Kr Ions Research Articles

Nanoscale pattern formation on silicon surfaces bombarded with a krypton ion beam: experiments and simulations

The nanoscale patterns produced by bombardment of the (100) surface of silicon with a 2 keV Kr ion beam are investigated both experimentally and theoretically. In our experiments, we find that the patterns observed at high ion fluences depend sensitively on the angle of incidence Θ. For Θ values between 74° and 85°, we observe five decidedly different kinds of morphologies, including triangular nanostructures traversed by parallel-mode ripples, long parallel ridges decorated by short-wavelength ripples, and a remarkable mesh-like morphology. In contrast, only parallel-mode ripples are present for low ion fluences except for Θ = 85°. Our simulations show that triangular nanostructures that closely resemble those in our experiments emerge if a linearly dispersive term and a conserved Kuramoto–Sivashinsky nonlinearity are appended to the usual equation of motion. We find ridges traversed by ripples, on the other hand, in simulations of the Harrison–Pearson–Bradley equation (Harrison et al 2017 Phys. Rev. E 96 032804). For Θ = 85°, the solid surface is apparently stable and simulations of an anisotropic Edwards–Wilkinson equation yield surfaces similar to those seen in our experiments. Explaining the other two kinds of patterns we find in our experiments remains a challenge for future theoretical work.

TEM-studies of the element segregation in irradiation induced defect structure in Zircaloy-4

In the study, Kr ion irradiation was performed in Zircaloy-4 to 20 dpa to investigate the irradiation-induced Zr–Fe–Cr particles dissolution and the element segregation in defect structure by transmission electron microscopy. Irradiation induced Zr–Fe–Cr particles dissolution is observed in cross-section sample. Microstructure observation confirms two types of defect structures in g = 0002 vector: c-loops and corduroy stripes. Corduroy stripes are visible in g = 0002 vector but invisible in g = 01 1‾ 0 vector, indicating the c-loop cluster nature. No Fe or Cr segregation in c-loops is observed, however, significant Fe segregation in corduroy stripes was observed in vicinity of Zr–Fe–Cr particles. The corduroy stripes show higher affinity for alloying element than c-loops.

In-situ irradiation-induced studies of grain growth kinetics of nanocrystalline UO2

The thermal conductivity of UO2 fuel needs to be high enough to dissipate the heat generated from the fission reaction. Since grain size affects thermal conductivity and grain size can evolve with irradiation, it is critical to understand in-reactor UO2 grain growth. Most studies of grain growth in UO2 are based on thermally driven processes at elevated temperatures. However, studies have shown that grain growth can occur even at cryogenic temperatures by ballistic processes. Such irradiation-induced grain growth in UO2 is yet to be studied. Advanced in-situ Kr ion irradiation and transmission electron microscopy were systematically performed on nanocrystalline UO2 thin films at temperatures ranging from 50 K to 1073 K; grain growth was observed at all temperatures. A combination of manual and machine learning techniques was used to measure and plot grain size evolution against irradiation fluence at various irradiation temperatures. The machine learning method has significantly improved the analysis efficiency and reduced human labors. The grain diameter data were fitted using classical grain growth and thermal spike models to describe grain growth kinetics with and without irradiation effect. Grain growth during low temperature irradiation (≤ 475 K) can be well described by the thermal spike model. Above 475 K, there were additional thermally assisted processes that further accelerate the grain growth. At the highest irradiation temperature about 1075 K, both irradiation-induced dislocation loops and cavities/bubbles were observed to form in the UO2. The effects of irradiation-induced defects on grain growth kinetics are discussed.

Energy deposition on nuclear emulsion by slow recoil ions for directional dark matter searches

The electronic energy deposited on nuclear emulsions by C ions of 5--200 keV and Kr ions of 5--600 keV is evaluated and compared with those deposited by fast ions for designing and fabricating fine-grain nuclear emulsions for directional dark matter searches. The nuclear quenching factor and the electronic linear energy transfer, which refers to the specific electronic energy deposited along the ion track, are evaluated. The so-called core and penumbra of heavy-ion track structure is modified to understand the track caused by recoil ions produced by dark matter candidate, i.e., weakly interacting massive particles, striking a nucleus in the AgBr crystal of nuclear emulsion. Very heavy recoil ions, 100--180 keV Pb ions, produced in $\ensuremath{\alpha}$ decay are also studied. Furthermore, the track structures due to protons of 25--80 keV are evaluated to consider the influence of background neutrons in underground laboratories.

