Swift Heavy Ion Research Articles

Atomic-scale insights into damage produced by swift heavy ions in polyethylene

Atomic-scale insights into damage produced by swift heavy ions in polyethylene

Study of Ion Velocity Effect on the Band Gap of CVD-Grown Few-Layer MoS2.

The present work reports on a simple chemical vapor deposition (CVD) technique that employs alkali halide (NaCl) to synthesize high-quality few-layer MoS2 by reducing growth temperature from 850 to 650 °C, and its ion irradiation study for band gap modification. The Raman peak position difference of A1g to E12g of ≈24.5 cm-1 for the synthesized MoS2 corresponds to a few layers (<5 monolayers) of MoS2 on the substrate, as also confirmed by atomic force microscopy (AFM). The optical image shows the continuous distribution of flakes throughout the substrate and the average area of flakes ≈0.2 μm2 as confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Swift heavy-ion (SHI) irradiation at 60, 100, and 150 MeV ion energies of 1 × 1012 ions/cm2 ion fluence have been used to modify the band gap in few-layer MoS2. The ions with two different energies are chosen at two sides of the Bragg peak of energy loss curve in such a way as to have the same value of electronic energy loss (Se) but different ion energies to examine the velocity effect for the ion-induced modification. The absorbance peaks for 60 and 150 MeV irradiated samples show the same effect in the band gap modification.

Thinning of Poly(methyl methacrylate) and Poly(vinyl chloride) Thin Films Induced by High-Energy Ions of Different Stopping Powers.

Ion bombardment is an important tool of materials processing, but usually leads to erosion of the surface and significant thickness reductions when thin layers are used. The growing use of polymer thin films in a variety of applications, from coatings and membranes to biomedical and electronic devices, calls for a deeper understanding of the thinning process induced by energetic ions espe-cially for very thin films. Here, thinning and surface morphology changes induced by high-energy ion bombardment in PMMA and PVC thin films were investigated, focusing on the role of the initial thickness of the films and the stopping power of the ions. We used thin films with initial thicknesses varying from 13 to 800 nm, and light and heavy ions as projectiles in the energy range of 2-2000 MeV, where the electronic stopping dominates. Thickness reductions as a function of fluence were monitored and thinning cross sections were extracted from curves. A supralinear scaling between the thinning cross sections and the electronic stopping power of the beams was observed, with a much enhanced thinning efficiency for the swift heavy ions. The scaling with the stopping power dE/dx is almost independent of the initial thickness of the films. At intermediate and large fluences, changes in the physicochemical properties of the irradiated polymers may modulate and decelerate the thinning process of the remaining film. The importance of this secondary process depends on the stopping power and the balance between erosion and the chemical transformations induced by the beam. We also observe a trend for the thinning efficiency to become larger in very thin films. Depending on the type of beam and polymer, this effect is more or less pronounced. PMMA films irradiated with 2 MeV H+ show the most systematic correlation between initial thickness and thinning cross sections, while in PVC films the initial thickness plays a minor role for all investigated beams.

Impact of swift heavy ion irradiation on as-grown gallium nitride epilayers by MOCVD technique

The as-grown GaN by Metalorganic Chemical Vapor Deposition was utilized to study the irradiation effects on GaN epilayers. The stopping range of ions in the matter is studied to choose the energy range for irradiation. The grown epilayers were irradiated with light and heavy ions of O7+ and Ag12+ by varying ion fluence. The X-ray Diffraction confirmed the wurtzite crystal structure for pristine and all the irradiated GaN epilayers. Atomic force microscopy showed high surface roughness for heavy ion irradiation when compared with light ion. Micro-Raman analysis was carried out through the Lorentz line fitting and calculated the carrier concentration and phonon lifetime. In light and heavy ion irradiation, the carrier concentration enhances with defect formations. X-ray Photoelectron Spectroscopy analysis showed that light ion irradiation caused oxygen bonding, while heavy ion irradiation led to the Ga–Ga bond shift, revealing film degradation.

