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MIAMI: Microscope and ion accelerator for materials investigations
Abstract
A transmission electron microscope (TEM) with in situ ion irradiation has been built at the University of Salford, U.K. The system consists of a Colutron G-2 ion source connected to a JEOL JEM-2000FX TEM via an in-house designed and constructed ion beam transport system. The ion source can deliver ion energies from 0.5 to 10 keV for singly charged ions and can be floated up to 100 kV to allow acceleration to higher energies. Ion species from H to Xe can be produced for the full range of energies allowing the investigation of implantation with light ions such as helium as well as the effects of displacing irradiation with heavy inert or self-ions. The ability to implant light ions at energies low enough such that they come to rest within the thickness of a TEM sample and to also irradiate with heavier species at energies sufficient to cause large numbers of atomic displacements makes this facility ideally suited to the study of materials for use in nuclear environments. TEM allows the internal microstructure of a sample to be imaged at the nanoscale. By irradiating in situ it is possible to observe the dynamic evolution of radiation damage which can occur during irradiation as a result of competing processes within the system being studied. Furthermore, experimental variables such as temperature can be controlled and maintained throughout both irradiation and observation. This combination of capabilities enables an understanding of the underlying atomistic processes to be gained and thus gives invaluable insights into the fundamental physics governing the response of materials to irradiation. Details of the design and specifications of the MIAMI facility are given along with examples of initial experimental results in silicon and silicon carbide.
... Irradiation-induced vacancies and injected He in the model systems were both expected to be mobile. Implantations of 6 keV 4 He + ions to a fluence of up to 6.1 × 10 16 cm −2 with a flux of 3.4 × 10 13 cm −2 s −1 were carried out using the Microscope and Ion Accelerator for Materials Investigation (MIAMI-1) facility, an in situ ion irradiation and transmission electron microscopy (TEM) system, at the University of Huddersfield [17] . Tilt implantations (7 °) of 200 keV 4 He + ions to fluences of 1 × 10 16 and 5 × 10 16 cm −2 with an average flux of 2 × 10 13 cm −2 s −1 were performed using the Danfysik Research Ion Implanter at the Ion Beam Materials Laboratory at Los Alamos National Laboratory (LANL). ...
... Tilt implantations (7 °) of 200 keV 4 He + ions to fluences of 1 × 10 16 and 5 × 10 16 cm −2 with an average flux of 2 × 10 13 cm −2 s −1 were performed using the Danfysik Research Ion Implanter at the Ion Beam Materials Laboratory at Los Alamos National Laboratory (LANL). For the MIAMI-1 system [17] , the samples were heated using a Gatan 652 double-tilt heating holder, and the He beam was 30 °off the sample normal during the experiments. The ion implanter consists of a Colutron G-2 ion source capable of accelerating ions from 0.5 to 10 kV and a post-acceleration tube, allowing acceleration to 100 kV in total. ...
... All the cross-sectional TEM images were obtained at the University of Michigan using a JEOL 3100 operated at 300 kV under twobeam conditions with g = [200] for the 1.5 MeV Ni-irradiated samples ( Fig. 2 ) and a JEOL JEM-2100F microscope on-zone [110] STEM for the 3.0 MeV irradiated samples ( Fig. 3 ). The MIAMI-1 facility [17] was used to follow the microstructural evolution under 6 keV He implantation. The system consists of a JEOL JEM-20 0 0FX operated at 200 kV, where the ion beam is 30 °off the electron beam. ...
Elemental specific chemical complexity is known to play a critical role in microstructure development in single-phase concentrated solid-solution alloys (SP-CSAs), including both He bubble formation and irradiation-induced void swelling. While cavity formation and evolution under ion irradiation at elevated temperature are complex nonequilibrium processes, chemical effects are revealed at the level of electrons and atoms herein in a simplified picture, using Ni and a special set of Ni-based SP-CSAs composed of 3d transition metals as model alloys. Based on Ni and the model alloys with minimized variables (e.g., atomic mass, size, and lattice structure), we discuss the effects of chemically-biased energy dissipation, defect energetics, sluggish diffusion, and atomic transport on cavity formation and evolution under both self-ion Ni irradiation and He implantation. The observed difference in microstructure evolution is attributed to the effects of d electron interactions in their integrated ability to dissipate radiation energy. The demonstrated impact of alloying 3d transition metals with larger differences in the outermost electron counts suggests a simple design strategy for tuning defect properties to improve radiation tolerance in structural alloys.
... The use of ion beams over a broad range of energies to synthesize and modify materials has evolved over the past several decades. Ion beam modification of materials is well established as a unique tool to shape and design materials at different length scales with controlled modification of electrical, optical, structural, mechanical and chemical properties for a wide range of research and applications, including advanced electro-optical devices, engineered nanostructures, nuclear materials, and space exploration [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Recent examples include swift heavy ion irradiation at oblique incidence to produce graphitic nanostripes on the surface of silicon carbides (SiC) as a result of silicon sublimation induced by intensive electronic energy deposition along the ions path [1]. ...
... In the framework of research on radiation tolerant materials for next generation fission and fusion reactors, nanocrystalline materials have demonstrated great potential because grain boundaries act as very efficient defect and impurity traps [5][6][7][8]. In order to understand the mechanisms of irradiation-induced defect production, volume swelling and phase stability that may occur in structural materials over their service lifetime, ion irradiation combined with computational studies were conducted in oxides, carbides and metals [8][9][10][11][12][13][14][15][16][17][18]. ...
... Understanding the mechanisms of damage formation in materials as a result of energy deposition is essential for the field of ionbeam materials modification and engineering [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The interaction of energetic particles with solids results in energy loss to both atomic nuclei and electrons in the solid. ...