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.

Thermal Effects in Multicomponent Equiatomic Ni-Based Alloys under High-Energy Irradiation with Kr Ions

Thermal Effects in Multicomponent Equiatomic Ni-Based Alloys under High-Energy Irradiation with Kr Ions

Optical, Structural, and Mechanical Properties of Gd3Ga5O12 Single Crystals Irradiated with 84Kr+ Ions

Herein, the optical absorption, X‐ray diffraction (XRD) analysis data, and mechanical properties along the ion path are analyzed for gadolinium gallium garnet (Gd3Ga5O12 or GGG) single crystals irradiated with fast 84Kr ions to fluences of 1013–1014 ion cm−2. It is found that the optical absorption spectra of Czochralski‐grown unirradiated GGG crystal consist of relatively narrow lines in the UV spectral range associated with the 4f–4f transitions in Gd3+ ions. Transitions from the 6S7/2 ground state to the 6P, 6J, and 6D states in the Gd3+ cation are visible. An additional absorption band is also observed at 350 nm, which is associated with an uncontrolled Ca impurity. In irradiated GGG single crystals, a shift of the fundamental absorption edge by ≈30 nm to the long‐wavelength part of the spectrum is observed. The observed changes are caused by structural disturbances caused by depletion of the surface layer and an increase in the number of displaced atoms accompanied by an increase in the crystal lattice parameter. XRD analysis shows the presence of size effects and deformation of interplanar distances due to the displacement of atoms from the sites of the crystal lattice with subsequent migration. Hardness measurements show ion‐induced softening, which may be due to ion‐induced amorphization.

Room‐Temperature Yellow Emission of a High Cd Content (x = 0.70), Highly Strained, Layer‐by‐Layer Grown Zn1−xCdxSe/ZnSe Quantum Well

The results of the growth and characterization of an 8 monolayers (MLs) thick Zn1−xCdxSe/ZnSe quantum well (QW) with quite high Cd content (x = 0.70) are presented. At room temperature (RT), the QW presents yellow excitonic emission at 2.179 eV (569 nm, same color as the yellow line of a Kr ion laser). Despite the large Cd content, the RT photoluminescence spectrum shows a well‐defined, symmetric excitonic peak with relatively narrow full width at half maximum, indicating a good structural quality of the QW that is attributed to the sequential layer‐by‐layer growth mode achieved by the use of the submonolayer pulsed beam epitaxy (SPBE) technique. The ZnSe barriers are grown by molecular beam epitaxy (MBE); the QW heterostructure is deposited on top of a GaAs(001) substrate at 275 °C. Scanning transmission electron microscopy indicates a homogeneous smooth QW layer. The evolution of the excitonic emission energy with increasing temperature in the 19–300 K range shows the well‐known S‐shaped behavior that is interpreted in terms of exciton migration.

Investigations of ion irradiation induced surface damage features in zirconium alloys by atomic force microscopy

Continuous Kr ion irradiation at 400 °C with damage level up to 40 dpa was performed in Zircaloy-4 to investigate the surface damage features of α-Zr matrix. Atomic force microscopy confirms that the irradiation induced surface damage is primarily in the form of damaged pits. The increasing Ra value indicates the gradual surface roughening process with continuous irradiation. The irradiation-induced surface roughening mechanism is suggested as three stages: stage I, the formation and growth along depth direction of damaged pits at low doses; stage II, the extension of damaged region within the surface; stage III, layer by layer removal of surface atoms once the undamaged matrix is depleted.

Angular distribution of particles sputtered from the vanadium target by 5 keV Kr ions: simulation study

The sputtering of vanadium particles at normal incidence was simulated. The SRIM-code combined to a new ANGULAIR and SDTrimSP simulation was employed to obtain the sputtering yields and the angular distribution of the atoms. The simulation was made for a large number of incident Kr+ ions with 5 keV energy, letting the computer count the number of emitted particles in the solid angle. The angular distribution of differential sputtering yields of vanadium shows an over-cosine tendency.

