No abstract available

No abstract available

[en] In this letter a simple procedure for calculating the initial dechanneling of ions is presented. The calculations show good agreement with both experimental data and computer simulation data on planar dechanneling. (author)

[en] A theory recently developed by the authors for slow and fast electrons is shown to be also applicable to channeled ions and to explain the experimental results about electron loss phenomena as a whole. The theory is based on the fundamental hypothesis of the nonadiabaticity of the ion-target interactions. How essential an exponential form of the interaction pseudo-potential is in explaining the energy exchange mechanism at the walls may be deduced from a quasi-classical development of the quantum model. The theory also allows a number of new experiments to be envisaged in the field of surface electron states

[en] The MARLOWE program was used to study the statistics of sputtering on the example of 1- to 100-keV Au atoms normally incident on static (001) and (111) Au crystals. The yield of sputtered atoms was examined as a function of the impact point of the incident particles (''ions'') on the target surfaces. There were variations on two scales. The effects of the axial and planar channeling of the ions could be traced, the details depending on the orientation of the target and the energies of the ions. Locally, the sputtering yield was very sensitive to the impact point, small changes in position often producing large changes yield. Results indicate strongly that the sputtering yield is a random (''chaotic'') function of the impact point

[en] Ion channeling along the [001] direction in high-quality single crystals of (Y/Er)Ba₂Cu₃O_7-x revealed an abrupt change in displace-ments in the a-b plane of the Cu and O atoms at the superconducting transition, T_c; normal 'Debye-like' vibrations were found for the Y/Er and Ba atoms. The anomalous change in Cu-O displacements was found to shift directly with stoichiometry-induced changes in T_c, implying a direct link between the observed phonon anomaly and the superconducting transition. Recent measurements of ion-channeling along the [001] axis in (Bi_1.7Pb_0.3)Sr₂Ca₁Cu₂O_x single-crystals revealed a similar change at T_c, suggesting that this phonon anomaly is a general feature of high-T_c superconductivity. In order to identify more specifically the crystallographic directions and displacement amplitudes associated with the anomalous phonon behavior, axial channeling scans using RBS, as well as characteristic x-ray production, were taken at several temperatures between 30 and 300K along the [301] and [331] directions of YBa₂Cu₃O_7-x single crystals. Twins present in the specimens, and the existing static atomic displacements present along these directions, caused the channeling to be poorer along these axes compared to the (001) direction. Also, a much stronger dependence of the minimum yield on depth was observed. However, since only one twin variant generally dominated over sufficiently wide areas of the specimens, reasonably good (approx 10 percent) minimum yields could be obtained along the appropriate [331] axis, and detwinned crystals produced good results along [301]. (author). 27 refs.; 5 figs

[en] The first experimental mapping of ion beam channels near the Si <001> axis is reported. All features are identified by theoretical plots of silicon planar channels and axial channels

[en] Short communication; 1 ref

[en] The model used by Briggs and Pathak to calculate the electronic energy loss of low-velocity channeled heavy ions has been explored further to study the velocity dependence of Z₁ oscillations in electronic stopping power. For increasing ion velocities, where the validity of neglecting the target-electron velocities increases, it is found that the magnitude of Z₁ oscillations decreases and by about 2-a.u. velocity the first maxima at Z₁=6 and the first minima at Z₁=10 are washed out completely

[en] In this work, the principal continuum radiative emission processes, which occur during the penetration of ions in solids or gases, are resumed. The characteristics of the following processes are discussed: secondary electron bremsstrahlung (SEB), atomic bremsstrahlung (AB), and internuclear bremsstrahlung (INB). Recent advances of the ion channeling effects in crystal solids on the spontaneous radiative spectra are exposed. (A.C.A.S.)