Showing papers on "Ion published in 1969"
TL;DR: In this article, an integrodifferential equation for the sputtering yield is developed from the general Boltzmann transport equation, and solutions of the integral equation are given that are asymptotically exact in the limit of high ion energy as compared to atomic binding energies.
Abstract: Sputtering of a target by energetic ions or recoil atoms is assumed to result from cascades of atomic collisions. The sputtering yield is calculated under the assumption of random slowing down in an infinite medium. An integrodifferential equation for the yield is developed from the general Boltzmann transport equation. Input quantities are the cross sections for ion-target and target-target collisions, and atomic binding energies. Solutions of the integral equation are given that are asymptotically exact in the limit of high ion energy as compared to atomic binding energies. Two main stages of the collision cascade have to be distinguished: first, the slowing down of the primary ion and all recoiling atoms that have comparable energies---these particles determine the spatial extent of the cascade; second, the creation and slowing down of low-energy recoils that constitute the major part of all atoms set in motion. The separation between the two stages is essentially complete in the limit of high ion energy, as far as the calculation of the sputtering yield is concerned. High-energy collisions are characterized by Thomas-Fermi-type cross sections, while a Born-Mayer-type cross section is applied in the low-energy region. Electronic stopping is included when necessary. The separation of the cascade into two distinct stages has the consequence that two characteristic depths are important for the qualitative understanding of the sputtering process. First, the scattering events that eventually lead to sputtering take place within a certain layer near the surface, the thickness of which depends on ion mass and energy and on ion-target geometry. In the elastic collision region, this thickness is a sizable fraction of the ion range. Second, the majority of sputtered particles originate from a very thin surface layer (\ensuremath{\sim}5 \AA{}), because small energies dominate. The general sputtering-yield formula is applied to specific situations that are of interest for comparison with experiment. These include backsputtering of thick targets by ion beams at perpendicular and oblique incidence and ion energies above \ensuremath{\sim}100 eV, transmission sputtering of thin foils, sputtering by recoil atoms from $\ensuremath{\alpha}$-active atoms distributed homogeneously or inhomogeneously in a thick target, sputtering of fissionable specimens by fission fragments, and sputtering of specimens that are irradiated in the core of a reactor or bombarded with a neutron beam. There is good agreement with experimental results on polycrystalline targets within the estimated accuracy of the data and the input parameters entering the theory. There is no need for adjustable parameters in the usual sense, but specific experimental setups are discussed that allow independent checks or accurate determination of some input quantities.
2,552 citations
TL;DR: The influences on ion energy of membrane thickness, ion-pair formation, “pores” and “carriers” have been estimated and it is shown that only “ pores" and "carriers" lower the energy barrier significantly.
Abstract: The influences on ion energy of membrane thickness, ion-pair formation, “pores” and “carriers” have been estimated. Only “pores” and “carriers” lower the energy barrier significantly.
778 citations
TL;DR: In this article, the authors examined radially by dc arcs drawn in a vacuum ambient on cathodes of several elements, as well as the axial (through-anode) ion flux from a copper cathode.
Abstract: We have examined the particles emitted radially by dc arcs drawn in a vacuum ambient on cathodes of several elements, as well as the axial (through‐anode) ion flux from a copper cathode. The axial results for copper agree grossly with the radial copper results. Significant quantities of multiply charged ions were seen for all elements examined. All arc volt‐ampere characteristics were positive in the range of currents observed: 30 to 250 A. We drew the following conclusions (normalizing energy in units of ion energy/ion charge): (1) The energy distributions for the various ions are similar, peaking at potentials well above the arc voltage. (2) The fraction of ions that are singly charged tends to increase with increasing arc current. (3) For a given element, as the degree of ionization increases the location of the ion‐energy distribution peak shifts to lower energies. (4) For a given degree of ionization, the location of the peak tends toward higher energies for elements with greater arc voltages. (5) Th...