Investigating the crystal structure of ZrB2 under varied conditions of temperature, pressure, and swift heavy ion irradiation

The influence of temperature, pressure, and swift heavy ions on the structural characteristics of a nano-sized zirconium diboride crystal (43 nm) was investigated using X-ray diffraction and Small-Angle X-ray Scattering/Wide-Angle X-ray Scattering (SAXS/WAXS) powder diffraction methods. Within the temperature range of 300–773 K, alterations in lattice parameters, lattice volume, coefficient of thermal expansion, and the kinetics of water molecule absorption on the active surface of the zirconium diboride crystal were comprehensively analyzed. Furthermore, the mechanism responsible for the structural degradation of absorbed water molecules was elucidated. The degree of amorphization in the ZrB2 nano crystal reached its maximum when subjected to irradiation by fast 132Xe26+ ions with an energy of 167 MeV, at fluences of up to 3.0 × 1014 ions/cm2. Additionally, the expansion mechanism of lattice parameters and the kinetics of the phase transformation process under the influence of swift heavy ions were studied. Notably, pressure variations did not induce a phase transition within the lattice structure. However, when exposed to an 8.0 GPa pressure, the lattice underwent substantial maximum contraction, reducing by up to 20.5 Å3.

Swift heavy ion irradiation induced modifications on the structure, optical and electrical properties of pulsed laser deposited anatase TiO2 thin films

The swift heavy ions of Ag7+ (100 MeV) were used to irradiate the anatase TiO2 thin films prepared by pulsed laser deposition (PLD) technique on quartz substrates. The effect of ion fluences (1×1012, 1×1013 and 1×1014 ions/cm2) on the structure, surface morphology, optical and electrical properties are investigated through several analytical techniques such as XRD, Micro-Raman, FTIR, XPS, AFM, FESEM, UV–visible and Hall measurements. The analysis of XRD data shows a gradual shift in the (101) plane toward higher diffraction angle on increasing the ion fluence which increases the lattice strain in the films. The EDS spectra reveal a modest Ti-rich composition with a significant shift following irradiation for both as-grown and irradiated films. The development of hillocks at increased ion fluence and considerable grain splitting following irradiation are observed in SEM micrographs. AFM images exhibit increase in surface roughness with the increase in ion fluence. Moreover, there is a significant drop in the band gap of the irradiated thin films from 3.92 to 3.44 eV with the increase in ion fluence. The various electrical parameters such as carrier concentrations (n), Hall mobility (μ), electrical resistivity (ρ), Hall coefficient (RH), etc., are determined by the Hall measurements at room temperature. This study indicates that the SHI irradiation plays a significant role in tunning the physical properties of anatase TiO2 thin films.

Response of ZrC to swift heavy ion irradiation

Zirconium carbide (ZrC) is commonly used for energy sector research, as well as a surrogate for the proposed advanced nuclear fuel candidate uranium carbide. This study investigates structural modifications to nanocrystalline and microcrystalline ZrC resulting from dense electronic excitations induced by swift heavy ion exposure. Samples were irradiated with 946 MeV Au ions to various fluences up to 6 × 1013 ions cm−2 and characterized using synchrotron-based x-ray diffraction. The evolution of the unit-cell parameter and heterogeneous microstrain were evaluated as a function of fluence and compared with those of nanocrystalline and microcrystalline CeO2 (a surrogate for UO2 fuel) irradiated under identical conditions. Distinct differences were observed in the radiation responses of the carbide and oxide across both grain sizes. Most notably, microcrystalline ZrC exhibits swelling characterized by two distinct regimes, which does not result in saturation at the ion fluences achieved. This contrasts with CeO2, which exhibits the well-documented direct-impact defect accumulation mechanism, reaching a steady-state saturation of swelling at higher fluences. Nanocrystalline CeO2 undergoes more pronounced swelling compared with microcrystalline CeO2, in contrast to nanocrystalline ZrC, which exhibits only minimal unit-cell changes. These results demonstrate that swift heavy ion-induced structural changes can be quite different in carbides and oxides, which must be considered when extrapolating fission-fragment type damage in current fuels to advanced fuels.

Optical and structural changes in intermediate phase Ge22Se78 thin film under 100 MeV Ag swift-heavy ion irradiation

Optical and structural changes in intermediate phase Ge22Se78 thin film under 100 MeV Ag swift-heavy ion irradiation

Interface engineering at Bi/As2Se3 bilayer thin film by 120 MeV Ag swift heavy ion irradiation at different fluence: Modifications in its structural, optical and morphological properties

Interface engineering at Bi/As2Se3 bilayer thin film by 120 MeV Ag swift heavy ion irradiation at different fluence: Modifications in its structural, optical and morphological properties

Impact of swift heavy oxygen ion irradiation on the performance of Pt/GaN Schottky diodes and epitaxial layers: A comparative study

Pt/GaN Schottky barrier diodes and GaN epitaxial layers on sapphire substrates were studied under swift heavy ion irradiation using 100 MeV O7+ ions having fluences in the range of 1 × 1010–6.4 × 1013 ions/cm2. It was observed that ideality factor, Schottky barrier height, and series resistance increased, while carrier concentration decreased with increasing ion fluence. The ex situ measurements, such as x-ray diffraction and UV–Vis spectroscopy, revealed that GaN layers exhibit negligible variation in structural and bandgap characteristics after irradiation with oxygen ions. The cross-sectional transmission electron microscopy images of the GaN epitaxial layer irradiated at 5 × 1012 ions/cm2 confirmed the absence of irradiation-induced tracks or defect clusters, indicating only point defects that can act as charge traps without structural damage.

