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In this work we investigate the energy-loss straggling of low and medium energy protons on available simple materials (C, Al, Si, Ni, Cu, Zn, Ge, Se, Pd, Ag, Sb, Pt, Au, Pb) and demonstrate that the well-known Yang-O’Connor-Wang empirical formula for the energy-loss straggling of protons in matter has a clear physical interpretation. This formula predicts, on empirical grounds, energy-loss straggling values for protons that exceed the values of traditional straggling formulas (e.g., by Lindhard and Chu) at energies around 0.3 MeV/amu by a factor of 2–3. This excess is correlated to the bunching effect, which comes from the inhomogeneity feature of the electron density. Although this effect is specific to each element and can be calculated using e.g. the CasP and PASS programs, a single formula correlates better with overall experimental values. The Yang-O’Connor-Wang formula was refined accounting for subsequent experimental data.

The scattering of ions in solids is accompanied with momentum transfer and electronic excitations resulting in the slowing down of the ion. The amount of energy transferred in a single scattering event depends on the particular trajectory which can be traced back through the scattering angle. Performing scattering angle dependent measurements of slow highly charged Xe ions transmitted through freestanding single-, bi-, and trilayer graphene allows us to determine the charge exchange and energy loss for different minimal interatomic distances. Interestingly, the charge exchange shows an increase with scattering angle by a factor of less than 2, while the energy loss increases by more than a factor of 10 for ${3}^{\phantom{\rule{0.16em}{0ex}}\ensuremath{\circ}}$ compared to forward direction. Our results can be compared to a time-dependent potential model and show that determination of the stopping cross section is not straightforward even with angle-dependent data at hand.

The stopping power and straggling of backscattered protons on nanometric Pt films were measured at low to medium energies (60-250 keV) by using the medium-energy ion scattering technique. The stopping power results are in good agreement with the most recent measurements by Primetzhofer Phy s. Rev. B 86, 094102 (2012) and are well described by the free electron gas model at low projectile energies. Nevertheless, the straggling results are strongly underestimated by well-established formulas up to a factor of two. Alternatively, we propose a model for the energy-loss straggling that takes into account the inhomogeneous electron-gas response, based on the electron-loss function of the material, along with bunching effects. This approach yields remarkable agreement with the experimental data, indicating that the observed enhancement in energy-loss straggling is due to bunching effects in an inhomogeneous electron system. Nonlinear effects are of minor importance for the energy-loss straggling.

Techniques like electron backscattered diffraction (EBSD) and angle-resolved electron Rutherford backscattering (ERBS) are sensitive to the lack of inversion symmetry in crystals and hence can determine the absolute crystal orientation. In this paper we demonstrate for the case of GaP that medium energy ion scattering (MEIS) can also be used to obtain the absolute crystal orientation. A comparison between the 2D-backscattering intensities as a function of the detection directions for electrons (as is measured in EBSD or ERBS) and protons (as is measured in MEIS) is made and discussed in terms of diffraction and classical subchanneling respectively.

It is investigated how the model used to describe a dielectric function (i.e. a Mermin, Drude, Drude–Lindhard, Levine–Louie with relaxation time dielectric function) affects the interpretation of a REELS experiment, the calculation of the electron inelastic mean free path as well proton stopping and straggling. Three dielectric functions are constructed that are based on different models describing a metal, but have identical loss functions in the optical limit. A loss function with the same shape, but half the amplitude, is used to derive four different model dielectric functions for an insulator. From these dielectric functions we calculate the differential inverse mean free path, the mean free path itself, as well as the stopping force and straggling for protons. The similarity of the underlying physics between proton stopping, straggling and the electron inelastic mean free path is stressed by describing all three in terms of the differential inverse inelastic mean free path. To further highlight the reason why observed quantities depend on the model dielectric function used we study partial differential inverse inelastic mean free paths, i.e. those obtained by integrating over only a limited range of momentum transfers. In this way it becomes quite transparent why the observable quantities depend on the choice of model dielectric function.

International audience; Sputtering experiments with swift heavy ions in the electronic energy loss regime were performed by using the catcher technique in combination with elastic recoil detection analysis. The angular distribution of particles sputtered from the surface of LiF single crystals is composed of a jet-like peak superimposed on a broad isotropic distribution. By using incident ions of fixed energy but different charges states, the influence of the electronic energy loss on both components is probed. We find indications that isotropic sputtering originates from near-surface layers, whereas the jet component may be affected by contributions from depth up to about 150 nm.

