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We have measured the electronic energy-loss straggling of protons, helium, boron and silicon ions in silicon using a transmission time-of-flight approach. Ions with velocities between 0.25 and 1.6 times the Bohr velocity were transmitted through single-crystalline Si(100) nanomembranes in either channelling or random geometry to study the impact parameter dependence of energy-loss straggling. Nuclear and path length contributions to the straggling were determined with the help of Monte Carlo simulations. Our results exhibit an increase in straggling with increasing ion velocity for channelled trajectories for all projectiles as well as for protons and helium in random geometry. In contrast for heavier ions, electronic straggling at low velocities does not decrease further but plateaus and even seems to increase again. We compare our experimental results with transport cross section calculations. The satisfying agreement for helium shows that electronic stopping for light ions is dominated by electron-hole pair excitations, and that the previously observed trajectory dependence can indeed be attributed to a higher mean charge state for random trajectories. No agreement is found for boron and silicon indicating the breakdown of models based solely on electron-hole pair excitations, and that local electron-promotion and charge-exchange events significantly contribute to energy loss at low velocities.

RM and FG acknowledge funding from EPSRC grants (RM: EP/506631/1; FG: EP/M029077/1). JAvdB and AKR acknowledge the EPSRC funding for the use of the MEIS facility at the University of Huddersfield within grant EP/M029077/1. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior -Brasil (CAPES) - Finance Code 001, by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and PRONEX-FAPERGS16/2551-0000479-0. Bimetallic catalysts are often more active and/or selective than their monometallic counterparts. The behaviour of such catalysts is frequently strongly dependent on the molar ratio of the two elements as well as nanoparticle size and the interaction with the support material. X-ray photoelectron spectroscopy (XPS) is an excellent surface analytical technique for probing the electronic properties of catalytic systems. When a mixture of pure and alloyed particles is present, it is more difficult to extract information from XPS given that it is a spatial averaging technique. Recently, the technique of medium energy ion scattering (MEIS) has been exploited to investigate the depth-dependent composition of nanoparticles on planar surfaces. Herein, we combine the two techniques to investigate the nature of Cu and Au nanoparticles deposited onto ultrathin CeO2 films on Si(111) examining their morphology and chemical composition as a function of annealing temperature for samples that have been maintained in an ultrahigh vacuum environment and exposed to air. The Cu/Au/CeO2/Si(111) is chosen as a model system in order to provide insight into how the catalytic properties of Cu/Au/CeO2 depend on the presence of discrete Cu and Au particles versus fully intermixed Cu/Au systems. Postprint

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.

Oxygen self-diffusion was investigated in TiO2 layers employed for resistive-switching memories using resonant nuclear reaction profiling (NRP) and 18O labeling. The layers were grown using physical vapor deposition technique (sputtering) and were polycrystalline. The diffusivity was measured over the temperature range 600–800 °C and the activation energy for oxygen self-diffusion in sputter-deposited TiO2 films determined to be 1.09 ± 0.16 eV, a value consistent with results obtained by previous studies (Marmitt et al., 2017).

The influence of the charge state q on surface modifications induced by the impact of individual fast, heavy ions on muscovite mica was investigated. Beams of 593 MeV 197Auq+ with well-defined initial charge states over a relatively broad range of values (30 to 51) and at different irradiation geometries were used. At normal incidence, the impact features are rounded protrusions (hillocks) with ≳20 nm in diameter. At grazing angles, besides the hillocks, craters and elongated tails (up to 350 nm-long) extending along the direction of ion penetration are produced. It is shown that the impact features at normal incidence depend strongly on the initial charge state of the projectiles. This dependence is very weak at grazing angles as the ion reaches the equilibrium charge state closer to the surface. At normal ion incidence, the hillock volume scales with q3.3±0.6. This dependence stems largely from the increase in the hillock height, as a weak dependence of the diameter was observed.

