Elastic Backscattering Research Articles

Charge Phenomena in the Elastic Backscattering of Electrons from Insulating Polymers.

Elastic peak electron spectroscopy (EPES) analyzes the line shape of the elastic peak. The reduction in energy of the elastic peak electrons is the result of energy transfer to the target atoms, a phenomenon known as recoil energy. EPES differs from other electron spectroscopies in its unique ability to identify hydrogen in polymers and hydrogenated carbon-based materials. This feature is particularly noteworthy as lighter elements exhibit stronger energy shifts. The energy difference between the positions of the elastic peak of carbon and the elastic peak of hydrogen tends to increase as the kinetic energy of the incident electrons increases. During electron irradiation of an insulating polymer, if the number of secondary electrons emitted from the surface is less than the number of electrons absorbed in the sample, the surface floats energetically until it stabilizes at a potential energy eVs. As a result, the interaction energy changes and modifies the energy difference between the elastic peaks of hydrogen and carbon. In this study, the charge effects are evaluated using the Monte Carlo method to simulate the EPES spectra of electrons interacting with polystyrene and polyethylene.

Upgrade of the ion beam analysis end-station with the wavelength dispersive X-ray spectrometer for use with the focused MeV ion beams

A novel modular end-station has been developed for use with focused MeV ion beams. It supports analysis of micro-samples using simultaneously several ion beam analysis (IBA) techniques, including wavelength dispersive (WD) and energy dispersive (ED) Particle Induced X-ray Emission (PIXE) spectrometry, Elastic Backscattering Spectrometry (EBS and RBS) and Nuclear Reaction Analysis (NRA). The end-station enables quantitative elemental analysis, including the creation of two-dimensional elemental maps based on the ED-PIXE and EBS/RBS/NRA measurements. The in-house developed wavelength dispersive X-ray (WDX) spectrometer can measure high energy resolution spectra on selected sample micro-regions. In this work the description of the modular end-station is presented, highlighting the features of the WDX spectrometer: i) in the complementary analysis of complex ED X-ray spectra with many overlapping peaks measured simultaneously and ii) in chemical speciation studies. An example is presented to demonstrate the capabilities of the modular system for simultaneous analytical measurements of selected heterogeneous micro-samples.

The quantitative damage and impurity depth profiling of the MgO single crystal

Ion implantation is frequently used method for the simulation of material damage caused by its exposure to harsh environments. The induced material damage and impurities accumulation will exhibit strong depth dependency in the case of its exposure to charged particles due to particle energy losses mechanisms. In presented study, we have performed an ion implantation of 4 MeV C3+ ions with three different fluences (1.5, 5 and 10 × 1015 cm−2) in the MgO [100] crystal in order to simulate structural damage induced by energetic particles. The damage depth profiles have been obtained by Elastic Backscattering Spectrometry in channeling orientation (EBS/C) using 1.86 MeV protons. EBS/C spectra were analyzed with the in house developed phenomenological Channeling SIMulation (CSIM) code. In addition to the damage depth profiles, with the new upgraded version of CSIM, concentration depth profile of implanted atoms (impurities) have also been determined. EBS/C spectra obtained profiles have been compared with the results of depth-resolved (micro) Photoluminescence spectroscopy (μPL) of the implanted MgO crystal cross-section. EBS/C and μPL obtained profiles for all investigated samples show very good consistency. This opens up the possibility for usage of EBS/C method in material analysis of lighter than bulk impurity concentration profiling.

Deuterium loading of redeposited-like W coatings present in tokamaks by ion implantation

Pulsed Laser deposition (PLD) is a suitable technique to reproduce W, W–O and W–N–O coatings resembling those present in tokamaks walls, as protective W coatings covering plasma facing components (PFCs) or W-based layers redeposited in PFCs during reactor operation. Nevertheless, difficulties still exist to codeposit deuterium in all such layers, and parallel methods need to be implemented to load it. W-based coatings with porous and columnar microstructures grown by PLD where loaded with flat depth contents of deuterium down to 0.4–0.6 μm using multiple ion implantation steps at distinct incident energies and fluences. Deuterium amounts close to 7 at.% were easily achieved. Similar deuterium contents are commonly observed in deposits in now-a-days tokamaks. Microstructural characterization of the coatings was carried out by scanning electron microscopy (SEM). Quantitative elemental analysis of as-deposited and as-implanted materials was accessed by elastic backscattering spectroscopy (EBS), nuclear reaction analysis (NRA) and by time-of-flight elastic recoil detection (ToF-ERDA). Secondary ion mass spectrometry (SIMS) revealed the depth profiles of the existing isotopes and, particularly, of retained deuterium. Beyond their use in ex-situ experiments, the production is useful to calibrate laser induced breakdown spectroscopy (LIBS) and SIMS setups, aiming a standard free depth-quantification of deuterium in W-based coatings.

