Accurate knowledge of the energy deposition of slow ions in solids is essential for modelling plasma-material interactions. While nuclear stopping can be reliably predicted through simulations electronic stopping at very low energies remains challenging to determine. Using molecular dynamics simulations, we investigate how crystallographic structure and surface orientation affect the backscattering probability and impact parameters of low-energy He in fcc and bcc metals. On this basis we evaluate challenges for typical approaches to assess electronic stopping. Close-packed surface orientations yield higher backscattering and smaller mean impact parameters due to reduced channel sizes, with characteristic differences for different crystal structures. For fcc Au, the (1 1 1) surface behaves similarly to a pseudo-amorphous target, whereas for bcc W, the (1 1 0) surface shows a significantly lower backscattering probability. These structural effects can explain the observed energy scaling of the electronic stopping power in some bcc material systems extracted from relative measurements using fcc reference materials. The results furthermore highlight that crystallographic orientation and impactparameter selectivity can strongly bias measurements of electronic stopping at low energies, severely challenging the applicability of a single global electronic stopping cross section.

The interaction of energetic ions with materials is a fundamental process that occurs in fusion reactors, impacting radiation damage, heat deposition, and overall material performance. While previous work has significantly advanced our understanding of electronic stopping in metals, the impact of alloying and irradiation-induced defects remains underexplored, despite their importance for materials in extreme environments. In this work, we combine ab initio simulations with measurements to study electronic stopping in both pristine and defect-containing Fe and EUROFER97. By systematically assessing the influence of alloying and defects, we examine the extent to which structural modifications alter energy dissipation. Our findings contribute to a more rigorous understanding of electronic stopping in fusion-relevant materials and the reliability of simplified approaches in radiation damage simulations.

Energy spectra of backscattered and transmitted ions with primary energies of 50 keV and 100 keV interacting with self-supporting foils were recorded with a Time-of-Flight Medium-Energy Ion Scattering setup in a single experiment. Self-supporting Au and W foils without backing material were used. For He ions transmitted through Au the spectrum of detected particles shows two distinct components corresponding to different energy losses in the film, whereas for protons no such phenomenon was observed. To determine the origin of these different contributions, measurements for different angles of incidence and scattering angles have been evaluated. The results suggest that the two components in the spectrum of transmitted He ions could be attributed to impact parameter dependent energy loss, being more prominent for He ions than for protons. The main origin of the necessary impact parameter selection along the different ion trajectories is expected to be texture in the Au-foils.

Electronic stopping cross section of tungsten for light ions was experimentally measured in a wide energy interval (20 to 6000 keV for protons and 50 to 9000 keV for helium) in backscattering and transmission geometries. The measurements were carried out in three laboratories (Austria, Germany and Sweden) using five different set-ups, the stopping data deduced from different data sets showed excellent agreement amongst each other, with total uncertainty varying within 1.5-3.8% for protons and 2.2-5.5% for helium, averaged over the respective energy range of each data set. The final data is compared to available data and to widely adopted semi-empirical and theoretical approaches, and found to be in good agreement with most adopted models at energies around and above the stopping maximum. Most importantly, our results extend the energy regime towards lower energies, and are thus of high technological relevance, e.g., in fusion research. At these low energies, our findings also revealed that tungsten-featured with fully and partially occupied f- and d-subshells, respectively-can be modeled as an electron gas for the energy loss process.

Experimental spectra from Medium-Energy Ion Scattering were compared to Monte-Carlo simulations (employing the TRBS code) to obtain information on the scattering potential. The impact of uncertainties in the interatomic potential on quantification of sample properties such as thickness, composition or electronic stopping was investigated for different scattering geometries: backscattering and transmission. For backscattered He ions with tens of keV primary energy the scattering potential was found to overestimate the multiple scattering background in the energy spectra resulting in an uncertainty of <3 % in quantitative analysis. Light ions transmitted through a sample for equivalent path length in the medium are only affected minorly by changes in the scattering potential. This effect becomes more distinct for heavier primary ions.

