Proton Backscattering Research Articles

Upper limit of the solar wind protons backscattering efficiency from Comet 67P/Churyumov-Gerasimenko

Context. Solar wind ions backscattering is a fundamental plasma-surface interaction process that may occur on all celestial bodies exposed to the solar wind and lacking a significant atmosphere or magnetosphere. Yet, observations have been limited to the regolith-covered Moon and Phobos, one of the Martian moons. Aims. We aim to expand our knowledge of the process to include comets by investigating the backscattering of solar wind protons from the surface of comet 67P/Churyumov-Gerasimenko. Methods. We used one of the ion spectrometers on board ESA’s Rosetta spacecraft to search for evidence of backscattered solar wind protons from the cometary surface. The signal of interest was expected to be very weak and several statistical treatments of the data were essential to eliminate any influence from background noise and instrumental effects. Due to limited knowledge of the signal location within the observed parameter space, we conducted a statistical analysis to identify the most probable conditions for detecting the signal. Results. No significant solar wind backscattered protons were ever observed by the instrument. The statement applies to the large spectrum of observation conditions. An upper limit of the backscattered proton flux is given, as well as an upper limit of the backscattering efficiency of 9 × 10−4. Conclusions. The surface of comet 67P/Churyumov-Gerasimenko distinguishes itself as a notably weak reflector of solar wind protons, with its backscattering efficiency, at most, as large as the lowest observed backscattering efficiency from the lunar regolith.

Numerical simulation of proton backscattering spectra in GEANT4 toolkit

Rutherford backscattering spectroscopy (RBS) is a widely used technique for the atomic-scale analysis of sample composition, lattice displacement and impurity profiling. RBS is based on the elastic scattering of incident charged particles by target nuclei and the subsequent detection of scattered particles. The interpretation of RBS spectra, however, poses challenges due to overlapping peaks, corresponding to scattering from different atomic species, and uncertainties from energy loss, scattering geometry and detector response. To address this, an open source simulation model based on the versatile GEANT4 simulation toolkit has been developed. The flexibility of the open source enables users to tailor the model to its specific requirements, such as the use of specific particle stopping powers, cross-sections, and physics processes. This work presents the results of the comparison between the experimental and simulated backscattering spectra in crystalline silicon, silicon carbide and silicon dioxide samples by 1–2.5 MeV energy protons, obtained in random orientation conditions. The results demonstrate the capability of the model to accurately simulate backscattering spectra in both amorphous materials and single crystals. The overall agreement between the simulated and experimental results is highly promising for future development and use in the interpretation and simulation of RBS spectra.

Gaseous nitriding of Co-10 at% and -15 at% Cr alloys at 400 °C and 450 °C

Co-10 at% and -15 at% Cr with the stable hexagonal close packed (hcp) crystal structure at room temperature have been subjected to gaseous nitriding treatment using nitriding temperatures of 400 °C and 450 °C far below the austenite start temperature. Using X-ray and electron backscatter diffraction (EBSD), structural changes as a result of nitrogen incorporation into the initial hcp lattice can be divided into the following steps: (i) expansion of the lattice due to N uptake yielding hcp (hcpexp) at nitriding temperature of 400 °C, (ii) gradual transformation of hcpexp into an expanded face-centered cubic phase (fccexp) by increasing time at 400 °C/ or temperature to 450 °C (mixture of two phases), (iii) development of stable nitrided layer containing fccexp using moderate nitriding times up to 3 h at 450 °C and (iv) decomposition of fccexp layer into CrN nitrides and less expanded austenite and the reverse transformation from fcc to hcp at near-surface regions at 450 °C after prolonged nitriding time of 24 h. Due to occurrence of step (iv), the square-root treatment-time dependence of the nitrided layer thickness breaks down. Nitrogen-depth profiles obtained for Co-15 at% Cr by glow-discharge optical emission spectroscopy (GDOES) along with the Non-Rutherford MeV proton backscattering spectrometry reveal a nitrogen supersaturation of around 20 at% at surface-adjacent areas in hcpexp. A relatively large unit volume expansion has been recognized for hcpexp with a change of c/a ratio of around 0.6%. Hardness-depth profiles obtained for nitrided Co-10 at% and -15 at% Cr alloys using nanoindentation evidence an increase in hardness inside the nitrided layer, compared to the untreated core.

