Showing papers on "Ion published in 1984"

Electrospray ion source: another variation on the free-jet theme

Abstract: Solutions passed through a small capillary at 2-10 kV relative to ground are electrosprayed into a bath gas to form a gaseous dispersion of ions that is expanded into vacuum in a small supersonic free jet A portion of the jet is passed through a skimmer to form a molecular beam that contains a variety of ionic species Mass spectrometric analysis reveals that these species include solute cations in aggregation with solvent molecules and/or nonionized solute species The nature of the product ions depends upon the composition and feed rate of the original solution, the temperature and composition of the bath gas, and the voltage applied to the capillary The exploratory experiments reported here suggest that this novel ion source may be useful for producing in vacuo a wide variety of cluster ions for examination by various spectroscopic techniques Also inviting is the prospect of extending the applicability of mass spectrometric analysis to large organic molecules that are too complex, too fragile, or too nonvolatile for ionization by more conventional methods Another intriguing possibility is to use the technique on probing the microscopic structure and properties of solutions

Negative ion production with the electrospray ion source

Abstract: Solution passed through a small capillary tube at several kilovolts relative to its surroundings is electrosprayed into a bath gas at slightly above atmospheric pressure to form a dispersion of ions that expands into vacuum through a small sonic orifice. A portion of the resulting supersonic free jet passes through a skimmer carrying ions into a quadrupole mass spectrometer. Previously reported results were obtained with positive ions formed when the capillary was at a positive potential. The present report concerns operation with the capillary at a negative potential to produce negative ions. As in the case of operation in the positive mode ions with varying degrees of solvation can be obtained from a variety of solute species including complex and nonvolatile organic molecules. No fragmentation of parent species is observed as long as electrical discharge is avoided in the gas phase. The presence of electron scavengers in the bath gas raises the potential at which discharge phenomena begin. Differences and similarities relative to operation in the positive mode are discussed.

Effects of energetic heavy ions on electromagnetic ion cyclotron wave generation in the plasmapause region

Abstract: An expression for electromagnetic ion cyclotron convective growth rates is derived. The derivation of the dispersion relation and convective growth rates in the presence of a multicomponent energetic and cold plasma is presented. The effects that multiple heavy ions in the ring current and cold plasma produce in the growth and propagation characteristics of ion cyclotron waves are explored. Results of growth rate calculations using parameters consistent with conditions in the plasmapause region during the early recovery phase of geomagnetic storms are presented and compared with ground-based and satellite observations of waves in this region. The geophysical implications of the results are discussed.

Determination of plasma-ion velocity distribution via charge-exchange recombination spectroscopy

Abstract: Spectroscopy of line radiation from plasma impurity ions excited by charge-exchange recombination reactions with energetic neutral beam atoms is rapidly becoming recognized as a powerful technique for measuring ion temperature, bulk plasma motion, impurity transport, and more exotic phenomena such as fast alpha particle distributions. In particular, this diagnostic offers the capability of obtaining space- and time-resolved ion temperature and toroidal plasma rotation profiles with relatively simple optical systems. Cascade-corrected excitation rate coefficients for use in both fully stripped impurity density studies and ion temperature measurements have been calculated to the principal ..delta..n = 1 transitions of He+, C/sup 5 +/, and O/sup 7 +/ with neutral beam energies of 5 to 100 keV/amu. A fiber optically coupled spectrometer system has been used on PDX to measure visible He/sup +/ radiation excited by charge exchange. Central ion temperatures up to 2.4 keV and toroidal rotation speeds up to 1.5 x 10/sup 7/ cm/s were observed in diverted discharges with P/sub INJ/ less than or equal to 3.0 MW.

Ion-exchange selectivity of Nafion films on electrode surfaces

Abstract: : Films of 1100 EW Nafion were coated onto glassy carbon electrode surfaces and these chemically modified electrodes were used to characterize the ion exchange selectivity of the polymer. This was accomplished by allowing electrodes to equilibrate with solutions of various electroactive counterions and then determining the quantity of ion incorporated into the films coulometrically. These data were used to calculate both ion exchange partition and selectivity coefficients. Ion exchange selectivity coefficients (vs. Na(+)) for hydrophobic, organic counterions were very large (10,000 to 6 x 6,000,000) confirming earlier work which suggested that Nafion preferentially incorporates such counterions. The implications of this unusual ion exchange selectivity to electroanalysis are discussed. (Author)

A Universal Relation for the Sputtering Yield of Monatomic Solids at Normal Ion Incidence

Abstract: The sputtering yield of polycrystalline monatomic solids at normal incidence show a universal behaviour for light and heavy ions in the threshold regime. For heavy ions at higher energies a similar behaviour has been explained, based on first principles. In this work a relation is derived valid for both of these energy regimes. The relation is based on reasonable assumptions for the momentum distribution of the recoil target atoms and on the usual emission condition (planar surface potential). A “surface correction” — important for light ion sputtering — is also introduced. It is shown that experimental data for light ion sputtering at higher energy are also in good agreement with this relation.

