Production Of Positive Ions Research Articles

Effect of transverse airflow on the deflection of negative corona discharge on the Trichel pulse mode at atmospheric pressure

Negative corona discharge can deflect in transverse airflow in pin-to-plane electrodes at atmospheric pressure. In this paper, we investigate the mechanism of Trichel pulse discharge deflection in transverse airflow and give a further understanding of the dynamic process of the deflection through experiments and simulations. In experiments, we quantitatively record the deflection angle by processing the discharge images, and they show that a larger airflow speed will lead to a larger deflection angle. In simulations, the discharge deflection angle is calculated through a 2D fluid model. Besides, the periodic fluctuation of the deflection angle with Trichel pulses is revealed, and this phenomenon can be explained by the alternative dominant effect of airflow or ionization on the net production of positive ions in the vicinity of the tip. When the effect of airflow is dominant, more positive ions will generate away from the center of the tip, which will lead to an increase in the deflection angle. On the other hand, when the effect of ionization prevails, more positive ions will generate near the center because the electric field here is stronger, and the deflection angle will decrease. In addition, if these two effects balance, the deflection angle will reach its maximum or minimum value.

Unexpected Negative-Ion Conversion in Grazing Scattering of Negative Ions on HOPG

An experimental study of 8.5-22.5 keV-energy C-, O-, and F- ion scattering from an HOPG surface has been performed at a grazing scattering angle. For a given incident angle or impact velocity, the F- fraction is the highest and the C- fraction is the smallest among these three projectiles, which is explained with the order of the electron affinity level of the projectile. Moreover, the unexpected observations are that the F- ion fraction increases monotonically with impact velocity and that the negative-ion fraction increases with the decrease in exit angle. It can be explained by the influence of the effective high work function of HOPG and the production of positive ions at short distances from the surface.

Towards prediction of the rates of antihydrogen positive ion production in collision of antihydrogen with excited positronium

We present a 4-body calculation of scattering between an antihydrogen atom () and a positronium (Ps) aiming at the prediction of cross sections for the production of antihydrogen positive ions . The antihydrogen positive ions are expected to be a useful source of ultra-cold anti-atoms for the test of matter-antimatter gravity. We convert the Schrödinger equation to a set of coupled integro-differential equations that involve intermediate states which facilitate the internal region description of the scattering wavefunction. They are solved using a compact finite difference method. Our framework is extended to scattering between an excited Ps and H. Cross sections of the reactions, Ps (1s/2s/3s) , in s-wave collisions, are calculated. It is found that the reactions originating from Ps (1s/2s) + produce with a constant cross section within 0.05 eV above the threshold while the reaction cross section from Ps (3s) decreases as the collision energy increases in the same energy interval. Just above the threshold, the cross section of production from Ps (3s) + in s-wave collision is 7.8 times larger than that from Ps (1s) + in s-wave and 2.3 times larger than that from Ps (2s) + in s-wave. The near-threshold de-excitation reaction from Ps (3s) + occurs more rapidly than the production.

Towards prediction of the rates of antihydrogen positive ion production in antihydrogen-excited positronium reaction

SynopsisWe present the 4-body calculation of the antihydrogen-positronium scattering aiming at the prediction of cross sections for the production of antihydrogen positive ions. The latter are expected to be a useful source of ultra-cold atoms for the test of matter-antimatter gravity. We convert the Schrödinger equation to a set of coupled integro-differential equations that involve intermediate states and are solved using the compact finite difference method. We will present the investigation of the rearrangement reaction between the ground-state antihydrogen atom and the excited positronium.