The phase effect in electronic stopping deals with the question wheth er the energy loss of an ion due to the interaction with electrons depends on the state of aggregation of the target. It is commonly accepted that charge changing collisions of the projectile and changes in the electronic states of the target contribute to the phase effect In addition, the energy loss measurements might possibly be influenced by different impact parameter selection in the two experiments (solid and gas phase). Quantitative results of our calculations show that generally the impact paramet er selection inherently present in a transmission experiment is quenched by the inevitable multiple scattering of the projectiles . Thus , electronic excitation and ionization in the projectile and the target are the only processes that contribute significantly to the phase effect.

Electronic stopping cross sections of different transition metals (Nb, Pd, Ta, and Pt) for light ions have been experimentally determined in a wide energy range. We performed relative measurements using different backscattering geometries for protons (from 50 to 5000 keV) and helium (from 80 to 10000 keV). Data are compared to values from the literature, as well as to the widely used semiempirical (SRIM) and modeling (DPASS) approaches. The magnitude and energy dependence of the deduced stopping power at energies around the Bragg peak, as well as the different trends observed within individual periods, are analyzed with respect to target atomic number and electronic structure. We also compare the observed magnitude of electronic stopping to several different theoretical approaches.

We investigated the impact of surface oxygen on the ion yield for He+ ions scattered from different single crystalline surfaces in low-energy ion scattering. Initially clean Al(111) and Ta(111) were exposed to molecular oxygen and ion spectra for different oxidation stages and different primary energies were recorded. A comparison of ion yields normalized to the differential scattering cross section as well as experimental factors allows obtaining information about the influence of oxygen on charge exchange processes. The decrease in the ion yield of both metals with exposure cannot be explained by different surface coverages exclusively, but requires the neutralization efficiency to be dependent on the chemical structure of the surface. For Ta, additionally, a different energy dependency of the ion yield obtained in the metal and oxide occurs. The ion yield for O shows in both surfaces a significantly weaker energy dependency than the investigated metals.

We investigated the specific electronic energy deposition by protons and He ions with keV energies in different transition metal nitrides of technological interest. Data were obtained from two different time-of-flight ion scattering setups and show excellent agreement. For protons interacting with light nitrides, i.e. TiN, VN and CrN, very similar stopping cross sections per atom were found, which coincide with literature data of N(2)gas for primary energies <= 25 keV. In case of the chemically rather similar nitrides with metal constituents from the 5(th)and 6(th)period, i.e. ZrN and HfN, the electronic stopping cross sections were measured to exceed what has been observed for molecular N(2)gas. For He ions, electronic energy loss in all nitrides was found to be significantly higher compared to the equivalent data of N(2)gas. Additionally, deviations from velocity proportionality of the observed specific electronic energy loss are observed. A comparison with predictions from density functional theory for protons and He ions yields a high apparent efficiency of electronic excitations of the target for the latter projectile. These findings are considered to indicate the contributions of additional mechanisms besides electron hole pair excitations, such as electron capture and loss processes of the projectile or promotion of target electrons in atomic collisions.

Electronic stopping cross sections (SCSs) of nickel, silicon, and nickel-silicon alloys for protons and helium (He) ions are studied in the regime of medium- and low-energy ion scattering, i.e., for ion energies in the range from 500 eV to 200 keV. For protons, at velocities below the Bohr velocity the deduced SCS is proportional to the ion velocity for all investigated materials. In contrast, for He ions nonlinear velocity scaling is observed in all investigated materials. Static calculations using density functional theory (DFT) available from the literature accurately predict the SCS of Ni and Ni-Si alloy in the regime with observed velocity proportionality. At higher energies, the energy dependence of the deduced SCS of Ni for protons and He ions agrees with the prediction by recent time-dependent DFT calculations. The measured SCS of the Ni-Si alloy was compared to the SCS obtained from Bragg's rule based on SCS for Ni and Si deduced in this study, yielding good agreement for protons, but systematic deviations for He projectiles, by almost 20%. Overall, the obtained data indicate the importance of nonadiabatic processes such as charge exchange for proper modeling of electronic stopping of, in particular, medium-energy ions heavier than protons in solids.

We present a thorough experimental study of electronic stopping of H, He, B, N, Ne and Al ions in TiN with the aim to learn about the energy loss mechanisms of slow ions. The energy loss was measured by means of time-of-flight medium-energy ion scattering. Thin films of TiN on silicon with a δ-layer of W at the TiN/Si interface were used as targets. We compare our results to non-linear density functional theory calculations, examining electron-hole pair excitations by screened ions in a free electron gas in the static limit, with a density equivalent to the expected value for TiN. These calculations predict oscillations in the electronic stopping power for increasing atomic number Z1 of the projectile. An increasing discrepancy between our experimental results and predictions by theory for increasing Z1 was observed. This observation can be attributed to contributions from energy loss channels different from electron-hole pair excitation in binary Coulomb collisions.

