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Silicon carbide has been considered a material for use in the construction of advanced high-temperature nuclear reactors. However, one of the most important design issues for future reactors is the development of structural defects in SiC under a strong irradiation field at high temperatures. To understand how high temperatures affect radiation damage, SiC single crystals were irradiated at room temperature and after being heated to 800 °C with carbon and silicon ions of energies ranging between 0.5 and 21 MeV. The number of displaced atoms and the disorder parameters have been estimated by using the channeling Rutherford backscattering spectrometry. The experimentally determined depth profiles of induced defects at room temperature agree very well with theoretical calculations assuming its proportionality to the electronic and nuclear-stopping power values. On the other hand, a significant reduction in the number of crystal defects was observed for irradiations performed at high temperatures or for samples annealed after irradiation. Additionally, indications of saturation of the crystal defect concentration were observed for higher fluences and the irradiation of previously defected samples. [ABSTRACT FROM AUTHOR]

This study uses photoluminescence (PL) and other carrier-recombination sensitive probes in combination with spreading resistance profiling (SRP), SIMS and IMSIL MC-calculations to monitor the ion range and damage levels in highly-channeled and random beam orientation 7.5 MeV B and 10 MeV P and As profiles and various combinations of co-implants with 50 keV Phosphorus implants in Silicon(100). The effects of annealing on the 10 MeV profiles showed the strong shifts in PL data from implant damage in the as-implanted and annealed samples. Curious “intermittencies” were seen in the PL signals from MeV implant defect centers.

Ion irradiation can cause burrowing of nanoparticles in substrates, strongly depending on the material properties and irradiation parameters. In this study, it is demonstrated that the sinking process can be accomplished with ion irradiation of cube‐shaped Ag nanoparticles on top of silicon; how ion channeling affects the sinking rate; and underline the importance of the amorphous state of the substrate upon ion irradiation. Based on these experimental findings, the sinking process is described as being driven by capillary forces enabled by ion‐induced plastic flow of the substrate. [ABSTRACT FROM AUTHOR]

Silicon carbide has been considered a material for use in the construction of advanced high-temperature nuclear reactors. However, one of the most important design issues for future reactors is the development of structural defects in SiC under a strong irradiation field at high temperatures. To understand how high temperatures affect radiation damage, SiC single crystals were irradiated at room temperature and after being heated to 800 °C with carbon and silicon ions of energies ranging between 0.5 and 21 MeV. The number of displaced atoms and the disorder parameters have been estimated by using the channeling Rutherford backscattering spectrometry. The experimentally determined depth profiles of induced defects at room temperature agree very well with theoretical calculations assuming its proportionality to the electronic and nuclear-stopping power values. On the other hand, a significant reduction in the number of crystal defects was observed for irradiations performed at high temperatures or for samples annealed after irradiation. Additionally, indications of saturation of the crystal defect concentration were observed for higher fluences and the irradiation of previously defected samples.

Abstract Ion irradiation can cause burrowing of nanoparticles in substrates, strongly depending on the material properties and irradiation parameters. In this study, it is demonstrated that the sinking process can be accomplished with ion irradiation of cube‐shaped Ag nanoparticles on top of silicon; how ion channeling affects the sinking rate; and underline the importance of the amorphous state of the substrate upon ion irradiation. Based on these experimental findings, the sinking process is described as being driven by capillary forces enabled by ion‐induced plastic flow of the substrate.

The unique capability of the new version of the McChasy code (called McChasy2) is to provide the possibility to simulate experimental energy spectra delivered by Rutherford Backscattering Spectrometry in channeling direction (RBS/C) using large atomic structures (ca. 108 atoms). Ni-based alloys are nowadays one of the most studied and promising materials that can be used in the power generation sector and in general for high-temperature applications because of their radiation resistance and proof against harsh environmental conditions. In this work, we present recent results of investigations regarding simulations of extended structural defects (edge dislocations and loops) developed in the directions typically observed in the fcc systems that are formed inside nickel-based single-crystal alloys. The extended defect models are created using ATOMSK and the Molecular Dynamics (MD)-LAMMPS thermalization process. The models are then used to create virtual samples and fit experimental RBS/C spectra. [ABSTRACT FROM AUTHOR]