Deuterium retention in co-deposition with lithium in Magnum-PSI: experimental analysis and comparison with SOLPS-ITER

The vapor-box, a liquid metal design for the divertor, utilizes lithium recirculation through evaporation and condensation. Safety concerns arise from Li-D/T formation and co-deposition on vapor-box walls and the first wall, affecting tritium retention. Additively manufactured tungsten capillary porous structure (CPS) samples with Li were exposed to high heat flux D plasmas in the linear plasma device Magnum-PSI, to study D retention in Li–D co-deposition dependence on substrate temperature (200 ∘ C–428 ∘ C) and distance from the plasma beam center (25–85 mm). The D:Li ratio was determined via in-situ ion beam diagnostics with simultaneously analyzed Nuclear Reaction Analysis and Elastic Backscattering Spectroscopy spectra to maximize the precision. Experimental results approach close to the theoretical maximum at 40:60 D:Li ratio and deposited film thickness ranging from 0.02 to 3.2 µm. Witness plate temperatures above 400 ∘ C yielded Li films under 150 nm in thickness with lower D:Li ratios (5:95 D:Li ratio). At this temperature LiD decomposition pressure is comparable with vessel pressure during plasma. SOLPS-ITER simulations narrowed CPS surface temperature to 650 ∘ C–700 ∘ C, indicating Li+ plasma dominance near the target surface. Redeposition ratio of lithium on the CPS surface was determined to be around 80 % , matching quartz crystal microbalance results. However, SOLPS-ITER simulations lacked accuracy in recreating observed Li and D deposition layers on WPs, improvements are needed to model plasmas with significant Li quantities. Extension of SOLPS-ITER simulations to include LiD molecules and enhance heat flux accuracy is crucial for better alignment with experimental data.

Mechanical properties of VC/ZrC and VC/HfC superlattices

Face-centered cubic transition metal carbides exhibit high melting points and hardness, making them prominent candidates for protective coating applications. Vanadium carbide (VC) has typical characteristics of transition metal carbides. It serves as model material in this study, in which we showcase the effect of superlattice architecture on mechanical properties and fracture toughness. While beneficial effects of superlattice arrangement have been demonstrated for a series of nitride-based coatings, transition metal carbides remain largely unexplored territory. Following density functional theory based ab initio predictions on lattice and shear modulus mismatch, we develop VC/ZrC and VC/HfC superlattice coatings synthesized via pulsed DC sputter deposition. The bilayer periods (Λ) of our fully fcc-structured polycrystalline coatings range between 2–50 nm (indicated by X-ray diffraction, transmission and scanning electron microscopy). The chemical composition is close to 1:1 stoichiometry (from X-ray fluorescence, elastic back-scattering spectrometry and elastic recoil detection analysis). Both superlattice series exhibit a strong dependence of hardness, elastic modulus, and fracture toughness on their bilayer periods, which can only be correlated with the in-plane stress variations for VC/ZrC. The VC/HfC superlattices provide their peak-hardness of 36.0 ± 1.6 GPa for Λ = 6 nm and their peak in fracture toughness of 3.5 ± 0.5 MPa√m for Λ = 10 nm.

The impact of formalin fixation in the elemental content of tissues: Parametrization up to 48 h

Formalin fixation is a crucial step in the preparation of tissue samples for anatomic pathology studies, however, research showed that prolonged formalin fixation, can alter the elemental composition of tissues with implications for pathology and biomedical research. In this study we aim to assess and parametrize the influence of short-term formalin fixation in tissues.Six sets of human colon tissue samples were exposed to different formalin fixation times, up until 48 h. The elemental content throughout time was compared to the elemental content of the snap-frozen sample of the same tissue that was not exposed to formalin using Energy Dispersive X-ray Fluorescence.Results showed a clear decrease of Cl and K concentration in the tissues solution reaching a plateau between 1 h and 3 h of fixation. Also, there is an uptake of P in the tissue, likely due to the buffered formalin solution, within the first 15 min of fixation. This behaviour was concomitant with an increase of Na determined using Particle Induced gamma-ray emission analysis (PIGE) and Elastic Backscattering Spectroscopy (EBS). The dynamic changes determined in the studied elements demonstrate that a better understanding of the fixation-related mechanisms is in demand as well as optimization of the fixation protocols implemented in anatomic pathology laboratories.

