Xe Ion Irradiation Research Articles

Computational simulation of primary damage in silicon carbide under ions irradiation

Silicon carbide (SiC) and its composites are promising structural materials for advanced nuclear energy applications. Due to the lack of advanced nuclear energy devices, ion beam irradiation is widely used to emulate reactor neutron irradiation. At the same time, different types of ion beam irradiation could produce different primary knock-on atom (PKA) energy spectra. PKA energy determines cascade damage sizes and defect clustering distributions, which may influence the irradiated materials’ long-term microstructural evolution and mechanical properties. This work used SRIM and Geant4 software to investigate the PKA characteristic produced by 1 MeV different noble gas ions and neutrons in the silicon carbide. The PKA energy spectra and weighted energy spectra of C and Si are calculated, respectively. The simulation results show that the PKA energy spectra calculated by the two kinds of software have obvious differences, but the weighted average PKA energies are close to each other. Simulation results verified that the weighted average PKA energy of Kr and Xe ion irradiation is close to that weighted average PKA energy spectrum for neutron irradiation of advanced reactors. The simulation results provide scientific references for understanding the difference in irradiation effects of different types of ions and also provide fundamental bases for the simulation of primary defect damage and long-term defect evolution in irradiated SiC.

Rate theory model of irradiation effects in UO2: Influence of electronic energy losses

To investigate the effect of electronic energy losses on nuclear damage in UO2, we use a simple Rate Theory (RT) model, based on the time evolution of single point defects, governed by their absorption at the surface of TEM lamellae, and by interstitial-type dislocation loops nucleation, solely characterized by their number and average size. We first parametrize the model by fitting six different experimental datasets at various temperatures, ion type and energy (0.39 MeV Xe and 4 MeV Au ion irradiations at 93, 298 and 873 K) where defect evolution in UO2 is dominated by displacement damage caused by nuclear energy losses. The model suggests that dislocation evolution kinetics is driven by monomers diffusion at 873 K. At lower temperature (93 and 298 K) monomer diffusion has little impact and the evolution is governed by the nucleation of loops within the collision cascade. Analysis of four additional experimental datasets at 93 and 298 K where electronic energy losses are strong (single 6 MeV Si and dual simultaneous Xe & Si ion irradiations) required modification of monomer's diffusion coefficients. In the case of single Si ion irradiation, evolution is temperature independent and the enhanced diffusion due to electronic excitations and ionizations are best captured by adding athermal component to the monomer diffusion coefficients. In case of the dual Xe & Si ions irradiation, electronic excitation caused by Si ions impacts the defects pre-generated by Xe ions and enhances defect diffusion by at local heating induced by the thermal spike of Si ions. This effect is best captured by artificially raising the irradiation temperature.

Microstructure Evolution of the Interface in SiCf/TiC-Ti3SiC2 Composite under Sequential Xe-He-H Ion Irradiation and Annealing Process.

A new type of SiCf/TiC-Ti3SiC2 composite was prepared by the Spark Plasma Sintering (SPS) method in this work. The phase transformation and interface cracking of this composite under ion irradiation (single Xe, Xe + He, and Xe + He + H ions) and subsequent annealing were analyzed using transmission electron microscopy (TEM), mainly focusing on the interface regions. Xe ion irradiation resulted in the formation of high-density stacking faults in the TiC coatings and the complete amorphization of SiC fibers. The implanted H ions exacerbated interface coarsening. After annealing at 900 °C for 2 h, the interface in the Xe + He + H ion-irradiated samples was seriously damaged, resulting in the formation of large bubbles and cracks. This damage occurred because the H atoms reduced the surface free energy, thereby promoting the nucleation and growth of bubbles. Due to the absorption effect of the SiCf/TiC interface on defects, the SiC fiber areas near the interface recovered back to the initial nano-polycrystalline structure after annealing.

Molecular dynamics simulations of silicon nitride atomic layer etching with Ar, Kr, and Xe ion irradiations

Molecular dynamics simulations were performed to understand the gas-surface interactions during silicon nitride (SiN) plasma-enhanced atomic layer etching (PE-ALE) processes with argon (Ar), krypton (Kr), and xenon (Xe) ion irradiations. Changes in the surface height, penetration depths of hydrofluorocarbon (HFC) species, and damaged layer thickness were examined over five PE-ALE cycles. The results showed that the PE-ALE process with Ar+ ions etched the SiN surface more efficiently than those with Kr+ or Xe+ ions under the otherwise same conditions. Slower etching in the case of Kr+ or Xe+ ion irradiation is likely caused by the accumulation of HFC species. It was also observed that the damaged layer thicknesses of the etched surfaces are nearly the same among those with Ar+, Kr+, and Xe+ ion irradiations.