Бага энергийн хурдасгагчийг ашиглах зарим боломж

The possibilities of applications of the 200 keV Cockroft - Walton accelerator for D-D neutron measurements, ion implantation. Rutherford backscattering analysis, ion channeling and proton induced X-ray analysis are discussed.

The free electron model and the electronic energy losses of protons at low velocities interacting with polycrystalline tantalum

In this letter, we report experimental data and theoretical work on the electronic energy loss and energy loss straggling of protons transmitted through self-supported thin films of tantalum in a polycrystalline tetragonal phase . Low-energy protons with energies below 10 keV and Ta films with nominal thickness of 6, 9 and 12 nm are used. The aim of this work is to understand the unexpected values of the Ta stopping power for low-energy proton backscattering reported recently, which are far from the prediction of the standard free electron gas model and semi-empirical approaches. This had led the authors to conclude the failure of the free electron model. Our transmission measurements confirm these experimental results. In this work, a qualitative discussion and quantitative explanation of our experimental results is given, using an approach based on the density functional theory within the framework of the free electron gas (FEG) model. We performed semiclassical deterministic trajectory simulations and employ the local density approximation model, using an inhomogeneous electron density distribution and the polycrystalline character of Ta samples.

Beam Scanning Controller for Proton-Beam Writing

A scanning control system of the ion beam of MeV energies has been developed for the nuclear scanning microprobe and proton-beam writing channel as a part of accelerator-analytical complex based on the Sokol electrostatic accelerator of the Institute of Applied Physics of the National Academy of Sciences of Ukraine. The system was put into operation to replace the obsolete one based on microcontrollers. The scanning control system is based on a National Instruments reconfigurable module with a Field Programmable Gate Array. The module operates in real time and is connected to a personal computer by a high-speed PCI-Express interface with data buffering. The system provides two main modes of operation: exposure of sample areas with a given profile and raster secondary electrons imaging of the sample or a calibration grid. Profile exposure is possible both in raster and functional scanning modes. Automatic calibration of the profile scale and scan raster is also implemented. Using of reconfigurable logic makes it possible to quickly adjust the system to the conditions of a particular experiment and the available equipment. The hardware capabilities of the scanning control system allows in the future to connect up to 4 spectrometric ADC for mapping the elemental composition of samples using Proton Induced X-ray Emission and Proton Backscattering. The first experiments on the irradiation of polymethylmethacrylate have been carried out; images of the obtained microstructures taken with a scanning electron microscope are shown. The aim of this work is to develop a control system for scanning a high-energy focused beam in proton beam writing technique to create small-sized structures for special purposes, as well as to demonstrate the efficiency of the developed system.

Symmetries of 13C tracer deposition in EAST D and He plasmas investigated on the sub-mm to 100 mm scale by deuteron nuclear reaction analysis

In continuation of an earlier study, this work focusses on deposit analysis in the mm region around the tracer injection hole of two 13CD4 injection experiments in EAST by using focussed 1.43 MeV deuteron ion beam analysis. This study adds ∼1500 data points to the former work on the same samples to assess more details on deposition patterns and symmetry and test the accuracy of former extrapolations.Mapping of the 13CD4 injection-hole vicinity using 0.2 mm lateral resolution yields compatible results as the former 1.8 mm resolution for the local co-deposit thickness. The new data reveal the deposition maximum to be 1 ± 0.2 mm away from the injection hole towards the ExB direction, resembling the triangular shape also seen on the larger scale. The analysis of 3 blocks along the magnetic field vector shows a dominant deposition along the surface area closest to the last closed flux surface. An edge with a factor ∼11 drop in deposit thickness within 2 mm spans here along the whole 150 mm tile size and along the axis of the magnetic field. The analysis using proton backscattering shows no He retention in the He plasma exposed co-deposits above the 1 % limit of detection.The total deposited 13C amount was underestimated by ∼5 % in the former study, a value not exceeding the measurement uncertainty. The combination of ∼0.2 mm spatial resolution around the injection-hole and at the deposit edge with ∼ 2 mm resolution but larger coverage outside these regions is found to provide a reasonable compromise of information quality and analysis effort.