Preliminary results of the theranostic 47Sc cyclotron proton-induced production with enriched 48Ti, 49Ti and 50Ti targets

The scientific community interest in the production of the theranostic 47Sc is due to its medical favourable decay characteristics suitable for both SPECT imaging and therapeutic purposes. Considering the SPES cyclotron, this work is focused on the measurement of the 48/49/50Ti(p,x)47Sc and 46Sc cross sections up to 70 MeV. In fact, 46Sc is the main co-produced contaminant, since it has a longer half-life than the theranostic 47Sc. Enriched 48/49/50Ti powder were deposited on aluminum backing by using the HIVIPP technique and the obtained targets were characterized by Elastic Back Scattering at the INFN-LNL. Experimental data are compared with the scarce literature and the TALYS results, obtained using the default parameters.

Nuclear Cross-Section of Proton-Induced Reactions on Enriched 48Ti Targets for the Production of Theranostic 47Sc Radionuclide, 46cSc, 44mSc, 44gSc, 43Sc, and 48V.

The cross-sections of the 48Ti(p,x)47Sc, 46cSc, 44mSc, 44gSc, 43Sc, and 48V nuclear reactions were measured from 18 to 70 MeV, with particular attention to 47Sc production. Enriched 48Ti powder was deposited on an aluminum backing and the obtained targets were characterized via elastic backscattering spectroscopy at the INFN-LNL. Targets were exposed to low-intensity proton irradiation using the stacked-foils technique at the ARRONAX facility. Activated samples were measured using γ-spectrometry; the results were compared with the data int he literature and the theoretical TALYS-based values. A regular trend in the new values obtained from the different irradiation runs was noted, as well as a good agreement with the literature data, for all the radionuclides of interest: 47Sc, 46cSc, 44mSc, 44gSc, 43Sc, and 48V. 47Sc production was also discussed, considering yield and radionuclidic purity, for different 47Sc production scenarios.

Elastic backscattering during boron implantation in Si1-xGex

We have investigated the elastic backscattering which occurs during ion implantation, and its impact on the retained implantation dose. A series of Si1-xGex (0 ≤ x ≤ 1) alloy films were implanted with 5 × 1014 atoms/cm2 of 11B at an energy of 10 keV. Nuclear reaction analysis (NRA) was used to characterize the retained boron dose within the Si1-xGex (0 ≤ x ≤ 1) samples by means of the 11B(p,α1)2α12 nuclear reaction. The experimental results show that the elastic backscattering effect is significant in this case, with the retained boron dose decreasing linearly as the target matrix varies from pure silicon to pure germanium. Our findings are in good agreement with simulations carried out using the SRIM-2013 software. Our study indicates that the backscattering effect during implantation must be accounted for when a specific concentration is targeted, or when adopting an implanted film as a reference standard, for example, in secondary ion mass spectrometry.

Determination of stopping power for light ions using resonance backscattering

A technique of the stopping power determination based on the analysis of the anomalies in elastic backscattering spectra is presented. It can be applied to both single element materials and compounds provided that they contain at least one element the elastic scattering cross-section for which has a resonance structure. The determination of the stopping power of alpha particles in carbon was chosen in this work for the case study.

Simulation of large angle backscattering spectra of channeled protons in Geant4

In this work a new open source simulation model based on GEANT4 toolkit is presented that allows the simulation of large angle elastic backscattering spectra of protons in single virgin crystals. The simulation model evaluates the backscattering yield based on the differential cross-section, modified by the close encounter probability with lattice atoms at a specific projectile position. Simulations were performed for 1–2.5 MeV energy protons channeled along the silicon, diamond, silicon dioxide and silicon carbide crystals. The comparison between experimental and simulated curves has shown that the developed model is capable of accurately simulating the channeling backscattering spectra of protons when angular beam spread is considered in the simulations. Although perfect match of the simulated spectra to the experimental ones was not achieved in all cases, the agreement between results is highly promising. The presented model is a proof of concept and further development of the model for the simulation of lattices with defects is underway.