Effects of ion irradiation on microstructures and mechanical properties of SiOC nanocomposites

SiOC polymer-derived ceramics (PDCs) are commonly used materials for advanced structural and functional applications. Especially, when in the form of fibers, they are used in the SiCf/SiC composites that is being considered an option for fuel cladding components in the current and next-generation light water reactors. But the radiation effects of the SiOC PDCs have been rarely reported (mostly focused on SiC). Here we prepared SiOC nanocomposites consisting of β-SiC nanocrystals and turbostratic graphite embedded in amorphous SiOC matrix, and irradiated them at room temperature with 4 MeV Kr ions to different damage levels. The irradiation-induced changes in the microstructures, surface morphologies, and mechanical properties were studied. It is indicated much severer irradiation condition leads to higher rearrangement degree of Si-containing tetrahedral units in the amorphous SiOC matrix, higher disordering degree of the turbostratic graphite, but crystallinity of the β-SiC is preserved. No obvious change is detected in the macro properties such as surface morphologies and mechanical properties (hardness and modulus). This study indicates the potential of SiOC PDCs to radiation damage.

Nanoindentation testing of Si3N4 irradiated with swift heavy ions

We report the results of the nanoindentation tests of silicon nitride irradiated with Ar (46 MeV), Kr (107 MeV), Xe (167 MeV, 220 MeV) and Bi (710 MeV) ions. The behaviour of hardness with respect to ion fluence was analyzed and correlated with the microstructure evolution examined using transmission electron microscopy. Insignificant changes in hardness are observed for ion species (Ar, Kr) for which the electronic stopping power is less than the threshold of latent track formation. Accumulation of latent tracks produced by Xe and Bi ions results first in hardening and then, after track region overlapping and amorphization of the crystalline matrix, in softening of irradiated silicon nitride.

Temperature dependence of irradiation-induced nanocrystallization in amorphous silicon carbide

Ion irradiation induced nucleation and growth of nanoparticles in amorphous SiC at elevated temperatures are investigated in this study. Both as-deposited amorphous and Kr ion irradiation-amorphized SiC films are used for the investigation. Similar behavior of particle precipitation in the two types of the films is observed. It is found that the threshold temperature for nucleation is between 550 and 700 K, which is considerably higher than the critical temperature for full amorphization in SiC irradiated with Kr ions. There is a temperature regime up to at least 900 K, where the nucleation and growth rates are only weakly dependent of the irradiation temperature. This temperature regime is potentially useful to tailor the size and density of nanocrystalline SiC precipitates by optimizing the ion irradiation conditions.

Impact of ion species on ion beam sputtered Ta2O5 layer quality parameters and on corresponding process productivity: A preinvestigation for large-area coatings

The demand for ion beam sputtering-coated substrates is growing. In order to introduce ion beam sputter deposition (IBSD) technology into new fields of application, the deposition area must be further increased. In this context, the ion species applied for the sputtering process is an important parameter. In the present investigation, an industrial scale IBSD process was characterized with respect to productivity and layer quality by varying the ion species. Ar, Kr, or Xe broad ion beams at an ion energy of 1.8 keV were used, and the evaluation was carried out on the basis of Ta2O5 layers. The dielectric films were produced in a reactive process through the sputtering of a metallic Ta target, and their two-dimensional distributions of the coating rate R, the refractive index n(320nm), and the extinction coefficient k(320nm) were determined over a planar area of 0.9 × 1.0 m2 above the target by the collection method. R served as a measure of productivity, while n(320nm) and k(320nm) were quality parameters. Additionally, the layer composition was determined for selected samples on the collector by an electron probe microanalyzer (EPMA). As expected, the different ion-solid interaction mechanisms resulted in significant differences with regard to productivity. Linear scaling of productivity as a function of ion mass was observed. Calculations of the sputtering yield with semiempirical models or SRIM-2013, a binary collision Monte Carlo simulation program, did not confirm the observed linearity. Furthermore, the configuration with the highest productivity, Xe, led to a locally occurring and significant reduction in layer quality, more precisely, an increase of k(320nm). Additionally, the layer compositions determined with EPMA confirmed that ions originating from the ion source were implanted in the thin films during their formation. A detailed evaluation of the angle-resolved energy distributions of the involved particles, simulated with SRIM-2013, was performed. However, the determination of the energies carried away from the target by backscattered ions and sputtered target atoms does not explain the observed degradation mechanism. This concludes that for the realization of future large-area coatings with IBSD, not all relevant mechanisms are yet understood in sufficient detail.

