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Showing papers on "Ion published in 1982"


Journal ArticleDOI
TL;DR: In this article, a hybrid simulation model with kinetic ions, massless fluid electrons, and phenomenological resistivity is used to investigate the perpendicular configuration of the bow shocks of the earth and other planets.
Abstract: A hybrid simulation model with kinetic ions, massless fluid electrons, and phenomenological resistivity is used to investigate the perpendicular configuration of the bow shocks of the earth and other planets. The range of parameters investigated includes the upstream Mach number, electron and ion beta (ratios of thermal to magnetic pressure), and resistivity. It is found that electron beta and resistivity have little effect on the overall shock structure. Quasi-stationary structures are obtained at moderately high ion beta, whereas the shock is found to become more dynamic in the low ion beta, large Mach number regime. The simulation results are shown to agree well with a number of observational features of quasi-perpendicular bow shocks, including the morphology of the reflected ion stream, the magnetic field profile throughout the shock, and the Mach number dependence of the magnetic field overshoot.

465 citations


Journal ArticleDOI
TL;DR: In this article, a helios solar probe survey of solar wind helium ion velocity distributions and derived parameters between 0.3 and 1 AU is presented, where the role of Coulomb collisions in limiting differential ion speeds and the ion temperature ratio is investigated.
Abstract: A Helios solar probe survey of solar wind helium ion velocity distributions and derived parameters between 0.3 and 1 AU is presented. Distributions in high-speed wind are found to generally have small total anisotropies, with some indication that, in the core part, the temperatures are greater parallel rather than perpendicular to the magnetic field. The anisotropy tends to increase with heliocentric radial distance, and the average dependence of helium ion temperatures on radial distance from the sun is described by a power law. Differential ion speeds with values of more than 150 km/sec are observed near perihelion, or 0.3 AU. The role of Coulomb collisions in limiting differential ion speeds and the ion temperature ratio is investigated, and it is found that collisions play a distinct role in low-speed wind, by limiting both differential ion velocity and temperature.

396 citations


Journal ArticleDOI
TL;DR: In this article, the probability of post-ionization of field evaporated ions is predicted as a function of field strength for all elements of interest in field evaporation, based on a physically realistic model potential.

332 citations


Journal ArticleDOI
TL;DR: In this paper, the transport of neutral atoms and molecules in the edge and divertor regions of fusion experiments has been calculated using Monte-Carlo techniques using a pseudocollision method.

296 citations


Journal ArticleDOI
TL;DR: In this paper, the technology of broad-beam ion sources used in sputtering applications is reviewed, and the most frequently used discharge chambers are described, together with procedures for predicting performance.
Abstract: The technology of broad‐beam ion sources used in sputtering applications is reviewed. The most frequently used discharge chambers are described, together with procedures for predicting performance. A new, compact ion source is described. Ion acceleration is reviewed, with particular emphasis on recent low‐energy techniques. Some of these techniques include three‐grid, small‐hole two‐grid, and one‐grid ion optics. A new material for fabrication of high‐precision ion optics is silicon. Because no stresses are introduced with the etching techniques used, the finished grid can be held to very close tolerances. A recent innovation for sputtering applications is the use of Hall‐current acceleration. This technique uses a magnetic field interacting with an electron current to provide the accelerating electric field, thereby avoiding the usual space‐charge limit on ion current density that is associated with gridded optics. Electron emission is also reviewed, with new hollow cathodes promising improved lifetimes. The overall picture is one of greatly improved ion source capability, with particularly large improvements in low‐energy ion current densities.