Polyvinyl chloride (PVC) is a material that decomposes rapidly when irradiated by charged particles. Here we use energy spectra of electrons reflected from the PVC films during electron radiation to monitor this process. This is accomplished by measuring the energy distribution of elastically scattered electrons which depends on the mass of the scattering atoms. Incoming electrons with energy between 5 and 40 keV are used. Information is obtained about both the relative amount of Cl, C and H present in the sample. Especially the Cl concentration decreases quickly during irradiation. At larger energy losses the signature of the band gap is visible in the energy loss spectrum. The number of excitations within the band gap increases rapidly when the composition of the film changes. The H intensity is somewhat less affected by the electron beam than the Cl intensity but accurate determination of the H content is complicated due to the changing background. Medium-energy ion scattering measurements (using 200 keV protons) and Rutherford backscattering measurements (using 2 MeV He ions) showed a strong decrease in the measured Cl intensity with ion fluence used. The Cl concentration as a function of fluence for electrons, protons and He ions can be described in a uniform way by considering the density of electronic excitations produced under the different irradiation conditions.

Gold-implanted aluminum films are used to investigate how reflection electron energy loss spectra (REELS) change due to the presence of a small concentration of heavy atoms at a specific depth. Au ions were implanted with 30, 100 and 300 keV energy. REELS spectra were taken at energies between 10 and 40 keV. Large changes in the REELS spectra are observed after Au implantation, but the nature of the change indicates that they are not due to modification of the dielectric function of the implanted layer, but should be interpreted as changes in the partial intensities that make up the spectrum. Two models are used to describe the results quantitatively. One method assumes v-shaped trajectories (i.e. only a single elastic deflection) and the REELS spectrum can then be calculated in a closed form. The other method is a Monte-Carlo based simulation which allows for multiple elastic deflections. Both methods describe the experimental spectra quite well, but at larger energy losses significant deviations occur between the measured and calculated intensity for both the implanted and not-implanted films. The difference in the REELS spectrum before and after implantation is less affected by these discrepancies, and can be used to obtain an estimate of both the depth and concentration of the implanted Au atoms. Due to the presence of sharp plasmon features in the energy loss spectrum of aluminum the experiment can tell us directly which partial intensities are affected by the Au impurities, as the recoil energies due to elastic scattering make it possible to identify the contribution of Au to the first few plasmons. As the Au implantation fluence is known the measurement can be used to determine the ratio of the Au and Al elastic scattering cross sections, which deviates strongly from that calculated from the Rutherford formula.

A nonlinear model for the stopping power of cluster ions based on partial-wave analysis is developed through the generalization of the induced density approach (IDA) model for the interaction of homo- and heteronuclear molecular ions with a free-electron gas (IDAMol). We apply IDAMol to the energy loss of H2+ dimers in SiO2 and Al2O3, where we find that the results are consistent with established linear (dielectric) models at higher speeds, as expected for small perturbations (small values of the projectile charge or high velocities). Specifically at low projectile energies, however, it is important that IDAMol goes beyond perturbation theory. This feature appears to be central for a good description of negative and positive vicinage effects, a measure of the deviation from the independent-atom model. The focus of this work, however, is the investigation of enhanced nonlinear effects. Here we present experimental results for a heteronuclear cluster ion namely HeH+ on Al2O3, in the energy range of few tens of keV/u using the medium energy ion scattering technique. The IDAMol results are corroborated by the experimental data and time-dependent density-functional calculations for this case. Strong nonlinearities are observed for the energy loss of the fragment H+ due to the higher charge of its He companion., We are indebted to the Brazilian agencies CNPq and FAPERGS for the partial support of this research project. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001. One of the authors (F.M.) acknowledges the Brazilian fellowship from CNPq. F.M. and N.E.K. acknowledge financial support by the Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. IT-756-13) and the Spanish Ministerio de Economía y Competitividad (Grants No. FIS2013-48286-C02-02-P and No. FIS2016-76471-P).

