MeV Kr Ions Research Articles

Processing of hafnium oxide thin films by 2 MeV Kr ion beam for opto-electronic applications

The ion irradiation on 100 nm and 200 nm HfO2 films was performed using a 2 MeV Kr8+ beam at three different fluences viz. 1.5 × 1015 ions/cm2, 2 × 1015 ions/cm2 and 2.5 × 1015 ions/cm2 and various characterization techniques were employed to analyze the as-deposited and irradiated films. The AFM analysis showed that contrary to 200 nm films, the surface roughness of 100 nm films increases with increasing the ion fluence as also validated by FE-SEM. For 100 nm films, the phase analysis done by XRD indicated that the pristine films co-exist in dual phases of cubic and monoclinic; which also prevailed with post-irradiation. However, the pristine 200 nm films coexisted in dual monoclinic and orthorhombic phases and changed to sole orthorhombic phase with increasing ion fluences. The pristine 200 nm film showed more conductivity, which decreases with increasing ion fluences. Interestingly, the optical reflectivity of as-deposited 200 nm film was higher than that of 100 nm film and upon ion irradiation, both films showed inverse trend of reflectivity change; in 100 nm thin films, it decreases with increasing ion fluences. Thus, the ion irradiation seems to be a fascinating tool to tailor HfO2 thin films for their device applications.

Microstructural evolution of ion-irradiated commercially pure titanium

Radiation-induced dislocation loop evolution in ion-irradiated commercially pure (CP) Ti was investigated through both ex situ 4 MeV Ar beams and by in situ TEM irradiation with 1 MeV Kr ion beams at different temperatures. The dominant mechanism for dislocation loop growth was loop coalescence. Both <a>- and c-component loops exhibited an increase in size and density with increased irradiation dose and temperature. C-component loops were observed only after reaching a threshold incubation dose (TID). In CP Ti, these loops initiated at lower doses compared to previous observations in Zr, and the TID decreased with increasing temperature.

In-situ irradiation creep behavior of dilute Al-Sc alloys: Using a thin film bulge test method

• In situ thin film bulge test on nc-AlSc is effective method for irradiation induced creep. • Preexisting Al 3 Sc precipitates suppress irradiation induced creep deformation. • Transition regime of AlSc binary system is located between room temperature and 75 °C. In-situ irradiation induced creep(IIC) measurements on a nanocrystalline AlSc 1.1 binary alloy were performed using a thin-film bulge test technique. A thin film bulge technique was employed since any substrate effect can be excluded, and hence is beneficial to analyze the intrinsic properties of specimen. Here, an as-deposited film and a pre-annealed film, both underwent heavy ion irradition with 1.8 MeV Kr ions. Al 3 Sc precipitates in the pre-annealed samples appear to reduce the irradiation creep compliance. Dissolution of these precipitates during irradiation led to increased irradiation creep rates. Microstructural evolution during irradiation was investigated by transmission electron microscopy and high resolution transmission electron microscopy.

Structural, morphological, and phase transformation studies of 1.4 MeV Kr ion beam irradiated zirconia thin films

Structural, morphological, and phase transformation studies of 1.4 MeV Kr ion beam irradiated zirconia thin films

Morphology of Columnar Defects Dependent on Irradiation Direction in High-T c Superconductors

The morphologies of ion tracks tilted at different angles were systematically investigated by TEM observations on GdBCO coated conductors irradiated with 80 MeV Xe ions. The 80 MeV Xe ion beam along the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis produced shortly segmented (discontinuous) columnar defects (CDs) along the ion path throughout the sample. When the ion beam was tilted at slight angle of 20° from the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis, by contrast, not discontinuous CDs but thick and elongated (continuous) ones were formed in the irradiation direction. The formation of continuous CDs was observed to a deeper depth from the surface for the irradiation tilted at larger angle from the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis. The variation of the microstructures against the irradiation angles was caused by the anisotropic temperature spread during the formation of CDs, which was attributed to the anisotropic thermal diffusivity in high- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconductors. We also demonstrated that discontinuous CDs could be formed at the irradiation angle of ±45° relative to the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis into YBCO thin films by using 50 MeV Kr ions, which was the irradiation condition estimated backwards from the directional dependent morphology of CDs.