There has been a long interest in the analysis of radiation damage caused by ion beams due to their presence in space or the nuclear industry and their application in materials modification. One of the methods used for that purpose is Rutherford Backscattering Spectrometry in channeling mode (RBS/C). However, the presence of different defect types makes it difficult to interpret RBS/C spectra so extended defects are often neglected in the data analysis. The McChasy Monte Carlo simulation code has been developed to analyze channeling data in crystals containing different defect types using periodically repeated relatively small simulation cells (∼102 atoms). Here we report and describe its recent feature: a model of dislocation loops. Having in mind that the interactions of the channeling ion beam with defects depend on the beam energy, the validity of the model was confirmed by analyzing RBS/C experiments performed at different energies for the case of 300 keV Eu-implanted GaN. [ABSTRACT FROM AUTHOR]

Focused ion beam (FIB) processing with low-energy ions has become a standard technique for the manipulation of nanostructures. Many underlying ion beam effects that deviate from conventional high-energy ion irradiation of bulk systems are considered today; however, ion channeling with its consequence of significant deeper penetration depth has been only theoretically investigated in this regime. We present here an experimental approach to determine the channeling of low-energy ions in crystalline nanoparticles by measuring the sputter yield derived from scanning electron microscopy (SEM) images taken after irradiation under various incident ion angles. Channeling maps of 30 and 20 keV Ga+ ions in Ag nanocubes have been identified and fit well with the theory. Indeed, channeling has a significant impact on the transport of energetic ions in crystals due to the large critical angle at low ion energies, thus being relevant for any FIB-application. Consequently, the obtained sputter yield clearly differs from amorphous materials; therefore, it is recommended not to rely only on, e.g., ion distribution depths predicted by standard Monte-Carlo (MC) algorithms for amorphous materials. [ABSTRACT FROM AUTHOR]

This study explores high-energy aluminum (Al) implantation above 10 MeV as a fabrication process to facilitate the creation of deep doping regions in silicon carbide (SiC). Experimental investigations were conducted to evaluate the technical feasibility of ultra-high energy implantation and high-energy channeling implantation of aluminum into 4H-SiC. Ultra-high-energy Al implantations at 30 and 48 MeV were performed, revealing limitations such as increased charge dispersion and decreased current near accelerator technical limits. In contrast, high-energy channeling implantations at 12, 15, and 20 MeV demonstrated successful Al channeling implantations into 4H-SiC, emphasizing the importance of precision in crystal orientation and mounting systems. Results indicate that channeling implantations, with precise instrumentation, are a preferred approach over non-channeled ultra-high-energy methods for fabricating deep doping regions in SiC, holding promise for advancing the next generation of high-voltage SiC devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • McChasy-1 and 2 codes were used to analyze the RBS/C spectra. • For the lowest fluence − small interstitial loops and 2–5 nm size SFT are present. • Above 7 × 1015 cm−2 − bubbles with small and large SFTs are visible. • Additional step in damage kinetics revealed for the highest fluence (∼25 dpa) • The impact of the bubbles formed is noticeable for nanomechanical and RBS/C results. High-temperature (∼800 K) ion irradiation with 380 keV Ar ions was used to modify the surface of Ni single crystals in order to generate radiation defects and mimic the effect of neutrons avoiding sample activation. The modified 800 nm thick layer was analyzed regarding structural and mechanical properties utilizing a combination of experimental and simulation techniques. The ion implantation fluence ranged from 1 × 1014 cm−2 up to 1 × 1016 cm−2, which corresponds to values of displacements per atom from 0.25 to 25, respectively. The structural characterization was performed by Rutherford Spectroscopy in Channeling mode (RBS/C) associated with scanning (SEM) and transmission electron microscopy (TEM). The experimental results were supported by Monte Carlo (McChasy) and Molecular Dynamics (MD-LAMMPS) simulations. The simulations performed using the second generation of the McChasy code show that the influence of bubbles formed inside the material is not negligible and affects the quantitative analysis of defects in the simulated spectra. A second step in damage kinetics was revealed for the highest dose (i.e., 25 dpa) as a consequence of the entanglement of dislocations and agglomeration of noble gas bubbles, which was confirmed by TEM analysis. Moreover, nanomechanical results confirm that Ar bubbles deteriorate mechanical properties such as hardness. [ABSTRACT FROM AUTHOR]

