effect of Ion Current Density on Target Etching in Radio Frequency-Magnetron Sputtering Process

The effect of ion current density of argon plasma on target sputtering in magnetron sputtering process was investigated. Using home-made ion probe with computer-based data acquisition system, the ion current density as functions of discharge power, gas pressure and positions was measured. A double-hump shape was found in ion current density curve after the analysis of the effects of power and pressure. The data demonstrate that ion current density increases with the increase in gas pressure in spite of slightly at the double-hump site, sharply at wave-trough and side positions. Simultaneously, the ion current density increases upon increase in power. Especially, the ion current density steeply increases at the double-hump site. The highest energy of the secondary electrons arising from Larmor precession was found at the double-hump position, which results in high ion density. The target was etched seriously at the double-hump position due to the high ion density there. The data indicates that the increase in power can lead to a high sputtering speed rate.

Controlled trial of safety and efficacy of bright light therapy vs. negative air ions in patients with bipolar depression

Treatment of bipolar disorder often results in patients taking several drugs in an attempt to alleviate residual depressive symptoms, which can lead to an accumulation of side effects. New treatments for bipolar depression that do not increase the side effect burden are needed. One nonpharmacological treatment with few side effects, bright light therapy, has been shown to be an effective therapy for seasonal affective disorder, yet has not been extensively studied for other forms of depression. Forty-four adults with bipolar disorder, depressed phase were randomized to treatment with bright light therapy, low-density or high-density negative ion generator for 8 weeks. The primary measure of efficacy was the Structured Interview Guide for the Hamilton Depression Rating Scale with Atypical Depression Supplement (SIGH-ADS). Adverse events were assessed using the Young Mania Rating Scale (YMRS) and Systematic Assessment for Treatment Emergent effects (SAFTEE). All outcome variables were statistically analyzed using a mixed model repeated measure analysis of variance (ANOVA). The results showed no statistically significant differences between groups in any outcome measures at study end point; adverse events, including switches into hypomania, were rare. Further research is needed to determine the efficacy of bright light therapy in this population.

Control of magnetic properties of MnBi and MnBiCu thin films by Kr+ ion irradiation

Mn52Bi48 (15 nm) and Mn54Bi24Cu21 (15 nm) thin films were prepared by the magnetron sputtering and vacuum annealing at 350 °C, and the variations of their structures and magnetic properties with 30 keV Kr+ ion irradiation were studied. The MnBi and MnBiCu films exhibited saturation magnetizations Ms of 180 emu/cc and 210 emu/cc, the coercivities Hc of 10 kOe and 3.4 kOe, respectively. The Ms and Hc of the MnBi abruptly vanished by the irradiation of ion dose at 3 × 1014 ions/cm2, while those of the MnBiCu film gradually decreased with increasing the ion dose and became zero at 5 × 1013 ions/cm2. The different trend on the ion irradiation between MnBi and MnBiCu films is understood by the surface structure of the film, i.e., the MnBi has convex islands on its surface, which protect the underneath NiAs-type MnBi from the irradiation, while the MnBiCu has rather flat surface, and its crystal structure was uniformly modified by the irradiation. From the surface flatness and the uniformity of the MnBiCu film, as well as the low annealing temperature of 350 °C, it was concluded that the MnBiCu film is one of the attractive materials for high-density ion irradiation bit patterned media.

On the Influence of Pore Size and Pore Loading on Structural and Dynamical Heterogeneities of an Ionic Liquid Confined in a Slit Nanopore

Molecular dynamics simulations were performed to investigate the structural and dynamical properties of varying amounts of the ionic liquid (IL) [EMIM+][TFMSI–] confined inside slit-like graphitic pores of different widths, H. The ions distributed in layers inside the slit pores, with the number of layers depending on pore size. A reduction in pore loading leads to the formation of regions of high and low density of ions in the center of the pore. Variations in pore size and pore loading seem to induce only slight changes in the local liquid structure of [EMIM+][TFMSI–] in the different layers, as compared with the liquid structure of the bulk IL. This finding, when combined with our previous work for a different IL (Singh, R.; Monk, J.; Hung, F. R. J. Phys. Chem. C2011, 115, 16544–16554), suggests that confinement inside slit-like nanopores may or may not induce changes in the local liquid structure depending on the specific IL. However, pore size and pore loading have a marked effect on the dynamics of ...

