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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.

Surface damage produced by single MeV-GeV heavy ions impacting ultrathin polymer films has been shown to be weaker than those observed under bulk (thick film) conditions. The decrease in damage efficiency has been attributed to the suppression of long-range effects arising from excited atoms lying deeply in the solid. This raises the possibility that the substrate of the films itself may be relevant to the radiation effects seen at the top surface. Here, the role of the substrate on cratering induced by individual 1.1 GeV Au ions in ultrathin poly(methyl methacrylate) (PMMA) layers is investigated. Materials of different thermal and electrical properties (Si, SiO2, and Au) are used as substrates to deposit PMMA thin films of various thicknesses from ∼1 to ∼300 nm. We show that in films thinner than ∼40 nm craters are modulated by the underlying substrate to a degree that depends on the transport properties of the medium. Crater size in ultrathin films deposited on the insulating SiO2 is larger than in similar films deposited on the conducting Au layer. This is consistent with an inefficient coupling of the electronic excitation energy to the atomic cores in metals. On the other hand, the damage on films deposited on SiO2 is not very different from the Si substrate with a native oxide layer, suggesting, in addition, poor energy transmission across the film/substrate interface. The experimental observations are also compared to calculations from an analytical model based on energy addition and transport from the excited ion track, which describe only partially the results.

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.

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.

The formation of nanopores by highly charged ion impacts on freestanding fluorine-functionalized graphene is demonstrated. The process is driven by potential sputtering, which becomes active by changing the semimetallic property of graphene into a strongly insulating state by fluorination. The interaction of fluorographene with highly charged ions is also studied in terms of charge exchange and kinetic energy loss. A higher number of captured electrons and a larger kinetic energy loss than in pristine graphene are observed, which can be well explained by an increase in the ion neutralization length and in the atomic areal density of the target, respectively. Using a computer code based on a time-dependent scattering potential model, a connection between the efficiency of charge exchange and the fluorine coverage is revealed. Our results suggest a competition of two distinct nanostructure formation processes, leading either to pore formation or fluorine desorption.

The dielectric function is often known in the optical limit (zero momentum) but knowledge away from zero momentum is required for the calculation of many physical properties, such as ion stopping and inelastic mean free path. We review the several extension schemes and compare the results with the available literature and investigate in particular the effect of the extension scheme on the calculated proton stopping for the case of Li.

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).

Many aspects of the interaction of charged particles with matter can be expressed in terms of the dielectric function e ( q , ω ) . The dielectric function is relatively well known in the optical limit ( q = 0 ) but, for example, stopping power calculations require the knowledge of the dielectric function for q ≠ 0 . Several approaches have been used to extend the dielectric function to q ≠ 0 for both the valence electrons, using variations of the Lindhard dielectric function and the core levels where an atomic description can be used. The intermediate case of shallow core levels is somewhat problematic. Here collective effects modify the atomic picture, and the hydrogenic approximation of the wave function is less accurate. In this paper we describe a new extension scheme of the contribution to the energy loss function of shallow core levels to q ≠ 0 and show that tor Al and Si it describes the experimental stopping data somewhat better than previous approaches. It also describes reasonably well the proton and electron induced ionization cross section of these shallow core levels. Lastly we investigate the dielectric function in the limit of high momentum, where it can be interpreted as a Compton profile. An approximation scheme in terms of Mermin dielectric function with an amplitude that depends on q works in all cases quite well.

It is well established that the shape of spectra acquired using reflection electron energy loss spectroscopy (REELS) is determined by the dielectric function. Extracting the dielectric function from REELS spectra is a real challenge as it is governed by strong multiple scattering. It is generally assumed that the contribution of shallow core levels (with binding energies over 100 eV) to the REELS data can be neglected when one interprets valence band REELS data that usually extends to, at most, 100 eV energy loss. Here we show that, especially when incoming energies over 1 keV are used, this is not the case and that the intensity of the REELS spectrum can only be calculated correctly if the shallow core levels are taken into account. The implications for this for the extraction of the dielectric function from REELS data is discussed.

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.

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.

Arsenic profiles in plasma doped silicon wafers were traced by scattering of H+ and H-2(+) ions at medium energies. Two wafers were doped with the same bias, gas pressure, total implanted dose and AsH3 concentration. After implantation, the wafers were submitted to industrial cleaning processes, resulting in the formation of a surface SiO2 layer, and one wafer was subjected to an additional thermal treatment. Scattering spectra of single and molecular ion beams with the same energy per nucleon and charge state differed only by the energy broadening due to the break-up of the molecule, allowing depth profiling by calculation of the dwell time before the backscattering collision. For the SiO2 layers of these samples a density reduction of, on average, 13% was observed, compared to thermally grown SiO2. In addition, the arsenic depth-profile determined were in close agreement with independent findings obtained by electron techniques.

We have experimentally determined electronic stopping cross sections of vanadium for 50–2750 keV protons and for 250–6000 keV He ions by relative measurements in backscattering geometry. To check the consistency of the employed procedure we investigate how to define adequate reference stopping cross section data and chose different reference materials. To proof consistency of different reference data sets, an intercomparison is performed to test the reliability of the evaluation procedure for a wide range of energies. This process yielded consistent results. The resulting stopping cross section data for V are compared to values from the IAEA database, to the most commonly employed semi-empirical program SRIM, and to calculations according to CasP. For helium, our results show a significant deviation of up to 10% with respect to literature and to SRIM, but are in very good agreement with the CasP predictions, in particular when charge-exchange processes are included in the model.

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.