Insight into What Is inside Swift Heavy Ion Latent Tracks in PET Film.

We present here a novel experimental study of changes after contact electrification in the optical transmission spectra of samples of both pristine and irradiated PET film treated with Kr+15 ions of energy of 1.75 MeV and a fluence of 3 × 1010 cm2. We used a non-standard electrification scheme for injecting electrons into the film by applying negative electrodes to both its surfaces and using the positively charged inner regions of the film itself as the positive electrode. Electrification led to a decrease in the intensity of the internal electric fields for both samples and a hypsochromic (blue) shift in their spectra. For the irradiated PET sample, electrification resulted in a Gaussian modulation of its optical properties in the photon energy range 2.3-3.6 eV. We associate this Gaussian modulation with the partial decay of non-covalent extended conjugated systems that were formed under the influence of the residual radial electric field of the SHI latent tracks. Our studies lead us to suggest the latent track in the PET film can be considered as a variband material in the radial direction. Consideration of our results along with other published experimental results leads us to conclude that these can all be consistently understood by taking into account both the swift and slow electrons produced by SHI irradiation, and that it appears that the core of a latent track is negatively charged, and the periphery is positively charged.

Optimized photoelectric performance of MoS2/graphene heterostructure device induced by swift heavy ion irradiation

Two-dimensional materials with exceptional electronic and photoelectric properties are expected to develop a new-generation of ultrathin, high efficiency, broadband, and flexible photodetectors. For the potential application towards outer space exploration, the harsh irradiation environment must be taken into consideration. In this work, irradiation effects of MoS2/Graphene heterostructure field effect transistors (MoS2/G FETs) induced by swift heavy ions (SHIs) were explored. After irradiation, a new Raman peak denoted as D peak emerged, which demonstrated that SHI irradiation induced damage in graphene. Photoluminescence investigation of MoS2 indicated that SHI irradiation activated the excitation conversion of trion A− to excitation A0. Latent tracks were observed on MoS2/G/SiO2 by using atomic force microscope. The decreased resistance and increased carrier mobilities were detected at fluence lower than 5 × 1010 ions/cm2, which could be ascribed to the localized annealing of graphene during irradiation. The increased photocurrent and responsivity at fluence lower than 1 × 1010 ions/cm2 could be interpreted as the enhanced photoinduced gate voltage resulting from the SHI irradiation induced defects in MoS2/G FET. The devices were deteriorated at fluence of 1 × 1011 ions/cm2. The optimized and degraded properties of the devices could be ascribed to competition among doping, local annealing and defect scattering.

SYNTHESIS OF ORTHORHOMBIC TIN DIOXIDE NANOWIRES IN TRACK TEMPLATES

In this work, the synthesis of orthorhombic SnO2 nanowires (NWs) was carried out by electrochemical deposition into prepared SiO2/Si-p ion-track template. Track formations in the SiO2/Si structure were created by irradiation on a DC-60 cyclotron with swift heavy Xe ions with an energy of 200 MeV (Ф = 108 cm−2). A 4% aqueous solution of hydrofluoric acid (HF) was used to form nanoporous templates. Electrochemical deposition (ECD) of SnO2 into the track template was carried out at room temperature, the voltage at the electrodes was 1.75 V. During the ECD process, an electrolyte with the following chemical composition was used: 6 g/l SnCl2 (Sigma-Aldrich) – 25 ml H2O – 2 ml HCl (“reagent grade”; 35%; ρ = 1.1740 g/cm3). The surface morphology of the samples, after the ECD process, was studied on a Zeiss Crossbeam 540 two-beam scanning microscope. The phase composition and crystallographic structure of nanoheterostructures (SnO2-NP/SiO2/Si) with nanopores filled with tin dioxide were studied using X-ray diffraction (XRD) on a multifunctional X-ray diffractometer Rigaku SmartLab. Photoluminescence was measured in the optical range of 320–600 nm using a CM2203 spectrofluorimeter (Solar). The electrical characteristics of the synthesized tin dioxide nanowires were studied using a VersaStat 3 potentiostat from Ametek.As a result, a SnO2-NWs/SiO2/Si nanoheterostructure with orthorhombic crystal structure of SnO2 nanowires was obtained. Photoluminescence excited by light with a wavelength of 240 nm has a low intensity, arising mainly due to defects such as oxygen vacancies and interstitial tin or tin with damaged bonds. Measurement of the current-voltage characteristic showed that the SnO2-NP/SiO2/Si nanoheterostructure obtained in this way contains arrays of p-n junctions.