Two-dimensional simulation of dynamic characteristics of N<sub>2</sub>–O<sub>2</sub> corona discharge at micro scale

Based on the principle of micro-scale discharge, the micro-nano ionization gas sensor has the characteristics of fast response, high precision and easy integration. It is expected to achieve rapid and accurate detection of gas. At present, there is a lack of systematic analysis of the inter-polar discharge process of the new sensor. This paper uses the fluid-chemical dynamics methodology to create a 2D space discharge model of the N<sub>2</sub>-O<sub>2</sub> mixed gas at the micron gap and the nano-tip field in ambient atmosphere at normal temperature and pressure. Meanwhile, by analyzing the mutual coupling between the space electron transport process, the discharge current density, and the space electric field strength, the paper clarifies the dynamics of space discharge in the field, improves how internal discharges work in such micro-nano structured ionization gas sensors, and analyzes the pattern of influence of different polar distances on space discharges. The results show that the electric field in the space remains constant as the production and consumption of positive and negative ions reaches a dynamic equilibrium in the field. It is reflected in the field strengthening effect of positive ion groups to the cathode plate and of negative ion groups to the anode plate, as well as in the field weakening effect between positive and negative ion groups. The resulting stable and strong electric field of the cathode makes sure that space discharge is maintained, and the discharge current density stabilizes. Initially, as the polar distance decreases gradually, the electric field strength between the poles and plates increases. It plays a leading role in the accumulation of electron energy and in the increase in the number density of electrons, thus leading to the increase of the output current density up to the peak value when the polar distance <i>D</i> = 50 μm. As the polar distance decreases, the field strength between the poles and plates increases. Despite that, when electrons accumulate energy up to such a level that gas molecules can be ionized, the necessary movement distance and the distance required to increase the number density of electrons decreases. As a result, the degree of ionization weakens, and the field strengthening effect of positive ions decreases. In other words, the increment of the field strength caused by positive ions at the tip decreases, and in turn, the discharge current density decreases. This pattern serves as a theoretical support in the optimization of the micro-nano structured ionization gas sensors.

The mechanism of negative and positive hydrogen ions production on the Ni surface

The studies about surface production of hydrogen negative ions play an important role in many technologies. In the present paper, a low energy molecular hydrogen ion beam was irradiated to the porous Ni sheet. It was found that negative atomic hydrogen ions were detected at the back of the porous Ni sheet when the energy of incident ion beam was lower than 180 eV. When the energy of the incident ions increased, the positive ions dominated at the back of the porous Ni sheet. The production of negative hydrogen on Ni surface can't be explained by comparing the electron affinity of Ni and H. The charge transferring during the process of H atoms reflected from Ni surface was calculated by using constrained DFT (cDFT). The results show the production of negative hydrogen on Ni surface may well be due to heterogeneous electron density on the Ni surface. However, the influence of incident energy on the production of negative and positive hydrogen ions is unable to be explained by cDFT. The problem may be solved by using TDDFT which is able to capture the transfer of energy to electrons during the collision between atoms.

Observation of significant electron loss in grazing scattering of negative ions off a LiF(100) surface

LiF has potential applications in developing intensive current negative-ion sources and neutral particle detection in space due to its wide band gap. Charge transfer processes on a LiF(100) surface have been studied for 10.5–22.5 keV negative oxygen and chlorine ions under a grazing angle of incidence. In contrast with previous studies, the electron loss of the projectile has been obviously observed. The most striking experimental result is that the positive and negative ion fractions nonmonotonically vary with increasing incident angle in the scattered beam. The positive-ion production is explained by the molecular orbital promotion mechanism. The nonmonotonic positive-ion fraction is well described by the Landau-Zener formula. Besides the complete destruction from the anion sites of the insulator surface, the channel of negative-ion destruction from the cation sites has been suggested and considered in the model calculation to understand the electron loss process. It demonstrates that incident angle is a sensitive parameter for the negative ion conversion during grazing ion surface scattering.