Despite all efforts to explore the structural properties of bimetallic nanoparticles, there is still a constraint of proper tools to successfully probe their composition and atomic arrangement. In this work, bimetallic PtPd nanoparticles with approximately 5 nm mean diameter were synthesized to achieve distinct atomic distributions: nanoalloys or core@shell. The samples were probed by medium energy ion scattering (MEIS) and space-resolved elemental analysis via energy-dispersive X-ray (EDX) spectroscopy in scanning transmission electron microscope (STEM) mode. The complementary association of STEM-EDX profiling with MEIS, which simultaneously surveys millions of nanoparticles, becomes a powerful tool for a statistically representative structural analysis. As a result, the measurements provided key details such as core size, shell thickness, and composition and even distinguished core@shell from core@alloy structures. PtPd nanoalloys and Pd-core structures were successfully obtained, while the attempt to p...

The Drude dielectric function is a simple way of describing the dielectric function of free electron materials, which have an uniform electron density, in a classical way. The Mermin dielectric function describes a free electron gas, but is based on quantum physics. More complex metals have varying electron densities and are often described by a sum of Drude dielectric functions, the weight of each function being taken proportional to the volume with the corresponding density. Here we describe a slight variation on the Drude dielectric functions that describes insulators in a semi-classical way and a form of the Levine-Louie dielectric function including a relaxation time that does the same within the framework of quantum physics. In the optical limit the semi-classical description of an insulator and the quantum physics description coincide, in the same way as the Drude and Mermin dielectric function coincide in the optical limit for metals. There is a simple relation between the coefficients used in the classical and quantum approaches, a relation that ensures that the obtained dielectric function corresponds to the right static refractive index. For water we give a comparison of the model dielectric function at non-zero momentum with inelastic X-ray measurements, both at relative small momenta and in the Compton limit. The Levine-Louie dielectric function including a relaxation time describes the spectra at small momentum quite well, but in the Compton limit there are significant deviations.

The diffusivity of oxygen in thin, sputter-deposited TiO 2 films, as can be used in RRAMs, is measured using electron and ion backscattering techniques. The as-grown sample consisted of two layers (Ti 16 O 2 and Ti 18 O 2 ) and was annealed between 500 °C and 900 °C. The depth profiles of 18 O, as measured with both techniques, were similar. The extent of diffusion was much larger than expected from the literature data for O diffusion in single-crystal rutile, suggesting that defects in the sputter-deposited film play an essential role in the diffusion process.

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.

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.

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.

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.

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.

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.

Implantation of Hf films with oxygen ions is shown to be an effective means of fabricating high-quality HfO

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).

In this communication we report on fluctuation conductivity experiments in several superconducting YBa 2 Cu 3 O 6 + d thin films grown by chemical solution deposition. These films are c -axis oriented and show granularity at a submicron scale. Two of the samples were submitted to ion implantation in order to study effects of local disorder. When the temperature approaches the superconducting transition from above we first observe the expected three-dimensional Gaussian fluctuation region. Then, a crossover occurs closely above the transition to a regime dominated by genuine critical fluctuations characterized by a large exponent. Based on previous theoretical predictions, we interpret these critical regimes as precursors of the superconducting chiral glass state.

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.

In this paper we report the application of a suitable methodology to study the morphology, structure and composition of core@shell nanoparticles (NPs) systems with polydispersity in the shell thickness, with subnanometer resolution and good sampling. Through the combination of Medium Energy Ion Scattering with Transmission Electron Microscopy, we perform a systematic investigation on core@shell Au@Ag NPs synthesized by an original wet chemical method. For samples synthesized with baths of different AgNO3 concentrations, the present approach allowed us to determine the NP's Ag shell thicknesses distribution of about a few nanometers around the Au core. Fil: Sanchez, Dario F.. Universidade Federal do Rio Grande do Sul; Brasil Fil: Moiraghi, Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Cometto, Fernando Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Perez, Manuel Alejo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Fichtner, Paulo F. P.. Universidade Federal do Rio Grande do Sul; Brasil Fil: Grande, Pedro L.. Universidade Federal do Rio Grande do Sul; Brasil

Recently two papers have been published deriving the dielectric function from hafnia from electron energy loss data (Jin et al. Applied Physics Letters 100 083713 (2006), Behar et al. Phys. Rev A. 80 062901 (2009)). The obtained dielectric functions are compared in their optical limit and differ considerably. Here we try to clarify the situation by presenting new experimental data and review the analysis procedure used in the earlier work. We conclude that the discrepancy is most likely caused by a shortcoming in the way that the momentum-dependence of the dielectric function is modelled.

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.

We report on measurements of the voltage difference between non-aligned electrical contacts placed on opposite edges of several YBa 2 Cu 3 O 6 + d (YBCO) thin films prepared by a chemical method. The experiments were performed while the samples were traversed by a longitudinal electrical current. Experiments are focused on the region of the superconducting transition. In many cases these transverse voltage results do not reproduce the measurements carried out with the conventional geometry, where the voltage contacts are aligned along the current orientation. An excess transverse voltage was identified in a narrow temperature range encompassing the critical temperature. The sign and detailed shape of the excess transverse voltage vary from sample to sample. The application of a magnetic field perpendicular to the film surface suppresses the effect above a certain field threshold. The shape and magnitude of the excess transverse voltage peaks are also strongly modified or suppressed in samples submitted to implantation with oxygen ions or to a slight deoxygenation process. The simplest models considering the occurrence of a transverse current flow generated by film inhomogeneities cannot explain the totality of the obtained results. We thus suggest an interpretation of the excess transverse voltage effect based on the stabilization of a chiral-glass superconducting phase in the studied YBCO films. The occurrence of this state is related to the submicron granularity that characterizes the microstructure of these films.

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.

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.

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.