The experimental data on the yield of d + d-reaction products for polycrystalline diamond target, obtained in the studies at the HELIS ion accelerator are presented. The equipment and neutron and charged particle detectors used in the study are described. The possibility of using the Unique Scientific Facility (USF) HELIS to verify operating characteristics of semiconductor detectors of alpha particles intended in studies of the boron–proton capture reaction at the Prometheus proton therapy complex is shown. [ABSTRACT FROM AUTHOR]

Gaining in-situ access to relaxation dynamics of radiation induced defectswill lead to a better understanding of materials and is important for theverification of theoretical models and simulations. We show preliminary resultsfrom experiments at the new Neutralized Drift Compression Experiment (NDCX-II)at Lawrence Berkeley National Laboratory that will enable in-situ access todefect dynamics through pump-probe experiments. Here, the unique capabilitiesof the NDCX-II accelerator to generate intense, nanosecond pulsed ion beams areutilized. Preliminary data of channeling experiments using lithium andpotassium ions and silicon membranes are shown. We compare these data tosimulation results using Crystal Trim. Furthermore, we discuss the improvementsto the accelerator to higher performance levels and the new diagnostics toolsthat are being incorporated.

In this work we show a way how the crystal rainbow channeling effect can be applied for obtaining the interaction potential between 2 MeV protons and the cubic crystallographic crystals, in the cases of axial channeling of protons along (0 0 1) and (1 1 1) crystal directions. The procedure for construction of this potential has been based on our previous work in which the rainbow morphology was crucial for their determination. However, important improvements have been made. As a result, the two axial channeling directions can be treated using the same physical arguments leading to more consistent values of the fitting parameters in the ion-atom interaction potential. [ABSTRACT FROM AUTHOR]

Ion irradiation of KTaO3 has been performed to investigate the evolution of irradiation damage with and without significant electronic energy deposition. Damage accumulation under irradiation with 2 MeV Au ions follows a direct-impact/defect-stimulated model, and occurs more rapidly than in SrTiO3 under similar conditions. Electronic energy deposition from 21 MeV Ni ions creates negligible damage in pristine KTaO3 to depths of 1 micron; however, damage is greatly enhanced in samples containing pre-existing defects, as evidenced by rapid amorphization due to track formation. The cross-sections for amorphous tracks show a nearly linear dependence on initial disorder, comparable with SrTiO3.

Abstract The reaction of GaN to ion implantation was studied in thin films grown on the a-plane (non-polar) and on the c-plane (polar). 300 keV argon ions were implanted at room temperature to fluences ranging from 5 × 1012 atoms/cm2 to 8 × 1015 atoms/cm2. The structural analysis was performed using Rutherford Backscattering/Channeling and X-Ray Diffraction. The results allow to reinforce the suggestion that perpendicular strain caused by ion implantation is the driving force behind defect transformation processes inside the lattice. Furthermore, they confirm a lower relative damage level for a-plane GaN implanted with the highest fluence, in comparison with c-plane GaN, as reported previously for low temperature implantation. [ABSTRACT FROM AUTHOR]

This work is devoted to the construction of the universal axial (0 0 1) rainbow channeling proton-crystal interaction potential. It has been done by modifying the Moliere's interaction potential. We show that for very thin crystals with the cubic crystallographic structure, in the (0 0 1) orientation with respect to 2 MeV proton beams, it is possible to obtain a universal proton-crystal interaction potential from the morphological analysis of the rainbows in the proton transmission angular plane. [ABSTRACT FROM AUTHOR]

Abstract Ion channeling is a powerful quantitative technique for studying ion-irradiation induced defect evolution in single crystalline materials. An iterative procedure to determine dechanneling yields has been developed for decades, serving as a major method for analyzing experimental channeling data. The applicability of such procedure is, however, generally limited to the crystalline damage with only point defects and local amorphous domains. For the other cases, such as irradiated metals, the assumption of direct-backscattering free has usually been made. In the present study, Ni, TiAl, MgO, and SrTiO 3 single crystals are selected as four model materials, representing metals, intermetallic alloys, and ceramic compounds with different defect evolution processes under irradiation, to investigate the fidelity of applying dechanneling analysis on various types of defects. The pure dechanneling assumption is shown oversimplified in Ni irradiated with low fluence self-ions and may result in error on the derived damage profile. Moreover, the iterative procedure of dechanneling analysis is shown valid for more general situations than the randomly distributed atoms, including those not exhibiting a peak in channeling spectra. The disappearance of damage peak in channeling spectra is attributed to the combined effects of small (but non-zero) scattering factor, long-range damage effects, and non-ignorable damage level in pristine crystals. Furthermore, the ratio of direct backscattering to dechanneling areas provides information on defect configurations in the materials containing a well-defined damage peak in channeling spectra. The contribution from dechanneling sources increases from SrTiO 3 , TiAl, to MgO, according to the derived scattering and dechanneling factors. Highlights • Dechanneling analysis is valid for materials containing various types of defects. • Pure dechanneling assumption in irradiated metals is oversimplified. • Lack of damage peak does not mean lack of direct-backscattering sources. • Information on defect types can be obtained from dechanneling analysis. [ABSTRACT FROM AUTHOR]