Over seventy years ago, Niels Bohr described how the charge state of an atomic ion moving through a solid changes dynamically as a result of electron capture and loss processes, eventually resulting in an equilibrium charge state. Although obvious, this process has so far eluded direct experimental observation. By peeling a solid, such as graphite, layer by layer, and studying the transmission of highly charged ions through single-, bi- and trilayer graphene, we can now observe dynamical changes in ion charge states with monolayer precision. In addition we present a first-principles approach based on the virtual photon model for interparticle energy transfer to corroborate our findings. Our model that uses a Gaussian shaped dynamic polarisability rather than a spatial delta function is a major step in providing a self-consistent description for interparticle de-excitation processes at the limit of small separations. Ion-solid interactions are governed by a range of complex processes the direct experimental observation of which pose their own set of challenges. Here, the authors present a joint experimental and first-principles approach to study and describe the underlying mechanism of electron capture for an ion travelling through layers of graphene with monolayer precision.

Bohr's centenary stopping-power formula is rederived for a free electron gas (FEG) system within the framework of nonrelativistic classical mechanics. A simple and more concise expression for the stopping power of charged particles in FEG is demonstrated on classical grounds. Using semiclassical arguments and the Euler-Maclaurin well-known mathematical formula, Bloch's correction that links Bethe's quantum theory to Bohr's classical model is also recovered. The proposed semiclassical stopping-power formula contains the main physical ingredients for a general stopping formula applicable for different systems and energies and facilitates computational calculations.

Gallium oxide, and in particular its thermodynamically stable β-Ga2O3 phase, is within the most exciting materials in research and technology nowadays due to its unique properties. The very high breakdown electric field and the figure of merit rivaled only by diamond have tremendous potential for the next generation “green” electronics enabling efficient distribution, use, and conversion of electrical energy. Ion implantation is a traditional technological method used in these fields, and its well-known advantages can contribute greatly to the rapid development of physics and technology of Ga2O3-based materials and devices. Here, the status of ion implantation in β-Ga2O3 nowadays is reviewed. Attention is mainly paid to the results of experimental study of damage under ion irradiation and the properties of Ga2O3 layers doped by ion implantation. The results of ab initio theoretical calculations of the impurities and defect parameters are briefly presented, and the physical principles of a number of analytical methods used to study implanted gallium oxide layers are highlighted. The use of ion implantation in the development of Ga2O3-based devices, such as metal oxide field-effect transistors, Schottky barrier diodes, and solar-blind UV detectors, is described together with systematical analysis of the achieved values of their characteristics. Finally, the most important challenges to be overcome in this field of science and technology are discussed.

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.

Synopsis Highly charged ions (HCIs) are an efficient tool for the perforation of suspended 2D materials. Only a fraction of their potential energy is transferred to the atomically thin target during the very short interaction time and is available for pore formation. Charge exchange spectra were measured for highly charged xenon ions transmitted through suspended, single layer MoS2 in order to determine the deposited potential energy available for pore formation. Additionally, charge exchange dependent ion stopping responsible for kinetic sputtering was measured simultaneously.

A method is described for extracting the dielectric function directly from a reflection electron energy loss spectrum taken at relatively high energies (2.5 to 40 keV). It makes simplifying assumptions on separation of surface and bulk losses. The approach uses a description based on partial intensities and surface excitation parameters and fits directly the reflection electron energy loss data. Several different model dielectric functions are implemented (extended Drude, Drude Lindhard, Mermin, and the Levine–Louie dielectric functions with relaxation time), and their advantages and disadvantages are discussed. Justification of this approach is in the end based on a comparison with the dielectric function as obtained by other means, which is generally quite good, provided that the solution obtained is restrained by sum rules to the right refractive index and electron density. The fitting program, to be used in conjunction with commercial plotting software, is provided. Copyright © 2017 John Wiley & Sons, Ltd.

Non-planar Fin Field Effect Transistors (FinFET) are already present in modern devices. The evolution from the well-established 2D planar technology to the design of 3D nanostructures rose new fabrication processes, but a technique capable of full characterization, particularly their dopant distribution, in a representative (high statistics) way is still lacking. Here we propose a methodology based on Medium Energy Ion Scattering (MEIS) to address this query, allowing structural and compositional quantification of advanced 3D FinFET devices with nanometer spatial resolution. When ions are backscattered, their energy losses unfold the chemistry of the different 3D compounds present in the structure. The FinFET periodicity generates oscillatory features as a function of backscattered ion energy and, in fact, these features allow a complete description of the device dimensions. Additionally, each measurement is performed over more than thousand structures, being highly representative in a statistical meaning. Finally, independent measurements using electron microscopy corroborate the proposed methodology.