Understanding the mechanisms of damage formation in materials irradiated with energetic ions is essential for the field of ion-beam materials modification and engineering. Utilizing incident ions, electrons, photons, and positrons, various analysis techniques, including Rutherford backscattering spectrometry (RBS), electron RBS, Raman spectroscopy, high-resolution X-ray diffraction, small-angle X-ray scattering, and positron annihilation spectroscopy, are routinely used or gaining increasing attention in characterizing ion beam modified materials. The distinctive information, recent developments, and some perspectives in these techniques are reviewed. Applications of these techniques are discussed to demonstrate their unique ability for studying ion-solid interactions and the corresponding radiation effects in modified depths ranging from a few nm to a few tens of μm, and to provide information on electronic and atomic structure of the materials, defect configuration and concentration, as well as phase stability, amorphization and recrystallization processes. Such knowledge contributes to our fundamental understanding over a wide range of extreme conditions essential for enhancing material performance and also for design and synthesis of new materials to address a broad variety of future energy applications.
... The evolution of the orientations and microstructures of the nanowires were monitored using TEM with in situ ion irradiation at the Microscopes and Ion Accelerators for Materials Investigations (MIAMI) facility at the University of Huddersfield. The MIAMI-1 system used in this work consists of a JEOL JEM-2000FX TEM coupled with an ion accelerator capable of delivering inert gas ions with energies from 1 to 100 keV at an angle of 30° to the electron beam [28]. In this work, a 30 keV Xe ion beam was used to irradiate Ge nanowires and a 40 keV Xe ion beam was used for the Si nanowires. ...
... Amorphisation of semiconductors occurs above a critical damage dose dependent on the irradiation conditions [3]; for Ge self-ion irradiation, this is reported to be 0.3 dpa at room temperature [28]. As heavier ions typically lead to denser atomic collision cascades and thus faster accumulation of damage, the threshold dpa at which Ge will amorphise under Xe (Z = 131) irradiation is expected to be lower than the value reported for Ge (Z = 73) ions [32,33]. ...
Nanowires can be manipulated using an ion beam via a phenomenon known as ion-induced bending (IIB). While the mechanisms behind IIB are still the subject of debate, accumulation of point defects or amorphisation are often cited as possible driving mechanisms. Previous results in the literature on IIB of Ge and Si nanowires have shown that after irradiation the aligned nanowires are fully amorphous. Experiments were recently reported in which crystalline seeds were preserved in otherwise-amorphous ion-beam-bent Si nanowires which then facilitated solid-phase epitaxial growth (SPEG) during subsequent annealing. However, the ion-induced alignment of the nanowires was lost during the SPEG. In this work, in situ ion irradiations in a transmission electron microscope at 400 °C and 500 °C were performed on Ge and Si nanowires, respectively, to supress amorphisation and the build-up of point defects. Both the Ge and Si nanowires were found to bend during irradiation thus drawing into question the role of mechanisms based on damage accumulation under such conditions. These experiments demonstrate for the first time a simple way of realigning single-crystal Ge and Si nanowires via IIB whilst preserving their crystal structure.
... Another avenue involves grain-boundary doping [21,[38][39][40], although challenges associated with intragranular fracture and fracture resistance of nanocrystalline W are still pending resolution and can be considered topics for further research [41][42][43][44]. Nevertheless, it is worth noting that recent radiation damage studies -carried out with light-and heavy-ion irradiation within in situ transmission electron microscopy (TEM) independently at both the IVEM facility in USA [45] and the MIAMI facility in UK [46,47] -have shown that even nanocrystalline W experience severe damage from energetic particle irradiation [5][6][7][8], thus raising questions regarding the overall feasibility of proposing W for fusion applications. It is important emphasizing that in situ TEM ion irradiation studies on coarse-grained W and select W-alloys also indicated extensive formation of radiation damage defects in a similar manner [48][49][50]. ...
Refractory High-Entropy Alloys (RHEAs) hold promising potential to be used as structural materials in future nuclear fusion reactors, where W and its alloys are currently leading candidates. Fusion materials must be able to withstand extreme conditions, such as (i) severe radiation-damage arising from highly-energetic neutrons, (ii) embrittlement caused by implantation of H and He ions, and (iii) exposure to extreme high-temperatures and thermal gradients. Recent research demonstrated that two RHEAs - the WTaCrV and WTaCrVHf - can outperform both coarse-grained and nanocrystalline W in terms of its radiation response and microstructural stability. Chemical complexity and nanocrystallinity enhance the radiation tolerance of these new RHEAs, but their multi-element nature, including low-melting Cr, complicates bulk fabrication and limits practical applications. We demonstrate that reducing the number of alloying elements and yet retain high-radiation tolerance is possible within the ternary system W-Ta-V via synthesis of two novel nanocrystalline refractory medium-entropy alloys (RMEAs): the W53Ta44V3 and W53Ta42V5 (in at.%). We experimentally show that the radiation response of the W-Ta-V system can be tailored by small additions of V, and such experimental result was validated with theoretical analysis of chemical short-range orders (CSRO) from combined ab-initio atomistic Monte-Carlo modeling. It is predicted from computational analysis that a small change in V concentration has a significant effect on the Ta-V CRSO between W53Ta44V3 and W53Ta42V5 leading to radiation-resistant microstructures in these RMEAs from chemistry stand-point of views. We deviate from the original high-entropy alloy concept to show that high radiation resistance can be achieved in systems with simplified chemical complexity.