532 citations
525 citations
TL;DR: This chapter describes the experimental and analytical techniques that have been developed for flowing afterglow applications to the quantitative study of ion–neutral reaction processes, and the dc discharge was found to be advantageous.
Abstract: Publisher Summary This chapter describes the experimental and analytical techniques that have been developed for flowing afterglow applications to the quantitative study of ion–neutral reaction processes. Most other techniques for the measurement of ion–molecule reaction rate constants are inherently unsuited for the examination of an ion reacting with a neutral where the neutral has the lower ionization potential, and sufficient data for this generalization did not exist prior to the flowing afterglow results. Charge transfer reactions of negative ions have sometimes been useful in establishing relative electron affinities of molecules, which are often difficult to measure. Positive ion charge-transfer reactions have, on occasion, been useful in establishing relative ionization potentials of molecules, generally known or better measured in more direct ways. The dc discharge had other advantages over the microwave discharge as well. Its geometrical configuration was more compatible with the detailed flow analysis, and it was more easily incorporated in metal flow tubes, which were soon found to be advantageous.
408 citations
TL;DR: Ionization equilibrium and radiative cooling of high temperature low density plasma, noting cosmic gas cooling curve of line emission from oxygen ion transitions, were discussed in this paper, where the authors also showed that the line emission of oxygen ion transition can be seen as a sign of low-density plasma.
Abstract: Ionization equilibrium and radiative cooling of high temperature low density plasma, noting cosmic gas cooling curve of line emission from oxygen ion transitions
395 citations
283 citations
TL;DR: Potassium conductance-voltage curves have been determined for a squid axon in high external potassium solution for a wide range of divalent cation concentrations, and the best value for charge density was found to be one electronic charge per 120 square angstroms, and a lower limit to be two electronic charges per 280 squareAngstroms.
281 citations
TL;DR: A compilation of ionization and appearance potentials of positive ions published from 1955 through June 1966 can be found in this article, where the heat of formation at 298 K of the positive ion has been computed using auxiliary thermochemical data.
Abstract: This is a compilation of ionization and appearance potentials of positive ions published from 1955 through June 1966. The compilation lists the ion formed, the parent species from which it was formed, the other products of the process, the threshold energy for the formation of this ion, and the method by which this data was obtained. Where feasible, the heat of formation at 298 K of the positive ion has been computed for each entry using auxiliary thermochemical data. From these computed values “best” values have been chosen.
261 citations
259 citations
TL;DR: The theoretical current-voltage curve agrees satisfactorily with the experimental data at a low ionic strength and at low voltages; at higher voltages the observed membrane conductance exceeds the predicted value.
01 Jan 1969
Journal Article•
TL;DR: In this article, the attachment of low-energy electrons (<4 eV) by the reaction e+N2O→ O−+n2 has been studied as a function of gas temperature from approximately 160 to 1040°K.
Abstract: The attachment of low‐energy electrons (<4 eV) by the reaction e+N2O → O−+N2 has been studied as a function of gas temperature from approximately 160 to 1040°K. The ions produced by a monoenergetic electron beam are detected by total ion collection or by mass analysis. The kinetic energy distributions of the O− ions have also been measured and found to be relatively insensitive to the electron energy when the latter exceeds 1.5 eV, in which case the most probable ion energy is 0.38 eV. The shape and magnitude of the cross section below 2 eV is found to be sensitive to gas temperature throughout the range studied. The differences in shape and threshold observed by previous workers occur below 2 eV and to a large extent may be reconciled in terms of the differing gas temperatures employed. The temperature insensitive portion of the cross section is ascribed to electron capture into the highest‐energy N2O− state connected to electronic ground state N2 + O−. The O− kinetic energy distributions arising therefr...
TL;DR: In this paper, the formation of the observed water cluster ions H3O+, H5O2+, H7O3+, etc. in the D region of the earth's ionosphere has been studied.
