Multiple scattering of low-energy rare-gas ions at solid surfaces

We have studied the multiple scattering of He⁺, Ne⁺, and Ar⁺ from a TaC(001) surface in the energy region of the order of 1 keV. The experimental data revealed large differences between the energy spectra of these ions. The spectral peak corresponding to quasi-double scattering is clearly observed for Ar⁺ but not observed for Ne⁺. The multiple scattering effect appearing in the energy spectra of rare-gas ions is discussed on the basis of electron exchange between these ions and solid surfaces.     

Transmission of 18 keV negative ions Cl through nanocapillariesin Al2O3 membrane

We investigate the angular distribution of the transmitted 18keV negative ions Cl^- through Al₂O₃ nanocapillaries of 50 nm in diameter and 10 μm in length. Elastic scattering ions and inelastic scattering ions are obtained simultaneously. The experimental result is partially consistent with the guiding effect. We can qualitatively explain our experimental result through a dynamic process.     

Electron Transitions during the Capture of an Electron by a He<Superscript>2+</Superscript> Ion at the Argon Atom

We have measured the absolute values of the total cross section of the one-electron capture by He²⁺ ions in the kinetic energy range 2–30 keV at the Ar atoms. The absolute values of the differential scattering cross sections of He⁺ ions formed during the one-electron capture and the electron capture with ionization at energies of 2.2, 5.4, and 30 keV have been determined. The electronic states of the formed ions have been determined using collision spectroscopy based on analysis of the change in the kinetic energy of He⁺ after the interaction. We have measured doubly differential (with respect to the kinetic energy and the scattering angle) cross sections of the formation of free electrons. The free electron formation channels (direct ionization and electron capture with ionization) have been analyzed by calculating the electron terms of the (HeAr)²⁺ system. The calculated cross section of capture with ionization is in conformity with the cross section measured using collision spectroscopy.     

Features of the electron exchange under grazing scattering of H− ions from a thin aluminum disk

The electron exchange under grazing scattering of a negative hydrogen ion from a thin Al disk is analyzed via the wave packet propagation method that does not use the perturbation theory. The probability of H^? ion fraction formation is calculated as a function of the ion velocity component (v_‖) parallel to the surface. It is shown that the yield of negative hydrogen ions has a bell-like dependence on the value of v_‖ under grazing scattering from a thin disk. The negative ion yield under grazing scattering from a disk is very close to the H^? ion yield under scattering from a film. The maximum of the probability of H^? fraction formation calculated for a thin disk is shifted to smaller values of v_‖ with respect to the maximum of the probability of H^? formation for a thin film.     

Scattering of F atoms and anions on a TiO2(1 1 0) surface

Results of a study of energy losses and electron transfer processes for grazing scattering of fluorine atoms and anions scattering along different azimuthal orientations of the TiO₂ crystal are presented. We observe strong variations in the overall intensity of scattered particles which are due to channelling effects. The energy losses do not show strong variations as a function of crystal azimuth except for the case of scattering along the (0 0 1) direction between the bridging oxygen atom rows, where we also observe differences in the energy losses of scattered ions and neutrals. We attribute this to the fact that larger F⁻ survival occurs for trajectories staying farther from the surface, when also the energy losses remain small. The overall characteristics of energy losses are attributed mainly to trajectory effects due to scattering in regions of different electron density. Measurements of the ratio of scattered ions to the total scattered flux, i.e. the ion fractions which reflect electron capture and loss processes, show that these are not the same for incident anions and atoms. A strong difference for scattering along the (0 0 1) direction is observed, where at low incident energies a strong survival of incident ions occurs. These results are tentatively discussed in terms of non resonant electron capture at lattice O⁻ sites and electron loss into the conduction band or by collisional detachment with bridging O atoms.     

Electron scattering based on a novel internal target technique: SCRIT

A novel technique for forming internal targets, named SCRIT (Self-Confining RI Ion Target), has been developed, which can make electron scattering off short-lived radioactive nuclei possible in an electron storage ring. SCRIT confines the ions of interest by utilizing the “ion trapping” phenomenon in the electron storage ring. Approximately 10⁷ stable ¹³³Cs ions were trapped in a three-dimensional configuration along the electron beam axis at an electron beam current of 75mA. The angular distribution of the electrons scattered from the trapped ¹³³Cs ions was successfully measured, and a collision luminosity of 10²⁶/(cm² s) was achieved.     

Resonances in an <Emphasis Type="Italic">S</Emphasis>-wave model of electron scattering off hydrogen-like ions

Irregularities in the cross section of electron scattering off hydrogen and hydrogen-like He⁺, Li⁺⁺, and Be⁺⁺⁺ ions are studied using an s-wave model. The resonance structure and irregularities in the scattering data are compared. A unified approach based on an exterior complex scaling method is used in performing calculations. The potential splitting approach is used for calculations of scattering in systems with asymptotic Coulomb interactions.     