Electron scattering experiments at keV energies from a TiO 2 surface are presented. The paper aims to give an overview of the wide variety of information that can be extracted from such experiments. If the elastic scattering cross sections are known these experiments give the sample composition, if the composition is known one can extract the ratio of the elastic cross sections. In the experiments described here the ratio of the Ti and O cross sections deviates noticeably from the one calculated from the Rutherford formula. The peak widths give access to the mean kinetic energies of the atoms present. We show that the mean kinetic energy of Ti atoms is less than that of O atoms, but both kinetic energies are still affected by quantum effects, i.e. are larger than 3 / 2 kT . We extract an estimate of the dielectric function of TiO 2 by extending the measurement up to 100 eV energy loss. At these high energies the determination of the dielectric function from the measured energy loss spectrum is relatively simple, as the contribution of surface excitations is small and the obtained loss function is closely related to the dielectric function in the optical limit. Finally, we use the technique to monitor the surface after sputtering with Ar + ions, and observe both differences in composition and electronic structure induced by sputtering that disappear again after annealing.

The self-consistent electron-ion potential V(r) is calculated for H ions in an electron gas system as a function of the projectile energy to model the electronic stopping power for conduction-band electrons. The results show different self-consistent potentials at low projectile-energies, related to different degrees of excitation of the electron cloud surrounding the intruder ion. This behavior can explain the abrupt change of velocity dependent screening-length of the potential found by the use of the extended Friedel sum rule and the possible breakdown of the standard free electron gas model for the electronic stopping at low projectile energies. A dynamical interpolation of V(r) is proposed and used to calculate the stopping power for H interacting with the valence electrons of Al. The results are in good agreement with the TDDFT benchmark calculations as well as with experimental data., We are indebted to the Brazilian agencies CAPES, CNPq and FAPERGS for the partial support of this research project. One of the authors (PLG) acknowledges funding by the Alexander-von-Humboldt foundation. NEK and RDM acknowledge financial support by the Basque Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. IT-756-13) and the Spanish Ministerio de Economía y Competitividad (Grants FIS2013-48286-C02-02-P and FIS2016-76471-P).

The short-time dynamics of amorphous beryllium oxide (a-BeO) has been investigated for electronic excitation/ionization by fast incident electrons, as well as by Ar 7+ , Ar 15+ , Xe 15+ , and Xe 31+ ions at velocities of 6–10% the speed of light. Site specific Auger-electron spectra induced by fast heavy ions are the central point of this investigation. Electron induced Auger spectra serve as a reference and electron-energy loss (EELS) spectroscopy as well as resonant inelastic X-ray scattering (RIXS) are invoked for quantitative understanding. For the heavy-ion case, we observe strong variations in the corresponding spectral distributions of Be–K and O–K Auger lines. These are related to local changes of the electron density, of the electron temperature and even of the electronic band structure of BeO on a femtosecond time scale after the passage of highly charged heavy ions.

The ever-growing demand of the semiconductor industry for smaller and faster chips is pressing for new developments on the characterization of ultra-thin films. In particular, ion scattering techniques are largely used to profile thin films and, as a general rule, the depth scale is given in atoms/cm 2 . We explore a new method to determine absolute thicknesses of ultra-thin amorphous films. This technique is based on the measurement of the dwell time of hydrogen fragments traversing amorphous films under the quasi-Coulomb explosion. High energy-resolution backscattering experiments were performed with incident H + and H 2 + ions interacting with ultra-thin films like LaAlO 3 , HfO 2 and LaScO 3 . The experimental results are corroborated by transmission electron microscopy (TEM) measurements and show the effectiveness of the proposed technique.

A formula for determining the electronic stopping power and the transport cross section in electron-ion binary collisions is derived from the induced density for spherically symmetric potentials using the partial-wave expansion. In contrast to the previous one found in many textbooks, the present formula converges to the Bethe and Bloch stopping-power formulas at high ion velocities and agrees rather well with experimental stopping-power data, as shown here for Al, C, and ${\mathrm{H}}_{2}\mathrm{O}$ targets. It can be employed in plasma physics and particularly in any application that requires electronic stopping-power values of quasifree electrons with high accuracy.

Ion cluster desorption yields from LiF were measured at PUC-Rio with ≈0.1 MeV/u N q+ (q = 2,4,5,6) ion beams by means of a time-of-fight (TOF) mass spectrometer. A 252Cf source mounted in the irradiation chamber allows immediate comparison of cluster emissions induced by ≈65 MeV fission fragments (FF). Emission of (LiF) n Li+ clusters are observed for both the N beams and the 252Cf fission fragments. The observed cluster size n varies from 1 to 6 for N q+ projectiles and from 1 to ≈40 for the 252Cf-FF. The size dependence of the Y(n) distributions suggests two cluster formation regimes: (i) recombination process in the outgoing gas phase after impact and (ii) emission of pre-formed clusters from the periphery of the impact site. The corresponding distribution of ejected negative cluster ions (LiF) n F− closely resembles that of the positive secondary (LiF) n Li+ ions. The desorption yields of positive ions scale as Y(n) ∼ q 5. A calculation with the CASP code shows that this corresponds to a cubic scaling ∼S 3 with the electronic stopping power S e , as predicted by collective shock wave models for sputtering and models involving multiple excitons (Frenkel pair sputtering). We discuss possible interpretations of the functional dependence of the evolution of the cluster emission yield Y(n) with cluster size n, fitted by a number of statistical distributions.