Abstract: Laboratory studies of the ions produced by the addition of water vapor into flowing streams of O2+ (or NO+) ions have led to a vapor phase reaction scheme starting with O2+ that seems likely to be responsible for the formation of the observed water cluster ions H3O+, H5O2+, H7O3+, etc. in the D region of the earth's ionosphere. Experimental difficulties have precluded quantitative rate constant measurements so far, and in addition the D-region water vapor concentration is uncertain so that only a qualitative scheme is possible at this time. The O2(¹Δg) photoionization source recently proposed by Hunten and McElroy is presumed to be the necessary precursor O2+ source. The reaction scheme involves O4+ and O2+·H2O as intermediate ions; these ions are possibly present in observable concentrations in the D region. Nitrous acid (HNO2) production is proposed to be an end result of successive hydrations of atmospheric NO+. The hydration of the atmospheric NO+ and O2+ ions and the formation of O4+ are expected to increase somewhat the effective electron recombination coefficient in the ionosphere.
TL;DR: In this paper, the ion microprobe mass analyzer accomplishes the chemical analysis of a microvolume of a solid sample by sputtering ions from its surface with a high-energy beam of bombarding ions.
TL;DR: In this article, a simple model was constructed which illustrates the origin of ionic space charge regions at surfaces of the AgCl and NaCl types, by considering explicitly the binding states of ions on surfaces and the surface density of such states.
TL;DR: In this article, the electron-ion and ion-ion recombination processes of importance in the upper atmosphere are considered, and available laboratory experimental and theoretical information concerning the relevant processes is discussed.
Abstract: The electron–ion and ion–ion recombination processes of importance in the upper atmosphere are considered, and available laboratory experimental and theoretical information concerning the relevant processes is discussed. For atomic ions the principal electron–ion recombination process is radiative, with theory indicating that the two-body coefficient at ∼200 °K is ∼10−11 cm3/s and decreases with increasing electron temperature. Microwave afterglow/mass spectrometer studies of diatomic ionospheric ions (e.g. NO+, O2+, and N2+) show a loss by dissociative recombination with a coefficient substantially in excess of 10−7 cm3/s at 250 °K and decreasing with increasing electron and ion temperature. There is some evidence from flame studies that H3O+ ions exhibit a very large coefficient (10−6–10−5 cm3/s) at 300 °K. Ion–ion recombination evidently proceeds by mutual neutralization, with laboratory studies of ions such as NO+ and NO2− indicating a two-body coefficient of the order of 10−7 cm3/s at 300 °K. In the ...
TL;DR: In this article, simple models for tunneling from the valence band and from non-interacting molecules are derived and applied to these systems and the experimental data applied to Ar yielded a bandgap of 13 eV, in excellent agreement with theoretical and optical measurements.
Abstract: Field ionization in liquid H2, Ar, He, N2, and O2 has been studied and approximate mobilities obtained for the respective positive ions. In the case of He, field ionization leads to charge multiplication because of sufficient ion acceleration in the high‐field region near the emitter. In the case of H2 and Ar linear lni or lni / V vs 1 / V plots could be obtained at low currents, indicating that current generation was controlled by tunneling. Simple models for tunneling from the valence band and from noninteracting molecules are derived and applied to these systems. For the experimental data applied to Ar the band model yielded a bandgap of 13 eV, in excellent agreement with theoretical and optical measurements. For H2 the noninteracting molecule and the band model give equally reasonable results.
TL;DR: In this article, the optical properties of cerium-activated garnet crystals have been investigated, and the wavelength maxima of the fluorescence-spectrum profiles are found to be host-dependent.
Abstract: The optical properties of cerium-activated garnet crystals have been investigated. In the garnet crystals showing luminescence, a bright-yellow fluorescence has been observed. The fluorescence exhibits structure at low temperatures, and the wavelength maxima of the fluorescence-spectrum profiles are found to be host-dependent. Energy transfer has been observed from the cerium ion to the neodymium ion.
TL;DR: In this article, the potential constants FO−O,LiO 2,LiO 3,FLi−O and FLi-O were derived from six isotopic molecules, and the oxygen−oxygen force constant for LiO 2 coincides with that calculated for O2−, suggesting that the LiO2 molecule is highly ionic and may be considered as a lithium cation bonded to a superoxide anion by Coulombic forces.