... Helium is insoluble in SiC and forms bubbles when irradiated into SiC with fluences between 5 × 10 16 and 1 × 10 17 ions/cm 2 (Gavarini et al., 2020;Liu et al., 2022). The formation of bubbles in SiC results in surface swelling, blistering, and exfoliation (Butterworth, 1989;Grisolia et al., 2000;Zhang et al., 2003;Hinks et al., 2011;Linez et al., 2013;Barcz et al., 2014;Li et al., 2014;Terrani et al., 2014;Li et al., 2015;Linez et al., 2015;Chen et al., 2016;Sun et al., 2018;Daghbouj et al., 2020;Gavarini et al., 2020;Zhang et al., 2021;Clay et al., 2022;Li et al., 2022;Liu et al., 2022;Mokgadi et al., 2022), which affect the structural integrity of SiC as the main barrier to FPs. Thus, it is crucial to study the microstructure of SiC due to the presence of FPs and He and its effect on the migration behaviour of fission products in SiC. ...
The presence of radiation-induced defects and the high temperature of implantation are breeding grounds for helium (He) to accumulate and form He-induced defects (bubbles, blisters, craters, and cavities) in silicon carbide (SiC). In this work, the influence of He-induced defects on the migration of strontium (Sr) implanted into SiC was investigated. Sr-ions of 360 keV were implanted into polycrystalline SiC to a fluence of 2 × 10 ¹⁶ Sr-ions/cm ² at 600°C (Sr-SiC). Some of the Sr-SiC samples were then co-implanted with He-ions of 21.5 keV to a fluence of 1 × 10 ¹⁷ He-ions/cm ² at 350°C (Sr + He-SiC). The Sr-SiC and Sr + He-SiC samples were annealed for 5 h at 1,000°C. The as-implanted and annealed samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and Rutherford backscattered spectrometry (RBS). Implantation of Sr retained some defects in SiC, while co-implantation of He resulted in the formation of He-bubbles, blisters, and craters (exfoliated blisters). Blisters close to the critical height and size were the first to exfoliate after annealing. He-bubbles grew larger after annealing owing to the capture of more vacancies. In the co-implanted samples, Sr was located in three regions: the crystalline region (near the surface), the bubble region (where the projected range of Sr was located), and the damage region toward the bulk. Annealing the Sr + He-SiC caused the migration of Sr towards the bulk, while no migration was observed in the Sr-SiC samples. The migration was governed by “vacancy migration driven by strain fileds.”
... The irradiations were carried out in the MIAMI-1 facility at University of Huddersfield. A JEOL JEM-2000FX TEM operating at 200 kV is coupled with an 100 kV ion implanter [37] . Images and videos were recorded using a Gatan ORIUS SC200 digital camera. ...
... For the applications mentioned above, there is a great need for experimental work to understand better the formation, accumulation, and recovery of radiation damage produced by energetic particles. A rather large number of papers were published in the last three decades on radiation damage in SiC [31][32][33][34][35]. Nevertheless, there are still some fundamental questions to be addressed, such as the mechanisms leading to the formation and evolution of He bubbles and He platelets, and the role of strain on the formation and geometry of extended defects. ...
The microstructural phenomena occurring in 6H–SiC subjected to different irradiation conditions and annealing temperatures were investigated to assess the suitability of 6H–SiC as a structural material for nuclear applications. To this aim, a single crystal of 6H–SiC was subjected to He+ irradiation at 300 keV with
different fluences and at temperatures ranging from 25 to 750 °C. Rutherford backscattering/channeling (RBS/C), X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were combined
to shed light on the microstructural changes induced by irradiation and subsequent annealing (750 to 1500 °C). At room temperature, amorphization starts to occur at a fluence of 2.5 × 1016 cm−2 (0.66 dpa). On the contrary, amorphization was prevented at high irradiation temperatures and fluences. Furthermore, a thin and highly strained region located around the maximum He concentration (Rp) formed. This region results from the accumulation of interstitial atoms which are driven toward the highly damaged region under the actions of a strain gradient and high temperature. Regardless of the fluence and irradiation temperature, the material stores elastic energy, which leads to the trapping of He in dissimilar defect geometries. For irradiation temperatures below 750 °C, helium was accumulated in bubbles which coarsened after annealing. On the other hand, for an irradiation temperature of 750 °C, helium was trapped in platelets (even for medium fluence), which evolved into a homogeneous dense array of cavities during annealing. DFT calculations show that the bubbles are under high pressure and contribute to developing the overall tensile strain in the single crystal 6H–SiC.
... Specimens were irradiated with 30 keV Xe ions in situ within a TEM at 1073 K (0.56T m , where T m is the estimated melting temperature of the alloy) using a double-tilt heating holder in both MIAMI-1 and -2 facilities at the University of Huddersfield: detailed description of both systems can be found elsewhere [65,66]. The ion flux was 4.2×10 13 ions·cm −2 ·s −1 measured at the specimen position. ...
The stability of the face-centred cubic austenite (γ-Fe) phase in a commercial stainless steel (AISI-348) was investigated through in situ transmission electron microscopy (TEM) with heavy ion irradiation at 1073 K up to a fluence of 1.3×10 17 ions·cm −2 (corresponding to a dose of 46 dpa). The γ-Fe phase was observed to decompose at a fluence of around 7.8×10 15 ions·cm −2 (3 dpa) when a new phase nucleated and grew upon increasing irradiation dose. Scanning transmission electron microscopy (STEM) with energy dispersive X-ray (EDX) spectroscopy and multivariate statistical analysis (MVSA) were used to characterise the irradiated specimens. The combination of such experimental techniques with calculated equilibrium phase diagrams using the CALPHAD method led to the conclusion that the new phase formed upon irradiation is the body-centred cubic Cr-rich α phase. At the nanoscale, precipitation of M 23 C 6 (τ-carbide) was also observed. The results indicate that ion irradiation can assist the austenitic stainless steel to reach a non-equilibrium state similar to a calculated equilibrium state observed at lower temperatures in which, under conventional conditions, is suppressed due to kinetic restrictions.