Neutrons and swift heavy ions irradiation induced damage in SiC single crystal

Radiation damage induced in SiC single crystal by neutrons and sequentially neutrons + 91.3 MeV Xe ions irradiations were characterised by optical measurements (absorption and photoluminescence) and Raman spectroscopy. The samples were first irradiated with neutrons then followed by irradiation with 91.3 MeV Xe ions. Our aim is to check electronic ionization-induced pre-existing defects annealing in SiC single crystal. The data obtained for samples irradiated by neutrons were compared to those of neutrons + ions. It is found that neutrons irradiation induced absorption band at 780 nm and two emission bands at 550 nm and 920 nm. Both bands 780 nm and 920 nm assigned to silicon vacancy (VSi). Compared to neutrons irradiation, the same absorption and emission bands are observed for neutron + ions irradiated samples, indicating similar types of defects formation by additional 91.3 MeV Xe ions. The bands growth rapid at low dose followed by a saturation effect above a dose of 2.0 × 10−4 dpa for neutrons and 10.6 × 10−3 dpa for neutrons + ions. The stress follows the same dose-dependence as the absorption band, suggesting a good correlation between the stress and the silicon vacancies (VSi). Raman results proved that additional 91.3 MeV Xe ions irradiation induced the pre-existing damage annealing in SiC crystal. However, at high pre-existing defects concentration and Xe ions dose a competition between defects creation and annealing takes place. To confirm the results experiments using Doppler Broadened Emission Spectroscopy (DBS) using Variable Energy Slow Positron Beam, are planned for our next study.

Ion track formation and porosity in InSb induced by swift heavy ion irradiation

Ion track formation, irradiation-induced damage (amorphization), and the formation of porosity in InSb after 185 MeV 197Au swift heavy ion irradiation are studied as a function of ion fluence and irradiation angle. Rutherford backscattering spectrometry in channeling geometry reveals an ion track radius of about 16 nm for irradiation normal to the surface and 21 nm for off-normal irradiation at 30° and 60°. Cross-sectional scanning electron microscopy shows significant porosity that increases when irradiation was performed off-normal to the surface. Off-normal irradiation shows a preferential orientation of the pores at about 45° relative to the surface normal. Moreover, when subjected to identical conditions, InSb samples demonstrate notably higher swelling compared to GaSb bulk samples.

Fabrication, swift heavy ion irradiation, and damage analysis of lanthanide targets

Abstract One limiting factor in progress in the discovery and study of new superheavy elements (SHE) is the maximum achievable thickness and irradiation stability of current generation actinide targets. The desired thickness of targets, using full excitation function widths, cannot be achieved with current target technology, especially the widely used molecular plating (MP). The aim of this study was to transfer progress in the electrochemistry of lanthanides and actinides to the production of targets. Here, we report on the production of lanthanide targets using anhydrous electrochemical routes. In a first irradiation series, thulium thin films with areal densities up to 1800 μg/cm2 were produced using anhydrous triflate compounds and subjected to irradiation tests, using 6.0 MeV/u 48Ca ions at a fluence of 3.9 × 1014 ions/cm2 and 8.6 MeV/u 197Au ions at fluences in the range of 3.0 × 1011 to 1.0 × 1013 ions/cm2. The thin films were characterised before and after the irradiations using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).

Radiation hardness evaluation of ε-Ga2O3 thin-film devices under swift heavy ion irradiation

The ultra-wide band gap (∼4.9 eV) and extremely large breakdown field strength (∼8 MV/cm) enable ε-Ga2O3 as an ideal materials candidate for high-performance power devices and solar-blind photodetectors. For the purpose of deep space applications explorations, comprehensive study of the effects of particle irradiation on the lattice stability and electronic properties of ε-Ga2O3 are of pivotal importance. In this work, leveraging a unique Ta radiation source, we interrogate the radiation hardness of ε-Ga2O3 thin films after 1907 MeV Ta swift heavy ion (SHI) irradiation. Detailed characterizations of the structural and optical properties show that the morphology and lattice structure are disrupted, with an increase of the band gap. Additionally, X-ray photoelectron spectroscopy experiments combining density functional theory calculations corroborate extrinsic flux-induced high concentration defects in the film, which lead to truncated photo-response performance of the device. However, even upon irradiation with a fluence of 5 × 1010 cm−2, the overall performance of the device remains robust and substantial. This outstanding radiation hardness of ε-Ga2O3 thin films rationalizes their potential usage for space applications.