The influence of helium and heavy ion irradiations on radiation responses of single crystal Cu with nanovoids: An in situ TEM study

Helium is a common nuclear reaction product, and it plays an important role in radiation-induced void swelling. Although extensive studies have been conducted to investigate the helium effects in metals and alloys, most of them were based on the post-irradiation analyses or computer simulations. Conclusive evidence that can demonstrate how voids evolve in the presence of He under high-temperature radiation remains limited. In this work, we performed in situ heavy ion radiation studies in a transmission electron microscope to compare the radiation response of the preexisting nanovoids in single crystal copper subjected to a single beam of 1 MeV Kr ions and a sequential dual beam of 14 keV He ion and 1 MeV Kr ion at 350 °C. Our studies revealed that the nanovoids would contract continuously until being eliminated when irradiated by a single beam of Kr ions. In comparison, the nanovoids in helium-injected Cu could reach a stable state and eventually stopped shrinking. Moreover, the influence of helium on the kinetics of void/bubble evolution under heavy ion irradiation was discussed within the framework of a proposed critical bubble model and bubble coarsening model.

In-situ TEM study of Kr ion irradiation tolerance of SiFeOC nanocomposite

In this work, ion irradiation of polymer derived SiFeOC nanocomposite was carried out using 1.2 MeV Kr ions at room temperature and 600°C. The starting composite was composed of Fe3Si, SiC, SiOC, SiO2, and graphitic C. In-situ TEM investigations show uniform distribution of nano-crystalline Fe3Si and SiC phases in the amorphous SiOC matrix. During ion irradiation, the SiOC bulk microstructure and interfaces between Fe3Si or SiC crystallites and the SiOC matrix remain defect-free and demonstrate outstanding ion irradiation resistance. At room temperature, the crystalline domains are stable up to 2 dpa. At 600°C, Fe3Si crystallites are more stable than SiC; SiC crystallites are stable up to 4 dpa while the Fe3Si crystallites are stable up to 10 dpa. These crystallites also coalescence and amorphize simultaneously during ion irradiation. The exceptional tolerance to defect formation and irradiation of the SiFeOC nanocomposite provides important guidance to developing irradiation resistant fuels for advanced gas cooled reactors.

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.

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.

Effect of sink strength on coherency loss of precipitates in dilute Cu-base alloys during in situ ion irradiation

In situ irradiations with 1 MeV Kr ions at 50~613 K up to a fluence of 6.25 × 1014 ions/cm2 (~1.25 displacements per atom, dpa) have been performed on pre-aged dilute Cu-0.9%Co, Cu-0.9%Fe and Cu-0.8%Cr alloys containing uniform matrix dispersions of coherent precipitates in order to study the effects of initial precipitate sink strength, damage dose and irradiation temperature on radiation-induced coherency loss of precipitates. Coherent precipitates with different point defect sink strengths (2πNd, where N and d are the precipitate density and diameter) were used in this work to examine potential differences in atomic relaxation during absorption of point defects. In all cases, irradiation to low doses (<~1 dpa) was very effective at inducing loss of precipitate coherency. At low sink strengths (~1013 m−2), loss of precipitate coherency could be induced for doses ~0.01 dpa. This suggests there might be an efficient preferential medium-range strain-induced bias for absorption of interstitial defects due to tensile strains emanating from the undersized precipitates, which induces relatively rapid loss of coherency at low precipitate sink strengths. High precipitate sink strength (~1014 m−2) conditions were relatively resistant to the radiation-induced loss of coherency (requiring higher doses approaching ~1 dpa) and this might be due to nearly equal numbers of interstitial and vacancy defects arriving at the precipitate interface for such high sink strength conditions. The precipitate coherency loss was observed to have a weak dependence on irradiation temperature. Molecular dynamics simulations confirm a strong effect of precipitate sink strength on the probability of interstitial absorption at precipitates.