A recent experimental study of the energy losses of various ions in titanium nitride, in the low-energy range [M. A. Sortica, Sci. Rep. 9, 176 (2019)2045-232210.1038/s41598-018-36765-7], showed a striking departure of the measured values from those predicted by density functional theory. They suggested electron promotion in atomic collisions between dressed atoms as an explanation. In this Rapid Communication, we investigate the process of energy loss of slow ions in TiN using theoretical formulations that are based, on one side, on self-consistent models of nonlinear screening and quantum scattering theory, and on the other, on ab initio computations of the electron-density profile of titanium nitride. Two theoretical approaches are considered to determine the average energy transfer: One is based on the local-density approximation for the inhomogeneous electron gas corresponding to the calculated density of TiN, and the other is based on the Penn model for the convolution of the inhomogeneous electron-gas response based on a measured electron-loss function. Both approaches produce very similar results and are in remarkable agreement with the experimental data, indicating that the observed enhancement in the energy-loss values is due to the contribution of a range of electron densities in the TiN compound. Fil: Matias Da Silva, Flávio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Grande, P. L.. Universidade Federal do Rio Grande do Sul; Brasil Fil: Vos, M.. The Australian National University; Australia Fil: Koval, Peter. Donostia International Physics Center; España Fil: Koval, Natalia E.. Comisión de Investigaciones Científicas. Nanogune; España Fil: Arista, Nestor Ricardo. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina

Manipulating the exchange coupling at magnetic interfaces is crucial to spintronic devices. This study shows that inserting a very thin ferromagnetic spacer at the interface of a ferromagnet/antiferromagnet Co/Ir-Mn film substantially strengthens the coupling (if there are no important interfacial defects or interdiffusion in the antiferromagnet). Furthermore, although a Fe spacer film presents the same exchange bias after annealing or He-ion irradiation, its coercivity increases threefold after irradiation. This provides a way to fine-tune the characteristics of such structures.

International audience; Abstract Damaged regions of cylindrical shapes called ion tracks, typically in nano-meters wide and tens micro-meters long, are formed along the ion trajectories in many insulators, when high energy ions in the electronic stopping regime are injected. In most cases, the ion tracks were assumed as consequences of dense electronic energy deposition from the high energy ions, except some cases where the synergy effect with the nuclear energy deposition plays an important role. In crystalline Si (c-Si), no tracks have been observed with any monomer ions up to GeV. Tracks are formed in c-Si under 40 MeV fullerene (C 60 ) cluster ion irradiation, which provides much higher energy deposition than monomer ions. The track diameter decreases with decreasing the ion energy until they disappear at an extrapolated value of ~ 17 MeV. However, here we report the track formation of 10 nm in diameter under C 60 ion irradiation of 6 MeV, i.e., much lower than the extrapolated threshold. The diameters of 10 nm were comparable to those under 40 MeV C 60 irradiation. Furthermore, the tracks formed by 6 MeV C 60 irradiation consisted of damaged crystalline, while those formed by 40 MeV C 60 irradiation were amorphous. The track formation was observed down to 1 MeV and probably lower with decreasing the track diameters. The track lengths were much shorter than those expected from the drop of S e below the threshold. These track formations at such low energies cannot be explained by the conventional purely electronic energy deposition mechanism, indicating another origin, e.g., the synergy effect between the electronic and nuclear energy depositions, or dual transitions of transient melting and boiling.

Electron Rutherford backscattering measures the near-surface composition of samples quantitatively. For interpretation one usually relies on the single-scattering approximation. Here we present results for four compounds, containing oxygen and other species, varying from very light to very heavy. Two Monte Carlo codes are described that model these measurements. From these simulations it is clear that for all samples multiple scattering occurs frequently, but also that the single scattering interpretation deduces the right composition, except for O atoms in a very heavy matrix, where interpretation is more difficult. The intrinsic width of the peaks, a consequence of Doppler broadening due to the velocity of the (vibrating) atoms, turns out to be more sensitive to multiple scattering effects.

