Interaction Of Fast Ions Research Articles

Position-dependent charge-exchange and energy-loss processes for MeV He ions near a crystal surface

Inelastic interaction of fast ions at glancing angles of incidence on a low index crystal surface is described by the probabilities, which depend on the distance of the ion from the surface; the charge state and energy distributions of the scattered ions are found to result from position-dependent interactions along their trajectories in vacuum. A stochastic equation to describe the charge exchange and energy loss of specularly reflected ions is proposed. Taking account of ion scattering at surface steps, the theory is applied to derive the position-dependent probabilities of electron loss and electron capture of MeV ions from the observed charge state and energy distributions of the scattered ions at glancing angle incidence on the (100) surface of SnTe.

Effect of ion implantation on the chemical composition and structure of surface layers of heat-resistant alloys

We present a critical analysis of literature data devoted to the effect of ion implantation on the physicochemical state of surface layers of heat-resistant materials. We pay special attention to the problem of choosing the type of ions to be implanted, the bombardment conditions, and the finishing heat treatment with the goal of achieving the optimal level of operating properties. We show that for complex heterogeneous systems, the optimal treatment conditions can be estimated by methods of local equilibrium thermodynamics, chemical kinetics, and the theory of interaction of fast ions with solids using the basic principles of bulk alloying of heat-resistant alloys. We consider the characteristics features of continuous and pulsed implantation in heat-resistant materials. We formulate the requirements for techniques for investigating the chemical composition and the structural phase state of the near-surface regions of the bombarded targets. Analysis of the literature data on the effect of the bombardment conditions on the structure of the metals has shown that the data are ambiguous, that different authors use different terminology, and that the question of the phenomenology of the “long-range effect” is under dispute.

Progress in X-ray and electron-optical investigations of structural changes by fast heavy ions in semiconductors

The interaction of fast ions with matter is of great interest to many scientists. The investigation of fast ion induced effects is very important for the determination of the influence of structural changes on some physical properties of materials. The main aim of this paper is to show which kinds of structural changes can be created by fast heavy ions in matter and particularly in dislocation-free silicon crystals as a model material. X-ray and TEM methods have been applied to the respective investigations.

Polarized light emission after grazing ion-surface scattering due to capture of spin-polarized electrons.

We have observed the capture of polarized electrons into excited terms of atoms after the interaction of fast ions with a magnetized Fe(110) surface at grazing incidence. The spin polarization of captured electrons results in a modified circular polarization fraction of fluorescence light. This experiment has considerable potential as a new analytical tool for investigating surface magnetism with extreme surface sensitivity, as a method for detailed studies of ion-surface interaction, and as a means to produce nuclear spin-polarized beams.

Specular reflection of fast ions at a single crystal surface

The interaction of fast ions with a solid surface is studied by the specular reflection of MeV H + and He + ions from clean (001) surfaces of SnTe single crystals. Oscillatory structure is observed in the energy spectra of the reflected He ions. This indicates that a part of the incident ions penetrate inside the crystal and travel for a few wavelengths of oscillatory motion in the (001) planar channel before reappearing at the surface. The position dependent stopping power is obtained to be proportional to E − 1 2 exp(−0.15x/a TF ) , where x is the distance from the surface. A large difference is observed in the charge state distribution between the specular reflection and the transmission through a self-supporting foil. This is attributed to the fact that the specularly reflected ions interact exclusively with the valence electrons. It is found that the velocity of convoy electrons emitted at the glancing-angle incidence of He ions is faster than that of the incident ions. This may be due to the acceleration of convoy electrons by the dynamical image potential induced by ions near the surface.

Glancing-angle scattering of fast ions at solid surfaces

The interaction of fast ions with solid surface is investigated by small angle scattering of MeV H +, He + and hydrogen molecular ions at grazing incidence on a clean (001) surface of SnTe single crystal. The secondary electrons with energies less than 25 eV shows an increase of the yield when the surface axial channelling occurs, while that of scattered ions shows a dip. This disappearance of the dip cannot be interpreted simply as due to the long dwell time of ions in the thin surface layer caused by surface channelling. The observed energy losses of the specularly reflected ions are 2 to 3 times as large as those calculated with the formula derived by Lucas. Anomalies in the charge state distributions of reflected ions are observed at specular reflection of incident ions at the surface. Further studies to elucidate the physical processes taking place at the surface are needed for the interpretation of these results.

Hyperfine interaction using grazing beams

The interaction of fast ions with solid surfaces at grazing incidence yields a large anisotropy in the spatial distribution of the orbital angular momenta of atoms and ions. This anisotropy is partially transferred via hyperfine interaction to the nuclear spin system so that high-resolution atomic spectroscopy and the polarization of nuclear spins are feasible.

Electronic interaction of fast ions with surfaces

A comparison of beam-tilted foil interaction with fast ion-surface interaction at grazing incidence shows that due to the largely different interaction times different mechanisms contribute to charge state distributions, intensities and polarization of the spectral line emission of the projectiles. Experimental evidence for the dominance of long-range interactions at grazing incidence is given and corroborated theoretically. A successful description of the dependence of the circular polarization on energy in the low energy regime is presented.

Nuclear orientation by anisotropic collisions

The anisotropic interaction of fast ions with atoms or a solid results in an orientation of the spatial distribution of the orbital angular momenta of excited electronic levels. This orientation of the electronic shell is transfered via hyperfine (hf) interaction to the nuclei and a vector polarization of the nuclear spins is observed. Since this kind of fast beam interaction generates an anisotropy in a rather general way, this technique seems to provide a universal source for polarized ions. General concepts of this type of interaction are discussed, and the applications to produce nuclear spin polarized ions and future developments in this field are outlined.

Recent developments in the study of fast ion-surface interactions at grazing incidence

Recent developments in the study of the interaction of fast ions with a solid surface at grazing incidence are discussed with respect to three aspects. The first part deals with the large orientation of orbital angular momenta after the ion-solid interaction and post collision interaction processes. Then measurements of charge state distributions are outlined, which lead to new aspects in the study of the microscopic interaction. Finally the current status of the application of the large atomic orientation for producing nuclear spin polarized ion beams is reported.

Anisotropic Interaction in Ion–Surface Collisions

The interaction of fast ions with thin foils and solid surfaces yields an anisotropy in the spatial distribution of the orbital angular momenta of the excited levels. The current status in investigating this phenomena and the applications in atomic spectroscopy and nuclear physics are discussed.