In situ transmission electron microscopy with dual ion beam irradiation and implantation

To study the helium effects and their interactions with displacement damage in irradiated materials, an in situ dual-ion beam irradiation capability with transmission electron microscopy was recently established at the IVEM-Tandem Facility at Argonne National Laboratory. Pure nickel was irradiated in situ individually with 1 MeV Kr ions for displacement damage study, 16 keV He ions for helium implantation, and simultaneously with 1 MeV Kr ions and 16 keV He ions at the rate of 1 at.% He/dpa to study the interaction of helium and displacement damage at 500 °C. Helium bubbles were formed and segregated within dislocation loops during the He implantation experiment and no bubbles were observed outside the loops. The loop size increased with increasing helium concentration. In contrast, helium bubbles were formed uniformly in the matrix when nickel was irradiated simultaneously with 1 MeV Kr ions and 16 keV He ions. It is suggested that the uniformly-distributed defect clusters formed under 1 MeV Kr ion irradiation serve as trapping sites of helium atoms resulting in homogeneous nucleation of helium bubbles under the dual-ion beam irradiation in nickel.

On the microstructure evolution of a nuclear-use steel after heavy ion irradiation

A nuclear-use ferritic-martensitic steel was irradiated by 196 MeV Kr ions. Both the low damage level area and the high damage level area were investigated by a transmission electron microscope (TEM), to reveal the irradiated microstructural features. In low damage level area ranging from surface to 6 μm depth, there were a few dislocation loops and black dots induced by Kr irradiation. The type of dislocation loops could be primarily ao<100> or ao/2<100> type. In addition, it was found that the sink effect of grain boundaries and stability of small precipitates were evident.

Irradiation-induced segregation at dislocation loops in CoCrFeMnNi high entropy alloy

To understand the redistribution of alloying elements in high entropy alloys under irradiation, a CoCrFeMnNi alloy was irradiated with 1 MeV Kr ions at room temperature and at 500°C, and characterized with atom probe tomography and transmission electron microscopy. At 500°C, Co and Ni were enriched around the interstitial, faulted and perfect, dislocation loops resulted from the ion irradiation. In contrast, no segregation was observed at room temperature. The inverse Kirkendall effect through vacancy flux, as opposed to the interstitial binding mechanism, was the primary underlying process attributing to the observed segregation. In addition, a ring-shaped segregation pattern was observed at the faulted dislocation loops, indicating a non-equilibrium nature of the defect clustering and solute segregation process in CoCrFeMnNi under irradiation at high temperature.

Microstructural evolution of a silicon carbide-carbon coated nanostructured ferritic alloy composite during in-situ Kr ion irradiation at 300°C 450°C

Abstarct This work focuses on irradiation behaviors of a novel silicon carbide and carbon coated nanostructured ferritic alloy (SiC-C@NFA) composite for potential applications as a cladding and structural material for next generation nuclear reactors. The SiC-C@NFA samples were irradiated with 1 MeV Kr ions up to 10 dpa at 300 and 450 °C. Microstructures and defect evolution were studied in-situ at the IVEM-Tandem facility at Argonne National Laboratory. The effects of ion irradiation on various phases such as α-ferrite matrix, (Fe,Cr)7C3, and (Ti,W)C precipitates were evaluated. The α-ferrite matrix showed a continuous increase in dislocation density along with spatial ordering of dislocation loops (or loop strings) at >5 dpa. The size of the dislocation loops at 450 °C was larger than that at 300 °C. The nucleation and growth of new (Ti,W)C precipitates in α-ferrite grains were enhanced with the ion dose at 450 °C. This study provides new insight into the irradiation resistance of the SiC-C@NFA system.