243 citations


Journal ArticleDOI
TL;DR: In this article, the generation process of ion cyclotron waves (ICWs) and the acceleration of He+ ions up to suprathermal energies were investigated. And the convective growth rate was calculated by applying two different methods, both of which are based upon the measured proton fluxes.
Abstract: This work is a continuation of paper 1 (Young et al., 1981) and is devoted to the generation process of ion cyclotron waves (ICWs) and the acceleration of He+ ions up to suprathermal energies. Simultaneous measurements are used from the ion composition experiment (0 < E < 16 keV), the energetic particle experiment (24 < E < 3 300 keV), and the ULF wave experiment (0.2–10 Hz) on board the GEOS 1 and GEOS 2 spacecraft. General characteristics of the local time distribution of ICWs will be presented and compared with those of the thermal anisotropy of energetic protons and the He+ abundance. Further calculations of the convective growth rate are conducted by applying two different methods, both of which are based upon the measured proton fluxes. The generation conditions of the ICWs in the presence of He+ ions will be investigated and three possible explanations will be discussed: (1) enhanced convection growth rates, (2) lowering of the threshold for absolute instabilities, and (3) change of the ICWs ray path (laser-like effect). Finally, it is shown that the flux of suprathermal He+ ions is modulated at the ICW frequency. Owing to nonlinear effects, part of the energy of the energetic protons is transfered via the ICWs to the He+ ions that are essentially accelerated in the direction perpendicular to the static magnetic field. Then in the otherwise collisionless plasma the friction between energetic anisotropic protons and thermal He+ ions is achieved through the ICWs.

241 citations


Journal ArticleDOI
TL;DR: In this article, semi-empirical pseudopotentials are used in calculating the ground-state potentials curves for single valence-electron molecular ions, and very accurate results are obtained and a number of predictions given.

229 citations



Journal ArticleDOI
15 Oct 1982-Science
TL;DR: Fast atom bombardment mass spectrometry has become a powerful structural tool since the first reports of its use in 1981, and it can be especially valuable in determining the sequences of amino acids in polypeptides.
Abstract: Fast atom bombardment mass spectrometry has become a powerful structural tool since the first reports of its use in 1981. Samples are ionized in the condensed state, usually in a glycerol matrix, by bombarding the matrix with xenon or argon atoms with energies of 5000 to 10,000 electron volts. This yields both positive and negative secondary ions, which are sputtered from the surface. The technique has been used to detect inorganic ion clusters to mass 25,800 and biologically active peptides to mass 5700, and it gives molecular ions of such highly polar or labile organic compounds as glycosphingolipids and polyene antibiotics. It can be especially valuable in determining the sequences of amino acids in polypeptides.

210 citations


Journal ArticleDOI
TL;DR: In this article, a fluid type model that takes into account ion heating and acceleration by resonant wave-particle interactions is presented to explain the ion temperature anisotropies and differential speeds, as observed in solar wind high-speed streams.
Abstract: In order to explain the ion temperature anisotropies and differential speeds, as observed in solar wind high-speed streams, a fluid type model is presented that takes into account ion heating and acceleration by resonant wave-particle interactions. Ion-cyclotron and fast magnetosonic waves propagating away from the sun parallel to the interplanetary magnetic field are considered. The radial evolution of the spectral wave energy density and of the bi-Maxwellian model ion distributions is calculated self-consistently for a spherically symmetric solar wind geometry. Numerical results are given for the dependence on heliocentric radial distance for the ion parallel and perpendicular temperatures and ion speeds relative to their center of mass frame. The respective ion flow speeds in the inertial frame are also calculated, based on momentum equations that include the self-consistent temperature gradients. It is shown that transfer of wave momentum to the ions can lead to a preferential acceleration of the alpha particles with respect to the protons. Owing to the combined action of the ion cyclotron and magnetosonic waves, the alphas are accelerated to a differential speed of about the local Alfven speed in close accord with in situ observations. By damping of wave energy the heavier ions are also preferentially heated with the result that alpha particle thermal speeds become equal or slightly larger than proton thermal speeds. Typical signatures in ion temperature anisotropies (like Tp⊥ > Tp∥) as predicted by the model agree fairly well with the observations in fast streams. The results are discussed with respect to the effects of various boundary conditions and the inhomogeneity of the expanding solar wind plasma.