Auger-electron spectra associated with Be atoms in the pure metal lattice and in an oxide have been investigated for 1.8 MeV/u Au-129(41+) ions and 2.7 keV primary electrons. The excitation and local energy transfer by such fast primary particles in solids is dominated by electronic processes. The electron-induced spectrum is compared to calculated band-structure results and it is relatively well understood. For the heavy-ion case, however, we observe a significant variation of the Auger electron spectrum, related to a variation of the electronic band structure. This spectrum points to a formation of a metal-like meta-stable electronic density of states. (c) 2010 Elsevier B.V. All rights reserved.

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.

In a recent paper, Smith, Inokuti, Karstens and Shiles discussed optical oscillator strengths (OOS) of graphite, Al and Si and compared the mean excitation energy I obtained by integration to that from stopping power measurements. They found agreement for graphite and Al, but disagreement for Si. In this paper, we discuss the OOS of Al, Si, Cu and Au and compare the stopping powers calculated from these OOS (or from a single I-value), using program CasP40, directly to experimental stopping power values for protons between 10 and 80 MeV. We find that the choice of proper shell corrections is essential: since the shell correction built into CasP is too small, we take the correction for Al, Si and Cu from the BEST program of Berger and Bichsel. For Au, better results are obtained using Bonderup’s shell correction. With these choices, we find fair agreement between experimental and calculated stopping data, both with the I-values from ICRU Report 49 and with OOS. Even in the case of Si, the stopping curve based on OOS is not in conflict with experimental data. In all cases, the curves calculated using SRIM are in good agreement with the data.

In this work we describe an extension of the convolution approximation for the ionization probability and energy-loss straggling as a function of the impact parameter for swift ions. Analytical formulas for these quantities are derived and compared to full first-order Born calculations. The physical inputs of the model are the electron density and oscillators strengths of the target as well as the screening function of the projectile (in the case of dressed ions). A very good agreement is obtained for all impact parameters. In addition, we propose a general schema to add contributions from distant and close collisions. In this way physical processes arising from large and small impact parameters can be easily included into a single expression valid for all impact parameters. This model is then used to investigate the projectile-charge q dependence of ionization, stopping and straggling cross-sections.

In principle, the depth distribution of the different chemical elements near the surface of solids can be determined quantitatively and absolutely with subnanometric depth resolution using medium energy ion scattering (MEIS), which is a refined version of Rutherford backscattering spectrometry (RBS). The energy resolution of current MEIS analyzers reveals spectral features that cannot be resolved using conventional RBS detectors. Thus, the usual data analysis framework based on a standard Gaussian approximation for the ion energy distribution in the target is applicable to regular RBS, but not generally to MEIS, in particular if one aims at subnanometric depth resolution. The observed asymmetry in the ion energy loss distributions is a direct consequence of the asymmetric character of inelastic energy transfers during individual atomic collisions and of the stochastic character of the resulting energy losses. We propose a model that accounts for the proper statistics of the small energy loss events and for an approximate electronic energy loss distribution during the backscattering event. The validity of this model is discussed and applied to the determination of HfO2 and TiO2 film thicknesses as well as to detect Al2O3 and HfO2 intermixing. This final application case also illustrates the potentialities as well as some inherent limitations of MEIS. The model developed here has been made available to the public in the form of a software for MEIS data analysis.