Damage microstructures in Ti3SiC2 under successive Xe-He-H ions irradiation and annealing process

Ti3SiC2 is recognized as a promising candidate material for nuclear energy applications; however, the microstructural defects resulting from complex irradiation processes remain elusive. This study investigates the microstructural evolution of Ti3SiC2 under sequential Xe-He-H ions irradiation at room temperature, followed by annealing at 900 °C, employing both experimental and first-principles computational approaches. A reverse phase transformation occurred following He irradiation, indicating that He facilitates the remote migration and recombination of Si vacancies through the formation of He-Si pairs during annealing. Post-annealing, the Xe-irradiated sample exhibited a widespread distribution of small Xe bubbles, whereas larger bubbles were prevalent at peak damage regions in the samples subjected to Xe+He and Xe+He+H irradiation. Concurrently, Si-rich precipitates with distinct distribution patterns were observed in samples irradiated with Xe, Xe+He, and Xe+He+H ions, significantly affecting the hardness. First-principles calculations reveal that the distinct damage profiles are primarily attributed to the dynamic behaviors of Si interstitials. The Ti-Si bonds are relatively weak and easily broken, leading to abundant Si interstitials in Xe ion irradiation, and He enhances Si diffusion. Conversely, H enhances Si segregation by preventing He from capturing Si interstitials. Within the TiC grains, He promotes Si migration, causing an approximately 700-fold increase in Si diffusivity at 900 °C. The Si segregation leads to the nucleation of 〈110〉 dislocation loops, culminating in the formation of distinctive strip-like Si clusters. This study elucidates the formation mechanism of Si segregation within Ti3SiC2, providing valuable insights for the design of irradiation-resistant materials.

Investigation of facet evolution on Si surfaces bombarded with Xe ions

This study investigates the formation of facets on Si surface under Xe ion irradiation using an ion energy of 0.5 keV. By examining the effects of ion incidence angle (60° –85°), fluence (4.5 × 1018 to 1.35 × 1019 ions/cm2), and temperature (RT to 200 ◦C), we explore the evolution of facets. The surface roughness displays a distinct trend, reaching its peak when the ion incidence angle is 80°, which indicates the formation of faceted structures due to a sudden change in roughness. Additionally, temperature studies highlight the important role of temperature in enhancing facet arrangement. To support experimental findings, numerical simulation using Anisotropic Kuramoto-Sivashinsky (AKS) equation is employed. These simulations provide valuable insights into the dynamics of facet evolution, allowing us to better understand how curvature-dependent sputtering yield, dispersion, and diffusion collectively influence the formation and morphology of facets on the Si surface under Xe ion irradiation.

Surface topography and microstructure changes of ultrafine-grained graphite prepared from filler of onion-like carbon spheres by Xe ions irradiation

Onion-like carbon spheres (OLC) were doped into the traditional graphite raw material system to decrease the pore diameter to ∼400 nm, with potential for use in molten salt reactors. The obtained graphite (OLCG) prepared from OLC was subjected to 7 MeV Xe26+ irradiation in this work, and a systematic investigation was conducted to verify its irradiation behavior. The surface morphology and microstructural evolution in graphite samples under different irradiation conditions were studied with different characterization methods. The surface roughness of OLCG increased and the hill appeared at lower irradiation doses, which was similar to that of IG-110, but the filler particles of OLCG gradually become spherical at 2.5 dpa. The analysis by X-ray diffraction reveals that OLCG's graphitization degree is approaching but slightly worse compared to IG-110. Raman studies indicate that the irradiation causes an increase in defect density and in-plane disorder both in graphite. The OLC filler exhibits a greater sensitivity to radiation, leading to OLCG being slightly sensitive to radiation as compared to IG-110. Neutron irradiation of the resulting graphite should be continued as OLCG showed good irradiation resistance at low irradiation doses and had a much smaller pore diameter.