Peripheral collisions of highly charged ions with metal clusters

Within the framework of the dynamical classical over-barrier model,the soft collisions between slow highly charged ions(SHCIs) Ar 17+ and the large copper clusters under large impact parameters have been studied in this paper.We present the dominant mechanism of the electron transfer between SHCIs and a large metal cluster by computational simulation.The evolution of the occupation of projectile ions,KL x satellite lines,X-ray yields,Auger electron spectrum and scattering angles are provided.     

Resonance scattering of electrons from orientated O2 physisorbed on graphite

We have studied inelastic electron scattering from a saturated monolayer of O₂ physisorbed on graphite at 25K. The cross-section for excitation of the v = 0–1 vibrational transition in O₂ peaks at 8.5–9eV, and is attributed to the ⁴Σ_u negative ion resonance. The angular distribution of electrons inelastically ejected out of the resonance orbital has been measured, and is found to peak at 15° from the normal to the crystal for several different incident electron beam angles, in accord with the theory of resonant electron scattering by an orientated molecule. We discuss the implications of this measurement for a determination of the orientation of the O₂ molecule on the surface, taking account of possible multiple scattering effects.     

HgSe:Fe—a mixed-valency system and the problem of the ground state

The dependence of the electron mobility on the iron impurity content N _Fe and temperature is studied for three variants of the ordering of Fe³⁺ ions in crystalline HgSe:Fe, a weakly correlated gas, states with near ordering like that in a strongly correlated Coulomb liquid, and long-range ordering. The electron mobilities owing to scattering on the correlated system of Fe³⁺ ions are determined. The temperature dependence of the mobility is analyzed for electron scattering on fluctuations in the charge density in a system of Fe²⁺-Fe³⁺ iron ions with mixed valency, and the correlation length is determined. It is shown that the ordering region for the Fe³⁺ ions encompasses only the first coordination sphere, i.e., near ordering in the position of the Fe³⁺ ions is established, as in a liquid. The coupling between the ordering of the Fe³⁺ ions and the formation of a correlation gap in the density of impurity d-states and its effect on the low-temperature behavior of the electron mobility in HgSe:Fe crystals are examined. Fiz. Tverd. Tela (St. Petersburg) 40, 425–432 (March 1998)     

Effects of the atomic structure and interference oscillations in the electron photorecombination spectrum in a strong laser field

Electron photorecombination in the presence of a strong low-frequency laser field has been analyzed using an exactly solvable quantum model. It has been shown that interference patterns in the electron photorecombination spectrum are more sensitive to the details of the atomic potential than those in the case of other non-linear processes. For electron photorecombination on Xe⁺ ions, the manifestation of the Ramsauer effect in the cross section for the elastic scattering of slow electrons on Xe⁺ ions has been predicted in the electron photorecombination spectrum modified by the laser field.     

Bragg scattering measurement of atmospheric plasma decay

The decay processes of the plasma layers generated by two intersecting microwave pulses in 1 torr dry air are investigated by Bragg scattering method. The results of measurement show that the electrons decay initially at the three-body attachment rate. However, when enough negative molecule ions are produced through the electron attachment process, the regeneration of electrons via detachment process is increased and eventually balances out the electron attachment loss. The net electron loss is then dominated by the recombination process. The temporal evolution of electron density has also been reproduced by the numerical result of a system of three modal equations for a best fit detachment rate v_d=2×10³sec^–1.     

Electron-spin-dependent 4He+ ion scattering on Bi surfaces

We studied low-energy (～ 1.55 keV) electron-spin-polarized ⁴He⁺ ion scattering on a Bi(111) ultrathin film epitaxially grown on a Si(111) substrate. We observed that the scattered ion intensity differed between the incident He⁺ ions with up and down spins even though Bi is a non-magnetic element. To analyze the origin of this spin-dependent ion scattering (the spin asymmetry), we investigated the detailed relationship between the spin asymmetry and the incident angle, the azimuthal angle, the scattering angle, and the incident energy. All the data indicate that the spin asymmetry originates from the scattering cross section owing to the non-central force in the He⁺–Bi atom binary collision. The non-central force is most likely attributed to the spin–orbit coupling that acts transiently on the He⁺ 1s electron spin in the binary collision.     

Formation of the ion fraction of keV-Energy argon ions upon double scattering by al, Ge, and in targets

The charge fraction of Ar⁺ ions singly or doubly scattered by Al, Ge, and In targets is studied by means of low-energy ion scattering spectroscopy. It is shown that the behavior of the ion fraction is not described by the electron tunneling model in the case of forward scattering by an Al target. The characteristic velocities of ions singly and doubly forward and back scattered by Ge and In targets are found.     