Ethane cation decomposition characterization by EBMI spectroscopy: gas‐phase dissociative recombination as a source of secondary products

The decomposition products of the d(6) -ethane cation following charge-transfer ionization with Ar(+) , under conditions of varying ionization electron current, have been isolated in solid argon matrices at 18 K and examined using Fourier transform infrared spectroscopy. Gas samples containing 1 : 1600 d(6) -ethane : Ar were subjected to electron bombardment by using either a high (pin) or a low (plate) ionization density anode configuration with ionization currents between 20 and 150 μA. Under high ionization density conditions, the observed major products were d(4) -ethene (C(2) D(4) ) and d(2) -acetylene (C(2) D(2) ), with smaller yields of C(2) D(5) , C(2) D(3) , and C(2) D. The yield of each dehydrogenation product was enhanced with increased current. Analogous experiments employing the low ionization density plate anode resulted in reduced C(2) D(6) destruction and the formation of only C(2) D(4) and C(2) D(2) . The results suggest the onset of dissociative recombination processes under high ion density conditions. In this context, the results can be interpreted as a dissociative recombination of primary ion products, which gives rise to further dehydrogenation, and appearance of additional neutral radical products.

プラズマ窒化処理がステンレス刃物鋼の表面性状に及ぼす影響

Plasma nitriding treatment is very effective for the hardening of precision metal parts. Especially, high density plasma nitriding can efficiently generate a high density ion with installed hollow cathode, which decreases the damage of the workpiece. As a result, the parts can be cleaned, etched, heated, and nitrided effectively. In this study, an improvement of surface integrity of stainless steel SUS440C is experimentally investigated by nitriding. The experimental analysis made it clear that the surface hardness of workpiece increased due to the generation of nitrided layer even under the low temperature condition like 513K. The nitrided layer was hardened with an increase of process temperature and process time, until a maximum surface hardness of 1700HV.

Negative ion treatment increases positive emotional processing in seasonal affective disorder

Antidepressant drug treatments increase the processing of positive compared to negative affective information early in treatment. Such effects have been hypothesized to play a key role in the development of later therapeutic responses to treatment. However, it is unknown whether these effects are a common mechanism of action for different treatment modalities. High-density negative ion (HDNI) treatment is an environmental manipulation that has efficacy in randomized clinical trials in seasonal affective disorder (SAD). The current study investigated whether a single session of HDNI treatment could reverse negative affective biases seen in seasonal depression using a battery of emotional processing tasks in a double-blind, placebo-controlled randomized study. Under placebo conditions, participants with seasonal mood disturbance showed reduced recognition of happy facial expressions, increased recognition memory for negative personality characteristics and increased vigilance to masked presentation of negative words in a dot-probe task compared to matched healthy controls. Negative ion treatment increased the recognition of positive compared to negative facial expression and improved vigilance to unmasked stimuli across participants with seasonal depression and healthy controls. Negative ion treatment also improved recognition memory for positive information in the SAD group alone. These effects were seen in the absence of changes in subjective state or mood. These results are consistent with the hypothesis that early change in emotional processing may be an important mechanism for treatment action in depression and suggest that these effects are also apparent with negative ion treatment in seasonal depression.

Stable ion radiation pressure acceleration with intense laser pulses

We have demonstrated the promising radiation pressure acceleration (RPA) mechanism of laser-driven ion acceleration at currently achievable laser and target parameters through a large number of two-dimensional particle-in-cell simulations and experiments. High-density monoenergetic ion beams with unprecedented qualities such as narrow-peaked spectrum, lower-divergence and faster energy-scaling are obtained, compared with the conventional target normal sheath acceleration. The key condition for stable RPA from thin foils by intense circularly polarized lasers has been identified, under which the stable RPA regime can be extended from ultrahigh intensities >1022 W cm−2 to a currently accessible range 1020–1021 W cm−2. The dependences of the RPA mechanism on laser polarization, intensity and on the target composition and areal density have been studied.