Evolution of the absorption edge of PET films irradiated with Kr ions after thermal annealing and ageing

This paper presents the results of a study of the ageing and annealing of films of polyethylene terephthalate (PET) after irradiation with Kr ions. For the studies of ageing, PET film samples were irradiated normally to the surface with Kr 15+ ions of energy of 1.75 MeV/a.u. and various fluences between (1–10)x10 10 cm −2 and then kept for 7.5 months (5400 h) at room temperature in the dark in sealed cases with air removal. The studies of annealing were made on a PET sample irradiated with Kr 13+ ions of energy 1.2 MeV/a.u. at an angle of 40° to the normal and a fluence of 5 × 10 10 cm −2 . Annealing was carried out in the dark in sealed cases with air removal for 160 and 500 h at a temperature lower than the glass transition. UV/vis/near IR differential spectra were obtained for each sample in the wavelength range 308–1050 nm (photon energy 4.03–1.18 eV). We used an established technique to obtain interference-free transmission curves T(λ) for both pristine and irradiated PET film samples and a differential spectroscopy technique to obtain differential transmission spectra ΔT(λ) of the changes in transmission after ageing and annealing. For all samples, a region of increased transmission at short (UV) wavelengths and a region of reduced transmission at longer (red/near IR) wavelengths were observed. These changes result from, respectively, the decay of the smallest irradiation-induced chromophores that are responsible for the absorption of short-wave radiation and the growth in the numbers and size of chromophores with larger conjugation values. They confirm our previous experiments showing that swift heavy ion irradiation of PET films creates reversible non-covalent π–π c onjugation bonds between neighbouring chain molecules in polymer films. These results also confirm our hypothesis that under annealing and ageing the smallest, least stable irradiation-induced conjugations decay while larger, more stable, conjugations grow. Our results also indicate that oblique irradiation, for which the electric field vector has a significant component perpendicular to the film texture, can enhance the polarization effects of the interaction of neighbouring polymer chain molecules leading to electro-optical amplitude enhancement. • Evolution of the absorption edge of PET films irradiated with Kr ions. • PET sample irradiated with 84 Kr 13+ ions of energy 1.2 MeV/a.u. and fluence of 5 × 10 10 cm −2 at an angle of 40° to the normal. • Electro-optical studies of the effect of an electric field on the optical properties. • Analyze the UV–Vis spectro-interferograms.

Irradiation-induced large bubble formation and grain growth in super nano-grained ceramic

In this work, 0.5TRPO•0.5Gd2Zr2O7 ceramic with an average grain size of only ∼15 nm was prepared by a high pressure (5 GPa/520 °C) sintering method. Phase evolutions and microstructure changes of the as-fabricated super nano and micron-grained ceramics under a high-dose displacement damage induced by 300 keV Kr2+ ions were investigated. The results show that the super nano-grained ceramic has low degree of amorphization, obvious grain growth (2–3 times in grain size) and big Kr bubbles (10–68 nm) formation after irradiation. The micron-grained ceramic was severely amorphized after irradiation and many microcracks were formed parallel to its surface. The formation mechanism of Kr bubbles in the super nano-grained ceramic is on account of grain boundary diffusion and migration induced by the accumulation of the injecting Kr ions and irradiation defects. Nevertheless, microcracks formed in the micron-grained sample are caused by the accumulation of Kr atoms.

Methodological and Conceptual Progresses in Studies on the Latent Tracks in PADC.

Modified structure along latent tracks and track formation process have been investigated in poly (allyl diglycol carbonate), PADC, which is well recognized as a sensitive etched track detector. This knowledge is essential to develop novel detectors with improved track registration property. The track structures of protons and heavy ions (He, C, Ne, Ar, Fe, Kr and Xe) have been examined by means of FT-IR spectrometry, covering the stopping power region between 1.2 to 12,000 eV/nm. Through a set of experiments on low-LET radiations—such as gamma ray-, multi-step damage process by electron hits was confirmed in the radiation-sensitive parts of the PADC repeat-unit. From this result, we unveiled for the first-time the layered structure in tracks, in relation with the number of secondary electrons. We also proved that the etch pit was formed when at least two repeat-units were destroyed along the track radial direction. To evaluate the number of secondary electrons around the tracks, a series of numerical simulations were performed with Geant4-DNA. Therefore, we are proposing new physical criterions to describe the detection thresholds. Furthermore, we propose a present issue of the definition of detection threshold for semi-relativistic C ions. Additionally, as a possible chemical criterion, formation density of hydroxyl group is suggested to express the response of PADC.