Calculation of von Neumann entropy for hydrogen and positronium negative ions

In the present work, we carry out calculations of von Neumann entropies and linear entropies for the hydrogen negative ion and the positronium negative ion. We concentrate on the spatial (electron–electron orbital) entanglement in these ions by using highly correlated Hylleraas functions to represent their ground states, and to take care of correlation effects. We apply the Schmidt decomposition method on the partial-wave expanded two-electron wave functions, and from which the one-particle reduced density matrix can be obtained, leading to the quantifications of linear entropy and von Neumann entropy in the H⁻ and Ps⁻ ions.     

Data and modeling of negative ion transport in gases of interest for production of integrated circuits and nanotechnologies

We review techniques to prepare, evaluate and apply sets of cross section and transport data for negative ions that are required for the modeling of collisional non-equilibrium plasmas used for processing of microelectronic circuits. We collect and discuss the transport coefficients and cross section sets.We have compiled data for negative ions in CF₄ and CF₄-related negative ions in rare gases. In addition, we consider data for F⁻ and CF₃⁻ in rare gases. Furthermore, we analyze the cross sections of halogen negative ions in rare gases and other molecules. This is followed by the data for SF₆ related ions in SF₆ and in rare gases. The cross section for scattering of O⁻ in O₂ has been derived from the transport data and used to make calculations of the transport properties. Finally we give a brief discussion of the availability of the data for H⁻ ions in H₂. We have derived cross sections in several cases but the basic aim is to show the basic features of transport coefficients. In particular we discuss the need to represent properly some details such as the non-conservative nature of transport coefficients and the anisotropy of diffusion. Application of approximate theories and representations of cross sections are also discussed.     

Über die Energieabhängigkeit von Ionen-Molekül-Reaktionen mit negativen Ionen

Some ion-molecule reactions with negative ions (OH^? and NH ₂ ^? ) have been studied using a primary ion source, in which the negative ions were produced by electron impacts with electron resonance capture, and a secondary ion source, in which the primary negative ions produced ion-molecule reactions with formation of secondary negative ions. The secondary ions were magnetically analyzed and registered by a multiplier. Cross sections of the reactions in function of the energy of the primary ions were measured in the region of low energies up to about 20 eV. In the low energy region the cross sections rapidly decrease with increasing energy ～E ^?1/2 as it has been the case with the energy dependence of the cross section of charge transfer reactions with negative ions at the same energies.     

Resonance behavior of electron scattering from nitrogen molecules adsorbed on metallic surfaces

We use the coupled angular modes theory of electron scattering from molecules to identify the important role played by substrate multiple scattering in determining the lifetime of transient negative ions in adsorbed molecules. For the ²Π_g negative ion resonance in N₂, we demonstrate the phenomenon of complete resonance quenchingwhich occurs when the resonance energy is such that the probe electron is strongly reflected from the substrate. This situation may occur when the resonance energy lies in a band-gap of the unoccupied states of a metallic substrate. It is proposed that the simple resonance energy shift and lifetime reduction observed in previous experimental and theoretical studies of resonance electron scattering from adsorbates is by no means a universal phenomenon. The importance of the unoccupied metallic band structure of the substrate in determining the properties of negative ions in adsorbed molecules is discussed.     

Interaction of negative ions with the surface of inert liquids

The interaction potential of negative ions (electron bubbles) with the surface of liquid ⁴He, ³He, and Ne has been found. In addition to the electrostatic repulsion, the contribution of the long-range Van der Waals attraction of the electron bubble to the liquid surface has been also taken into account. Competition of these repulsion and attraction forces results in the formation of a potential barrier that prevents the motion of a negative ion from the liquid to the vacuum. The temperature and electric-field dependences of the lifetime of the bubble have been determined. The theory has been compared with the experiments with negative ions in liquid ⁴He. In contrast to the conventional idea based on the hypothesis of the quantum tunneling of an electron from a bubble to a vacuum, our theory is based on the Kramers’ diffusion model of the classical escape of the bubble over the potential barrier. In this model, a low-dynamic-friction approximation is applicable to liquid ⁴He owing to a high mobility of negative ions in the superfluid.     

Secondary Electron and Negative-Ion Emission from Metal Surface under the Bombardment by Positive Ions (H<Superscript>+</Superscript>, Cl<Superscript>+</Superscript>, HCl<Superscript>+</Superscript>)

A trap for positive ions (H⁺, Cl⁺, HCl⁺) is created within a time-of-flight mass spectrometer. The yields of secondary electrons and negative ions (HCl^?, H^?) formed due to forward and backward scattering of positive ions by steel wire at different kinetic energies (200–750 eV) are measured.