Fourier Transform Ion Cyclotron Resonance Mass Resolution and Dynamic Range Limits Calculated by Computer Modeling of Ion Cloud Motion

Particle-in-Cell (PIC) ion trajectory calculations provide the most realistic simulation of Fourier transform ion cyclotron resonance (FT-ICR) experiments by efficient and accurate calculation of the forces acting on each ion in an ensemble (cloud), including Coulomb interactions (space charge), the electric field of the ICR trap electrodes, image charges on the trap electrodes, the magnetic field, and collisions with neutral gas molecules. It has been shown recently that ion cloud collective behavior is required to generate an FT-ICR signal and that two main phenomena influence mass resolution and dynamic range. The first is formation of an ellipsoidal ion cloud (termed "condensation") at a critical ion number (density), which facilitates signal generation in an FT-ICR cell of arbitrary geometry because the condensed cloud behaves as a quasi-ion. The second phenomenon is peak coalescence. Ion resonances that are closely spaced in m/z coalesce into one resonance if the ion number (density) exceeds a threshold that depends on magnetic field strength, ion cyclotron radius, ion masses and mass difference, and ion initial spatial distribution. These two phenomena decrease dynamic range by rapid cloud dephasing at small ion density and by cloud coalescence at high ion density. Here, we use PIC simulations to quantitate the dependence of coalescence on each critical parameter. Transitions between independent and coalesced motion were observed in a series of the experiments that systematically varied ion number, magnetic field strength, ion radius, ion m/z, ion m/z difference, and ion initial spatial distribution (the present simulations begin from elliptically-shaped ion clouds with constant ion density distribution). Our simulations show that mass resolution is constant at a given magnetic field strength with increasing ion number until a critical value (N) is reached. N dependence on magnetic field strength, cyclotron radius, ion mass, and difference between ion masses was determined for two ion ensembles of different m/z, equal abundance, and equal cyclotron radius. We find that N and dynamic range depend quadratically on magnetic field strength in the range 1-21 Tesla. Dependences on cyclotron radius and Δm/z are linear. N depends on m/z as (m/z)(-2). Empirical expressions for mass resolution as a function of each of the experimental parameters are presented. Here, we provide the first exposition of the origin and extent of trade-off between FT-ICR MS dynamic range and mass resolution (defined not as line width, but as the separation between the most closely resolved masses).

The plasma environment of Titan: The magnetodisk of Saturn near the encounters as derived from ion densities measured by the Cassini/CAPS plasma spectrometer

[1] We analyze ion densities derived from the data of the Cassini Plasma Spectrometer for the time period of the prime mission till the end of May 2008, in the low latitude outer magnetosphere near Titan encounters. We have found that the central line of the magnetodisk is surrounded by a structured plasma sheet, a smooth, broad ion layer composed of light ions, and a heavy ion layer displaying narrow substructures. The heavy ion densities are spiky; the co-location of the observed enhanced ion plasma densities with the change of sign of the radial component of the magnetic field is demonstrated. At these locations the heavy ion density is the highest. The plasma sheet is denser and wider on the dayside of Saturn than on the nightside; in the lobes the protons were dominant. Based on a statistical analysis for proton densities measured between radial distances from 10 RS to 22 RS we project densities to Titan's orbital distance. We show that the projected proton density in the magnetodisk in organized by SLS3 longitude and, therefore, is modulated by SKR. In the lobes, the proton density is nearly constant. High heavy ion density in the sheet is accompanied by low heavy ion temperature. The magnetospheric interaction with Titan is primarily defined by the SLS3 phase of the encounter and the distance of the moon from the magnetic equator. Accordingly, the incoming plasma flow impinging on Titan cannot be stable for a few hours before the encounter.