209 citations


Journal ArticleDOI
13 May 1982-Nature
TL;DR: In this paper, the structure of the Ca2+-D2O conformation as a function of concentration was studied. But the results of this study were limited to a single concentration of Ca2+.
Abstract: The ion Ca2+ is common in nature and has an important role in many biochemical processes1. However, the way in which this ion behaves in aqueous solution is the subject of much controversy. There are two structural parameters which are necessary for a fuller understanding of Ca2+ in solution: the number of water molecules to which Ca2+ coordinates in solution, n, and the configuration which a water molecule adopts relative to it (defined by Φ, the angle between the plane of the water molecule and the Ca–O axis and rCaO, the Ca–O separation). The technique of neutron diffraction in conjunction with isotopic substitution has been successful in giving unambiguous information regarding, n, Φ and r for a variety of aqueous solutions2. Studies have been carried out on Li+, Ni2+ and Cl− at several concentrations3 and Ca2+ at one concentration4. We report here the results of a study of the structure of the Ca2+–D2O conformation as a function of concentration.

Journal ArticleDOI
TL;DR: In this article, a simple parameterization of pressure ionization, discussed limitations of the Debye-Huckel model for plasma perturbations, and survey an approximate description of X-ray spectra based on the WKB approximation.
Abstract: Modern inertial-confinement fusion experiments subject matter to extreme physical conditions previously studied only in theoretical astrophysics. At very high plasma density, atomic energy states are significantly altered by electric fields of neighboring ions and by free electrons; the resulting phenomena of pressure ionization and continuum lowering may be analyzed with a sequence of models, each adding new subtleties to a complex picture. In this paper, we develop a simple parameterization of pressure ionization, discuss limitations of the Debye-Huckel model for plasma perturbations, and survey an approximate description of X-ray spectra based on the WKB approximation. WKB theory leads to a simple derivation of the screened hydrogenic model for plasma ionization and radiative properties. Electron eigenvalues are obtained from the total ion energy in agreement with Koopman's theorem, and the representation of spectral terms is improved by a new set of screening coefficients.

Journal ArticleDOI
TL;DR: In this article, gas phase ion clustering reactions were studied using high pressure mass spectrometry Equilibrium constants together with enthalpy, entropy, and free energy changes were determined for stepwise clustering reaction.
Abstract: Gas phase ion clustering reactions of the form A+(L)n+L⇄A +(L)n+1 were studied using high pressure mass spectrometry Equilibrium constants together with enthalpy, entropy, and free energy changes were determined for stepwise clustering reactions of water about the Ag+ ion with n=0 to5 and the Cu+ ion with n=2 to4, ammonia about the Ag+ and Cu+ ions from n=1 and n=2 to4, respectively, and pyridine about the Ag+ and H+ ion from n=2 and n=1 to 3, respectively These results, together with those of other studies, show evidence for the existence of structure in some cluster ions Considerations of bonding and entropy, together with comparisons with the results of ion chemistry in the liquid phase, suggest that such structures can be attributed to several types of cluster ion systems, including gas phase analogs of traditional ’’coordination complexes’’ known in the aqueous phase

Journal ArticleDOI
TL;DR: In this paper, the role of ions in film formation is discussed under three headings: the effect of inert gas ion bombardment after or during film formation, the impact of the kinetic energy of source material ions, and the effect effect of the charges of the ions.

Journal ArticleDOI
TL;DR: In this paper, two ion-transport mechanisms are described for ion transport in polyether-alkali metal salt complexes: an intrahelical jumping process along crystalline (helical) regions of the polymer, and a transport process in the amorphous regions which is dependent on formation of fourfold coordination sites via mutual motion of ether oxygens from two or more polymer chains.
Abstract: Two ion‐transport mechanisms are described for ion transport in polyether‐alkali metal salt complexes: an intrahelical jumping process along crystalline (helical) regions of the polymer, and a transport process in the amorphous regions which is dependent on formation of fourfold coordination sites via mutual motion of ether oxygens from two or more polymer chains. The intrahelical jumping process may exhibit Arrhenius behavior, while transport in the amorphous regions should behave like a configurational entropy dominated process, showing a temperature dependence like , where is the equilibrium glass transition temperature. For the highly crystalline poly(ethylene oxide) complexes, an Arrhenius behavior is observed to dominate, whereas for the amorphous polyether salt complexes the configurational entropy behavior is observed. Even for the highly crystalline complexes, however, amorphous regions separate the crystalline regions of the polymer, and segmental motion of the polymer chains is postulated to be crucial here as well. The models are consistent with the observed frequency‐dependent ionic conductivity, as well as spectroscopic, x‐ray, thermal, and physical characterization measurements. They provide a reasonable microscopic picture for ion motion and yield testable predictions concerning the dependence of the ionic conductivity on pressure, temperature, and crystallinity.