Angular distribution of particles sputtered from a copper target by 5‐keV Kr ions: Experiment and simulation study

Angular distributions of atoms sputtered from a copper target under 5‐keV Kr+ bombardment at normal incidence were simultaneously and independently studied by experiments and computer simulation. The sputtered particles are collected on a Mylar™ foil placed around the target. Deposited particles on the substrate were analyzed by optical transmission spectroscopy. The surface roughness of the irradiated target was studied by atomic force microscopy, surface profilometry, and scanning electron microscopy. The experimental results were compared with the simulated angular distributions (programs OKSANA, SDTrimSP, and SRIM) and were found to be in reasonable agreement. In all cases, the angular distribution of sputtered particles showed an over‐cosine shape, which may be associated with noncompensated scattering of ejected particles by surface atoms when exiting the target. The results obtained are compared with the data from the literature.

Defect and Structural Evolution Under High-Energy Ion Irradiation Informs Battery Materials Design for Extreme Environments

Defect and structural evolution can have a broad influence on battery materials ranging from electrochemistry to batteries for extreme environments.1–3 In this presentation, the fundamental interplay of defect and structural evolution promoted by high-energy ion irradiation in layered oxide cathodes are discussed. Li and Na layered oxides are subjected to Kr ion irradiation (1 MeV) at various fluences and the transformations of the materials are studied in situ. Our study shows that Li layered oxides are more structurally stable under irradiation than Na layered oxides. The better structural stability of Li layered oxides can be explained in terms of the facile formation of cationic antisite defects because of the smaller size difference between Li and the transition metals. Moreover, a mathematical model is presented to quantitatively probe the defect evolution in these materials under irradiation. Our model shows that the defect clusters induced by ion irradiation preferentially align along the Na/Li diffusion channels in the materials. This study presents critical information for the design of battery materials for extreme environments where materials damage due to irradiation can be significant. Fundamental defect evolution in layered oxide cathodes is also unraveled.1 Acknowledgement This work is primarily supported by The Thomas F. and Kate Miller Jeffress Memorial Trust, Bank of America, Trustee, and the Jeffress Trust Awards Program in Interdisciplinary Research. F.L. and X.-M.B. also acknowledge their startup funds at Virginia Tech. The Na cathode was developed based on a project funded by the National Science Foundation (No. CBET-1912885). The Li cathode was developed based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Award Number: DE-EE0008444. The irradiation work at the IVEM User Facility at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07-051D14517 as part of a Nuclear Science User Facilities experiment. X.-M.B. acknowledges the high-performance computing facilities at Virginia Tech’s Advanced Research Computing. Reference M. M. Rahman, W.-Y. Chen, L. Mu, Z. Xu, Z. Xiao, M. Li, X.-M. Bai, and F. Lin, Nat. Commun., 11, 4548 (2020).Z. Xu, D. Hou, D. Kautz, W. Liu, R. Xu, X. Xiao, and F. Lin, Adv. Mater., 32, 2003417 (2020).M. M. Rahman, J. Mao, W. H. Kan, C.-J. Sun, L. Li, Y. Zhang, M. Avdeev, X.-W. Du, and F. Lin, ACS Mater. Lett., 1, 573–581 (2019).

Mechanism of nanocrystallization temperature shifting during ion irradiation of metallic glasses

Nanocrystallization temperature changes of metallic glasses upon ion bombardment were investigated. For Zr50Cu35Al7Pd5Nb3 metallic glass membranes irradiated by 1 MeV Kr ions, in situ transmission electron microscopy characterization show that nanocrystallization temperatures decrease with increasing ion fluences. The higher the ion fluence, the lower the temperature at which nanocrystals start to form. Using Monte Carlo ion transport simulations and molecular dynamics simulations, we show that upon ion bombardment, spatial distributions of positive free volume are slightly shallower than that of negative free volume. Following local recombination of the free volume of opposite signs, positive (excessive) free volume is introduced in the near surface region, and glass transition temperatures and crystallization temperatures decrease as a function of excessive free volumes.