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).

A combination of medium energy ion scattering (MEIS), grazing incidence small angle X-ray scattering and transmission electron microscopy techniques was used to investigate a planar set of Pb nanoparticles (NPs) located at the SiO2/Si interface synthesized by ion implantation, and the bimodal NPs’ shape nature of this system was revealed. The present results help to improve the understanding of the use of MEIS on the investigation of the microstructural and morphological properties of buried nanostructured systems and show the importance of the combination with appropriate complementary techniques.

This work was partially supported by the Basque Departamento de Educacion, Universidades e Investigacion, the University of the Basque Country UPV/EHU (Grant No. IT-756-13) and the Spanish Ministerio de Economia y Competitividad (Grants No. FIS2016-76471-P and No. MAT2016-78293-C6-4-R). We are indebted to the Brazilian agencies CAPES, CNPq, and FAPERGS for partial support of the experimental part of this work.

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.

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.

Recent theoretical developments in the unitary convolution approximation (UCA) for electronic energy losses of bare and screened ions are presented. Examples are given for proton beams and rare-gas targets. For gas targets there exists a sufficient amount of experimental data on charge exchange, for pinpointing the largely unknown stopping-power contribution of electron-capture processes at low and intermediate energies.

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.

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.

We show direct experimental evidence that radiation effects produced by single MeV heavy ions on a polymer surface are weakened when the length of the ion track in the material is confined into layers of a few tens of nanometers. Deviation from the bulk (thick film) behavior of ion-induced craters starts at a critical thickness as large as ∼40nm, due to suppression of long-range additive effects of excited atoms along the track. Good agreement was found between the experimental results, molecular dynamic simulations, and an analytical model. Fil: Papaléo, R. M.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Thomaz, R.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Gutierres, L.I.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: De Menezes, V.M.. Universidade Federal Da Fronteira Sul; Brasil Fil: Severin, D.. GSI Helmholtz Centre; Alemania Fil: Trautmann, C.. GSI Helmholtz Centre; Alemania. Universitat Technische Darmstadt; Alemania Fil: Tramontina Videla, Diego Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Grande, P. L.. Universidade Federal do Rio Grande do Sul; Brasil

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.

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 (Al 87 La 7 Ni 5 Zr 1 , Ni 78 B 14 Si 8 , Co 66 Si 16 B 12 Fe 4 Mo 2 ). 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.

In this work we demonstrate that Medium Energy Ion Scattering (MEIS) measurements in combination with Transmission Electron Microscopy (TEM) or Grazing Incidence Small Angle X-Ray Scattering (GISAXS) can provide a complete characterization of nanoparticle (NP) systems embedded into dielectric films. This includes the determination of the nanoparticle characteristics (location, size distribution and number concentration) as well as the depth distribution and concentration of the NP atomic components dispersed in the matrix. Our studies are performed considering a model case system consisting of planar arrangements of Au NPs (size range from 1 to 10 nm) containing three distinct Au concentrations embedded in a SiO2 film.

We present experimental evidence for a deceleration of convoy electrons produced by 5MeV/u ions (N{sup 7+} , Ne{sup 10+} , S{sup 13+} , Ni{sup 23+} , and Ag{sup 37+} ) 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. Different possible mechanisms and quantitative estimates for the slowing down of convoy electrons are presented. {copyright} {ital 1997} {ital The American Physical Society}

We present measurements of the stopping power of 800-keV $^{4}\mathrm{He}$ ions channeled along the Si〈100〉 axis, as a function of the incidence angle. We compare the experimental results with theoretical calculations by using the impact-parameter-dependent energy loss obtained from the solution of the time-dependent Schr\"odinger equation through the coupled-channel method. This nonperturbative calculation provides reliable energy-loss results which are in good agreement with the experimental results.