Study on radiation damage effects on CdZnTe detectors under 3 MeV and 2.08 GeV Kr ion irradiation

The survivability of CdZnTe gamma ray detectors, when exposed to energetic particles in a radiation environment, is a key issue for their application. Nevertheless, very little attention has been paid to the irradiation particle energy influences on CdZnTe detector performance. The effects of 3 MeV and 2.08 GeV Kr ion irradiation at fluences of 1 × 1012 ions/cm2 on CdZnTe detector performance are investigated. Variations in performance were determined by comparing pre- and post-irradiation detector current-voltage (I–V) curves and the measured energy spectrum of a 59.5 keV gamma ray source, 241Am. Monte-Carlo simulations of the irradiation process were performed using SRIM software to help explain the observed changes in detector performance. Thermally stimulated current measurements were used to reveal crystal defects newly introduced by the Kr ion irradiation. The 3 MeV Kr ion principally losses its energy in the CdZnTe detector due to nuclear collisions and therefore creates more damage than the 2.08 Kr ion irradiation.

Ion beam irradiation of ABO4 compounds with the fergusonite, monazite, scheelite, and zircon structures

AbstractThe effects of irradiation on CaWO4, SrWO4, BaWO4, YVO4, LaVO4, YNbO4, and LaNbO4 were investigated on thin crystals using 1.0 MeV Kr ions at 50‐1000 K. All of the ABO4 compounds can be amorphized with calculated damage cross sections (σa = 1/Fc0) in the range of ~0.30‐1.09 × 10‐14 cm2 ion−1 at zero Kelvin. The analysis of fluence‐temperature data returned critical temperatures for amorphization (Tc) of 311 ± 1, 358 ± 90, 325 ± 19, 415 ± 17, 541 ± 6, 636 ± 26, and 1012 ± 1 K, respectively, for the compounds listed above. Compared with previous in situ irradiation of ABO4 orthophosphate samples using 0.8 MeV Kr ions, the Tc values of LaVO4 and YVO4 are higher than those of LaPO4 and YPO4 by 82 K and 124 K, respectively. The Tc values of the three scheelite structures, CaWO4, SrWO4, and BaWO4, indicate that they are the most radiation tolerant compounds under these conditions. The A‐B cation anti‐site energies, EfAB, determined by DFT range from 2.48 to 10.58 eV and are highly correlated with the A‐B cation ionic radius ratio, rA/rB, but are not correlated with Tc across the different structure types, suggesting that the formation and migration energies of Frenkel defects play a more important role in damage recovery in these compounds. We also discuss the role of cation and anion charge/iconicity as determined by DFT. ABO4 compounds with the zircon structure and B = P or V have a distinct advantage over those with B = Si as the damaged regions do not appear to be significantly affected by polymerization of (PO4)3− or (VO4)3− groups which might stabilize the amorphous fraction and ultimately lead to phase separation as observed in zircon (ZrSiO4).

The formation and accumulation of radiation-induced defects and the role of lamellar interfaces in radiation damage of titanium aluminum alloy irradiated with Kr-ions at room temperature

A transmission electron microscopy (TEM) specimen of a titanium aluminide (TiAl) alloy was irradiated in-situ, at the IVEM-TANDEM facility, with 1 MeV Kr ions to a maximum fluence of 1.25 × 1019 ions m−2 at room temperature. The irradiated microstructure was then investigated ex-situ using advanced analytical TEM in combination with TEM image simulations and molecular dynamics (MD) simulations. The TEM examination showed that dot-like defects first formed in both the α2-Ti3Al and γ-TiAl phases of the irradiated microstructure. With increasing irradiation dose planar defects formed and propagated within the γ phase, and most of the planar defects were accompanied by the dot-like defects. The TEM image simulations and MD irradiation simulations revealed that the origins of the dot-like and planar defects were interstitial clusters and stacking faults, respectively, and large interstitial clusters were surrounded by dislocation loops. The interstitial clusters formed and grew in the irradiated microstructure due to much faster diffusion of interstitials than that of vacancies at room temperature. Local stress concentrations increased near large interstitial clusters and lamellar interfaces, which resulted in the nucleation and propagation of stacking faults. Moreover, the configurations of the lamellar interfaces in the start microstructure were found to play an important role in the formation and accumulation of the radiation-induced interstitial clusters and stacking faults at room temperature.