... In-situ irradiation experiments were performed on the MIAMI-II TEM/ion accelerator system located at the University of Huddersfield [48]. The in-situ irradiation facility comprises a Hitachi H-9500 transmission electron microscope (TEM) with a maximum operating voltage of 300 kV, coupled to a 350 kV National Electrostatics Corporation ion accelerator incorporating a Danfysik 921A ion source capable of providing ions of most species up to Au. ...
... The irradiations were carried out in the MIAMI-1 facility at University of Huddersfield. A JEOL JEM-2000FX TEM operating at 200 kV is coupled with an 100 kV ion implanter [37]. Images and videos were recorded using a Gatan ORIUS SC200 digital camera. ...
Radiation-induced precipitation has been examined in an Nb-stabilised austenitic stainless steel (AISI-348) during heavy ion irradiation in situ within a transmission electron microscope (TEM) at 1073 K. Selected-area electron diffraction (SAED), bright- and dark-field TEM were used to investigate the nature of the precipitates within the austenite phase (γ-Fe). The crystal structure of the precipitates was investigated using TEM and matched with reference data for the Cr23C6 phase. The results herein reported indicate that the concurrent formation of inert gas bubbles may accelerate clustering and precipitation kinetics in the austenite phase during irradiation.
... Implantations were performed at room temperature in order to minimise bulk diffusion. MIAMI-1 consists of a JEOL JEM-2000FX TEM coupled with a 100 kV ion accelerator, while MIAMI-2 couples a Hitachi H-9500 TEM with a 300 kV ion accelerator [39]. The energies of the light and heavy ions were selected to approximate both implanted ion range and damage profile as predicted from SRIM quick Kinchin-Pease damage calculations (see section 2.3). ...
Concentrated solid solution alloys (CSAs) – including high entropy alloys – are known for their remarkable mechanical and corrosion resistances with superior tolerance against the deleterious effect of irradiation exposure when compared with pure metals and dilute alloys. To date, however, the mechanisms responsible for such improvements are still unclear and remain a subject of investigation. The present work reports in situ Transmission Electron Microscopy (TEM) study under simultaneous ion irradiation of the face-centred cubic (FCC) FeCrMnNi quaternary CSA, comparing with a non-equiatomic Fe-based alloy, the AISI-348 austenitic stainless steel that has Cr, Ni and Mn as alloying elements. The alloys were irradiated under the same conditions, with 6 keV He + and 134 keV Xe + ions at 298 K up to 1.7 × 10 17 ions⋅cm −2 (4 displacements-per-atom or dpa) and 2.7 × 10 15 ions⋅cm −2 (4 dpa), respectively. The nucleation of inert gas bubbles was tracked upon post-irradiation extended annealing up to 673 K. He and Xe bubbles were observed to grow at a rate slightly slower in the CSA. Trends from the bubble size analyses show that the nucleation and growth of inert gas bubbles may be suppressed or delayed in some conditions in the CSA.
... The first Microscope and Ion Accelerator for Materials Investigations (MIAMI-1) system [33] was originally constructed at the University of Salford between 2007-2010 and moved to the University of Huddersfield in 2011. It consists of a 200 kV JEOL JEM-2000FX TEM coupled to a 100 kV ion accelerator and continues to be used to perform TEM with in-situ ion irradiation experiments. ...
Radiation damage is a complex dynamic process with multiple atomic mechanisms interacting and competing to determine the end state of the material. Transmission electron microscopy (TEM) with in-situ ion irradiation allows direct observation of the microstructural evolution of a sample from the virgin to end state. A new TEM with in-situ ion irradiation has been established at the University of Huddersfield: the Microscope and Ion Accelerators for Materials Investigations (MIAMI-2) system. MIAMI-2 combines a 300 kV TEM with medium-energy 350 kV and low-energy 20 kV ion beamlines. Whilst the medium-energy beamline can be used for most species up to Au, the low-energy beamline is primarily designed for implanting light-ion species such as H and He. These can be used individually or mixed prior to entering the TEM allowing dual-ion-beam irradiation experiments to, for example, simulate the combined effects of displacement damage and the introduction of He from (n, α) nuclear reactions. The TEM can operate from 60–300 kV and is equipped with a 16 megapixel digital camera, an energy-filtered imaging system and an energy-dispersive X-ray spectrometer for elemental and chemical analysis. Sample temperature can be varied from –170 °C to 1300 °C and a gas injection system enables gaseous environments at pressures of up to 10 ⁻² mbar at the sample position. The new MIAMI-2 system is a powerful tool for the investigation of radiation damage in a wide range of materials which are exposed to irradiating environments either during processing and/or whilst in-service in areas including nuclear applications, nanotechnology, semiconductor processing and extraterrestrial environments.
... Next, 4-keV normal-incidence helium ion irradiation at RT and 773 K were performed using the neutron irradiation material ion implantation experiment (NIMIIX), at Idaho National Laboratory, with an average ion dose of 3.46 × 10 17 m −2 s −1 , a total dose of 2.14 × 10 20 m −2 , and a corresponding peak dose of 0.91 dpa. Then 2-keV helium irradiation was performed at 1223 K in situ in the JEOL JEM-2000FX TEM at the Microscope and Ion Accelerator for Materials Investigations (MIAMI) facility at the University of Huddersfield [49]. The dose rate and the final dose were 1.73 × 10 17 m −2 s −1 and 3.2 × 10 20 m −2 , respectively, and the peak dpa was ∼1.1 dpa. ...