Abstract: Lithium superoxide has been synthesized by reacting lithium atoms and oxygen molecules at high dilution in inert and oxygen matrices. Isotopic substitution at all atomic positions and use of isotopic mixtures verify the molecular identity and indicate an isosceles triangular structure. Eighteen frequencies from six isotopic molecules determine the potential constants FO–O = 5.59 ± 0.05, FLi–O = 1.18 ± 0.02, and FLi–O,Li–O = − 0.21 ± 0.03 mdyn / A. The oxygen–oxygen force constant for LiO2 coincides with that calculated for O2−, which suggests that the LiO2 molecule is highly ionic and may be considered as a lithium cation bonded to a superoxide anion by Coulombic forces.
TL;DR: In this paper, structural measurements of Si and Ge were compared and interpreted in terms of the annealing of identified defects, and it was shown that the center temperatures for both Ge and Si were approximately 0.35 and 0.5 times the melting temperature.
Abstract: Structural measurements of neutron and ion damage annealing in Si and Ge are compared and interpreted in terms of the annealing of identified defects. Either or both of two prominent isochronal annealing stages above room temperature in neutron irradiated Si are exhibited by X-ray, electron microscope, infrared, and electrical measurements. It is shown that the same two annealing stages are observed in Rutherford scattering measurements of ion implanted Si. Two similar prominent annealing stages are also observed for structural measurements of neutron and ion irradiated Ge. For both Ge and Si the center temperatures for the two annealing stages are approximately 0.35 and 0.5 times the melting temperature. The annealing kinetics and activation energies for the lower temperature stage in Si are correlated with the kinetics and activation energies obtained by analyzing previously reported results on the effects of the substrate temperature and the ion irradiation rate. From a comparison of the time ...
TL;DR: A nuclear magnetic resonance survey has been undertaken in order to gain a better insight into the nature of the complex species present in aqueous solutions of the rare earth ions as discussed by the authors, showing that the shifts observed in solutions of perchlorate salts are due to a single hydrated species persisting over a wide range of concentrations.
Abstract: A nuclear magnetic resonance survey has been undertaken in order to gain a better insight into the nature of the complex species present in aqueous solutions of the rare‐earth ions Oxygen‐17 and proton chemical shifts of water are reported and the effects of concentration and added anions upon them discussed Nuclear magnetic resonance evidence is presented, showing that the shifts observed in solutions of the perchlorate salts are due to a single hydrated species persisting over a wide range of concentrations and that no “inner‐sphere” complex is formed with perchlorate It appears, also, that all the water molecules in the first solvation shell are equivalent with respect to their contribution to the shift, owing to their relatively short residence time The sign, magnitude, and temperature dependence of the oxygen‐17 shifts as contrasted to those of protons support the suggestion that the former are mainly due to contact interaction, whereas the latter are dominated by dipolar interaction with the unpaired electrons of the rare‐earth ions Examination of the chemical shifts of nuclei of the anions unequivocally demonstrates that “inner‐sphere” complexes are formed with nitrate and acetate It is suggested that both nitrate and acetate act as bidentate ligands A marked decrease of the number of water molecules contributing to the observed oxygen‐17 shift is noted in presence of acetate, nitrate, and sulfate Chloride also gives rise to some dehydration of the rare‐earth ion, although in this case the mechanism of the process is as yet unclear An approach to the estimation of equilibrium quotients for complex formation using water chemical shift data is outlined in an Appendix Equilibrium quotients are estimated for the formation of nitrato–dysprosium complexes A comparison of water and other ligand proton shifts of the acetate and tropolonate complexes along the lanthanide series suggests that in both complexes there is a similar ligand arrangement around a given cation and that a change of configuration occurs at erbium
TL;DR: In this article, the rate coefficients for the various processes of aeronomic interest are discussed, including the three-body attachment to O2, the radiative attachment, and the dissociative attachment process.
