P. Yu. Babenko

Neutral particle analyzer/isotope separator for measurement of hydrogen isotope composition of JET plasmas

This article describes a neutral particle analyzer/isotope separator (ISEP) developed for measurement of the relative hydrogen isotope composition of Joint European Torus (JET) plasmas. The ISEP deployed on the JET can be regarded as a prototype of an instrument proposed for measurement of the spatial profile of the ratio of the density of deuterium and tritium ions in the plasma, nD(r)/nT(r), in the International Thermonuclear Experimental Reactor (ITER). The ISEP makes simultaneous measurements of the energy distribution of efflux of hydrogen isotope atoms (H, D, and T) from the plasma. From such measurements it is possible to deduce the radial profile of the relative hydrogen isotope ion composition of the plasma and radial transport of ions of one isotope across the plasma of another isotope species. The main elements of the ISEP are (a) use of a thin carbon foil for reionization of the incident atoms, thereby eliminating gas stripping cells and gas sources of conventional neutral particle analyzers (...

Inelastic energy losses in single and double collisions of keV-energy Ar + ions with Be, C, Al, Si, Ge, and in targets

Inelastic energy losses Q in scattering of Ar+ ions with an initial energy of E0 = 5 keV from Be, C, Al, Si, Ge, and In targets are determined using low-energy ion scattering spectroscopy. In spite of the fact that Ar+ ion beams are used in the overwhelming majority of applied studies devoted to analysis of the elemental composition and structure of materials for modern electronics, information on inelastic losses for these bombarding particles is scarce. It is shown that the knowledge of the value of Q makes it possible to correctly interpret the energy spectra of particles emitted during ion bombardment of the surface.

Focusing of particles scattered by a surface

It has been shown by computer simulation that the coefficient of reflection of argon atoms scattered by crystalline aluminum and germanium targets at glancing angles of less than 4° is close to unity and the beam of scattered particles exhibits focusing (the angular distributions of particles are strongly compressed). Whereas beam focusing with respect to the azimuth is well known and has already been studied, sharp focusing in the surface-normal direction at small glancing angles has not been studied so far. This effect is confirmed by the experimental results. It is associated with multiple scattering of incident particles by the atomic chain. The simulation results allowed finding quite accurately the amplitude of thermal vibrations of surface atoms ((0.123 ± 0.007) Å for aluminum), which agrees well with the experiment.

Simulation of multiple scattering in argon ion collisions with an aluminum target at grazing angles of 5°–10°

A model for calculating the atom scattering from a polycrystalline surface consisting of randomly oriented single crystals is proposed. In the calculation it is possible to distinguish the contribution of scattering from any surface layer, and it also takes into account inelastic energy losses in primary ion collisions with target atoms. A comparison with the measurements shows that the proposed model well describes the peak positions in the energy spectra of the scattered atoms. A comparison of the calculated and experimental peak-to-background ratios for scattering from polycrystalline and amorphous targets allows a conclusion to be made about the degree of order of surface layers in the material under investigation.

Scaling of the L -vacancy-production cross section at kiloelectronvolt-ion collisions

A method is proposed for determining the vacancy-production probability from the dependence of the emission cross section of Auger-electrons or characteristic radiation on the collision energy. Based on the generalization of the existing experimental data on the collisions of atomic particles in gas and solid phases, a universal character of the dependence of the vacancy production probability on the closest approach distance is established for the first time. Scaling is proposed that makes it possible to calculate an L-vacancyproduction cross section from the universal dependence.

Anomalous Coefficient of Ion Reflection from a Crystal under Surface-Channeling Conditions

A significant difference in behavior between the coefficients of deuterium-atom reflection upon scattering at crystal and amorphous tungsten is shown. The region where the reflection coefficient is close to 100% is determined by scattering at the first and second crystal layers and depends on the orientation. The effect of ion focusing on second-layer atoms and also various orientation effects are observed. It is shown that, at small grazing angles, the dependence of the reflection coefficient on the energy of transverse particle motion is universal. The dependences on the azimuthal exit angle ϕ exhibit the rainbow scattering effect caused by particle motion in the surface semichannel, while the dependences on the polar angle demonstrate the effect of angular distribution narrowing (ion focusing).

Diagnostics of indium clusters in indium nitride by low-energy ion scattering spectroscopy

Using diagnostics based on analysis of single and double scattering of argon ions with energies in the keV range, we study the fraction of indium clusters in an indium nitride sample.

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.

Cluster diagnostics in Si1−xGex solid solutions using low-energy ion backscattering spectroscopy

The fraction of germanium clusters in solid solutions of the Si1−xGex system with a small germanium content (x ∼ 5%) was determined using a method based on the energy analysis of argon ions scattered, upon single and double collisions in the sample, at an angle of θ = 129° relative to the primary beam of ions with an energy of several kiloelectronvolts. Using the proposed low-energy ion backscattering spectroscopy (LEIBS) technique, it was found that the fraction of germanium clusters in the samples studied was ≤20%. The LEIBS method provides a several-fold decrease in the detection threshold for a cluster component in the semiconductor compound as compared to the traditional method based on the measurements of ion scattering at small angles.

Observation of the emission of positive and negative ions in triple and quadruple collisions in a solid under bombardment with keV argon ions

Particles that leave a solid as a result of several consecutive binary collisions are detected in the energy spectra of positive and negative ions emitted upon the irradiation of C, Si, Ge, and In targets with 2-to 5-keV Ar+ ions. The appearance of a spectral structure due to the sequence of three and four collisions in the solid can be attributed to the selective role of the surface, which is similar to the channeling effect in crystals.