Study of morphological, physical and mechanical properties of thin NbN films synthesized via DC magnetron sputtering system

PurposeNiobium Nitride (NbN) was interesting material for its applications in the medicinal tools or tools field (corresponding to saline serum media) as well as in mechanical properties. The aim of this work was depositing NbN thin films on two types of substrates (stainless steel (SS304) and silicon (100)) using plasma technique at varied powers (100–150 W).Design/methodology/approachDC magnetron sputtering technique at different powers were used to synthesis NbN films. Film structure was studied using X-ray diffraction (XRD) pattern. Rutherford elastic backscattering and energy dispersive X-ray were used to examine the deposited film composition. The films morphology was studied via atomic force microscopy and scanning electron microscopy images. Corrosion resistance of the three NbN/SS304 films was studied in 0.9% NaCl environment (physiological standard saline).FindingsAll properties could be controlled by the modification of DC power, where the crystallinity of samples was changed and consequently the corrosion and microhardness were modified, which correlated with the power. NbN film deposited at higher power (150 W) has shown better corrosion resistance (0.9% NaCl), which had smaller grain size (smoother) and was thicker.Originality/valueThe NbN films have a preferred orientation (111) matching to cubic structure phase. Corrosion resistance was enhanced for the NbN films compared to SS304 substrates (noncoating). Therefore, NbN films deposited on SS304 substrate could be applied as medicinal tools as well as in mechanical fields.

Theory of glide symmetry protected helical edge states in a WTe2 monolayer

Helical edge states in quantum spin Hall (QSH) materials are central building blocks of topological matter design and engineering. Despite their principal topological protection against elastic backscattering, the level of operational stability depends on manifold parameters such as the band gap of the given semiconductor system in the 'inverted' regime, temperature, disorder, and crystal orientation. We theoretically investigate electronic and transport properties of QSH edge states in large gap 1-T' WTe$_{2}$ monolayers. We explore the impact of edge termination, disorder, temperature, and interactions on experimentally addressable edge state observables, such as local density of states and conductance. We show that conductance quantization can remain surprisingly robust even for heavily disordered samples because of an anomalously small edge state decay length and additional protection related to the large direct gap allowed by glide symmetry. From the simulation of temperature-dependent resistance, we find that moderate disorder enhances the stability of conductance by localizing bulk states. We evaluate the edge state velocity and Luttinger liquid parameter as functions of the chemical potential, finding prospects for physics beyond linear helical Luttinger liquids in samples with ultra-clean and well-defined edges.

On the Influence of Spatial Fluctuations of the Water Inherent Optical Properties on the Energy of a Lidar Echo Signal Coming from a Water

Theoretical models of the statistical characteristics of the lidar echo signal have been developed to interpret the results of optical sounding of heavily eutrophicated water bodies. Formulas are obtained for calculating the statistically average value and coefficient of variation of the energy of the elastic backscattering signal coming from the near-surface layer of water with randomly inhomogeneous absorption and scattering coefficients. Examples of the dependence of the indicated signal characteristics on the coefficients of variation of the optical characteristics of water are given. It has been established that fluctuations in the absorption coefficient lead to an increase in the average energy of the received signal, and fluctuations in the scattering coefficient to its slight decrease. A significant decrease in the average echo signal energy can be observed with cross-correlated fluctuations in the absorption and scattering coefficients, i. e. in the case when the attenuation coefficient fluctuates at a constant single scattering albedo. Considerations are made on how algorithms for estimating the average values of the optical characteristics of water and the parameters of their inhomogeneities from the average value and the coefficient of variation of the echo signal energy can be constructed.