Journal ArticleDOI
TL;DR: In this article, the potential for high spatial resolution surface analysis of polymers via fingerprint mass spectra and the use of a focused ion beam was investigated using short chain hydrocarbon and films of polystyrene and polytetrafluoroethylene.
Abstract: Secondary ion mass spectrometry has the potential for high spatial resolution surface analysis of polymers via fingerprint mass spectra and the use of a focused ion beam. Several problems stand in the way of realizing this potential, namely: (a) the expected high rate of ion beam damage, (b) the need for charge neutralization leading to (c) the uncertainty of surface potential and (d) the possibility of electron stimulated desorption of secondary ions. The importance of these effects have been studied using a model short chain hydrocarbon and films of polystyrene and polytetrafluoroethylene.

Journal ArticleDOI
TL;DR: In this paper, thermal spike and Coulomb repulsion models for erosion in this temperature regime were discussed and the dependence of the low temperature erosion yield on electronic stopping power is nonlinear and approximately quadratic for light ions.

Journal ArticleDOI
TL;DR: In this article, the reorientation of crystallites in vapour-deposited thin metal films under ion bombardment and texture formation induced by ion beams during vacuum condensation are surveyed.

Journal ArticleDOI
TL;DR: In this paper, the effect of ion bombardment on film stress was studied by evaporating Nb thin films in the presence of a controlled ion beam from a Kaufman ion source, where films were deposited at 4 A/s by electron-beam evaporation with ion bombardment over the energy range 100-800 eV, at ion current densities of 0.001 to 1.1 mA/cm2.
Abstract: The effect of ion bombardment on film stress was studied by evaporating Nb thin films in the presence of a controlled ion beam from a Kaufman ion source. Films were deposited at 4 A/s by electron‐beam evaporation with ion bombardment over the energy range 100–800 eV, at ion current densities of 0.001 to 1.1 mA/cm2. Film stress was measured by an x‐ray bending‐beam technique on Si substrates. Stress values were found to depend strongly on both ion flux and sample temperature. For films deposited at 400 °C, film stress is tensile in the absence of ion bombardment. Increasing argon ion flux causes a change toward compressive stress, in some cases passing through zero. For films deposited at room temperature, film stress is compressive in the absence of ion bombardment, due to incorporation of oxygen. Argon ion bombardment causes a change toward tensile stress, correlating with an improvement in film purity by preferential resputtering of oxygen. With 100 eV argon ions, an ion‐to‐atom ratio of only 3–10 % is ...

Journal ArticleDOI
TL;DR: In this paper, the formation of negative hydrogen ions by scattering protons from a metal surface is described with two models: a probability model and an amplitude model, where the electron motion is described quantum mechanically and the nuclear motion classically.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrated the first post-ionization of neutral atoms sputtered from ion bombarded solids by multiphoton resonance ionization, which has been applied in the characterization of the chemistry and structure of solid surfaces and in the trace analysis of a wide variety of materials.

