Gy. Vikor

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.

Low-energy electron transmission through high aspect ratio Al2O3 nanocapillaries

Electron transmission through insulating Al2O3 nanocapillaries of different diameters (40 and 270 nm) and 15 mu m length has been investigated for low-energy electrons (2-120 eV). The total intensity of transmitted current weakly depends on the incident electron energy and tilt angle defined with respect to the capillary axis. On the other hand, the intensity of elastically transmitted electrons significantly varies with the alteration of electron energy and tilt angle. In addition, we measured an energy distribution of electrons transmitted both in the straightforward direction and at large tilt angle. The measured spectra show that inelastic processes dominate and, in particular, a large amount of low-energy electrons. These low-energy electrons can be either inelastically scattered projectiles or secondary electrons emitted within the capillaries. Furthermore, a change of the tilt angle appears to influence significantly only the intensity of the elastic transmission. The present results suggest a more complex nature of low-energy electron transport through insulating nanocapillaries than proposed for positive ions. Copyright (C) EPLA, 2009

Angular dependence of the PCI line shape for photoionized Ne K-LL and Ar L-MM Auger transitions

We have studied the effect of post-collision interaction (PCI) on the Auger line shape after photoionization as a function of the emission angle relative to the primary photon beam and its polarization vector. For Ne K-LL Auger lines the photon energy was in the 900–1200 eV region, for Ar L-MM lines it was in the 320–440 eV region. Our calculations, which were made on the basis of the eikonal approach, were found to be in good agreement with our measurements at these energy ranges. The angular dependence of peak asymmetry is greater when the energy difference of the photoelectron and the Auger electron is smaller: for Ar at 440 eV photon energy it even changes the sign, i.e. the PCI line distortion disappears completely at a certain angle.

High resolution carbon and oxygen K-LL Auger spectra of carbon dioxide

Abstract The proton excited carbon and oxygen K–LL Auger spectra of carbon dioxide were measured using the high-resolution, angular resolving ESA-21 electron spectrometer. The proton impact energy was 1.0 MeV. The transition energies of both K–LL Auger-spectra (oxygen and carbon) are determined and compared with the existing theoretical and earlier experimental data. The experimental line widths full width at half maximum (FWHM) and relative intensities of the Auger lines are determined. The Auger emission was found to be isotropic within the experimental accuracy.

Auger-electron lineshapes in electron impact ionization: a calculation for non-coincidence experiments

The distortion effects of the post-collision interaction on argon L2,3M2,3M2,3 Auger-electron lineshapes have been calculated for 300 eV, 500 eV and 2 keV electron impact inner-shell ionization. The calculations were based on the model of Kuchiev and Sheinerman (Kuchiev M Yu and Sheinerman S A 1987 Sov. Phys.-Tech. Phys. 32 879) applying our cross section data for secondary electrons, determined by a classical trajectory Monte Carlo method and in addition a continuum distorted wave method for 2 keV. The asymmetry parameters of the calculated peak shapes have been examined as a function of the projectile energy and the Auger emission angle and for some cases compared with our previous experimental results.

Study of the Ar LMM spectra by He+ projectile at 1250 keV, 1500 keV and 2000 keV bombardment energies

Abstract The influence of He + ion impact on the Ar LMM spectra was investigated at the ESA-21 electron spectrometer using three different ion energies. Observed line relative energies to the L 3 M 2,3 ( 1 D 2 ) line agree well with other results, but the relative intensities of five angular-isotropic lines deviate significantly from other measurements and theory. The angular dependence of energy shifts agrees with the quantum PCI theory of Barrachina and Macek, except for directions close to 180°, where a slight enhancement of energy shift was observed. Finally, the angular distributions of the L 2 M 2,3 ( 1 S 0 ), ( 1 d 2 ) and ( 3 P 0,1,2 ) line intensities were compared to the alignment theory of Sizov and Kabachnik.

Transmission of electrons through Al2O3 nanocapillaries

We investigate transmission of low-energy electrons (250 eV) through insulating Al2O3 nanocapillaries (270 nm diameter and 15 ?m length). Kinetic energy distribution of electrons transmitted through the nanocapillaries in the straightforward direction, time dependence of the transmission rate both in the straightforward direction and for tilted capillaries and angular distributions of electrons transmitted at the incident energy are presented and discussed.

Rainbow and glory effects: Coulomb focusing and defocusing post-collision interaction in fast proton and antiproton impact

The angular dependence of the neon K-L2,3L2,3 ( 1 D2) Auger line intensity is measured and calculated for proton-neon collisions at two projectile impact energies. At one of the energies the projectile moves faster than the Auger electron and at the other energy the projectile moves slower. The Auger line intensity measured along the beam direction shows a significant energy dependence compared with other directions. The shape and the intensity of the neon K-L2,3L2,3 ( 1 D2) Auger line is calculated for proton and antiproton impact, respectively. It is used to compare the Coulomb focusing and defocusing effect as a special case of the post-collision interaction along the beam direction. It is shown that these two types of projectile have opposite effects on Auger electrons. The analysis confirms that the post-collision interaction of a structureless heavy particle and light Auger electron emitted along the beam direction, as studied here, is a particular case of the so-called glory and rainbow effects, known from optics.

Post-collision effects in the beam direction in fast ion-atom collisions

Auger line shifts induced by post-collision interaction are studied for proton-atom (argon, neon) collisions. The energy shift is determined for Auger electrons emitted in the beam direction, in the Auger electron-projectile matching velocity region, for several acceptance angles for electron detection. For projectile velocities above the matching velocity, the Auger line energy shifts determined by the experiment agree with the values calculated by the existing theories, while for projectile velocities below the matching velocity, the measured and the calculated energy shifts show unambiguous disagreement. The advantage of the present work is the achievement of very small acceptance angles for electron detection (±0.2°, ±0.3°). For these acceptance angles, in the case when the projectile is slower than the Auger electron, the determined energy shift is negative, which is reported for the first time for fast-ion-atom collision processes.

Guiding of low-energy electrons by highly ordered Al{sub 2}O{sub 3} nanocapillaries

We report an experimental study of guided transmission of low-energy (200-350 eV) electrons through highly ordered Al2O3 nanocapillaries with large aspect ratio (140 nm diameter and 15 mu m length). The nanochannel array was prepared using self-ordering phenomena during a two-step anodization process of a high-purity aluminum foil. The experimental results clearly show the existence of the guiding effect, as found for highly charged ions. The guiding of the electron beam was observed for tilt angles up to 12 degrees. As seen for highly charged ions, the guiding efficiency increases with decreasing electron incident energy. The transmission efficiency appeared to be significantly lower than observed for highly charged ions and, moreover, the intensity of transmitted electrons significantly decreases with decreasing impact energy.