Positive-ion accelerator mass spectrometry at ATLAS: Peaks and pits

Electron Cyclotron Resonance (ECR) ion sources and the production of multiple-charge positive ions with high efficiency in combination with a heavy-ion accelerator have opened the way to an alternative and complementary version of accelerator mass spectrometry (AMS). A notable strength of positive-ion over traditional AMS is the capability of ultra-high sensitivity detection of radioactive isotopes of noble gases, in particular 37Ar (t1/2 = 35 d) and 39Ar (269 y). The complete dissociation of molecular ions in the ECR and in particular of hydride ions of neighboring stable isotopes results in superior isotopic separation. However, the use of high charge states, necessary for acceleration to high energy, entails the existence of severe transmission degeneracies with stable ions having nearly equal mass-to-charge ratios, in addition to that of stable isobaric ions. Separation or discrimination of these parasitic ions require powerful and sophisticated dispersive systems at detection stage. We review here work performed and in progress at the ATLAS facility of Argonne National Laboratory (ANL) where an ECR ion source, a Radio-Frequency Quadrupole (RFQ), a superconducting linear accelerator and a Gas-Filled Magnet (GFM) are used as an AMS setup.

Production and analysis of multiply charged negative ions by liquid atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry.

RationaleLiquid atmospheric pressure matrix‐assisted laser desorption/ionisation (AP‐MALDI) has been shown to enable the production of electrospray ionisation (ESI)‐like multiply charged analyte ions with little sample consumption and long‐lasting, robust ion yield for sensitive analysis by mass spectrometry (MS). Previous reports have focused on positive ion production. Here, we report an initial optimisation of liquid AP‐MALDI for ESI‐like negative ion production and its application to the analysis of peptides/proteins, DNA and lipids.MethodsThe instrumentation employed for this study is identical to that of earlier liquid AP‐MALDI MS studies for positive analyte ion production with a simple non‐commercial AP ion source that is attached to a Waters Synapt G2‐Si mass spectrometer and incorporates a heated ion transfer tube. The preparation of liquid MALDI matrices is similar to positive ion mode analysis but has been adjusted for negative ion mode by changing the chromophore to 3‐aminoquinoline and 9‐aminoacridine for further improvements.ResultsFor DNA, liquid AP‐MALDI MS analysis benefited from switching to 9‐aminoacridine‐based MALDI samples and the negative ion mode, increasing the number of charges by up to a factor of 2 and the analyte ion signal intensities by more than 10‐fold compared with the positive ion mode. The limit of detection was recorded at around 10 fmol for ATGCAT. For lipids, negative ion mode analysis provided a fully orthogonal set of detected lipids.ConclusionsNegative ion mode is a sensitive alternative to positive ion mode in liquid AP‐MALDI MS analysis. In particular, the analysis of lipids and DNA benefited from the complementarity of the detected lipid species and the vastly greater DNA ion signal intensities in negative ion mode.

Time-dependent one-dimensional simulation of atmospheric dielectric barrier discharge in N2/O2/H2O using COMSOL Multiphysics

The results of time-dependent one-dimensional modelling of a dielectric barrier discharge (DBD) in a nitrogen–oxygen–water vapor mixture at atmospheric pressure are presented. The voltage–current characteristics curves and the production of active species are studied. The discharge is driven by a sinusoidal alternating high voltage–power supply at 30 kV with frequency of 27 kHz. The electrodes and the dielectric are assumed to be copper and quartz, respectively. The current discharge consists of an electrical breakdown that occurs in each half-period. A detailed description of the electron attachment and detachment processes, surface charge accumulation, charged species recombination, conversion of negative and positive ions, ion production and losses, excitations and dissociations of molecules are taken into account. Time-dependent one-dimensional electron density, electric field, electric potential, electron temperature, densities of reactive oxygen species (ROS) and reactive nitrogen species (RNS) such as: O, O−, O+, {text{O}}_{2}^{ - } , {text{O}}_{2}^{ + } , O3, {text{N}}, {text{N}}_{2}^{ + } , N2s and {text{N}}_{2}^{ - } are simulated versus time across the gas gap. The results of this work could be used in plasma-based pollutant degradation devices.

Comment on "Non-linear photoelectron effect contributes to the formation of negative matrix ions in UV-MALDI".