Abstract This is a theoretical study of the superfocusing and zero-degree focusing effects appearing in channeling of protons of energy of 2 MeV in the {1 1 0} channel of a thin silicon crystal. We prove that the ultimate origin of these effects is the crystal rainbow effect, which has been discovered and explored in ion transmission through axial crystal channels, nanotubes and graphene. Moreover, the effect is the origin of the shapes of the whole spatial and angular distributions of channeled protons. The incident proton velocity vector is taken to be parallel to the channel midplane. We use the Molière's approximation of the Thomas-Fermi proton-atom interaction potential and the continuum approximation. The effect of thermal vibrations of the crystal's atoms is included. We solve numerically the proton equation of motion and analyze the spatial and angular proton transmission functions. The extrema of these functions are the spatial and angular rainbow points, respectively. When the whole proton beam is taken into account, a spatial rainbow pattern, composed of the lines emerging from the superfocusing points, and an angular rainbow pattern, consisting of the lines emerging from the origin and the zero-degree focusing points, appear along the channel. We consider the region of crystal thickness comprising the first, second and third superfocusing and zero-degree focusing points. When the effect of thermal vibrations is neglected, each of these rainbow lines look like the bifurcation set of the cusp catastrophe, and when the effect is included, the line resembles the bifurcation set of the butterfly catastrophe. We demonstrate that the spatial and angular distributions of transmitted protons are fully determined by the spatial and angular rainbow lines, respectively. The superfocusing and zero-degree focusing effects weaken with the increase of the crystal thickness. This is a consequence of the anharmonicity of the continuum proton-crystal interaction potential, which makes the proton beam propagation through the channel incoherent. We also explore the influence of the effect of proton collisions with the crystal's electrons on the beam dynamics in the channel. This effect additionally contributes to the incoherence of the beam motion along the channel. Our opinion is that the peaks of the spatial and angular distributions of ions transmitted through the planar channels lying off the origin registered before were in fact the rainbow peaks. [ABSTRACT FROM AUTHOR]

Abstract Three applications based on the passage of channeled ions through a crystalline membrane are proposed for the accelerator mass spectrometry (AMS) technology. (i) A channeling degrader for the separation of isobars suppresses the angular straggling even if a sufficient energy difference is created between the AMS nuclide and its isobars using a relatively thick membrane. A proof-of-principle experiment showed its potential comparative advantage. Feasibility will be discussed for two other potential applications; the experimental demonstrations are under consideration. (ii) A channeling stripper simultaneously provides a sufficient stripping function to remove interfering molecules in the AMS and low gas pressure to prevent ion scattering. This helps in overcoming a crucial problem in the development of an (A)MS systems in the range of 50 keV. Surface channeling by grazing incidence onto a stack of mono-crystalline substrates is introduced to address the high particle load. (iii) A novel isobar separation technique, using resonant coherent excitation based on periodical field induced by ions passing through the lattice, assists in controlling the charge state of the AMS nuclide and its isobars directly. For practical use, the thickness of the crystalline membrane should be reduced to satisfy the charge state distribution in the non-equilibrium states. [ABSTRACT FROM AUTHOR]

Ion irradiation of KTaO3 has been performed to investigate the evolution of irradiation damage with and without significant electronic energy deposition. Damage accumulation under irradiation with 2MeV Au ions follows a direct-impact/defect-stimulated model, and occurs more rapidly than in SrTiO3 under similar conditions. Electronic energy deposition from 21 MeV Ni ions creates negligible damage in pristine KTaO3 to depths of 1 micron; however, damage is greatly enhanced in samples containing pre-existing defects, as evidenced by rapid amorphization due to track formation. The cross-sections for amorphous tracks show a nearly linear dependence on initial disorder, comparable with SrTiO3. IMPACT STATEMENT Structural modification in KTaO3 is sensitive to both electronic and nuclear energy deposition that can be controlled to exploit promising electronic and optical functionalities. [ABSTRACT FROM AUTHOR]

