G. Schiwietz

Femtosecond dynamics: snapshots of the early ion-track evolution

The energy dissipation and femtosecond dynamics due to fast heavy ions in matter is critically reviewed with emphasis on possible mechanisms that lead to materials 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

Auger electrons from ion tracks

Abstract The target KVV Auger electron emission has been investigated experimentally and theoretically for heavy-ion irradiation of amorphous carbon at an ion velocity of 14.1 a.u. (5 MeV/u). We extend previous investigations of multiple ionization and electronic nuclear-track temperatures to a large variety of charged projectiles, covering electrons to uranium ions. Experimental data are compared with non-pertubative calculations of multiple ionization and with results of two thermal-spike models.

An experimental determination of electron temperatures in the center of nuclear tracks in amorphous carbon

Abstract In this work we present carbon K-Auger electron spectra from amorphous carbon foils induced by fast heavy ions and by electrons. The high-energy tail of the experimentally determined Auger structure shows a clear projectile-charge dependence. Model electron-spectra for the Auger decay of the K vacancy, calculated from the known density of states, are in good agreement with electron induced Auger spectra. The experimental data for heavy ions could be fitted with the model results by using the mean electron temperature in the track center as the only free parameter. These temperatures are presented and discussed in comparison with theoretical estimates for the electron temperature in the thermal spike.

Ionization and Energy Loss Beyond Perturbation Theory

Abstract A review is given on the application of the coupled-channel method for the calculation of the electronic energy loss of ions as well as ionization in matter. This first principle calculation, based on the solution of the time-dependent Schrodinger equation, has been applied to evaluate the impact parameter and angular dependence of the electronic and nuclear energy losses of ions as well as the ionization due to high-power short laser pulses. The results are compared to experimental data as well as to other current theoretical models.

Si-Auger electrons from the center of nuclear tracks

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 Ne 9þ and Ar 16þ ions at 5 MeV/u, Xe 15þ and Xe 31þ 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. 2002 Published by Elsevier Science B.V.

Analytical energy loss distribution for accurate high resolution depth profiling using medium energy ion scattering

An analytical approach to ion energy loss distributions capable of simplifying medium energy ion scattering (MEIS) spectral analysis is presented. This analytical approach preserves the accuracy of recent numerical models that evaluate energy loss effects overlooked by standard calculations based on the Gaussian approximation. Results are compared to first principle calculations and experimental MEIS spectra from 0.2-to1.5-nm-thick HfO2 films on Si, supporting the application of this analytical model for proton scattering in the kinetic energy range from 100to200keV.

Spectroscopy of Si-Auger electrons from the center of heavy-ion tracks

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(1xa01xa01) 7×7 gives clear evidence for phase effects in the short-time dynamics of ion tracks.

The role of basic energy-loss processes in layer-resolved surface investigations with ions

Abstract Ab initio quantum mechanical calculations have been performed for the energy loss of protons backscattered from an Al surface. Results from first-order perturbation theory are compared to full numerical atomic-orbital coupled-channel calculations. It is shown that both inner shells and non-perturbative effects are important for the understanding of ion energy-loss spectra.

Al-K-Auger energy spectra: Probing the electron dynamics in ion-solid interactions

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 5 MeV/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.

Impact-parameter dependence of the electronic energy loss

In this work, we discuss the application of the coupled-channel method for the calculation of the electronic energy loss of ions in matter. Special emphasis will be given to the formulation of simple models that account for the basic energy-loss processes without being a large-scale calculation. The results are compared to experimental channeling data as well as to other current energy-loss models.