The role of grain boundaries in limiting irradiation damage in nanocrystalline materials is often correlated with the grain boundary sink efficiency. Here, we demonstrate on a tungsten material system (which has very distinct vacancy and interstitial mobilities) that sink efficiency does not unequivocally describe how grain boundaries impact irradiation damage. Rather, it reflects a particular defect diffusion equation that can change if any of the bulk conditions change. Even when denuded zone formation does not occur and grain boundaries have zero sink efficiencies, grain boundaries still impact the performance of nanocrystalline materials under irradiation by acting as a saturable defect storage site. However, denuded zone formation can occur under a necessary requirement of extra defect recombination at the grain boundaries (which, for example, is not possible when vacancy migration does not occur). These insights provide answers to several outstanding questions regarding the sink efficiency of a grain boundary and assist in parametrizing the role of grain boundaries in limiting irradiation damage in nanocrystalline materials.
... TEM with in situ ion irradiation experiments were performed at room temperature in the Microscopes and Ion Accelerators for Materials Investigations (MIAMI-1) facility at the University of Huddersfield which is described in detail elsewhere [67]. This technique allows an individual NW to be followed throughout the irradiation (see video clip S2 in the supplementary material); not only does this allow the dynamic behaviour to be captured but it also ensures that the same nanostructure is being studied both before and after irradiation (a particular concern in experiments designed to induced significant morphological changes). ...
The miniaturisation of technology increasingly requires the development of both new structures as well as novel techniques for their manufacture and modification. Semiconductor nanowires (NWs) are a prime example of this and as such have been the subject of intense scientific research for applications ranging from microelectronics to nano-electromechanical devices. Ion irradiation has long been a key processing step for semiconductors and the natural extension of this technique to the modification of semiconductor NWs has led to the discovery of ion beam-induced deformation effects. In this work, transmission electron microscopy with in situ ion bombardment has been used to directly observe the evolution of individual silicon and germanium NWs under irradiation. Silicon NWs were irradiated with either 6 keV neon ions or xenon ions at 5, 7 or 9.5 keV with a flux of 3 × 1013 ions cm-2 s-1. Germanium NWs were irradiated with 30 or 70 keV xenon ions with a flux of 1013 ions cm-2 s-1. These new results are combined with those reported in the literature in a systematic analysis using a custom implementation of the transport of ions in matter Monte Carlo computer code to facilitate a direct comparison with experimental results taking into account the wide range of experimental conditions. Across the various studies this has revealed underlying trends and forms the basis of a critical review of the various mechanisms which have been proposed to explain the deformation of semiconductor NWs under ion irradiation.
... The in-situ experiments were performed at the MIAMI-1 facility at the University of Huddersfield31 . This consists a low energy, Colutron ion-accelerator coupled to a JEOL JEM-2000FX TEM in which the ions are incident on the specimen at 30° to the direction of the electron beam. ...
Damage caused by implanted helium (He) is a major concern for material performance in future nuclear reactors. We use a combination of experiments and modeling to demonstrate that amorphous silicon oxycarbide (SiOC) is immune to He-induced damage. By contrast with other solids, where implanted He becomes immobilized in nanometer-scale precipitates, He in SiOC remains in solution and outgasses from the material via atomic-scale diffusion without damaging its free surfaces. Furthermore, the behavior of He in SiOC is not sensitive to the exact concentration of carbon and hydrogen in this material, indicating that the composition of SiOC may be tuned to optimize other properties without compromising resistance to implanted He.
... Methods section) before and after irradiation with 6 keV Xe at room temperature to a fluence of ~6×10 14 ions/cm 2 . All the images were recorded during in situ implantation in a TEM at the MIAMI facility at the University of Huddersfield [17]. Several differences such as disappearance of small grains (Figure 1 a,c); a decrease of contrast suggesting mass loss and decrease of crystallinity (Figure 1 b, d) are immediately observable. ...
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Nanoparticles are ubiquitous in nature and are increasingly important for technology. They are subject to bombardment by ionizing radiation in a diverse range of environments. In particular, nanodiamonds represent a variety of nanoparticles of significant fundamental and applied interest. Here we present a combined experimental and computational study of the behaviour of nanodiamonds under irradiation by xenon ions. Unexpectedly, we observed a pronounced size effect on the radiation resistance of the nanodiamonds: particles larger than 8 nm behave similarly to macroscopic diamond (i.e. characterized by high radiation resistance) whereas smaller particles can be completely destroyed by a single impact from an ion in a defined energy range. This latter observation is explained by extreme heating of the nanodiamonds by the penetrating ion. The obtained results are not limited to nanodiamonds, making them of interest for several fields, putting constraints on processes for the controlled modification of nanodiamonds, on the survival of dust in astrophysical environments, and on the behaviour of actinides released from nuclear waste into the environment.
... The experimentally-measured sputter yields varied from −2.1 to 30.1 whereas the molecular dynamics simulations gave an average value of 254. The vastly different sputter yields, varying by up to two orders of magnitude, measured in the experiments reported here under 1.7 MeV Au ion irradiation have similarly been observed in previous work 12,13 using 80 keV Xe at the MIAMI facility 26 . Several explanations could account for the large range of sputter yields observed across the nanorods studied as discussed below. ...