Radiation impact of swift heavy ion beams on double-interface CoFeB/MgO magnetic tunnel junctions

A double-interface CoFeB/MgO magnetic tunnel junction (MTJ) has a high thermal stability barrier (E) and high-efficiency magnetization switching with the scaling of device dimensions. However, compared to a single-interface CoFeB/MgO MTJ, its more complicated film stacks and interfaces are more vulnerable to irradiation-induced swift heavy ions. We have studied the irradiation effects of Ta/Kr ions on double-interface CoFeB/MgO MTJs. Structural and physical analyses are performed through transmission electron microscopy, energy dispersive x-ray spectroscopy, and vibrating sample magnetometry. 1907 MeV Ta-ion irradiation damages the interfaces of the double-interface MTJ, resulting in the irreversible decrease in coercivity, while 2060 MeV Kr-ion irradiation damages the bulk properties of the MTJ, leading to the decrease in saturation magnetization. However, the electronic properties of the double-interface MTJ are almost immune to Kr-ion irradiation.

Irradiation-Induced Segregation at Dislocation Loops in CoCrFeMnNi High Entropy Alloy

To understand the redistribution of alloying element in high entropy alloys (HEAs) under irradiation, a CoCrFeMnNi alloy was irradiated with 1 MeV Kr ions at room temperature and 500oC, and characterized with atom probe tomography (APT) and transmission electron microscopy. At 500oC, Co and Ni were enriched at interstitial dislocation loops resulted from the ion irradiation. In contrast, no segregation was observed at interstitial dislocation loops formed at room temperature. It is inferred that the inverse Kirkendall effect through vacancy flux, as opposed to interstitial binding, was the primary mechanism attributing to the observed segregation. In addition, APT concentration contour plots show a ring-shaped segregation pattern instead of a disk-shaped pattern at the faulted dislocation loops, indicating the non-equilibrium nature of the defect clustering and solute segregation process of the CoCrFeMnNi under irradiation at high temperature.

Effect of Sink Strength on Coherency Loss of Precipitates in Dilute Cu Base Alloys During in Situ Ion Irradiation

In situ irradiations with 1 MeV Kr ions at 50~613 K up to a fluence of 6.25 × 1014 ions/cm2 (~1.25 dpa) have been performed on pre-aged dilute Cu-0.9%Co, Cu-0.9%Fe and Cu-0.8%Cr alloys containing uniform matrix dispersions of coherent precipitates in order to study the effects of initial precipitate sink strength, damage dose and irradiation temperature on radiation-induced coherency loss of precipitates. Coherent precipitates with different sink strengths (2πNd , where N and d are the precipitate density and diameter) were used in this work to examine potential differences in atomic relaxation during absorption of point defects. At low sink strengths (~1013 m-2 ), loss of precipitate coherency could be induced for doses below ~0.1 dpa. There might be a preferential medium-range strain-induced bias for absorption of interstitial defects due to tensile strains at the undersized precipitates, which induces relatively rapid loss of coherency at low precipitate sink strengths. High sink strength (~1014 m-2 ) conditions were relatively resistant to the radiation-induced loss of coherency and this might be due to nearly equal numbers of interstitial and vacancy defects arriving at the precipitate interface for such high sink strength conditions. The precipitate coherency loss was observed to have a weak dependence on irradiation temperature. Molecular dynamics simulations confirm a strong effect of precipitate sink strength on the probability of interstitial absorption at precipitates.