Alonso and Zenobi (AZ) recently claimed "a comprehensive theoretical description of negative ion formation in UV-MALDI" (Phys. Chem. Chem. Phys., 2016, 18, 19574). Emphasizing photoelectrons, it is found to be unphysical in several respects, including violation of charge and mass conservation, and in the treatment of ablation, expansion and electron capture. It is not internally consistent, and ions created by the photoelectron mechanism are given artificial preference. Although AZ claimed the "first proposal for a comprehensive theoretical description of negative ion formation in UV-MALDI", the Coupled Physical and Chemical Dynamics model has successfully reproduced a number of phenomena relevant to negative ion production over many years.

Two-Dimensional Numerical Study on Characterization of Low-Pressure Capacitively Coupled Argon Discharges

This paper presents an investigation of argon capacitively coupled plasma at low pressure. A two-dimensional, time-dependent fluid model is used to describe the production, transport, and destruction of electrons and positive ions. The model is solved for a GEC(gaseous electronics conference) Cell reactor type (with 4cm diameter and 2.5cm interelectrode distance) operating at frequency 13.56MHz, pressure 1Torr and applied voltage 1000V, in pure argon. Two-dimensional distributions are presented in the stationary state, including electron temperature and species density i.e. electron, ion and metastable atom. The electric field and electric potential at different phases in one RF cycle is also studied.

Role of projectile electrons for target-recoil-charge-state production in intermediate-energy B2+-Ne collisions

We apply an independent electron model to study $q$-fold target-charge-state production in 25--600 keV/nucleon B${}^{2+}$-Ne collisions for which experimental and theoretical results were published recently [W. Wolff et al., Phys. Rev. A 84, 042704 (2011)]. The model treats projectile and target electrons using a common potential and makes use of a single-determinant wave function for the combined system. The calculated total cross sections for positive recoil ion production as well as for Ne${}^{q+}$ production ($q=1,...,4$) determined in coincidence with an unchanged projectile charge state agree well with experiment where available, i.e., in the 30--400 keV/nucleon energy range. At energies below 200 keV/nucleon the projectile electrons are shown to play a crucial role in reproducing the experimental data for $q=1,...,4$. For the $q\ensuremath{\ge}2$ channels the inclusion of projectile electron contributions is needed even at energies above 200 keV/nucleon in order to reproduce the experimental data. As expected, the predictions for the $q=5$ recoil charge state overestimate the experimental data due to a failure of the independent electron model for this extreme channel.

Influence of support materials on carbon clusters formation from fullerene C60 and TOF parameters

In the present paper the effect of different fullerene C60 substrates on the production of positive and negative ions has been examined. The ions were produced by the laser desorption/ionization method (LDI). All measurements were carried out using a linear time of flight mass spectrometer (TOF). Usually stainless steel is a substrate for the tested samples. Silver was also examined. In some cases dielectrics are used as sample substrates. In this work insulating substrates such as mica, glass and floppy disc foil were used. The influence of these different materials on the positive and negative ions mass spectra was observed. During the experiment, the electric charging of dielectric substrates affects the spectrometer: ion time of flight and distribution of potentials inside the ion source.

Inelastic collisions of the uracil molecules with electrons

Ionization and excitation of the uracil molecules by electron impact is investigated. Production of positive ions of uracil molecules (nucleic acid base) was studied using a crossed electron and molecular beam technique. The method developed by the authors enabled the molecular beam intensity to be measured and the electron dependences and the absolute values of the total cross sections of production of both positive ions to be determined. It is shown that the total positive uracil ion production cross section reaches its maximal value of (1.0 ± 0.1) × 10(-15) cm(2) at the 95 eV electron energy. Dissociative ionization cross sections were also determined. The luminescence spectra of isolated uracil molecules in the wavelength range of 200-500 nm under the influence of slow electrons are obtained. In the spectrum, more than 20 spectral bands and lines at 100 eV electron energy are observed. It is shown that the uracil radiation spectrum is formed by the processes of molecules dissociative excitation, dissociative excitation with ionization, excitation of electronic levels of the initial molecule and molecular ion.

