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.     

Effect of metallic surface microroughness on the probability and spectrum of plasmon excitation by a fast charged particle moving parallel to the surface

The Green’s function of the electric field of plasmons is determined in a semi-infinite medium with an abrupt plasma boundary where nonequilibrium conduction electrons either undergo elastic reflection from the boundary or “stick” to it and give rise to a stationary surface charge. The angular reflection of elastically scattered electrons can be either specular or diffuse. The Green’s function is used to find the singleevent spectrum of energy loss by a fast electron moving parallel to the boundary. The effect of electronboundary scattering parameters on the structure of bulk and surface plasmon resonances is analyzed. The probability of transition radiation of bulk plasmon by an electron moving in vacuum is examined. A new type of surface resonance is found under conditions of perfectly elastic scattering of conduction electrons from the plasma boundary, similar in structure to a tangential surface plasmon.     

Energy transfer in hyperthermal Xe-graphite surface scattering

The scattering of a hyperthermal Xe from a graphite (0001) surface has been studied using a molecular beam-surface scattering technique and molecular dynamics (MD) simulations. The angular and velocity distributions of scattered Xe atoms were measured at incidence energies from 0.45 to 3.5 eV, three incidence angles of 15°, 35° and 60° and the surface temperatures of 300 K and 550 K. The observed time-of-flight spectra exhibit a sharp velocity distribution with only one velocity component, which is ascribed to the direct inelastic scattering process. The angle-resolved energy ratios of the mean final translational energy over the mean incidence energy E_f/E_i agree well with those predicted based on the assumption of the conservation of the momentum parallel to the surface. The Hard-Cube model, where the mass of the cube is approximately 310 u, has reproduced the angle-resolved flux distributions of scattered Xe atoms. In the Hard-Cube model almost 80% of the normal component of the incidence translational energy is found to be lost in collision. The MD simulations reproduce well the experimental results by using the Brenner potential for intralayer C atoms and a Lennard-Jones potential for interlayer C–C pair interactions.     

Energy and charge distributions of fast hydrogen ions and atoms reflected from Cu in the case of grazing incidence

The energy and charge distributions of protons and hydrogen atoms reflected from the Cu surface in the case of grazing incidence angles are measured at energies of incident particles (H⁺ and H⁰) of 200 and 250 keV. The charged fractions of reflected particles are analyzed. A weak dependence of the neutral fraction of reflected particles on the scattering angle is discovered for incidence angles of 1°–2° and an energy of scattered particles of 60 keV or less. It is shown that the neutral fraction of reflected particles with an energy of 60–80 keV or more is independent of the scattering angle and is determined by the ratio of the cross sections for the electron capture and loss by ions in the material.     

Thermalization of neutrons on cold atoms in magnetic traps

A new method is proposed for cooling polarized neutrons by thermalizing neutrons in spherical and torroidal magnetic traps with elastic triplet scattering by cold, double spin-polarized, hydrogen atoms. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 9, 570–572 (10 November 1999)     

Detection of low-energy hydrogen atoms from a tokamak plasma by means of H-formation on tungsten surfaces

Formation of negative hydrogen ions by scattering of protons from a cesiated tungsten (110) surface has been studied in the incident energy range from 15 to 500 eV. From the results a new type of diagnostic for studying the plasma boundry is proposed.     

Capture of polarized electrons into excited atomic states in grazing scattering from a magnetized Ni(110) surface

The spin polarization of electrons captured into excited atomic levels of atoms during the scattering of fast ions from a magnetized Ni(110) surface under a grazing angle of incidence is deduced from the polarization of the fluorescence light. In our studies we have investigated the dependence of the spin polarization on projectile velocity and angle of incidence and observed generally small polarizations for captured electrons.     

Electromagnetic waves refraction on the interface of transparent with absorptive right or left-handed media

The expressions for the time-averaged Pointing’s vector in absorptive left-handed medium based on the classical vector Maxwell’s equations for a continuum have been obtained. It was found that in the case of inclined incidence with mixed polarization the additional plane component of Poynting’s vector perpendicular to incidence plane has appeared for negative effective refraction. This addition of the in-plane component leads to non-coincidence of refraction and incidence plane.     

Grazing incidence scattering of vibrationally excited H2 molecules from metal surfaces

We have studied the scattering of vibrationally excited H₂ molecules from metal surfaces under fast grazing incidence conditions, by means of quasi-classical calculations based on six-dimensional potential energy surfaces. We show that, in spite of the fast parallel motion, the reorientation of the molecule along the trajectory plays a fundamental role on the scattering, being responsible for the nonmonotonic behavior observed as a function of the normal incidence energy, similar to that observed under slow normal incidence conditions. The present study has allowed us to further prove that the interaction between a H₂ molecule and an ordered metal surface under fast grazing incidence conditions is, in general, governed by the normal momentum of the molecule.     

Electronic excitations during grazing scattering of hydrogen atoms on KI(001) and LiF(001) surfaces

The energy loss of hydrogen atoms with energies of 400 eV and 1 keV is studied in coincidence with the number of emitted electrons during grazing scattering from atomically clean and flat KI(001) and LiF(001) surfaces. The energy loss spectra for specific numbers of emitted electrons are analyzed in terms of a binary interaction model based on the formation of transient negative ions via local capture of valence band electrons from anion sites. Based on computer simulations we derive for this interaction scenario probabilities for the production of surface excitons, for electron loss to the conduction band of KI, for emission of electrons, and for formation of negative hydrogen ions. The pronounced differences of data obtained for the two surfaces are attributed to the different electronic structures of KI and LiF.     