Cation‐Vacancy Model for MnO2

Abstract: A cation‐vacancy model for electrochemically active manganese dioxides ( and ) is presented According to this model, the crystal structure, composed of closely packed O2− ions which are octahedrically coordinated to Mn4+ ions, the octahedra sharing edges and corners, contains Mn vacancies Each vacancy is coordinated to, and electrostatically compensated by, four protons The protons are present in the form of OH− ions, these latter replacing O2− in the lattice, without noticeable change in lattice parameters Many hitherto unexplained phenomenological and experimental facts, relating to chemical composition (water content), density, electrochemical capacity, proton‐transfer rate, electronic conductivity, and electrode potential of , can be reconciled, and quantitatively predicted, on the basis of the present theory In particular, electrochemical reactivity of in battery electrodes is shown to be due to the presence of cation vacancies in the lattice

Ion Acoustic Soliton in Plasma with Negative Ion

Abstract: Ion acoustic solitons are investigated theoretically in a plasma composed of electron, positive ion and negative ion. Due to the presence of negative ion, the property of the ion acoustic soliton is drastically modified. At the critical density of the negative ion, the nonlinear coefficient of the Korteweg-de Vries equation vanishes and then the ion acoustic wave is described by the modified Korteweg-de Vries equation. The transition from the Korteweg-de Vries soliton to the modified Korteweg-de Vries soliton is also studied by means of an evolution equation with quadratic and cubic nonlinearities.

Diffuse ions produced by electromagnetic ion beam instabilities

Abstract: The evolution of the electromagnetic ion beam instability driven by the reflected ion component backstreaming away from the earth's bow shock into the foreshock region is studied by means of computer simulation. The linear and quasi-linear stages of the instability are found to be in good agreement with known results for the resonant mode propagating parallel to the beam along the magnetic field and with theory developed in this paper for the nonresonant mode, which propagates antiparallel to the beam direction. The quasi-linear stage, which produces large amplitude delta B approximately B, sinusoidal transverse waves and 'intermediate' ion distributions, is terminated by a nonlinear phase in which strongly nonlinear, compressive waves and 'diffuse' ion distributions are produced. Additional processes by which the diffuse ions are accelerated to observed high energies are not addressed. The results are discussed in terms of the ion distributions and hydromagnetic waves observed in the foreshock of the earth's bow shock and of interplanetary shocks.

Modification of the optical and structural properties of dielectric ZrO2 films by ion‐assisted deposition

Abstract: Low‐energy bombardment by argon and oxygen ions has been used in the deposition of thin dielectric films of ZrO2. The film packing density has been improved from 0.83 to unity with a corresponding increase in the refractive index from 1.84 to 2.19. The highest stable refractive index measured was 2.23 for oxygen ion‐assisted deposition of ZrO2 on a substrate heated to 300 °C. Ion bombardment during condensation of evaporated ZrO2 on a room temperature substrate results in crystallization into the cubic phase which is consistent with previous studies of ion impact crystallization by thermal‐spike processes. At elevated substrate temperatures the monoclinic phase is also present.

Influence of chemical driving forces in ion mixing of metallic bilayers

Abstract: The effective interdiffusion coefficient of metallic bilayers under ion irradiation has been correlated with the heat of mixing of corresponding binary alloys. The results are interpreted according to Darken's theory of chemically enhanced diffusion.

Attachment coefficients for the reactions of electrons with CCl4, CCl3F, CCl2F2, CHCl3, Cl2 and SF6 determined between 200 and 600 K using the FALP technique

Abstract: The rate coefficients, beta , for the attachment reactions of electrons with CCl4, CCl3F, CCl2F2, CHCl3, Cl2 and SF6 have been measured under truly thermal conditions over the approximate temperature range 200-600K using a flowing-afterglow/Langmuir probe apparatus. The beta values obtained at 300K are 3.9*10-7, 2.6*10-7, 3.2*10-9, 4.4*10-9, 2.0*10-9 and 3.1*10-7 cm3 s-1 respectively. From the variation with temperature of beta for the CCl2F2, CHCl3 and Cl2 dissociative attachment reactions, activation energies, Ea, of 0.15, 0.12 and 0.05 eV respectively were derived. The beta for CCl4, CCl3F and SF6 are close to their theoretical limiting values within the temperature range investigated. While Cl- was the only product ion observed for the reactions involving chlorine-containing molecules, both SF6- and SF5- were observed for the SF6 reaction. The data obtained are compared with previous data and the separate influences of electron temperature and gas temperature are noted.