Toward laser ablation Accelerator Mass Spectrometry of actinides

A project to measure neutron capture cross sections of a number of actinides in a reactor environment by Accelerator Mass Spectrometry (AMS) at the ATLAS facility of Argonne National Laboratory is underway. This project will require the precise and accurate measurement of produced actinide isotopes in many (>30) samples irradiated in the Advanced Test Reactor at Idaho National Laboratory with neutron fluxes having different energy distributions. The AMS technique at ATLAS is based on production of highly-charged positive ions in an electron cyclotron resonance (ECR) ion source followed by acceleration in the ATLAS linac and mass-to-charge (m/q) measurement at the focus of the Fragment Mass Analyzer. Laser ablation was selected as the method of feeding the actinide material into the ion source because we expect it will have higher efficiency and lower chamber contamination than either the oven or sputtering techniques, because of a much narrower angular distribution of emitted material. In addition, a new multi-sample holder/changer to allow quick change between samples and a computer-controlled routine allowing fast tuning of the accelerator for different beams, are being developed. An initial test run studying backgrounds, detector response, and accelerator scaling repeatability was conducted in December 2010. The project design, schedule, and results of the initial test run to study backgrounds are discussed.

Ionization of electron-excited molecules in a strong electric field

In this paper, we prove the direct effect of a strong electric field on the ionization process occurring in dense hightemperature mixtures of molecular gases containing electronexcited particles. Our proof is based on the analysis of systematic divergences of experimental and theoretical data on the value of the electric current onto an electric probe placed into these mixtures. For a wide number of mixtures of var� ious compositions, the electric current calculated on the basis of the conventional theory of electric probes always turns out to be several times lower than the measured current. Introducing into the conventional theory an additional ionization source stipulated by the strong electric field near the probe surface has resulted in satisfactory consistency between the calcu� lated data and the available experimental data. The electricprobe theory for dense chemically reacting plasmas at normal pressure was developed by the authors (together with G.S. Aravin, P.A. Vlasov, and Yu.K. Karasevich, Institute of Chemical Physics, Russian Academy of Sciences) in the 1980s (1-5). A review of these studies was presented in (6). The theory is based on experimental data on the unsteady chemi� calionization process in a shock tube beyond the reflected shock wave in various gas mixtures. In these measurements, a twoconductor microwave interfer� ometer was used, with one of the conductors being a cylindrical probe maintained at a constant negative electric potential. Upon significantly elevating the temperature in the region beyond the reflected shock wave in the gas mix� ture under study, unsteady chemical processes began to develop. Among them, chemicalionization reac� tions including the production of positive ions and electrons were present. In the experiment, the unsteady electric current onto a probe was measured. Then, in accordance with microwave measurements, the electronconcentration profiles were plotted as functions of time. These data have made it possible to find the effective timedependent ionization rate. This function obtained experimentally was used for numer� ically solving the probe problem. The conventional setting of the problem of immobile lowtemperature ( T ~ 2000-3500 K) ionized gas mixtures at pressures on the order of atmospheric pressure can be formu� lated in the following manner. The unsteady set of equations in a cylindrical coor� dinate system can be written out in the form

Influence of high-dose nitrogen implantation on the positive charge density of the buried oxide of silicon-on-insulator wafers