Wear mechanism of medium carbon steel after its plasma electrolytic nitrocarburising

This article considers the change in the tribological characteristics of medium carbon steel after its anodic plasma electrolytic nitrocarburising in a carbamide electrolyte. Phase and elemental composition of the nitrocarburised layer was studied using X-ray analysis and nuclear backscattering of protons. Optical and electron microscopes were used to observe friction tracks. It has been found out that the wear process in nitrocarburised samples is followed by plastic displacement of the metal in the friction contact zone according to the molecular-mechanical and fatigue theory of wear and application of the Kragelsky criterion. It has been shown that an increase in the sliding velocity of 0.5 m/s to 1.5 m/s results in a linear decrease in the friction coefficient from 0.65 to 0.45. The minimum wear rate is achieved after nitrocarburising of steel at 750 °C for 7 min and a sliding speed of (0.4–0.55) m/s. Anodic nitrocarburising increases the wear resistance of steel by 40% compared to quenching at a sliding speed of 0.9 m/s.

Stopping and straggling of 60–250-keV backscattered protons on nanometric Pt films

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 Phys. 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.

Influence of a thin amorphous surface layer on de-channeling during aluminum implantation at different temperatures into 4H-SiC

Ion implantation is an important technique in semiconductor processing and has become a key technology for 4H-SiC devices. Today, aluminum (Al) implantations are routinely used for p-type contacts, p+-emitters, terminations and many other applications. However, in all crystalline materials, quite a few ions find a path along a crystal channel, so-called channeling, and these ions travel deep into the crystal. This paper reports on the channeling phenomenon during Al implantation into 4H-SiC, and in particular, the influence of a thin native oxide will be discussed in detail. The effects of thermal lattice vibrations for implantations performed at elevated temperatures will also be elucidated. 100 keV Al ions have been implanted along the [000-1] direction employing samples with 4° miscut. Before implantation, the samples have been aligned using the blocking pattern of backscattered protons. Secondary ion mass spectrometry has been used to record the Al depth distribution. To predict implantation profiles and improve understanding of the role of crystal structure, simulations were performed using the Monte-Carlo binary collision approximation code SIIMPL. Our results show that a thin surface layer of native oxide, less than 1 nm, has a decisive role for de-channeling of aligned implantations. Further, as expected, for implantations at elevated temperatures, a larger degree of de-channeling from major axes is present due to increased thermal vibrations and the penetration depth of channeled aluminum ions is reduced. The values for the mean-square atomic displacements at elevated temperatures have been extracted from experimental depth profiles in combination with simulations.

Decrease of the interplanetary magnetic field strength on the lunar dayside and over the polar region

The Moon interacts with the incident solar wind plasma in various ways, and most of these interactions are accompanied by variations of the interplanetary magnetic field (IMF) around the Moon. Here we first report decreases of the IMF strength observed at 100 km altitude on the lunar dayside and over the polar region, comparing upstream solar wind data from ACE with Kaguya (SELENE) data. We note that the magnetic field decreases are observed above non-magnetized regions or very weakly magnetized regions. In one event the IMF is weakened in the dayside northern hemisphere when the IMF is roughly anti-parallel to the solar wind flow. We estimate that the decrease in the magnetic pressure can be partly compensated by the thermal pressure of the back-scattered solar wind protons, which suggests that the magnetic field decrease is interpreted as diamagnetic effect by the back-scattered protons. In another event an IMF decrease is continuously detected from the northern polar region to the dayside mid-latitude region, which is not fully explained by the thermal pressure of the back-scattered protons. We also discuss the diamagnetic current system in the upstream (fore-moon) solar wind region formed by the back-scattered protons.