Journal ArticleDOI
TL;DR: The density functional theory for a system of ions and electrons having overall charge neutrality is presented in this paper, where the theory self-consistently determines the various pair-distribution functions, bound states, and the effective ion charge.
Abstract: The density-functional theory (DFT) for a system of ions and electrons having overall charge neutrality is presented. For a given temperature and free-electron density, the theory self-consistently determines the various pair-distribution functions, bound states, and the effective ion charge $\overline{Z}=Z\ensuremath{-}{n}_{b}$, where ${n}_{b}$ is the mean number of bound electrons per ion. With the use of a sufficiently large correlation sphere to represent the "physically relevant" part of the plasma, a Kohn-Sham-type Schr\"odinger equation is solved for the electrons. The density-functional equations for the ions reduce to a Gibbs-Boltzmann equation containing an effective ion-correlation potential. The latter is obtained from the hypernetted-chain equation. The electron exchange-correlation potential is obtained from quantum many-body theory. The method is applied to an electron-proton plasma (EPP) for a number of physical situations. The machine-simulation (MS) results in the classical one-component-plasma limit, as well as the standard "proton-in-jellium" results, are correctly recovered in suitable limits. The MS results for the EPP plasma are limited by classical approximations, but are found to be in reasonable agreement with our DFT results which are probably more well founded. A shallow $1s$-like bound state appears with increase of temperature or decrease of density. The proton-pair distribution function in the EPP shows the onset of short-range order only when $\ensuremath{\Gamma}\ensuremath{\gtrsim}5$ or more. The electron-proton distribution function is found to be relatively insensitive to the details of the ion distribution for the static properties studied in this paper.

Journal ArticleDOI
TL;DR: In this paper, a simple model relating the temperature dependence of the erosion yield to the formation and annealing of active surface states is proposed, and the dependence of this high temperature erosion process on ion mass, energy and angle of incidence is presented.


Journal ArticleDOI
TL;DR: In this paper, it was shown that large scale convection electric fields are responsible for substantial enhancements in the ion temperature at high latitudes, and that there is a clear relationship between large ion velocities and ion temperature enhancements.
Abstract: The Atmosphere Explorer C data base of ion temperature and ion drift velocities has been used to study the long recognized principle that large scale convection electric fields are responsible for substantial enhancements in the ion temperature at high latitudes. As had been indicated by various authors previously, the present study shows that there is a clear relationship between large ion velocities and ion temperature enhancements. Furthermore, with the help of a more quantitative study, it is found that, since ion heating is sensitive to the relative motion between the ion and neutral gases, the ion temperature and drift measurements can be used to extract neutral wind and neutral temperature information along the satellite track. From a study of several examples, it is concluded that the present approach can be used with varying degrees of accuracy for the diagnostic of thermospheric dynamical properties above 300 km when those properties are not measured directly. When neutral dynamical properties are measured, the approach could be used for a detailed study of the ion energy balance at high latitudes.

Journal ArticleDOI
TL;DR: In this article, high-resolution scanning electron microscopy has been used to observe the effects of self-ion bombardment on the topography of germanium surfaces and the observed effects can be qualitatively explained by the formation of large voids.
Abstract: High‐resolution scanning electron microscopy has been used to observe the effects of self‐ion bombardment on the topography of germanium surfaces. Holes (mean separation 400 A) appeared in the surface at doses above 2×1015 ions/cm2 (ion energy 50 keV). These enlarged with increasing ion dose and developed into a complex cell structure. This structure underwent no further gross change for doses above 1×1017 ions/cm2, where the mean cell diameter was ∼1200 A. The surface preparation was found to have no influence on the appearance of this cellular structure. Some specimens were fractured after bombardment to observe a section of the bombarded surface. A porous layer of thickness 2.5 times the projected range (Rp) was observed at doses just below those where changes in surface topography were first observed. At the highest dose (4×1017 ions/cm2) the thickness of this layer was 6Rp. The cellular surface structure was observed at all ion energies chosen so long as the energy deposited in the surface by the ion beam was kept below 0.5 W cm−2. The observed effects can be qualitatively explained by the formation of large voids. When these intersect the surface the effects of sputter etching and redeposition combine to enlarge the cell structure. At surface loadings above 0.6 W cm−2 different topographies were observed, as a consequence of the surface temperature exceeding the amorphous/crystalline transition temperature during bombardment.