Monte Carlo determination of the distribution of ions about a cylindrical polyelectrolyte

Abstract: We report a calculation of the distribution of small ions around a charged cylinder representing a polyelectrolyte molecule in solution. The Monte Carlo method of Metropolis, Rosenbluth, and Teller was used to avoid the inaccuracies known to be associated with the Poisson-Boltzmann equation. The systems examined contained a long polyelectrolyte cylinder with charge parameter, χ, equal to 4.2, corresponding approximately to a DNA molecule. In one model, the cylinder had charges on its axis and an exclusion radius to the center of the small ions equal to 10 A, while the small ions had various radii in the range from 1 to 10 A and one or two protonic charges. Various systems were studied; some had one species of small ion alone, others had mixtures of different types. The results showed good agreement with the solution of the Poisson-Boltzmann equation when only the species with 1-A radius was present, but considerable discrepancies appeared with larger ions as a result of excluded volume interactions between the latter. Deviations from the Poisson-Boltzmann equation also appeared when both positive and negative small ions were present; the deviations were in the direction of a higher concentration of both counter- and co-ions, but particularly co-ions, close to the polyelectrolyte. In another model, the charges were arranged along two helices on the surface of the cylinder; the resulting radial distribution of small ions was not much different from that found when the charges were situated on the axis. In all cases there was a striking accumulation of counterions in a layer of concentration exceeding 1 mol/L at the surface of the polyion.

Relaxation of solvent protons by paramagnetic ions and its dependence on magnetic field and chemical environment: implications for NMR imaging.

Abstract: Paramagnetic ions have been used to alter the magnetic relaxation rates 1/T1 and 1/T2 of solvent water protons since the first observations of a proton resonance signal almost four decades ago. The earliest theories of relaxation indicated that the influence of solute paramagnetic ions on relaxation rates of solvent protons should depend both on the chemical environment of the solute ions and on the magnetic field strength. Much knowledge, both experimental and theoretical, has since been amassed regarding relaxation effects in solutions of hydrated ions (aquoions) and of complexes of these ions with macromolecules, mainly proteins. The phenomena are well understood at this point, though the understanding is more retrospective than predictive for ion-protein complexes. Nonetheless, from what is now known about homogeneous solutions, and from current reports on the introduction of paramagnetic ions into tissue to alter contrast in NMR images by affecting relaxation rates, it is clear that the solution results are particularly germane, and transferable, to tissue investigations. The main features of relaxation of solvent protons in the presence of solute paramagnetic ions, as hydrated aquoions and complexed with protein, are presented here, with attention to those ions most relevant to in vivo studies, and with emphasis on the influence of the magnetic field and the chemical environment of these ions on solvent proton relaxation rates.

Ion–surface interactions during thin film deposition

Abstract: The interactions of ion beams with surfaces are strongly dependent on the incident kinetic energy and the amount of ionic charge. Fundamental effects of ion bombardment by atomic and cluster ion beams have been elucidated in terms of kinetic energy of the ion beams. These fundamental effects include enhancement of adatom migration, desorption of physically absorbed atoms, displacement of the surface atoms, sputtering, shallow ion implantation, and trapping of impinging atoms. The importance of low energy ion beams for film formation is shown by taking into account the binding energies of the atoms in a solid. Emphasis has been placed on interactions of ionized cluster beams (ICB) during film formation because ICB offers unique capabilities for deposition due to the properties of the clusters and also to characteristic low energy ion beam transport over a range from thermal energy to a few hundred eV.

Ion‐neutral coupling in the high‐latitude F region: Evaluation of ion heating terms from Dynamics Explorer 2

Abstract: Ion and neutral motions in the high latitude F layer were studied simultaneously during six passes of the Dynamics Explorer 2 spacecraft. The passes were made over the south polar cap in October 1981. An ion energy balance equation was defined to express the exchange of energy between the F layer and other atmospheric constituents. A momentum equation expressed the momentum exchange between the species. An approximate form of the energy balance equation was also formulated. The time constant for ion-neutral collisional momentum transfer significantly affected Joule heating in the F layer. Regions of large velocity disparities and ion temperature enhancements were detected as hot spots. The results indicate that a feedback mechanism may arise in terms of neutral compositional changes and enhanced ionospheric recombination. The approximate equation furnished values for ion heating rates which matched the data.