Channeled Implantations of p-Type Dopants into 4H-SiC at Different Temperatures

Channeling of B and Al ions in 4H-SiC(0001), has been investigated by secondary ion mass spectrometry (SIMS). Ion implantations have been performed between room temperature (RT) and 600 °C at various fluences. Before implantation, the major crystal axes were determined and the sample was aligned using the blocking pattern of backscattered protons. As expected, the depth distribution of the implanted ions along a crystal direction penetrates much deeper compared to non-channeling directions. At elevated temperatures, the channeling depth for 100 keV Al-ions is decreased due to lattice vibrations. For 50 keV B-ions, the temperature effect is minor, indicating a smaller interaction between target atoms and B. Simulations has been performed using SIIMPL, a Monte Carlo simulation code based on the binary collision approximation, to predict experimental data and get a deeper insight in the channeling process.

Defect Formation under Nitrogen-Ion Implantation and Subsequent Annealing in GaAs Structures with an Uncovered Surface and a Surface Covered with an AlN Film

The concentration profiles of defects produced in structures upon the implantation of nitrogen ions into GaAs epitaxial layers with an uncovered surface and that covered with an AlN film and subsequent annealing are studied. The ion energies and the implantation doses are chosen so that the nitrogen-atom concentration profiles coincided in structures of both types. Rutherford proton backscattering spectra are measured in the random and channeling modes, and the concentration profiles of point defects formed are calculated for the samples under study. It is found that the implantation of nitrogen ions introduces nearly the same number of point defects into structures of both types, and the formation of an AlN film by ion-plasma sputtering is accompanied by the formation of an additional number of defects. However, the annealing of structures of both types leads to nearly the same concentrations of residual defects.

The benchmarking procedure: Implementation in the case of proton backscattering

The benchmarking procedure in IBA regards the validation of charged-particle differential cross- section data via the acquisition of EBS spectra from uniform thick target of known composition followed by their detailed simulation. In the present work such benchmarking measurements have been performed for the elastic scattering of protons on 23Na, 31P and natS in the energy range of 1– 3.5 MeV in steps of 250 keV at three backward angles, at 120.6°, 148.8° and 173.5° in order to validate the corresponding existing evaluated cross-section datasets from SigmaCalc and to facilitate their extension at higher energies. The measurements were performed using the 2 MV Tandetron Accelerator of the Ion Beam Center of the University of Surrey. The EBS spectra acquired were compared with simulated ones using the DataFurnace code, along with an a posteriori treatment of the surface roughness. All the experimental parameters were thoroughly investigated and the results obtained and the discrepancies found are discussed and analyzed. Moreover, the benchmarking procedure in complicated cases, such as the natB(p,p) studied at NCSR “Demokritos”, where background contributions exist, is also discussed.

Образование дефектов в структурах GaAs с непокрытой и покрытой пленкой AlN поверхностями при имплантации ионов азота и последующем отжиге

AbstractThe concentration profiles of defects produced in structures upon the implantation of nitrogen ions into GaAs epitaxial layers with an uncovered surface and that covered with an AlN film and subsequent annealing are studied. The ion energies and the implantation doses are chosen so that the nitrogen-atom concentration profiles coincided in structures of both types. Rutherford proton backscattering spectra are measured in the random and channeling modes, and the concentration profiles of point defects formed are calculated for the samples under study. It is found that the implantation of nitrogen ions introduces nearly the same number of point defects into structures of both types, and the formation of an AlN film by ion-plasma sputtering is accompanied by the formation of an additional number of defects. However, the annealing of structures of both types leads to nearly the same concentrations of residual defects.