The knowledge of the energy loss distribution in a single ion atom collision is a prerequisite for subnanometric resolution in depthprofiling techniques such as nuclear reaction profiling NRP and medium energy ion scattering MEIS . The usual Gaussian approximation specified by the stopping power and energy straggling is not valid for near surface regions of solids, where subnanometric or monolayer resolution can be achieved. In this work we propose an analytical formula for the line shape to replace the usual Gaussian distribution widely used in low resolution ion beam analysis. Furthermore, we provide a simple physical method to derive the corresponding shape parameters. We also present a comparison with full coupled channel calculations as well as with experimental data at nearly single collision conditions

The Coulomb explosion of small cluster beams can be used to measure the dwell time of fragments traversing amorphous films. Therefore, the thickness of thin films can be obtained with the so-called Coulomb depth profiling technique using relatively high cluster energies where the fragments are fully ionized after breakup. Here we demonstrate the applicability of Coulomb depth profiling technique at lower cluster energies where neutralization and wake effects come into play. To that end, we investigated 50--200 keV/u ${{\mathrm{H}}_{2}}^{+}$ molecular ions impinging on a 10 nm ${\mathrm{TiO}}_{2}$ film and measured the energy of the backscattered ${\mathrm{H}}^{+}$ fragments with high-energy resolution. The effect of the neutralization of the ${\mathrm{H}}^{+}$ fragments along the incoming trajectory before the backscattering collision is clearly observed at lower energies through the decrease of the energy broadening due to the Coulomb explosion. The reduced values of the Coulomb explosion combined with full Monte Carlo simulations provide compatible results with those obtained at higher cluster energies where neutralization is less important. The results are corroborated by electron microscopy measurements.

In this work we have measured the contribution of the Coulomb explosion to the electronic stopping power of molecular hydrogen ions ( H 2 + and H 3 + ) channeling along the Si 〈1 0 0〉 direction. We have used a SIMOX target, consisting of crystalline Si 〈1 0 0〉 with a buried layer of SiO2. The measurements of the energy loss of H+, H 2 + and H 3 + have been carried out using the standard channeling Rutherford backscattering spectrometry. The energy loss has been measured around the Si 〈1 0 0〉 channel at a fixed energy per nucleon (150 keV/amu) as a function of the tilt and azimuthal angles. The present results show the effect of Coulomb explosion, which enlarges the protons traversal energy and consequently the channeling energy loss. This heating effect due to H 3 + ions is about two times larger than H 2 + molecules and amounts to about 5% of the total stopping power.

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.

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.

The convolution approximation for the impact-parameter dependent energy loss is reviewed with emphasis on the determination of the stopping force for heavy projectiles. In this method, the energy loss in different impact-parameter regions is well determined and interpolated smoothly. The physical inputs of the model are the projectile-screening function (in the case of dressed ions), the electron density and oscillators strengths of the target atoms. Moreover, the convolution approximation, in the perturbative mode (called PCA), yields remarkable agreement with full semi-classical-approximation (SCA) results for bare as well as for screened ions at all impact parameters. In the unitary mode (called UCA), the method contains some higher-order effects (yielding in some cases rather good agreement with full coupled-channel calculations) and approaches the classical regime similar as the Bohr model for large perturbations (Z/v≫1). The results are then used to compare with experimental values of the non-equilibrium stopping force as a function of the projectile charge as well as with the equilibrium energy loss under non-aligned and channeling conditions.

In this work we report on measurements of channeling stopping powers of 16 O ions along Sih 100 i axial direction for the energy range between 250 keV/u and 1 MeV/u by using the Rutherford backscattering technique with separated by implanted oxygen targets. In connection with the recent developed unitary convolution approximation, we are able to extract the Barkas contribution to the energy loss with high precision. This effect is clearly separated from other processes and amounts to about 15%. The observed Barkas contribution from the valence-electron gas is in agreement with the Lindhard model for higher energies. However, in contrast to recent investigations for Li ions, the Barkas effect at the lowest energies seems to saturate, indicating other non-perturbative terms in the polarization field induced by the O ions in Si. 2002 Elsevier Science B.V. All rights reserved.

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.

In the present contribution, we report results on random stopping power and range straggling of 16 O ions into amorphous Si target. The measurements were performed in a 300 keV–13.5 MeV energy interval by using the Rutherford backscattering technique together with a marker system. The present stopping results were compared with the TRIM predictions based on the Ziegler, Biersack and Littmark calculations, the theoretical values being always higher than the experimental ones. On the other hand, the calculated straggling data are compared with the Bohr predictions. For low energies, the calculated values over-estimate the experimental ones. For energies larger than 2 MeV, the experimental results became larger than the Bohr predictions. However, with increasing energies, the experimental results approach the Bohr values, and above 12 MeV a quite good theoretical experimental agreement was found.