Mechanical properties of Xe-ion-irradiated high-entropy-alloy-based multilayers

In this Letter, we investigate the mechanical stability of HEA-based multilayers after Xe-ion irradiation. CrFeCoNi/TiNbZrTa metallic and nitride thin films with a bilayer thickness of 30 nm were grown by reactive dc-magnetron sputtering on Al2O3(0001) substrates for irradiation studies and on Si(100) substrates for other characterizations. The films were subjected to 3-MeV Xe-ion irradiation at room temperature (RT) and at 500 °C. The crystal structure and mechanical properties of the films before and after irradiation were studied by x-ray diffraction and nanoindentation. Before irradiation, both the metallic and nitride multilayers displayed a lower hardness (7 and 20 GPa, respectively). Annealing at 500 °C for 150 min increased the hardness of the multilayer samples, but it also induced intermixing of elements between the sublayers of the metallic multilayer. Irradiation hardening was observed only in the metallic multilayer at room temperature. When comparing the effects of irradiation damage vs the effects of annealing on the mechanical properties, it was observed that annealing the multilayers had a more pronounced effect.

Surface Activated Si-Si Wafer Bonding Using Different Ion Species

Surface activated bonding (SAB) on wafer level is enabled by the EVG ComBond® system for irradiation with different ion species. In this process, the native oxide of 200 mm Si wafers is sputter-removed, and an amorphous layer is generated. After ion treatment, the wafers are bonded in ultra-high vacuum (UHV) at room temperature. The impact of Ar, Kr and Xe ion irradiation on the amorphous layer thickness (ALT) was investigated with the goal of optimizing the bonding process. This was i.a. motivated by the fact, that the presence of an amorphous layer reduces the electrical conductivity across the wafer interface [1].The ALT of unbonded wafers was evaluated via spectroscopic ellipsometry (SE) for varying ion species, ion energies and angles of incidence. The results show that heavier ions generate a thinner amorphous layer than light ions (see Fig. 1). This is most likely due to the higher scattering cross section of heavy ions resulting in a lower penetration depth. For each ion type there is a minimum in the ALT as a function of the ion energy which can be attributed to sputter-implantation dynamics. Furthermore, the ALT is decreasing with the angle of incidence as the incoming ions are projected into the material.Transmission electron microscopy (TEM) measurements were conducted on bonded wafer pairs and confirm the trend of heavy ions generating a thinner amorphous layer. Moreover, the TEM measurements show that post-bond annealing at 450°C for 5 h reduces the ALT due to recrystallization near the bonding interface.To ensure mechanical stability for further wafer processing and for the final device, bonding energy measurements were conducted via the Maszara method [2]. Although maximum bonding energy can be achieved for specific parameters with each ion species, Xe irradiated samples tend to have a higher overall bonding energy.[1] P.A. Stolk et al., “Contribution of defects to electronic, structural, and thermodynamic properties of amorphous silicon”, in Journal of Applied Physics, vol. 75, no. 11, pp. 7266-7286 (1994).[2] W.P. Maszara et al., “Bonding of silicon wafers for silicon-on-insulator”, in Journal of Applied Physics, vol. 64, no. 10, pp. 4943-4950 (1988). Figure 1

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.

Surface Activated Si-Si Wafer Bonding Using Different Ion Species

Surface activated bonding on wafer level is enabled by an advanced direct wafer bonding system for irradiation with different ion species. In this process, the native oxide of 200 mm Si wafers is sputter-removed and an amorphous layer is generated. After ion treatment, the wafers are bonded in ultra-high vacuum at room temperature. The impact of Ar, Kr and Xe ion irradiation on the amorphous layer thickness was investigated with the goal of optimizing the bonding process for establishing interfaces with electronic functionality. This was i.a. motivated by the fact, that the presence of an amorphous layer reduces the electrical conductivity across the wafer interface.

Defect evolution under intense electronic energy deposition in uranium dioxide

The coupled effects of nuclear and electronic energy losses were investigated in uranium dioxide (UO2). Single and sequential ion irradiations were carried out with 92 MeV Xe ions and 0.9 MeV I ions. Raman spectroscopy and X-ray diffraction analyses were combined with the inelastic thermal spike (iTS) model to investigate the effect of electronic ionizations on the ballistic damage. It appears that the high-energy ions induce a significant change in the defect distribution with an amplitude that depends on the level of pre-existing disorder. This modification essentially results in an acceleration of the transformation from the dislocation loops to the dislocation lines, a process that is accompanied by a stress relaxation. Surprisingly, with the fluence increase of 92 MeV Xe ions, the stress starts to increase again, highlighting a possible synergetic effect between the pre-existing defects and those generated by the 92 MeV Xe ions irradiation.

