N. Stolterfoht

Guided transmission of 3 keV Ne7+ ions through nanocapillaries etched in a PET polymer

Abstract We measured the transmission of 3 keV Ne 7+ ions through capillaries of 100 nm diameter and 10 μm length produced by etching ion tracks in a polyethylene terephthalate polymer foil. The foils were tilted up to ±25° for which the incident ions are forced to interact with the capillary surface. The majority of Ne 7+ ions were found to survive the transmission in their initial charge state. For tilted foils the angular distributions of the transmitted particles indicate propagation of the Ne 7+ ions parallel to the capillary axis. This capillary guiding of the Ne 7+ ion provides evidence that part of the ions deposit charges within the capillaries in a self-organizing process so that a considerable fraction of the ions is transmitted through the capillaries. A non-linear model is introduced to describe the essential features of the capillary guiding.

Guided transmission of slow Ne6+ ions through the nanochannels of highly ordered anodic alumina

A highly ordered hexagonally close-packed nanochannels array was prepared using the self-ordering phenomena during a two-step anodization process of a high purity aluminium foil. The anodized aluminium oxide, with pore diameters of about 280 nm and interpore distances of about 450 nm was prepared as a suspended membrane of about 15 mu m thickness on the aluminium frame to which it belongs. The Al2O3 capillaries were bombarded with 3 keV Ne6+ ions. The first results unambiguously show the existence of ion guiding observed at 5 degrees and 7.5 degrees tilt angles of the capillaries compared to the beam direction. To the best of our knowledge, such ion guiding effects of slow ions through hexagonally ordered nanochannels in alumina has not been reported previously.

Fermi-shuttle acceleration of electrons in ion–matter interaction

Abstract Large electron yields, compared to theoretical predictions, have often been observed in the high-energy part of the electron spectra in collisions of energetic ions with atomic, molecular or solid targets. The relative enhancement of the electron emission yield at high energies can be especially strong in ion–solid collisions. In this work, following a brief overview, recent experimental evidences are presented for Fermi-shuttle type accelerating electron scattering sequences in ion–atom collisions. Signatures for double (projectile–target, P–T), triple (projectile–target–projectile, P–T–P) and quadruple (P–T–P–T) scattering sequences have been found in different collision systems. Our new results indicate the presence of even higher-order scattering contributions in the collisions of few keV energy N + ions with inert gas atoms. The observations support that high-energy electrons produced by accelerating scattering sequences may play a significant role in ion–solid collisions.

Continuous electron spectra from 150 keV/u C+ + He, Ne, Ar collisions at electron emission angles from 0° to 180°

Electron spectra in the 20–550 eV energy range and in the full angular range of 0–180° were measured by the impact of 150 keV/u C+ ions on He, Ne and Ar atoms. Double differential cross sections for electron emission have been determined. We observed an unexpected, broad structure around 300 eV electron energy at backward emission angles relative to the beam direction. Our calculations support the hypothesis that the new structure is due to double scattering of the target electrons on the screened fields of the projectile and the target. The calculations also show that both electron-emitting partners are multiply ionized in the collision.

Multiple Electron Scattering in Ion‐Atom Collisions: Fermi‐Shuttle Acceleration in Ionization

We present experimental evidences for consecutive multiple projectile‐target‐projectile‐… (P‐T‐P‐… or T‐P‐T‐…) scattering of the electrons liberated in ion‐atom collisions. The highest order of the observed multiple scattering sequences is a quadruple P‐T‐P‐T scattering. We observed the P‐T scattering in different collisions, and found strong indications for the accelerating T‐P scattering. Distinct signatures of the P‐T, P‐T‐P and P‐T‐P‐T multiple electron scattering contributions to the high‐energy part (300 – 3400 eV) of the double differential electron spectra have been separated and identified with the help of reference measurements and auxiliary calculations in single C+ + Xe collisions at 150 and 233 keV/u impact energies. In the collisions of few keV energy ions with inert gas atoms, preliminary results indicate the presence of even higher order scattering contributions.

Energy dependence of neutralization in scattering of slow highly charged Ar ions from an Au surface

Abstract The energy dependence of neutralization of slow highly charged Arq+ (q=7,9,13) ions scattered at large angle (Ψ=37.5°, θ=75°) from a clean Au(1xa01xa01) single crystal surface was studied for incidence energies E0=2, 4 and 8 keV. For Ar7+ the neutralization yield is almost constant for all incoming ion energies, while with L-shell vacancies (q=9,13) , the neutralization yield increases with increasing energy. The experimental results are compared with model calculations that contain side-feeding process of the Ar inner shells, the electron recapture to the surface and the Auger transitions during the ion–surface interaction.

Inelastic energy loss in large angle scattering of Ar9+ ions from Au(111) crystal

Abstract The azimuthal angle dependence of the energy loss in large-angle scattering of slow (v≈0.06 a.u.) Ar9+ ions from a Au(1xa01xa01) single crystal was investigated. Regarding the kinematics of quasi-single collisions, the smallest energy loss is expected for the azimuthal orientations which correspond to the closest packed atomic row of the crystal. This agrees with the prediction of a trajectory simulation (Marlowe code), but the experimental results don’t show such dependence. Thus, we discuss possible inelastic processes as image charge energy gain, electronic energy loss in close collision and the electronic energy loss in the interaction with the electron gas. The observed azimuthal dependence is explained by the change of the electronic stopping power due to the variation of effective electron density sampled by the projectile.