Journal ArticleDOI
TL;DR: In this article, the laser photoelectron spectra of the negative ions Ni(CO);, n = 1-3, obtained with a fixed-frequency argon-ion laser operating at 488 nm are reported.
Abstract: Photoelectron spectra of the negative ions Ni(CO);, n = 1-3, obtained with a fixed-frequency argon-ion laser operating at 488 nm are reported. The spectra provide the electron affinities for this series, EA(Ni(CO)) = 0.804 0.012 eV, EA(Ni(CO),) = 0.643 & 0.014 eV, and EA(Ni(CO)3) = 1.077 f 0.013 eV. The symmetric C-0 vibrational frequencies for the neutral complexes are obtained from the spectra. Metal-carbonyl bond strengths for the neutral carbonyls, Ni(CO),, n = 1-4, are derived from these and other data. Electronic and geometric structure of ions and neutrals is also discussed. We report the laser photoelectron spectra of the nickel carbonyl ions, Ni(CO),-, n = 1-3. These data provide insight into the electronic and geometric structure of ion and neutral, yield carbonyl vibrational frequencies for the neutral, and, in conjunction with other data, provide the nickel-carbonyl bond energies for all the Ni(CO),, n = 1-4. Several techniques have been utilized to study both the nickel carbonyl ions and neutrals. The ions Ni(CO),-, n = 0-3, are all observed in the negative ion mass spectrum of Ni(CO),; they are produced by dissociative attachment of an electron to Ni(CO),, reaction 1.8 The Ni(CO),- ion is not bound with respect to loss of CO.8 Ni(C0)4 + e - Ni(C0); + (4 - n)CO (1) The appearance potentials, AP, of the ions in process 1 have been determined by Compton and Stockdale.8 These data provide the nickel carbonyl bond dissociation energies for the negative ions, as given by eq 2. D(Ni(CO),,--CO) = AP(Ni(CO),,-) - AP(Ni(CO),-) (2) The photochemistry of Ni(C0)3- has been studiedg using the techniques of ion cyclotron resonance spectroscopy (ICR). This molecule was observed to "photodisappear" when irradiated, with a threshold at about 2.0 eV and a peak at about 2.5 eV photon energy. The photoproduct was not conclusively identified; pro- duction of C1- with added CCll was observed and is probably an indication of electron detachment occurring, but this could not be quantified. Finally, the Ni(CO)3- ion has been produced by vacuum-UV photolysis of Ni(C0)4 isolated in an argon matrix, and identified by infrared spectroscopy.lOJ n = 0-3


Journal ArticleDOI
TL;DR: In this paper, Axner and Rubinszteinteintein-Dunlop discussed the fundamental mechanisms of laser-enhanced ionization and its application in the field of signal detection.
Abstract: Fundamental Mechanisms of Laser-Enhanced Ionization: The Production of Ions (O Axner & H Rubinsztein-Dunlop) Fundamental Mechanisms of Laser-Enhanced Ionization: Signal Detection (J Travis & G Turk) Analytical Performance of Laser-Enhanced Ionization in Flames (G Turk) Applications of Laser-Enhanced Ionization Spectrometry (R Green) Non Flame Reservoirs for Laser-Enhanced Ionization Spectrometry (N Zorov) Ions and Photons: Interplay of Laser-Induced Ionization and Fluorescence Techniques in Different Atomic and Molecular Reservoirs (N Omenetto & P Farnsworth) Index

Journal ArticleDOI
TL;DR: In this article, a series of single-particle detectors for the detection of ions with keV energies has been built and investigated by experiment and by computer simulation, where the incident ions hit a converter electrode and produce secondary electrons which are accelerated onto the funnel of a channel electron multiplier (CEM).
Abstract: A series of three single‐particle detectors for the detection of ions with keV energies has been built and investigated by experiment and by computer simulation. The incident ions hit a converter electrode and produce secondary electrons which are accelerated onto the funnel of a channel electron multiplier (CEM). Experimental information was obtained for secondary electron yields, γ, of slow multiply charged ions and the influence of γ on the detector efficiency e is discussed. Efficiencies e near unity have been achieved for ions incident on an effective area of more than 20 mm diameter. e is greater than 90% for all ions and for count rates up to 3×104 s−1. The performance at higher count rates can probably be improved with a CEM of lower resistance.