The influence of nitrogen implantation on the properties of silicon-on-insulator buried oxide using separation by oxygen implantation was studied. Nitrogen ions were implanted into the buried oxide layer with a high-dose of 1016 cm-2. The experimental results showed that the positive charge density of the nitrogen-implanted buried oxide was obviously increased, compared with the control sampes without nitrogen implantation. It was also found that the post-implantation annealing caused an additional increase of the positive charge density in the nitrogen implanted samples. However, annealing time displayed a small effect on the positive charge density of the nitrogen implanted buried oxide, compared with the significant increase induced by nitrogen implantation. Moreover, the capacitance-voltage results showed that the positive charge density of the unannealed sample with nitrogen implanted is approximately equal to that of the sample annealed at 1100 ℃ for 2.5 h in N2 ambient, despite an additional increase brought with annealing, and the buried oxide of the sample after 0.5 h annealing has a maximum value of positive charge density. According to the simulating results, the nitrogen implantation resulted in a heavy damage to the buried oxide, a lot of silicon and oxygen vacancies were introduced in the buried oxide during implantation. However, the Fourier transform infrared spectroscopy of the samples indicates that implantation induced defects can be basically eliminated after an annealing at 1100 ℃ for 0.5 h. The increase of the positive charge density of the nitrogen implanted buried oxide is ascribed to the accumulation of implanted nitrogen near the interface of buried oxide and silicon, which caused the break of weak Si-Si bonds and the production of positive silicon ions in the silicon-rich region of the buried oxide near the interface, and this conclusion is supported by the results of secondary ion mass spectrometry.

State-specific enhanced production of positive and negative ions of gaseous SiCl 4 and solid-state analogues following core-level excitation

We investigated dissociation dynamics of positive and negative ions of gaseous SiCl 4 and SiCl 4 adsorbed on Si(1 0 0) at ∼90 K following Cl 2 p core-level excitations. The Cl 2 p → 8 a 1 * excitation of SiCl 4/Si(1 0 0) leads to a significant enhancement of the yields of Cl + and Cl −. Excitation of Cl 2 p electrons to Rydberg orbitals near the Cl 2 p ionization thresholds of gaseous SiCl 4 enhances the production of anionic fragments Si − and Cl −.

The So-Called Positive Photo-Electric Emission (Inverse Effect) and the Reality of the Sub-Electron

A few observers have reported the discharge of positive electricity produced by ultra-violet light. Dember found that a metal plate exposed to ultra-violet light in vacuum had the power to communicate a positive charge to a receiving cylinder when the proper accelerating field was applied. His experiments have recently been repeated by DuBridge, who reports that Dember’s results can be entirely accounted for on the basis of the photo-electric effect produced on the collecting cylinder by scattered ultra-violet light against which no precautions had been taken. His conclusions are there is no measurable photo-electric production of either gaseous or metallic positive ions by the range of wave lengths emitted by the quartz mercury lamp. R. Bar and F. Luchsinger working with small particles of paraffin and selenium in a Millikan electron apparatus found that some of the particles showed the inverse effect, that is, they became charged negatively when illuminated by ultra-violet light. This has been construed by some workers as indicating the discharge of positive electricity. However, as these men were only using the ultra-violet light to charge up their particles in order to measure the charge communicated, and were not interested in the source of the photo-electric effect it is natural to assume that no special precautions were taken against the light striking the metallic plates of the condenser. The photo-electrons liberated from these metal surfaces being caught by the paraffin and selenium particles would make it seem as if the particles had lost a positive charge. S. Taubes, working in the same laboratory as Luchsinger and Bar and presumably with the same apparatus, reported this inverse effect when dealing with particles that had a large positive charge and showed that it is due to the photo-electrons given off by the condenser plates, for when these were coated with paraffin the inverse effect entirely disappeared. M. Hake, working at Vienna and using a diminutive Millikan electron apparatus designed by Professor Ehrenhaft, has recently reported results on nineteen different materials. He found that metals show both the inverse and the normal effect, depending on the gas in which the metal particles are suspended, and that some insulators, for example glycerine, always show the inverse effect in all gases. Wasser, working in the same laboratory as Hake gives results on mercury drops in N and CO2. He claims that drops of larger radius than 1.9 x 10-5 cm. always show the normal effect, that those between 1.1 and 1.9 x 10-5 cm. show both normal and the inverse effect, while those of smaller radius than 1.1 x 10-5 cm. always show the inverse effect. The following investigation was undertaken to test the correctness of the foregoing conclusions and to determine whether the changes in charge experienced by minute mercury droplets are of a magnitude corresponding to the electronic charge or to a charge smaller than this, as the Vienna physicists have maintained.