The energy loss of an ion passing along a major crystal axis before and/or after undergoing a large-angle collision is strongly enhanced, because its path is close to a lattice-site atom located at the crystal axis; this is the so-called skimming effect. One may find this effect in high-resolution medium-energy ion scattering (MEIS) spectra from submonolayers of single crystals. In the present study, the MEIS spectra were observed for medium-energy He${}^{+}$ ions backscattered from KI(001) and RbI(001) crystals at various scattering geometries. The observed surface peaks were decomposed into scattering components from top-, second-, and third-layer atoms considering the hitting probabilities, which were derived from Monte Carlo simulations of ion trajectories, taking account of the enhanced and correlated thermal vibrations. The results obtained here demonstrate that the energy loss of the ions which move skimming trajectories is expressed reasonably well by the impact-parameter-dependent energy loss calculated using the nonperturbative coupled-channel method.

We demonstrate the application of high-energy elastic electron backscattering to the analysis of thin (2–20 nm) HfO2 overlayers on oxidized Si substrates. The film composition and thickness are determined directly from elastic scattering peaks characteristic of each element. The stoichiometry of the films is determined with an accuracy of 5%–10%. The experimental results are corroborated by medium energy ions scattering and Rutherford backscattering spectrometry measurements, and clearly demonstrate the applicability of the technique for thin-film analysis. Significantly, the presented technique opens new possibilities for nm depth profiling with high spatial resolution in scanning electron microscopes.

The electron-loss cross section of He{sup +} ions impinging upon noble-gas targets (2{le}{ital Z}{sub 2}{le}36) is calculated by using the coupled-channel method for the active projectile electron in the static screened field of the target atom. The calculations show a saturation of the projectile-electron-loss cross section with increasing target atomic number. This saturation effect due to neutral target systems is much more pronounced than for ionization or excitation by charged particles. Comparison with experimental data indicates a small electron-loss contribution from electron-electron interaction processes for heavy targets at intermediate velocities. Remaining discrepancies in the data are discussed in the light of the approximations involved in our theoretical treatment. {copyright} {ital 1996 The American Physical Society.}

Recent developments in the theoretical treatment of electronic energy losses of bare and screened ions in gases are presented. Specifically, the unitary-convolution-approximation (UCA) stopping-power model has proven its strengths for the determination of nonequilibrium effects for light as well as heavy projectiles at intermediate to high projectile velocities. The focus of this contribution will be on the UCA and its extension to specific projectile energies far below 100 keV/u, by considering electron-capture contributions at charge-equilibrium conditions.

molecules. The results show small enhancements (about 5% and 15% for H + and H + molecules, respectively) of the stopping ratios. The values obtained by the simulation code SEICS indicate small vicinage effects as well and are in satisfactory agreement with the experimental data. Moreover, the same simulations carried out for carbon foils yield relatively higher stopping ratios. The differences between the vicinage effects obtained for C and Au are interpreted in terms of different excitation spectra of each material. Finally, our results obtained for Au are in clear disagreement with those reported in the seminal work of Brandt, Ratkowski, and Ritchie [Phys. Rev. Lett. 33, 1325 (1974)].

The present work reports on the influence of ion irradiation in exchange-coupled bilayers. Magnetron-sputtered IrMn4 /Co films were irradiated with 40 keV He+ ions and the dependence of their magnetic properties was studied as function of ion fluence and current used during the irradiations. The effects of ion damage and electronic excitation were also studied through additional irradiations with H+ and Ne+ ions. The results show a clear dependence of the exchange-bias field on the defects caused by the ion bombardment. No correlations with other irradiation effects were observed.

The electronic stopping power of hydrogen beams penetrating He gas has been calculated by solving the time-dependent Schr\"odinger equation. Special attention has been given to low incident energies where capture and loss of the projectile electron are the most important energy-loss mechanisms. These mechanisms are included in a consistent theoretical treatment and good agreement with experimental data has been obtained for high- as well as for low-energy projectiles in a gas target.

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 Ar(7+) and Ar(15+) ions as well as Xe(15+) and Xe(31+) 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.