Nanostructures may be exposed to irradiation during their manufacture, their engineering and whilst in-service. The consequences of such bombardment can be vastly different from those seen in the bulk. In this paper, we combine transmission electron microscopy with in situ ion irradiation with complementary computer modelling techniques to explore the physics governing the effects of 1.7 MeV Au ions on gold nanorods. Phenomena surrounding the sputtering and associated morphological changes caused by the ion irradiation have been explored. In both the experiments and the simulations, large variations in the sputter yields from individual nanorods were observed. These sputter yields have been shown to correlate with the strength of channelling directions close to the direction in which the ion beam was incident. Craters decorated by ejecta blankets were found to form due to cluster emission thus explaining the high sputter yields.
... In situ ion irradiation was performed using the Microscopes and Ion Accelerators for Materials Investigations (MIAMI-1) facility 45 . This consists of a JEOL JEM-2000FX TEM operating at 200 kV coupled to an ion accelerator operating at energies of up to 100 keV. ...
The self-organisation of void and gas bubbles in solids into superlattices is an intriguing nanoscale phenomenon. Despite the discovery of these lattices 45 years ago, the atomistics behind the ordering mechanisms responsible for the formation of these nanostructures are yet to be fully elucidated. Here we report on the direct observation via transmission electron microscopy of the formation of bubble lattices under He ion bombardment. By careful control of the irradiation conditions, it has been possible to engineer the bubble size and spacing of the superlattice leading to important conclusions about the significance of vacancy supply in determining the physical characteristics of the system. Furthermore, no bubble lattice alignment was observed in the <111> directions pointing to a key driving mechanism for the formation of these ordered nanostructures being the two-dimensional diffusion of self- interstitial atoms.
... Huddersfield [41]. The ion flux was 9:6 Â 10 13 ions$cm À2 $s À1 measured at the specimen position. ...
Zirconium alloys are of great importance to the nuclear industry as they have been widely used as cladding materials in light-water reactors since the 1960s. This work examines the behaviour of these alloys under He ion implantation for the purposes of developing understanding of the fundamental processes behind their response to irradiation. Characterization of zircaloy-4 samples using TEM with in situ 6 keV He irradiation up to a fluence of in the temperature range of 298–1148 K has been performed. Ordered arrays of He bubbles were observed at 473 and 1148 K at a fluence of in αZr, the hexagonal compact (HCP) and in βZr, the body centred cubic (BCC) phases, respectively. In addition, the dissolution behaviour of cubic Zr hydrides under He irradiation has been investigated.
... In this study, we attempt to answer the above questions using in situ ion irradiation of nanocrystalline and ultrafine tungsten (where nanocrystalline and ultrafine grains coexist) within the JEOL JEM-2000FX transmission electron microscope (TEM) at the Microscope and Ion Accelerator for Materials Investigations (MIAMI) facility at the University of Huddersfield which is described in detail elsewhere [10]. The in situ observation during the experiment confirmed that the sample was irradiated uniformly and that no grain growth or bubble coalescence occurred during irradiation; two possible phenomena that can disturb bubble density and size determination. ...
Nanocrystalline metals are considered highly radiation-resistant materials due to their large grain boundary areas. Here, the existence of a grain size threshold for enhanced irradiation resistance in high-temperature helium-irradiated nanocrystalline and ultrafine tungsten is demonstrated. Average bubble density, projected bubble area and the corresponding change in volume were measured via transmission electron microscopy and plotted as a function of grain size for two ion fluences. Nanocrystalline grains of less than 35 nm size possess ∼10–20 times lower change in volume than ultrafine grains and this is discussed in terms of the grain boundaries defect sink efficiency.
... -2 .s -1 in the Microscope and Ion Accelerator for Materials Investigations (MIAMI-1) facility (described in detail elsewhere [9]) at temperatures of 500, 750 and 1000ºC. Figure 2 shows micrographs of three irradiations to 1.0 DPA at three different points along the temperature axis. ...
div class="title"> TEM with in situ Ion Irradiation of Nuclear Materials under In-Service Conditions
- Volume 22 Issue S3 - R.W. Harrison, H. Amari, G. Greaves, S.E. Donnelly, J.A Hinks
... In order to understand the behavior of existing materials and to develop new technologies for use in irradiating environments, observation of the microstructural evolution during ion irradiation is highly advantageous. Such experiments can be performed by transmission electron microscopy (TEM) with in situ ion irradiation using instruments such as the MIAMI facility [47,48]. Examples of such studies have been reported by Donnelly et al. on the ion irradiation of different material systems [49][50][51]. ...
Background: Focused Ion Beam (FIB) nanofabrication technology has an important status in micro-nano manufacturing technology for its advantages of direct writing, nanoscale fabrication, SEM in-situ observation, high reproducibility, and 3D complex micro/nanofabriction, etc. This review aims to present some recent developments in Focused Ion Beam and its application in nanotechnology. Methods: The new developments of FIB equipment and their performance were introduced. The FIB fundamental research of ion-sample interaction, FIB application in material properties study at the micro/nanoscale and 3D nanostructures fabrication were presented and discussed. Results: Seventy papers were included in the review. The developments of new ion sources of Xe plasma FIB and helium ion (He⁺) microscopy and their performances were introduced, which can offer higher material removal rate of ~ 100 times faster than traditional Ga+ source FIB and fabrication of sub-10 nm scales structures, respectively. Then, the fundamental research of FIB induced modification on substrate material has studied by methods of microscopy characterization, molecular dynamics (MD) simulation and FIB induced material redistribution (Rayleigh-Plateau instability). Finally, FIB application in material properties study at the micro/nanoscale and 3D nanostructures fabrication were discussed. Conclusion: The findings of this review confirm the importance of FIB nanofabrication and its applications in delicate 3D nanostructures, functional devices and material fundamental research, etc. With the developments of FIB advanced equipment and ion-sample interaction mechanism research, FIB technique can give more and more contributions to nanotechnology.