Because they exhibit very similar diffraction patterns, the γ and γ′ phases of nickel-based superalloys cannot be distinguished by the conventional EBSD technique alone. This paper presents an original method which discriminates those phases on an orientation map by exploiting their chemical differences. Performed with a Focused Ion Beam (FIB) microscope, the method is the combination of the ion CHanneling ORientation Determination technique (iCHORD) – recently developed by Langlois et al. [1] – with the chemical information obtained from Secondary Ion (SI) images. The performances of the method are compared to the EDS-EBSD coupling which also discriminates phases based on their chemical compositions. Applied filters, angular resolution, spatial resolution of the phase discrimination and acquisition time are discussed. It results that the iCHORD–SI combination offers an orientation map with an angular resolution slightly decreased compared to that of the EBSD technique, but with a good phase resolution (down to 150 nm) and within a reasonable acquisition time. Thus, the iCHORD–SI combination appears to be an interesting method for the crystallographic systems where phases are difficult to discriminate by the EBSD technique alone but present a significant chemical contrast. [ABSTRACT FROM AUTHOR]

Lattice site position of O 18 in the presence of vacancy defects in Fe(100) crystal is measured by ion channeling and the corresponding oxygen-vacancy cluster configuration is predicted with Density Functional Theory (DFT) calculations. Energy dependent dechanneling and Slow Positron Doppler broadening analysis show the defects to be vacancy dislocation loops. In O 18 ion implanted Fe, O 18 is found to be in tetrahedral interstitial position. If self ion is irradiated together with O 18 to increase vacancy defects, O 18 is found to be trapped at 1.2 Å away from the lattice position along <111>. From DFT calculations, similar lattice site of O is predicted with a displacement of 1.1 Å along <111> for the interaction of oxygen with ½ <111> vacancy loop structure. Upon increasing vacancy defects further by increasing the fluence of self ions, O 18 is found to shift near octahedral interstitial site displaced by 0.6 Å along <100>. DFT calculations show a similar displacement of 0.46 Å along <100> for the interaction of oxygen with <100> vacancy loop structure. Our combined experimental and DFT studies provide strong evidence of O trapping at vacancy dislocation loops and O trapping site is sensitive to ½ <111> and <100> type vacancy dislocation loops. [ABSTRACT FROM AUTHOR]

The O 18 and self ions are implanted at same depth in Fe (1 1 0) crystal and annealed to study the oxygen trapping under excess self interstitial defects. Rutherford backscattering spectrometry, nuclear reaction analysis and channeling measurements have been performed to determine the lattice site position of O 18 . The presence of dislocation loops is confirmed by energy-dependent dechanneling parameter measurements. From the tilt angular scans of Fe and O 18 signals along 〈1 0 0〉, 〈1 1 0〉 axes, O 18 is found to be displaced 0.2 Å from tetrahedral towards octahedral interstitial site in O 18 . Similar lattice site location of oxygen with the displacement of 0.37 Å is predicted by density functional theory calculations for the interaction of oxygen with 〈1 0 0〉 interstitial dislocation loop structure. Our results provide strong evidence on oxygen trapping at interstitial dislocation loops in the presence of excess interstitial defects in iron. [ABSTRACT FROM AUTHOR]

A new modular and high versatility hodoscope, OSCAR, has been developed and characterized. The aim of this hodoscope is to work as an ancillary detector of present large acceptance heavy ion detectors in specific angular regions where low thresholds and high granularities are needed. We discuss the capabilities of OSCAR in the Δ E–E identification of very low energy light particles, providing a precise map of the thickness uniformity of the Δ E (SSSSD, 20 μ m ) stage and showing how the thickness gradient affects the identification of particles. Energy spectra of light identified particles produced in Ca+Ca collisions at 35 AMeV are used to investigate isospin transport phenomena involving the emission of low energy particles from the quasi-target (QT) source in semi-peripheral nuclear collisions. The possibility to explore particle–particle correlations are also discussed. [ABSTRACT FROM AUTHOR]