The energy loss of H2 and H3 molecules along the 〈1 1 0〉 and non-aligned directions of Si was measured through the Rutherford backscattering technique in combination with a SIMOX target. The experiments were performed at 300, 500 and 700 keV/atom. The results show the following features: First, the random and channeling molecular stopping powers are larger than the corresponding atomic one. Second, at a given energy per atom, the H3 energy loss is larger than the one of H2. Third, within the experimental errors, the channeling and random molecular stopping powers are equal. Finally, there are strong indications that the contribution of the screened Coulomb explosion to the energy straggling of molecular beam increases with the molecular velocity.

Our current understanding of the short-time interaction of fast heavy ions with matter is reviewed. Fast ions move along straight line trajectories and loose their energy mainly via collisions with electrons in the close surrounding of the ion path. Thus, the initial stages of corresponding ion tracks are highly excited cylindrical regions with diameters of the order of nanometers that extend over some micrometers in length. The energy dissipation inside these cylinders and the different possible pathways from dense electronic excitations to atomic motions and phase transitions are discussed in the light of recent experimental results.

The energy spectra of scattered ions in Rutherford backscattering and elastic recoil scattering experiments are commonly described using stopping power and straggling data. These, in turn, are based on statistical approximations and thus neglect the characteristics of individual ion–atom collisions. This simplified analysis is not justified when considering experiments with high-energy resolution. We have performed theoretical and experimental studies to understand the shape of high-energy resolution ion scattering spectra. The impact parameter dependent energy loss in single ion–atom collisions has been calculated using the semi-classical approximation (SCA). We show that limitations for extracting monolayer depth resolution become obvious from this non-statistical approach. Experiments were performed using a medium energy ion scattering (MEIS) system. For the case of 100 keV protons scattered on sulfur atoms, good agreement between the theoretical description and experimental data was found. The influence of thermal vibrations of the sample atoms on the backscattering spectra is discussed.

In the present work, we report on measurements of angular dependent energy loss for 1.2 and 2.0 MeV He ions incident near the Si 〈1 1 0〉 and 〈1 1 1〉 axes parallel to the {1 0 0} and {1 1 0} planes, respectively. The measurements were done using the Rutherford backscattering technique (RBS) combined with a SIMOX sample. The experimental results are well reproduced by calculations based on the convolution approximation for the impact-parameter dependence of the energy loss of the core electrons.

In the present work we have measured the random 7Li stopping power and range straggling into Si. With this aim we have employed the Rutherford backscattering (RBS) technique together with a multilayer Sb/Si marker. The stopping power measurements were performed in the 280–8500 keV energy interval, while the range straggling ones were done in the 380–2500 keV energy interval. The present results were compared with the TRIM predictions and the semi-empirical calculations by the Kalbitzer group, and an overall good agreement was found for both cases.

A large set of experimental charge-state distributions is analyzed in this work. Two fit formulas are presented for mean equilibrium charge states of projectiles ranging from protons to uranium. One formula is given for all ions in gas targets and another one for solid targets. The deviation from the experimental data is reduced by roughly a factor of two in comparison with the widely used formula by Nikolaev and Dmitriev as well as with the Bohr stripping criterion as revised by Northcliffe. Finally, the influence of the projectile charge state on the prediction of stopping powers for fast projectiles in carbon is shown and comparison is made with experimental energy-loss data.

The energy dissipation 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. Experimental evidence for a highly charged track region as well as for hot electrons inside tracks is presented. As follows mainly from Auger-electron spectroscopy, there are strong indications for different track-production mechanisms in different materials.

We report experimental results on the charge equilibration process of both He+ and He++ ions at energies from 0.4 to 1.5 MeV in the Si 〈1 0 0〉 direction. The characteristic equilibration distance increases with energy from 3 nm to about 10 nm at the highest energy. The experimental findings are compared with Monte Carlo calculations describing the particle motion in a continuum potential for the 〈1 0 0〉 channel.

We describe a simple model for the electronic energy loss as a function of the impact parameter for screened projectiles at high velocities. The physical inputs are the projectile screening potential, the electronic density and the oscillators strengths for the target electrons. An excellent agreement with full first-order Born calculations is obtained. The results are then used to compute the angular dependence of the electronic energy loss under channeling conditions.

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.

We report experimental results on the charge-equilibration process of both He+ and He++ ions at energies from 0.4 up to 1.5 MeV in the Si 〈1 0 0〉 direction. The characteristic equilibration distance increases with energy from 3 nm to about 10 nm at the highest energy.