Ion-beam analysis of insulator samples

During the bombardment of insulator materials with high-energy particles, the samples are often emitting light and are sparking. This fact makes both the ion-beam analysis and the ion implantation of insulating materials more difficult. Light may disturb the detectors, sparks usually disturb the current-integration systems and electronics. Moreover, the accumulation of positive charges alters the results of the experiments via decelerating the incoming ions and accelerating the outgoing particles. In case of ion implantation, the projected range may be changed, while in ion-beam analysis the shape of the spectra can be changed resulting evaluation problems.To avoid the charge accumulation several methods have been used in the daily practice such as applying thin cover layers, wrapping or masking the samples, applying relatively low beam currents or electron sources in the experimental chamber.A short review of the above mentioned methods to avoid the charge accumulation is given. Moreover, the evaluation problems of the spectra taken on sparking (or at least charged-up) samples are also discussed. Proton and helium backscattering spectrometry as well as elastic recoil detection analysis are used to demonstrate the capability of a simple model of charge accumulation which is implemented to DEPTH code.

LHC/FCC-based muon colliders

In recent years, three schemes for producing low-emittance muon beams have been proposed: (1) positron-electron annihilation above threshold using a positron storage ring with a thin target, (2) laser/FEL-photon back-scattering off high-energy proton beams circulating in the LHC or FCC-hh, (3) the Gamma factory concept where partially stripped heavy ions collide with a laser pulse to directly generate muons. The Gamma factory would also deliver copious amounts of positrons which could in turn be used as source for option (1). On the other hand the top-up booster of the FCC-ee design would be an outstanding positron storage ring, at the right beam energy, around 45 GeV. After rapid acceleration the muons, produced in one of the three or four ways, could be collided in machines like the SPS, LHC or FCC-hh. Possible collider layouts are suggested.

Monte Carlo Simulations of the Interaction of Fast Proton and Hydrogen Atoms With the Martian Atmosphere and Comparison With In Situ Measurements

AbstractWe present model results of the interaction of proton and hydrogen atom precipitation with the Martian atmosphere. We use a kinetic Monte Carlo model developed earlier for the analysis of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA‐3) Mars Express data. With the availability of Mars Atmosphere and Volatile Evolution Mission in situ measurements, not only the flux of protons incident on the atmosphere but also their degradation along the orbit may now be described. The comparison of the simulations with data collected with the Solar Wind Ion Analyzer shows that the Monte Carlo model reproduces some of the measured features. The results of comparison between simulations and measurements of the proton fluxes at low altitudes make it possible to infer the efficiency of charge exchange between solar wind and the extended hydrogen corona if the value of the magnetic field is measured simultaneously. We also find that the induced magnetic field plays a very important role in the formation of the backscattered flux and strongly controls its magnitude. At the same time, discrepancies between the modeled and the measured energy spectra of the backscattered protons are pointed out. We suggest that some of the physical processes controlling the upward flux are not fully understood or that the data processing of the measured backscattered proton flux should be improved.

The Effect of Dose of Nitrogen-Ion Implantation on the Concentration of Point Defects Introduced into GaAs Layers

Secondary-ion mass spectrometry and Rutherford proton backscattering have been used to measure the concentration profiles of nitrogen atoms and examine the defect structure of epitaxial GaAs layers implanted with 250-keV N+ ions at doses of 5 × 1014–5 × 1016 cm–2. It was found that no amorphization of the layers being implanted occurs at doses exceeding the calculated amorphization threshold, a concentration of point defects that is formed is substantially lower than the calculated value, and a characteristic specific feature of the defect concentration profiles is the high defect concentration in the surface layer.

Влияние дозы имплантации ионов азота на концентрацию точечных дефектов, введенных в слои GaAs

AbstractSecondary-ion mass spectrometry and Rutherford proton backscattering have been used to measure the concentration profiles of nitrogen atoms and examine the defect structure of epitaxial GaAs layers implanted with 250-keV N^+ ions at doses of 5 × 10^14–5 × 10^16 cm^–2. It was found that no amorphization of the layers being implanted occurs at doses exceeding the calculated amorphization threshold, a concentration of point defects that is formed is substantially lower than the calculated value, and a characteristic specific feature of the defect concentration profiles is the high defect concentration in the surface layer.