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ABSTRACT: Auger-electron spectra associated with Be atoms in the pure metal lattice and in the stoichiometric oxide have been investigated for different incident charged particles. For fast incident electrons, for Ar7+ and Ar15+ ions as well as Xe15+ and Xe31+ ions at velocities of 6% to 10% the speed of light, there are strong differences in the corresponding spectral distributions of Be-K Auger lines. These differences are related to changes in the local electronic band structure of BeO on a femtosecond time scale after the passage of highly charged heavy ions.
Physical Review Letters 10/2010; 105(18):187603. · 7.37 Impact Factor
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ABSTRACT: Solid-state Auger-electron angular distributions are known to be largely independent of the type of excitation, following roughly a cosine law for low ejection energies. In this Letter it is shown that the ion-track dynamics and the corresponding high electron temperatures lead to significant variations of these Auger distributions. Ratios for different degrees of inner-shell ionization versus angle are sensitive to the high-energy-deposition density. The ratios show a minimum for emission angles close to the ion-track direction, consistent with enhanced inelastic electron-energy losses or electron absorption, respectively. Thus Auger-electron yields are influenced by the spatial electronic excitation distribution.
Physical Review Letters 12/2007; 99(19):197602. · 7.37 Impact Factor
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Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 11/2004; 226:682. · 1.21 Impact Factor
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ABSTRACT: High resolution Auger-electron spectroscopy has been applied to the interaction of swift heavy ions with atomically clean metallic solids. Spectra have been taken for fast projectile electrons and for charge-state equilibrated ions at normal incidence on microcrystalline beryllium samples, Al(1 0 0) single crystals and several metallic glasses (Al87La7Ni5Zr1, Ni78B14Si8, Co66Si16B12Fe4Mo2). From the energy shift and from the Auger-line width we have extracted ion-track potentials and also electron temperatures inside ion tracks. A first determination of the angular distribution of multiple-ionization lines is presented as well.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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ABSTRACT: Using a new ultra-high vacuum system we were able to measure ion-induced Auger electron spectra with high resolution for atomically clean amorphous Si surfaces. Measurements were performed with Ne9+ and Ar16+ ions at 5 MeV/u, Xe15+ and Xe31+ ions at 1.78 MeV/u as well as with incident electron at the two speeds, corresponding to 2.7 keV respectively 1.0 keV. The ion-induced spectra show peaks due to multiple ionization, indicating 7- or 8-fold ionization in the center of ion tracks for fast Xe ions. The Auger peaks are shifted and broadened with respect to the electron reference data. This is an indication for the nuclear-track potential and for hot electrons being present during the decay of the Auger states.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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ABSTRACT: The energy dissipation and femtosecond dynamics due to fast heavy ions in matter is critically reviewed with emphasis on possible mechanisms that lead to material modifications. Starting from a discussion of the initial electronic energy-deposition processes, three basic mechanisms for the conversion of electronic into atomic energy are investigated by means of Auger-electron spectroscopy. Results for amorphous Si, amorphous C and polypropylene are presented and discussed. Experimental evidence for a highly charged track region as well as for hot electrons inside tracks is shown. As follows mainly from Auger-electron spectroscopy, there are strong indications for different track-production mechanisms in different materials.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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ABSTRACT: Electronic sputtering of thin BeO films induced by Au26+ and Au41+ ions has been studied at the beam energy of 1.8 MeV/u and compared to the experimental results obtained under nuclear sputtering conditions. Energy spectra and angular distributions of secondary positive ions (Be+ and O+) as well as negative ions (O−, BeO− and BeO2−) have been measured using a quadrupole mass spectrometer. Contrary to the nuclear sputtering, the data for swift heavy-ion irradiation show significant differences in the sputtering process between positive and negative ions. Whereas the angular distribution of the negative ions is nearly isotropic, the emission of the positive ions is strongly anisotropic and enhanced at the directions corresponding to the incident half-space. Additionally, an enhanced high-energy contribution in the energy spectra of positive ions can be observed. The electronic sputtering process of positive ions cannot be explained in the frame of the simple thermal spike model assuming a thermal equilibrium within the ion-track in the target material. An application of the gas-flow model describing an adiabatic expansion of high temperature plasma outside the target has been proposed.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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ABSTRACT: High resolution electron spectra haven been taken for fast heavy ions at 1.78 and 5 MeV/u as well as for electrons of equal velocity incident on atomically clean Si targets. Various LVV-Auger electron structures are identified and for amorphous Si these peaks show a shift towards lower energy when the charge of the projectile is increased. This finding points to a nuclear-track potential inside the ion track. The comparison of the Auger electron spectra for amorphous Si and crystalline Si(1 1 1) 7×7 gives clear evidence for phase effects in the short-time dynamics of ion tracks.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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ABSTRACT: Auger angular distributions are known to be largely independent of the type of excitation. Here it will be shown that the high degree of excitation induced by fast heavy ions or the corresponding electron temperature lead to significant variations of the distributions compared to incident electrons. Even multiple inner shell ionization ratios are sensitive to the high energy deposition density
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ABSTRACT: Auger energy and angular distributions serve as sensitive probes of the atomic and electronic solid state structure, of the excitation dynamics during the interaction of fast ions with solid matter and of the subsequent vacancy decay dynamics, involving also the atomic and electronic material properties. In this work, we will concentrate on the short time dynamics, especially on the energy spectra with less attention on the geometrical sample structure
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ABSTRACT: This work focusses on the production and decay properties of inner shell vacancies and valence band excitations induced by swift highly charged ions interacting with amorphous and crystalline Si. High resolution electron spectra have been taken for fast heavy ions at 1.78 5 MeV u as well as for electrons of similar velocity incident on atomically clean Si targets of well defined phase. Various Augerelectron structures are analyzed concerning their width, their intensity and exact peak position. All measured peaks show a small shift towards lower energy when the charge of the projectile is increased. This finding is an indication for a nuclear track potential inside the ion track. A detailed analysis of the Auger electron spectra for amorphous Si and crystalline Si 111 7 x 7 points to a small but significant phase effect in the short time dynamics of ion tracks
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ABSTRACT: K Auger electron emission has been investigated for incident electrons and for different types of heavy ions interacting with mono crystalline aluminum 100 targets at specific kinetic energies of 3 to 5MeV u. In an effort to gain a profound knowledge about the ionization and vacancy decay dynamics for the K shell in Al, spectra have been measured with different energy resolutions and angular distributions have been taken as well. Here we concentrate on the energy spectra; we identify the measured peak structures and we investigate different line intensities and mean target charge states quantitatively, in comparison with theoretical results