Structural stability under Xe-ion irradiation of TiZrNbTaV-based high-entropy alloy and nitride films

Refractory high-entropy protective coatings are of interest for nuclear fuel cladding applications due to their corrosion resistant properties and irradiation resistance at elevated temperature. Here, TiZrNbTaV metallic and (TiZrNbTaV)N films were deposited by magnetron co-sputtering. The metal elemental contents of both films were nearly equiatomic. These films were irradiated by Xe ions at room temperature and 500 °C, and examined by X-ray diffraction and transmission electron microscopy. The as-deposited (TiZrNbTaV)N film showed a single NaCl-type fcc phase and a pronounced columnar growth structure, which could remain intact after irradiation treatments. In contrast, the as-deposited TiZrNbTaV film exhibited an amorphous structure and formed a bcc phase structure after irradiation at 500 °C. The TiZrNbTaV film after irradiation at 500 °C composed of depth-dependent size of grains. This distribution of grain size is consistent with simulated displacement damage. The stable structure of (TiZrNbTaV)N film under high temperature irradiation indicates that these materials have potential for use as protective coatings for nuclear fuel claddings.

High-Throughput Nanopore Fabrication and Classification Using Xe-Ion Irradiation and Automated Pore-Edge Analysis.

Large-area nanopore drilling is a major bottleneck in state-of-the-art nanoporous 2D membrane fabrication protocols. In addition, high-quality structural and statistical descriptions of as-fabricated porous membranes are key to predicting the corresponding membrane-wide permeation properties. In this work, we investigate Xe-ion focused ion beam as a tool for scalable, large-area nanopore fabrication on atomically thin, free-standing molybdenum disulfide. The presented irradiation protocol enables designing ultrathin membranes with tunable porosity and pore dimensions, along with spatial uniformity across large-area substrates. Fabricated nanoporous membranes are then characterized using scanning transmission electron microscopy imaging, and the observed nanopore geometries are analyzed through a pore-edge detection and analysis script. We further demonstrate that the obtained structural and statistical data can be readily passed on to computational and analytical tools to predict the permeation properties at both individual pore and membrane-wide scales. As an example, membranes featuring angstrom-scale pores are investigated in terms of their emerging water and ion flow properties through extensive all-atom molecular dynamics simulations. We believe that the combination of experimental and analytical approaches presented here will yield accurate physics-based property estimates and thus potentially enable a true function-by-design approach to fabrication for applications such as osmotic power generation and desalination/filtration.

Dynamics of nanoscale triangular features on Ge surfaces

Ion beam sputtering, known as potential technique for producing nanoripple on various surfaces having wide range of applications. Along with nanoripple, triangular features are also superimposed, limiting their use for some potential applications. Here we are reporting evolution of triangular features on Ge (100) surfaces under low energy (300–1000 eV) Xe ion irradiation at room temperature for angles of incidence (61°–80°) and ion fluences of (5.34 × 1017−8.01 × 1018 ions cm−2). Triangular features appear with the onset of ripple formation and disappear when the ripple periodicity is lost. These features formation depend not only on material but also depend on the ratio of the ion/target mass. In comparison with numerical simulations based on modified anisotropic Kuramoto-Sivanshinsky equation, we find good agreement for the evolution of base angle and lateral length for the triangular features with ion incidence angle. The dynamics of triangular feature with ion incidence angle and ion fluence have been reported. Ion-incidence angle dependency is adequately replicated in numerical simulations. Experimentally the base angle and lateral length increases with increase in ion incidence angle, similar trend is observed in numerical simulation.

Raman spectroscopy study of damage in swift heavy ion‐irradiated ceramics

AbstractRaman scattering is applied to probe the radiation damage in swift heavy ion‐irradiated ceramics, namely zirconium nitride (ZrN), ceria (CeO2), and yttria‐stabilized zirconia (ZrO2: Y, or YSZ) for about the same high electronic stopping power of heavy ions. Raman spectra show that these ceramics are radiation‐resistant materials that are not amorphized by such irradiations even for large ion track overlap at high fluences. However, for ZrN, the increase of the TA/LA and TO/LO band intensities versus fluence is evidenced after 100‐MeV Xe ion irradiation up to a saturation for the fluence of 3 × 1012 cm−2. The band growths are ascribed to the increase of the concentration of Zr and N vacancies induced by electronic excitations inside tracks. However, the diffuse reflectance spectra do not exhibit any clear modifications of the electronic structure. For ceria, the decrease and broadening of the main F2g peak of the fluorite‐like structure and the growth of a broad defect band assigned to oxygen vacancy formation is observed versus fluence up to 1014 cm−2 for 200‐MeV Xe ion irradiation. For YSZ, Raman spectra mainly give evidence of the intrinsic lattice disorder due to the native oxygen vacancies even up to high fluences of about 3 × 1013 cm−2 for 200‐MeV I and 200‐MeV Au ion irradiation. Results are discussed on the basis of the interplay between the native structural disorder and the radiation‐induced disorder by electronic excitations in these three materials.