Abstract: Techniques for the study of electron attachment and detachment are reviewed. The rate coefficients for the various processes of aeronomic interest are then discussed. The rates of three-body and dissociative attachment by thermal electrons have been successfully determined by swarm techniques and by high frequency studies of electrons produced by high energy particles and by photoionization. Collisional and associative detachment rates for thermal energy negative ions have been measured using the swarm and flowing afterglow techniques. Radiative attachment rates for some atmospheric negative ions have been calculated from measurements of photodetachment cross sections using crossed photon and ion beam techniques. Electron beam studies and measurements of ion kinetic energy have provided much useful information regarding the dissociative attachment process and the structure of molecular negative ions. Rate coefficients for low energy processes such as the three-body attachment to O2, the radiative attachme...
TL;DR: In this paper, the luminescence of the unactivated and Bi3+- and Eu3+activated compounds ABO4 (A is Sc, In; B is P, V, Nb) is reported and compared with the luminecence of corresponding rare-earth and yttrium compounds.
Abstract: The luminescence of the unactivated and Bi3+- and Eu3+-activated compounds ABO4 (A is Sc, In; B is P, V, Nb) is reported and compared with the luminescence of the corresponding rare-earth and yttrium compounds. The ScNbO4 shows a weak, blue emission, ScVO4 a blue-green, and InVO4 a green emission. The other host lattices show no or only a very weak emission at room temperature. The color of the vanadate emission depends strongly on the choice of A. This was studied by replacing part of the A ions by other ions or a combination of ions. The shift of the vanadate emission is ascribed to two effects, viz., metal–metal interaction (e.g., Bi3+–VO4) and the effect of the size of the metal ions at the A sites (e.g., Sc3+). The Eu3+-activated phosphors show some interesting features. The intensity of the forced electric dipole emission from the Eu3+ ion seems to depend strongly on the position of the lowest strong absorption band. In the zircon structure the 5D0−7F2 emission is hypersensitive to the surroundings,...
TL;DR: In this article, a novel technique involving a straightforward modification of an ion cyclotron resonance spectrometer was developed which utilizes the excitation of the characteristic oscillatory motion of the ions, due to the trapping field, for ejecting ions from the cycloton resonance cell.
Abstract: A novel technique involving a straightforward modification of an ion cyclotron resonance spectrometer has been developed which utilizes the excitation of the characteristic oscillatory motion of the ions, due to the trapping field, for ejecting ions from the cyclotron resonance cell. By pulsing the rf ejection field and referencing the detection system to the pulsing frequency, a spectrum of ions whose number density is modulated by the pulsed ejection field is obtained. This is directly applicable in studying ion‐molecule reactions for the determination of product ion distributions, even when other processes, such as direct ionization or concurrent ion‐molecule reactions, contribute to product ions of interest.
TL;DR: In this paper, an electrohydrodynamic (EHD) technique is used to generate ions from liquid metals, where liquid metal is fed to the tip of a needle emitter with a voltage difference applied between the emitter and an extractor electrode to produce an intense electric field at the liquid surface.
Abstract: An electrohydrodynamic (EHD) technique is used to generate ions from liquid metals. Liquid metal is fed to the tip of a capillary needle emitter with a voltage difference applied between the emitter and an extractor electrode to produce an intense electric field at the liquid surface. Electrostatic forces overcome surface tension forces to produce ions by field emission. When using liquid cesium, time‐of‐flight mass analysis showed the ion current to be primarily Cs+ with a small percentage of Cs2+ and Cs3+. Electron currents of over 1 mA have been produced by operating the emitter at 2 kV negative. Besides cesium, alkali ion beams have been generated using NaK/cesium alloy and sodium. Calculations show that liquid metals of low work functions appear more suitable for production of atomic ions while higher work functions metals may produce multiatomic ions and charged droplets in addition to atomic ions.
TL;DR: The result shows that the ion injection effect gives a contribution to the current-voltage characteristic only at low ionic strength (< 10 (3)M) of the aqueous solution.