... In-situ ion irradiation experiments were performed using the MIAMI in-situ ion irradiation TEM facility at the University of Huddersfield, UK. This instrument consists of a JEOL JEM-2000FX TEM modified to allow the sample to be ion irradiated while microstructural changes can be continuously monitored via TEM imaging and diffraction 53 . In the current study 30 keV He or 6 keV Ar ions beams were used at an angle of 30u to the imaging electron beam. ...
Ion irradiation has been observed to induce a macroscopic flattening and in-plane shrinkage of graphene sheets without a complete loss of crystallinity. Electron diffraction studies performed during simultaneous in-situ ion irradiation have allowed identification of the fluence at which the graphene sheet loses long-range order. This approach has facilitated complementary ex-situ investigations, allowing the first atomic resolution scanning transmission electron microscopy images of ion-irradiation induced graphene defect structures together with quantitative analysis of defect densities using Raman spectroscopy.
... Each of these large, complex facilities operates under different experimental parameters dictated by the TEM utilized, the ion accelerator(s) attached, and the ion beamline specifics. These facilities have provided a wealth of fundamental insight into radiation-solid interactions over the last half century [15][16][17][18][19][20][21]. Over the same time period, in situ TEM deformation and failure studies have become increasingly refined. ...
An in situ ion irradiation transmission electron microscope has been developed and is operational at Sandia National Laboratories. This facility permits high spatial resolution, real time observation of electron transparent samples under ion irradiation, implantation, mechanical loading, corrosive environments, and combinations thereof. This includes the simultaneous implantation of low-energy gas ions (0.8–30 keV) during high-energy heavy ion irradiation (0.8–48 MeV). Initial results in polycrystalline gold foils are provided to demonstrate the range of capabilities.
... Samples were He 1 ion irradiated in situ at 950uC within the JEOL JEM-2000FX TEM at the Microscope and Ion Accelerator for Materials Investigations (MIAMI) facility at the University of Huddersfield which is described in detail elsewhere 52 In the MIAMI facility, the angle between the sample surface at zero tilt and the ion beam is 60u giving a projected range for 2 keV He 1 in tungsten of 10.6 nm as calculated by the Stopping Range of Ions in Matter (SRIM) 53 Monte Carlo computer code version 2013. This projected range was within the nominal characteristic length of the ultrafine-and nanocrystalline-grains in the tungsten samples irradiated. ...
The accumulation of defects, and in particular He bubbles, can have significant implications for the performance of materials exposed to the plasma in magnetic-confinement nuclear fusion reactors. Some of the most promising candidates for deployment into such environments are nanocrystalline materials as the engineering of grain boundary density offers the possibility of tailoring their radiation resistance properties. In order to investigate the microstructural evolution of ultrafine- and nanocrystalline-grained tungsten under conditions similar to those in a reactor, a transmission electron microscopy study with in situ 2 keV He(+) ion irradiation at 950°C has been completed. A dynamic and complex evolution in the microstructure was observed including the formation of defect clusters, dislocations and bubbles. Nanocrystalline grains with dimensions less than around 60 nm demonstrated lower bubble density and greater bubble size than larger nanocrystalline (60-100 nm) and ultrafine (100-500 nm) grains. In grains over 100 nm, uniform distributions of bubbles and defects were formed. At higher fluences, large faceted bubbles were observed on the grain boundaries, especially on those of nanocrystalline grains, indicating the important role grain boundaries can play in trapping He and thus in giving rise to the enhanced radiation tolerance of nanocrystalline materials.
... TEM with in situ ion irradiation was performed using 60 keV Xe + ions at room temperature in the Microscope and Ion Accelerator for Materials Investigations (MIAMI) facility at the University of Huddersfield which is described in detail elsewhere [56]. At this energy around 30% of the Xe will have been stopped in the TEM sample but at the low fluences used the effect of this amount of inert gas is expected to be negligible as discussed below in section 3.5.3. ...
Graphitic materials and graphite composites experience dimensional change when exposed to radiation-induced atomic displacements. This has major implications for current and future technological ranging from nuclear fission reactors to the processing of graphene–silicon hybrid devices. Dimensional change in nuclear graphites is a complex problem involving the filler, binder, porosity, cracks and atomic-level effects all interacting within the polygranular structure. An improved understanding of the atomistic mechanisms which drive dimensional change within individual graphitic crystals is required to feed into the multiscale modelling of this system.
In this study, micromechanically exfoliated samples of highly oriented pyrolytic graphite have been ion irradiated and studied in situ using transmission electron microscopy (TEM) in order to gain insights into the response of single graphitic crystals to displacing radiation. Under continuous ion bombardment, a complex dynamic sequence of deformation evolves featuring several distinct stages from the inducement of strain, the creation of dislocations leading to dislocation arrays, the formation of kink band networks and localised doming of the sample. Observing these ion irradiation-induced processes using in situ TEM reveals previously unknown details of the sequence of microstructural developments and physics driving these phenomena. A mechanistic model consistent with the microstructural changes observed is presented.