The electronic stopping cross section (SCS) of Ni for slow H+, H2+, D+ and D2+ ions has been investigated for different types of targets in two complementary experimental geometries, i.e., in transmission and backscattering. To warrant sample purity, both a high purity nickel sheet and nanometer Ni layers were prepared in-situ under ultra-high-vacuum conditions. In an alternative approach, ultra-thin samples were prepared ex-situ as self-supporting foils and as nanometer films on a polished substrate (silicon). Identical SCS results are obtained in backscattering using the in-situ prepared film and the high purity sheet. The ex-situ prepared targets contained considerable concentrations of impurities of low atomic numbers, whose contribution to the SCS can be rectified by applying Bragg's rule using TRIM stopping for the impurities. In this way for the ex-situ targets the accuracy of the resulting SCS data is improved considerably. Concordant stopping cross section data are obtained in both geometries. The achieved accuracy does, however, not permit to spot a possible influence of different impact parameter regimes explored in transmission and in backscattering geometries.

Background/aim A detrimental role of saturated fatty acids (SFA) on blood lipids has been suggested but not confirmed in adolescents. Physical activity (PA) may influence blood lipids by altering the metabolic fate of nutrients. To understand the integrated role of these lifestyle factors we tested the association of SFA intake with blood lipids in 15-year-olds, considering interactions with different PA levels. Methods Children from the GINIplus and LISA cohorts with data on SFA, PA and blood lipids at age 15 years were included (n=830). SFA intake (% of total kcal) was estimated from food frequency questionnaires. PA (average min/day) was measured over one week by accelerometers and classified into sedentary, lifestyle (LSPA), or moderate-to-vigorous (MVPA). Blood lipids (total cholesterol, LDL, HDL, and triglycerides) were measured in serum and those with skewed distribution were log-transformed (all except HDL). Sex-stratified associations between SFA and blood lipids were assessed by linear regression, adjusting for potential confounders. Interaction terms were included between SFA and PA levels, and for significant interactions analyses were performed stratified by tertiles of the relevant PA level. Results No significant association was observed between dietary SFA and any of the blood lipid outcomes. Interactions were observed with time spent sedentary for the outcomes total cholesterol and HDL in females, and with time spent in LSPA for LDL and triglycerides, in males and females, respectively (p<0.1). Stratified analyses indicated a significant inverse association between SFA (per interquartile increase) and triglycerides in females, only in the lowest LSPA tertile (means ratio: 0.91 (95% confidence interval: 0.85; 0.98), p=0.01). Further, a significant positive association was observed with total cholesterol and LDL in males in the middle tertile of LSPA (1.08 (1.03; 1.14), p=0.004; and 1.12 (1.03; 1.21), p=0.01, respectively). Conclusion Our findings do not indicate a significant association between SFA intake and blood lipids among adolescents. The role of dietary SFA on the lipid profile might vary in an activity-specific manner, although interpretation may be complicated due to non-intended noise arising from methodological limitations. For further insight, future analyses might consider other, possibly correlated nutrients.

Electronic stopping measurements in chemically reactive targets, e.g., transition and rare earth metals are challenging. These metals often contain low Z impurities, which contribute to electronic stopping. In this article, we present two ways how one can correct for the presence of impurities in the evaluation of proton and He stopping in Ni for primary energies between 1 and 100 keV, either considering or ignoring the contribution of the low Z impurities to multiple scattering. We find, that for protons either method leads to concordant results, but for heavier projectiles, e.g. He ions, the influence on multiple scattering must not be neglected.