Formation and self-organisation of nano-porosity in swift heavy ion irradiated amorphous Ge

Nano-porosity in amorphous Ge formed by swift heavy ion irradiation displays a peculiar self-organisation process. Initially almost randomly distributed pores grow with increasing irradiation fluence and segregate in layers orientated parallel to the sample surface. This self-organisation mechanism depends on the ion energy, thickness of the amorphous Ge layer and the angle of ion incidence and shows a characteristic length depending on ion energy and irradiation angle. Molecular dynamics simulations of individual ion tracks show that voids form due to the transition from the low-density amorphous to the high-density liquid phase, which also gives rise to a flow directed away from large pores and surfaces. The flow results in a characteristic distance from surfaces and larger pores, below which new voids do not form, and supports the formation of voids at the amorphous/crystalline interface. Simulations also demonstrate that, while direct impacts can reposition small voids, partial or nearby impacts promote their growth at the same location. These processes are plausible drivers for the self-organization.

Optical Characteristics of MgAl2O4 Single Crystals Irradiated by 220 MeV Xe Ions.

In In this study, the optical properties of magnesium-aluminate spinel were examined after being irradiated with 220 MeV Xe ions. The research aimed to simulate the impact of nuclear fuel fission fragments on the material. The following measurements were taken during the experiments: transmission spectra in the IR region (190-7000) nm, optical absorption spectra in the range (1.2-6.5) eV, and Raman spectra were measured along the depth of ion penetration from the surface to 30 µm. A peak with a broad shape at approximately 5.3 eV can be observed in the optical absorption spectrum of irradiated spinel crystals. This band is linked to the electronic color centers of F+ and F. Meanwhile, the band with a maximum at ~(3-4) eV is attributed to hole color centers. Apart from the typical Raman modes of an unirradiated crystal, additional modes, A1g* (720 cm-1), and Eg* (385 cm-1), manifested mainly as an asymmetric shoulder of the main Eg mode, are also observed. In addition, the Raman spectroscopy method showed that the greatest disordering of crystallinity occurs in the near-surface layer up to 4 μm thick. At the same time, Raman scattering spectroscopy is sensitive to structural changes almost up to the simulated value of the modified layer, which is an excellent express method for certifying the structural properties of crystals modified by swift heavy ions.

Response of nonstoichiometric pyrochlore composition Nd1.8Zr2.2O7.1 to electronic excitations

AbstractIn response of swift heavy ion (100 MeV I9+) irradiation, the irradiation‐induced disordering in nonstoichiometric pyrochlore composition (Nd1.8Zr2.2O7.1) was compared to that of stoichiometric composition Nd2Zr2O7. Both compositions were prepared through auto gel‐combustion followed by sintering under the identical conditions. Systematic analysis of the compositions before and after irradiation was performed with X‐ray diffraction (XRD), Raman spectroscopy, and plane‐view high‐resolution transmission electron microscopy (HRTEM) techniques. Irradiation caused pyrochlore to amorphous phase transformation was observed in both compositions except the slower rate of amorphization in Nd1.8Zr2.2O7.1. The amorphization was achieved as a consequence of isolated disordered track overlapping at higher ion fluence with the estimated track diameter 2.73 ± 0.05 and 3.46 ± 0.30 nm for Nd1.8Zr2.2O7.1 and Nd2Zr2O7, respectively, employing the framework of single‐ion impact model to XRD results. HRTEM micrographs also revealed the less prevalence of irradiation‐induced amorphization in Nd1.8Zr2.2O7.1 with the observed irradiation‐induced modified track region composed of defect‐rich pyrochlore structure, anion‐deficient fluorite structure, and amorphous domains; with the diameter of 3.0 ± 1.0 nm and 5.0 ± 1.0 nm in Nd1.8Zr2.2O7.1 and Nd2Zr2O7, respectively. The preexisting anion‐deficient fluorite structure in Nd1.8Zr2.2O7.1 helps in its epitaxial growth as recovered structure from melted ion track during irradiation‐induced rapid cooling.