Plasma sheath transmission factors for tokamak edge plasmas

Abstract: Simple analytic relations are derived for the floating potential of a solid object in contact with a magnetized plasma as a function of the electron/ion mass ratio, the electron/ion temperature ratio, and the secondary electron emission coefficient. Simple analytic relations are also obtained for the sheath transmission factors, i.e., the particle and energy fluxes to floating and nonfloating surfaces. These analytic formulations, derived from a fluid model treatment of ion flow, are found to give results in close agreement with results derived from more complex analysis based on kinetic theory and numerical models. Tokamak scrape‐off plasmas are often characterized by ion distributions which have finite drift velocities at the point where the ions enter the scrape‐off plasma from the main plasma (via cross‐field diffusion). The Bohm criterion governing the drift velocity of ions as they enter the electrostatic sheath in front of a limiter, divertor plate, or probe is generalized for this case.

Electron attachment to the perfluoroalkanes n‐CNF2N+2 (N=1–6) using high pressure swarm techniques

Abstract: The electron attachment rate constants and negative ion formation mechanisms for six perfluoroalkanes [n‐CNF2N+2(N=1–6)] have been studied in a high pressure swarm experiment within the mean electron energy range from thermal energy (≊0.04 eV) to ≊4.9 eV. These experiments were performed over a total gas number density range of 3.2×1019 to 3.9×1020 cm−3 using N2 and argon as buffer gases. Dissociative electron attachment was found to be the only negative ion formation process for CF4 and C2F6. For C3F8, n‐C4F10, and n‐C5F12 the electron attachment rate constant measurements exhibited a large total pressure dependence which was strongest for C3F8 and decreased with increasing size of the perfluoroalkane molecule. These measurements have been interpreted as electron attachment by parent negative ion formation due to three‐body stabilization processes of the initially excited, short‐lived (5×10−11 s <τ<10−8 s) parent anion. The lifetimes of these transient parent anions have been found to depend on the natur...

Apparatus and methods for ion implantation

Abstract: A system for implanting ions into a target element including a source arrangement for producing an ion beam; a beam analyzing arrangement for receiving the ion beam and selectively separating various ion species in the beam on the basis of mass to produce an analyzed beam; and a beam resolving arrangement disposed in the path of the analyzed beam for permitting a preselected ion species to pass to the target element. The analyzing arrangement has an ion dispersion plane associated therewith. The source arrangement has an associated ion emitting envelope including an area of substantial extension in a plane parallel to the ion dispersion plane and producing ions entering said analyzing arrangement which are travelling substantially either toward or from a common apparent line object lying in a plane perpendicular to the ion dispersion plane.

Observation of Ion-Acoustic Rarefaction Solitons in a Multicomponent Plasma with Negative Ions

Abstract: The propagation of ion-acoustic solitons in a plasma with negative ions has been observed. For sufficiently large concentration of negative ions, applied rarefactive (negative) voltage pulses break up into solitons, whereas compressive pulses evolve into wave trains, with exactly the opposite behavior as that for a plasma composed only of positive ions. There is a critical value of the negative-ion concentration for which a finite-amplitude pulse propagates without steepening.

Californium-252 plasma desorption time of flight mass spectroscopy of proteins

Abstract: Fast heavy ions, i.e. fission fragments from a 252Cf-source, have been used to desorb and ionize peptides and proteins from a sample surface. Masses of the desorbed ions have been determined by the time-of-flight technique. The mass interval of the molecules studied is 1000-14 000 u. Quasi-molecular ions of higher masses than earlier reported have been observed. The results include the detection of quasi-molecular ions of proinsulins, cytochrome-C, ribonuclease and two phospholipases. The general features of mass spectra of proteins using this ionization method are described. Emphasis is put on the discussion of metastable ion decay, neutral components, multiply charged ions, isotopic broadening, and cluster ion formation. Also the precision which can be obtained with a straight time-of-flight mass spectrometer will be discussed. Future applications of the technique are outlined.

Direct evidence for two-stage (bimodal) acceleration of ionospheric ions

Abstract: Energetic ion composition spectrometer data gathered on hybrid conical ion distributions by the Dynamics Explorer 1 in the topside ionosphere are reported. The observed ion distributions were field-aligned and upward flowing, with energies up to 5 keV. Increases in ion energy were accompanied by a departure from field-alignment and a cone patterned upward flow, with the apex in the auroral field lines and the cone angle widening upward as the energy increased. Both transverse and parallel accelerations were imparted to the ions, with the transverse heating occurring in a 5000 km extent region centered at 18,000 km altitude. A bi-Maxwellian distribution, a temperature of 1.2 keV and a 260 eV parallel temperature were found at the top of the region.