Studying the initial stages of surface oxidation is of great relevance to understand how oxygen alters the physical and chemical properties at the interface of the host material to the environment and is therefore, crucial for improvement in manifold technological applications. We investigated the influence of surface oxygen on ion spectra recorded for keV noble gas ions backscattered from metal surfaces in low energy ion scattering (LEIS). Initially pure Zn and Ta surfaces, chosen for their well-characterized properties in ion-neutralization in LEIS, have been oxidized and ion spectra for pure and oxidized surfaces have been compared. Oxygen on the surface significantly influences shape and intensity of the backscattered ion spectrum at all energies: for both metal systems, the surface scattered ion yield of the metal is drastically decreasing under oxygen presence. The observed decrease, however, cannot be explained by the reduction in the surface areal density of the metal constituents exclusively. At least for Zn an additional significant change in charge exchange behavior is necessary to explain the observations. In contrast to the generally observed decrease in the yield of ions scattered from the outermost surface, the change in shape and intensity of the reionization background are found to show opposing trends and different energy dependencies for Zn and Ta.

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.

A stringent limitation in many optoelectronic devices, such as solar cells and light emitting diodes, is the intrinsic need for a transparent electrode. Uniting relevant aspects, indium tin oxide (ITO) is often the material of choice, however, alternatives are sought and being in particular found in conductive polymers. In this work, we present a novel doping strategy to arrive at highly conducting polymeric material based on poly-3,4-ethylenedioxythiophene (PEDOT). Based on commercial high conductivity PEDOT:PSS (Clevios PH 1000), and a post processing with aqueous triflic acid delivers a material that is both transparent and of low resistivity (5.23 × 10−4 Ω cm). Furthermore, this material retains its conductive character over a large temperature range, indicating metallic behaviour. This is further supported by positive magnetoconductance effects at low temperatures (1.8–10 K) and extended mean free paths of the conduction electrons are observed—evidencing for a metallic state in this polymer.

Electronic stopping of slow protons in ZnO, VO_{2} (metal and semiconductor phases), HfO_{2}, and Ta_{2}O_{5} was investigated experimentally. As a comparison of the resulting stopping cross sections (SCS) to data for Al_{2}O_{3} and SiO_{2} reveals, electronic stopping of slow protons does not correlate with electronic properties of the specific material such as band gap energies. Instead, the oxygen 2p states are decisive, as corroborated by density functional theory calculations of the electronic densities of states. Hence, at low ion velocities the SCS of an oxide primarily scales with its oxygen density.

Depth profiling using surface sensitive analysis methods in combination with sputter ion etching is a common procedure for thorough material investigations, where clean surfaces free of any contamination are essential. Hence, surface analytic studies are mostly performed under ultra-high vacuum (UHV) conditions, but the cleanness of such UHV environments is usually overrated. Consequently, the current study highlights the in principle known impact of the residual gas on metal surfaces (Fe, Mg, Al, Cr and Zn) for various surface analytics methods, like X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and low-energy ion scattering (LEIS). The investigations with modern, state-of-the-art equipment showed different behaviors for the metal surfaces in UHV during acquisition: (i) no impact for Zn, even after long time, (ii) solely adsorption of oxygen for Fe, slight and slow changes for Cr and (iii) adsorption accompanied by oxide formation for Al and Mg. The efficiency of different counter measures was tested and the acquired knowledge was finally used for ZnMgAl coated steel to obtain accurate depth profiles, which exhibited before serious artifacts when data acquisition was performed in an inconsiderate way. (C) 2017 Elsevier B.V. All rights reserved.

The revival of interest in Ge1−xSnx alloys with x ≥ 10% is mainly owed to the recent demonstration of optical gain in this group-IV heterosystem. Yet, Ge and Sn are immiscible over about 98% of the composition range, which renders epilayers based on this material system inherently metastable. Here, we address the temperature stability of pseudomorphic Ge1−xSnx films grown by molecular beam epitaxy. Both the growth temperature dependence and the influence of post-growth annealing steps were investigated. In either case we observe that the decomposition of epilayers with Sn concentrations of around 10% sets in above ≈230 °C, the eutectic temperature of the Ge/Sn system. Time-resolved in-situ annealing experiments in a scanning electron microscope reveal the crucial role of liquid Sn precipitates in this phase separation process. Driven by a gradient of the chemical potential, the Sn droplets move on the surface along preferential crystallographic directions, thereby taking up Sn and Ge from the strained Ge1−xSnx layer. While Sn-uptake increases the volume of the melt, single-crystalline Ge becomes re-deposited by a liquid-phase epitaxial process at the trailing edge of the droplet. This process makes phase separation of metastable GeSn layers particularly efficient at rather low temperatures.