Lattice damage in InGaN induced by swift heavy ion irradiation

The microstructural responses of In0.32Ga0.68N and In0.9Ga0.1N films to 2.25 GeV Xe ion irradiation have been investigated using x-ray diffraction, Raman scattering, ion channeling and transmission electron microscopy. It was found that the In-rich In0.9Ga0.1N is more susceptible to irradiation than the Ga-rich In0.32Ga0.68N. Xe ion irradiation with a fluence of 7 × 1011 ions⋅cm−2 leads to little damage in In0.32Ga0.68N but an obvious lattice expansion in In0.9Ga0.1N. The level of lattice disorder in In0.9Ga0.1N increases after irradiation, due to the huge electronic energy deposition of the incident Xe ions. However, no Xe ion tracks were observed to be formed, which is attributed to the very high velocity of 2.25 GeV Xe ions. Point defects and/or small defect clusters are probably the dominant defect type in Xe-irradiated In0.9Ga0.1N.

Ion-Track Template Synthesis and Characterization of ZnSeO3 Nanocrystals

ZnSeO3 nanocrystals with an orthorhombic structure were synthesized by electrochemical and chemical deposition into SiO2/Si ion-track template formed by 200 MeV Xe ion irradiation with the fluence of 107 ions/cm2. The lattice parameters determined by the X-ray diffraction and calculated by the CRYSTAL computer program package are very close to each other. It was found that ZnSeO3 has a direct band gap of 3.8 eV at the Γ-point. The photoluminescence excited by photons at 300 nm has a low intensity, arising mainly due to zinc and oxygen vacancies. Photoluminescence excited by photons with a wavelength of 300 nm has a very low intensity, presumably due to electronic transitions of zinc and oxygen vacancies.

Hardness variation in nanocrystalline SiC irradiated with heavy ions

This study reports on the hardness of nanocrystalline silicon carbide (nc-SiC) with different grain sizes using nanoindentation technique. Both amorphous SiC (am-SiC) and single-crystal SiC (sc-SiC) are also investigated for a comparison study. Irradiation experiments were performed for the different types of SiC using Kr and Xe ions at elevated temperatures. It is found that the hardness of the am-SiC increases after Kr ion irradiation at 550 K, which is attributed to the irradiation-induced densification of the amorphous network structure. At higher temperatures (≥700 K), irradiation leads to crystallization of spherical nanograins in the am-SiC. The hardness values of the resulting nc-SiC with average grain sizes of ∼7 and 10.5 nm from the Kr and Xe ion irradiations, respectively, are found to be similar (∼40 GPa) and comparable to that of sc-SiC (38 GPa). In contrast, as-deposited SiC with a nano-columnar texture full of stacking faults (SFs) and twins exhibits super high hardness of 52.7 GPa, likely due to the suppression of the formation and propagation of indentation-induced dislocations in SiC. After Xe ion irradiation at 700 K, the hardness of the nano-columnar SiC decreases to 41.8 GPa, although the SF structure within the grains is well retained after irradiation. This is attributed to generation of radiation defects (such as invisible defect clusters) in the nano-columns, which could cause the hardness to decrease.

Memristive FG-PVA Structures Fabricated with the Use of High Energy Xe Ion Irradiation.

A new approach based on the irradiation by heavy high energy ions (Xe ions with 26 and 167 MeV) was used for the creation of graphene quantum dots in the fluorinated matrix and the formation of the memristors in double-layer structures consisting of fluorinated graphene (FG) on polyvinyl alcohol (PVA). As a result, memristive switchings with an ON/OFF current relation ~2–4 orders of magnitude were observed in 2D printed crossbar structures with the active layer consisting of dielectric FG films on PVA after ion irradiation. All used ion energies and fluences (3 × 1010 and 3 × 1011 cm−2) led to the appearance of memristive switchings. Pockets with 103 pulses through each sample were passed for testing, and any changes in the ON/OFF current ratio were not observed. Pulse measurements allowed us to determine the time of crossbar structures opening of about 30–40 ns for the opening voltage of 2.5 V. Thus, the graphene quantum dots created in the fluorinated matrix by the high energy ions are a perspective approach for the development of flexible memristors and signal processing.