In the present contribution we present results on molecular H2 and H3 energy loss measurements in the 〈1 1 1〉 Si direction by using Rutherford backscattering/channeling spectrometry and a SIMOX target. With this aim, we have used atomic and molecular H2 and H3 beams with energies of 250, 400 and 800 keV/atom. From the present results it was determined that the H2 molecular stopping is larger than the atomic one. Moreover, our measurements show that the H3 stopping is of the order of the H2 one. In addition we have determined that the coherent distances of the H2 clusters vary between 20 and 33 nm.

In the present work we report on measurements of the electronic stopping power of 1.2 MeV 7Li+ ions channeled through the Si 〈1 0 0〉 axis as a function of the incident angle between −1.2° and 1.2°. The experiments were done using the Rutherford backscattering technique with a SIMOX sample. The measured ratio α between the channeling and random stopping powers as a function of the angle show an upside down Gaussian-like angular dependence with a minimum of α=0.84±0.04 and a FWHM of 0.67°±0.10°. From the experimental data the impact parameter dependent energy loss is estimated and compared with first order calculations.

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 atomic units (5 MeV/u). We present experimental evidence for an influence of the target excitation density on the shape of carbon Auger-electron spectra for O7+, Kr17+ and Kr30+ ions. An analysis of the Auger structures allows for the first time to extract electron temperatures at the center of nuclear tracks and comparison is made with results of two thermal-spike models.

We report on the results of the charge equilibration process of 1.2 MeV He+ and He++ ions along the Si〈1 0 0〉 direction. Present and previous results indicate that the charge equilibrium distance increases as a function of the He energy, being about 20 nm for 1.2 MeV.

We report measurements on the electronic stopping power of 7 Li ions along the 〈1 0 0〉 Si direction in the energy region between 1 and 8 MeV. The measurements were carried out using the standard RBS/Channeling technique with SIMOX targets. The results show that the stopping power decreases for increasing energies, from 48 eV/A at 1 MeV down to 19 eV/A at 8 MeV. The general features obtained for the stopping power of 7 Li resemble those obtained for He ions measured previously.

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.

We present measurements of the electronic stopping power in the 0.8–2.0 MeV energy range of 4 He 2+ ions channeled through the Si〈1 0 0〉 axis as a function of the incident angle. The measurements were carried out using the Rutherford Backscattering (RBS) technique with a SIMOX sample that consists of a single Si crystal on the top of a 500 nm buried layer of SiO 2 built into a Si〈1 0 0〉 wafer. The measured ratios between the angular dependent and random stopping powers have almost the same width near the maximum of the 4 He 2+ stopping power and decrease for higher energies.

Ab-initio calculations of the electronic stopping power are important not only as benchmark tests for many simplified models but also because they provide fundamental insights into the underlying physics of the energy dissipation of ions penetrating matter. In this work we investigate the electronic energy loss processes by using the coupled-channel method. This first-principle calculation is based on the solution of the time-dependent Schrodinger equation in the framework of the independent particle model. A brief review of such calculations is presented and special emphasis is given on recent calculations of the energy dependence of the stopping power for He ions channeling along the Si 〈1 0 0〉 direction, a system of interest for ion beam analysis.

Convoy-electron emission has been investigated experimentally and theoretically for heavy-ion irradiation of conducting and insulating solid-state targets at a particle velocity of 14.1 a.u. (5 MeV/u). We present experimental evidence for a deceleration of convoy electrons produced by N 7+ , Ne 10+ , S 13+ , Ni 23+ and Ag 37+ ions during the interaction with insulator foils at normal incidence. The deceleration first increases with increasing projectile charge, reaches a maximum at a projectile charge of about 16 and seems to approach zero for even higher charges. It is proposed that there is a significant fraction of nuclear-track guided electrons emitted close to the convoy-electron velocity. The high ionization density inside the solid leads to an attractive potential that may guide electrons along the track, similar to the particle motion under channeling conditions.

A review is given on the use of the coupled-channel method to calculate the electronic energy loss of ions penetrating matter. This first principle calculation, based on an expansion of the time-dependent electronic wave function in terms of atomic orbitals, has been applied to evaluate the impact parameter and angular dependence of the electronic energy loss and the stopping cross-section of ions (antiprotons, H and He) colliding with H and He atoms at energies of 1–500 keV/amu. The results are compared to experimental data as well as to others current energy-loss models.