On quantitative off-axis Scanning Transmission Ion Microscopy (STIM)

Spurred by a need to determine major (C, H, N and O) contents in biological tissue sections, a formalism for quantitative off-axis Scanning Transmission Ion Microscopy (OA-STIM) has been established. This can be used with, or without, simultaneous Elastic Backscattering Spectroscopy (EBS) to provide quantitative major element composition and thickness information. As part of the work, an empirical predictor with one free parameter for the proton–proton differential scattering cross section was implemented. The predictor values were in extremely close agreement with high accuracy literature data. For 2 MeV p–12C elastic scattering at forward angles ≤45°an interpolation procedure was used to determine the relative deviations from the Rutherford cross sections were determined to be ≤6.4%. The interpolation was based on a Coulomb field, angular momentum quantum number and nuclear structure dependent nuclear penetration factor. Finally, the quantitative combination of simultaneous OA-STIM and EBS data is discussed.

Sequestration of Ca in simian nasal mucosa: Determination of Ca molarity in ex vivo tissue by simultaneous off-axis Scanning Transmission Ion Microscopy, Particle Induced X-Ray Emission and Elastic Backscattering Spectrometry

A technique to determine the molar concentration of elements in ex vivo tissue sections by Particle Induced X-ray Emission (PIXE) has been developed. The method is based on simultaneous off-axis scanning transmission ion microscopy (OA-STIM) and Elastic Backscattering Spectrometry (EBS) measurement of the sample thickness and major element (H, C, N, O) composition. The method was applied to determine the molarity of localised Ca concentration hot-spots in the outer epithelium tissue of nasal mucosa of a rhesus macaque subject infected with simian immunodeficiency virus (SIV). The results show Ca sequestration in concentration hot-spots and outer epithelial tissue that significantly exceeded the Ca concentration in the surrounding tissues. This may originate from mineralisation and/or Ca enhancement in goblet cells.

Proton beam induced degradation of Pioloform® (polyvinyl butyral (PVB)) support films used for analysis of biomedical tissue sections

Pioloform®, an often used support film for ion microprobe research is a terpolymer of polyvinyl butyral (PVB) and ≲ 18 mass % polyvinyl alcohol (PVA). Simultaneous off-axis Scanning Transmission Ion Microscopy (OA-STIM) and Elastic Backscattering Spectrometry (EBS) measurements have been used to measure the evolution of the C, H and O contents for an increasing proton fluence. The results showed that the composition at zero proton-fluence was in close agreement with the theoretical atomic composition. This strongly suggests OA-STIM measurements. With increasing proton fluences preferential loss of H and O was observed from the films.

External Beam IBA Measurements for Cultural Heritage

Ion beam analysis (IBA) methods refer to a set of analytical techniques based on the interactions of energetic ions, produced by a particle accelerator, with matter. The result of such interactions is the emission of characteristic radiation, X and gamma rays, and charged particles, which, upon detection, provide valuable information on the absolute concentration and depth distribution of the elements in the bombarded material. Moreover, IBA techniques can be performed while maintaining the object to be investigated at atmospheric pressure, without placing it in vacuum, in an analysis chamber, with the impinging ion beam extracted from the in-vacuum beamline of the accelerator, avoiding the need of invasive sampling and greatly easing the object positioning, thus allowing precious and big or large artefacts to be studied. This feature has opened the way for applications of IBA techniques for compositional analysis in cultural heritage studies, providing detailed and complete information about elemental compositions and depth distributions of analysed materials that are otherwise difficult or impossible for other analytical techniques. In this paper, the basic principles of the main IBA techniques applied to cultural heritage, namely, particle induced X-ray emission (PIXE), particle induced Gamma-ray emission (PIGE), and Rutherford or elastic backscattering spectrometry (RBS/EBS), will be recalled, and specific and practical details on how these techniques can be used for analysing cultural heritage objects with external beam set-ups will be provided.

Calibration of a PIXE system at Peking University

A method combining particle-induced X-ray emission spectrometry (PIXE) and elastic backscattering spectrometry (EBS) was used to calibrate the PIXE system at Peking University. The selected thin standard samples were typically 50 μg/cm2 and the thicknesses of two thick standard samples are 3 mm. The calibration of PIXE system was divided into the calibration curve measurement of thin standard samples and the external standard method of thick standard samples. Both thin and thick samples cover the commonly used PIXE X-ray energy range 1.4–18.0 keV. GUPIXWIN introduces an Instrument factor H to describe the calibration process. It is found that the measured H(Z) curve can be approximated as a Z-independent line with an average value of 3.30×10−4. The deviation of multiple measurements of a single element is between 0.42% and 4.75%. For thick samples, the incident particles are protons and 3He+, a H value of (4.97±0.01)×10−4 was obtained.