In the present work we report on the energy loss ratio Rn of fast H2 clusters in thin films 30‐50 A of LaScO3 and HfO2. The medium energy ion scattering technique was employed covering a broad energy range 40‐200 keV/amu. The energy loss ratio data showed no clear evidence of collective excitations in these materials. The experimental results were interpreted in terms of three different theoretical approaches: the dielectric formalism with the Brandt-Reinheimer theory for semiconductor materials; the detailed simulation of the molecular fragments dynamics through the target; and finally the unitary convolution approximation adapted for hydrogen molecules. Only the simulation agrees with the experimental results for both oxides. The unitary convolution approximation works quite well for HfO2 but overestimates slightly the LaScO3 data. The overall results indicate that the energy loss ratio depends critically on the description of the electronic properties of such oxides.

The energy spectrum associated with scattering of 100 keV H+ ions from the outermost few atomic layers of Cu(111) in different scattering geometries provides direct evidence of trajectory-dependent electronic energy loss. Theoretical simulations, combining standard Monte Carlo calculations of the elastic scattering trajectories with coupled-channel calculations to describe inner-shell ionization and excitation as a function of impact parameter, reproduce the effects well and provide a means for far more complete analysis of medium-energy ion scattering data.

In the present work, we have explored the interference effects which arise when ${\mathrm{H}}_{2}^{+}$ and ${\mathrm{H}}_{3}^{+}$ cluster ions interact with a thin layer of $\mathrm{Si}{\mathrm{O}}_{2}$ in order to obtain a clear signature of plasmon excitations induced by these energetic projectiles. For this purpose, high-energy-resolution experiments were carried out as a function of the incoming projectile energy, covering an energy range between 40 and $200\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{amu}$. The ratio ${R}_{n}$ between the energy loss of the cluster and the sum of the energy loss of its constituents has a steep increase between 70 and $100\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{amu}$ for both cluster ions, which is associated with the plasmon excitation threshold.

Asymmetric line shapes for medium energy H and He ions backscattered from topmost adatoms such as $\text{Si}(111)\text{\ensuremath{-}}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\text{-Sb}$ and $\text{Ni}(111)\text{\ensuremath{-}}2\ifmmode\times\else\texttimes\fi{}2\text{-O}$ are measured by a toroidal electrostatic analyzer with an excellent energy resolution. The spectra exhibit a pronounced asymmetric nature and are well fitted by an exponentially modified Gaussian profile. It is found that the nonperturbative coupled-channel calculations reproduce well the observed asymmetric line shapes for ${\text{He}}^{+}$ impact on different materials, although slightly overestimate the asymmetry for ${\text{H}}^{+}$ impact on Au. On the other hand, the CASP 3.2 program (involving additional approximations) gives large underestimates for He ions and overestimates for H ions. This problem has been partially solved by modifying the order of the implementation of the shell corrections and higher-order effects in the CASP model.

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 to 1.5 nm thick HfO2 films on Si, supporting the application of this analytical model for proton scattering in the kinetic energy range from 100 to 200 keV

The aim of this work is to investigate the effects of 593 MeV Au irradiation using two different projectile charges, namely Au 30+ and Au 46.3+ on the structural, transport and magnetization properties of Co/NiFe/Co/Cu multilayers. X-Ray diffraction and extended X-ray absorption fine structures measurements show no significant structural change for as deposited and irradiated multilayers. On the other hand, the magnetoresistance amplitude decreases with the ion fluence but it is insensitive to the projectile charge state. The correlation between changes in the magnetoresistance and remanent magnetization suggests that the main effect responsible for the decrease of the magnetoresistance is the creation of ferromagnetic pinholes. These results are discussed on basis of the electronic thermal spike model and nuclear cascades theory and show similarities to the effects observed at low-energy ion-beam irradiation.

We report on craters formed by individual $3\text{ }\text{ }\mathrm{MeV}/u$ ${\mathrm{Au}}^{{q}_{\mathrm{ini}}+}$ ions of selected incident charge states ${q}_{\mathrm{ini}}$ penetrating thin layers of poly(methyl methacrylate). Holes and raised regions are formed around the region of the impact, with sizes that depend strongly and differently on ${q}_{\mathrm{ini}}$. Variation of ${q}_{\mathrm{ini}}$, of the film thickness and of the angle of incidence allows us to extract information about the depth of origin contributing to different crater features.

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 Auger-electron 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(1 1 1) 7 × 7 points to a small but significant phase effect in the short-time dynamics of ion tracks.

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 iontrack 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