Influence of topological transitions in a quantizing magnetic field and anisotropy of current carrier scattering by acoustic phonons on the longitudinal electrical conductivity of layered crystals with open fermi surfaces

It is demonstrated that the dependence of Fermi’s energy on the magnetic field causes a set of the Shubnikov – de Haas (SDH) oscillation frequencies to change, and their relative contribution to the total longitudinal conductivity of layered crystals depends on whether the scattering of current carriers is isotropic or anisotropic. Owing to the topological transition in a strong magnetic field, Fermi’s surface (FS) is transformed from open into closed one and is compressed in the magnetic field direction. Therefore, in an ultraquantum limit, disregarding the Dingle factor, the longitudinal electrical conductivity of the layered crystal tends to zero as a reciprocal square of the magnetic field for the isotropic scattering and as a reciprocal cube of the magnetic field for the anisotropic scattering. All calculations are performed in the approximation of relaxation time considered to be constant versus the quantum numbers for the isotropic scattering and proportional to the longitudinal velocity of current carriers for the anisotropic scattering.     

Theoretical prediction of the scattering of spherical bubble clusters under ultrasonic excitation

Due to the nonlinear vibration of ultrasound contrast agent bubbles, a nonlinear scattered sound field will be generated when bubbles are driven by ultrasound. A bubble cluster consists of numerous bubbles gathering in a spherical space. It has been noted that the forward scattering of a bubble cluster is larger than its backscattering, and some studies have experimentally found the angular dependence of a bubble cluster’s scattering signal. In this paper, a theory is proposed to explain the difference of acoustic scattering at different directions of a bubble cluster when it is driven by ultrasound, and predicts the angular distribution of scattered acoustic pressure under different parameters. The theory is proved to be correct under circumstances of small clusters and weak interactions by comparing theoretical results with numerical simulations. This theory not only sheds light on the physics of bubble cluster scattering, but also may contribute to the improvement of ultrasound imaging technology, including ultrasonic harmonic imaging and contrast-enhanced ultrasonography.     

On the effect of the parallel velocity on Li− formation in Li+-surface scattering

Li⁻ formation is studied by scattering a Li⁺ beam from a cesium covered tungsten (110) surface. The primary energy ranges from 1000 to 3000 eV. The measurements show that variation of the velocity component of the scattered particles parallel to the surface, can either enhance or decrease the Li⁻ formation probability. The sign of this parallel velocity effect depends on the value of the normal velocity component. The experimental results are qualitatively explained by a semi-classical model.     

Peculiarities of the electron exchange upon collision of a negative hydrogen ion with a cluster of aluminum atoms

The resonant electronic transition upon normal-to-surface collision of a negative hydrogen ion with a cluster of aluminum atoms has been considered. The dependence of the probability of ion survival on the distance to the cluster surface is calculated for different collision velocities. It is shown that, depending on the incident particle velocity, a cluster of atoms can behave as a bulk sample or a nanostructure with energy quantization over two coordinates.     

Cold emission of negative ions from porous graphite

The electric field strength in the near-wall layers of thermonuclear facilities can be sufficient for the emission of negative ions from the surface of plasma facing materials. The mass spectra of negative ions from MPG-8 porous graphite at electric field strengths up to 4 × 10⁶ V/m and the surface composition of the target have been studied by ion scattering spectroscopy. The dependence of the mass composition of negative ion emission and residual gas on the sample’s temperature has been measured and a correlation between the intensity of negative hydrogen-ion emission and the desorption of water has been established. The temperature dependence of the emission of negative ions and clusters of carbon and hydrocarbon is in qualitative agreement with the chemical erosion of graphite.     

Low frequency pressure waves in a vapor-liquid medium with a fixed layer of spherical particles

The features of the propagation of low-frequency pressure waves in a liquid-vapor flow through a layer of close-packed spherical solid particles have been studied. Principal measurements have been performed at two pressure values, mainly 0.2 and 0.6 MPa; in a cylindrical channel using lead balls sized 3 and 8 mm. The experimental results allowed defining the characteristic parameters and conditions providing that the wave’s propagation velocity coincides with the thermodynamic equilibrium’s acoustic speed in the vapor-liquid mixture. The results show the dispersive nature of the acoustic speed in the vapor-liquid medium.     

Effect of the bombarding-ion mass in alloy sputtering

It is shown experimentally that a change in the mass of bombarding ions from ⁴⁰Ar⁺ to ⁴He⁺ has a strong effect on the spatial distributions of the components sputtered from the alloy NiMoRe. A mechanism of sputtering by backscattered ions is proposed to describe the observed preferential ejection of the light component in the direction normal to the surface of the sample under bombardment by ⁴He⁺ ions. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 7, 507–510 (10 April 1996)     

Magnetooptical Kerr effect in the near field of a nanowire supporting surface plasmons

In terms of Green’s functions, a theory is developed describing the resonant magnetooptical Kerr effect in light scattering by a linear probe that is parallel to the surface of a magnet and placed at a subwavelength distance from it. The probe is supposed to be a metal nanowire supporting long-lived surface plasmons and forming the near field of the “probe + image” complex. The resonant interaction between the probe and the sample is taken into account within a self-consistent approximation of multiple-scattering theory, and the magnetooptical interaction is included in the linear approximation in magnetization. The problem of scanning near-field magnetooptical microscopy with a linear probe is solved analytically in the case where the magnetization is parallel to both the magnet surface and the plane of incidence of light (longitudinal magnetooptical Kerr effect). The polarization, spectral, and angular characteristics of scattered light modulated by magnetization are discussed. It is shown that the magnetooptical modulation of the scattered light intensity is significantly enhanced when surface plasmons are resonantly excited in the nanowire.