Many multicomponent concentrated solid solution alloys (CSAs), including high-entropy alloys (HEAs), exhibit improved radiation resistance and enhanced structural stability in harsh environments. To study and assess irradiation resistance of nuclear materials, energetic ion and electron beams are commonly used to create displacement damage. Moreover, charged particles of ions, electrons, and positrons are unique tools to create and characterize radiation effects. Ion beam analysis (e.g., Rutherford backscattering spectrometry, nuclear reaction analysis, and time-of-flight elastic recoil detection analysis), electron microscopy techniques (e.g., transmission or scanning electron microscopy, and electron diffraction), and positron annihilation spectroscopy have been applied to characterize irradiated CSAs or HEAs to understand defect formation and evolution together with chemical and microstructural information. Their distinctive analyzing power and some perspectives in these techniques are reviewed. In developing structural alloys desirable for applications in advanced reactors, neutron exposure is a critical test but the limitation in achievable high damage levels is, however, a bottleneck. Ion irradiation is often used as a surrogate for neutron irradiation, and the associated reduced transmutations and higher displacements per atom (dpa) rates are desirable for materials research. Nevertheless, cautions need to be taken when relying on ion irradiation results for reactor evaluations. Literature on differences between ions and neutrons is briefly reviewed. In addition, the links to bridge the current advances on fundamental understandings to reactor applications are discussed to lay the groundwork between neutrons and ions for radiation effects studies.
Understanding the structural evolution of SiC implanted with fission product surrogates in the presence of helium (He) is of importance for its application in both fission and fusion rectors. In this study, polycrystalline SiC wafers were sequentially co-implanted with 360 keV Sr and 21.5 keV He ions to a fluence of 2 ×1016 cm-2 and 1 × 1017 cm-2 at room temperature, respectively. The samples were then isochronally annealed in temperatures ranging from 1000 to 1300 °C for 5 h. Transmission electron microscopy (TEM) showed the formation of He-nanobubbles corresponding to helium's projected range. While scanning electron microscopy (SEM) revealed the formation of cornflower-like structures on the surface of the Sr + He–SiC samples after annealing. These were confirmed to be holes by atomic force microscopy (AFM), as a result of exfoliation and pressurized out-diffusion of helium gas from the samples. The Sr + He–SiC samples were completely amorphized characterized by the formation of the homonuclear bonds in Raman spectroscopy. The recovery process after annealing in the Sr + He–SiC samples resulted in the formation of graphite due to antisite defects driven by the growth of holes above the threshold chemical disorder. Time-of-flight heavy ions elastic recoil detection analysis (Tof-ERDA) showed that almost all helium out-diffused after annealing at 1000 °C and Sr atoms trapped in He cavities.
The xenon content of a Zircaloy-4 thin film was quantified in a spatially resolved way using high angle annular dark field (HAADF) images and DualEELS, a type of electron energy loss spectroscopy that takes spectra from the high- and low-loss regions in quick succession. The xenon in the films was implanted using a tandem accelerator. The HAADF images show that the xenon had coalesced into bubbles. A semi-empirical standard was used created for the quantification using pre-existing xenon data and experimental data scaled using a Hartree Slater cross-section. This standard was used to calculate the number of atoms in the xenon bubbles and their densities and pressures were then calculated. In total, 244 were bubbles were analysed. The mean diameter, density and pressure across all the bubbles were 21.2 Å, 2355 kg/m3 and 5.27 GPa respectively. Most of the bubbles were gaseous xenon. The separation of the bubbles was also analysed. This work is a good demonstration of a characterisation technique for end-of-life structural materials and the technique can be easily applied to small gas bubbles in other materials.
Following the IAEA Technical Meeting on 'Advanced Methodologies for the Analysis of Materials in Energy Applications Using Ion Beam Accelerators', this paper reviews the current status of ion beam analysis (IBA) techniques and some aspects of ion-induced radiation damage in materials for the field of materials relevant to fusion. Available facilities, apparatus development, future research options and challenges are presented and discussed. The analysis of beryllium and radioactivity-containing samples from future experiments in JET or ITER represents not only an analytical but also a technical challenge. A comprehensive list of the facilities, their current status, and analytical capabilities comes alongside detailed descriptions of the labs. A discussion of future issues of sample handling and the current status of facilities at JET complete the technical section.
To prepare the international IBA community for these challenges, the IAEA technical meeting concludes the necessity for determining new nuclear reaction cross-sections and improving the inter-laboratory comparability by defining international standards and testing these via a round-robin test.
In this project, we have assessed the structural tolerance of advanced refractory alloys to simulated nuclear fusion reactor environments, by using intense proton beams to mimic fusion neutron damage and analyzing the proton damaged structures using in-situ/ex-situ transmission electron microscopy and nano-hardness measurements. Refractory metals such as tungsten or tantalum, and their binary alloy combinations, are considered as promising structural materials to withstand the unprecedented high heat loads and fast neutron/helium fluxes expected in future magnetically-confined fusion reactors. Tungsten is currently the frontrunner for the production of plasma-facing components for fusion reactors. The attractiveness of tungsten as structural material lies in its high resistance to plasma-induced sputtering, erosion and radiation-induced void swelling, together with its thermal conductivity and high-temperature strength. Unfortunately, the brittle nature of tungsten hampers the manufacture of reactor components and can also lead to catastrophic failure during reactor operations.
We have focused on two potential routes to enhance the ductility of tungsten-containing materials, namely alloying tungsten with controlled amounts of tantalum, and using alternatively tantalum-based alloys containing specific tungsten additions, either as a full-thickness structural facing material or as a coating of first wall reactor components. The aim was to investigate the formation and evolution of radiation-induced damaged structures in these material solutions and the impact of those structures on the hardness of the material. The main results of this work are: (1) the addition of 5wt%Ta to W leads to saturation in the number density and average dimensions of the radiation-induced a/2<111> dislocation loops formed at 350°C, whereas in W the loop length increases progressively and evolves into dislocation strings, and later into hydrogen bubbles and surface blisters, (2) the recovery behaviour of proton irradiated W–5wt.%Ta alloy is characterized by dislocation loop growth at 600-900°C, whereas voids form at 1000°C by either vacancy absorption or loop collapse, (3) the presence of radiation-induced a<100> loops at 590°C in Ta hinders the formation and ordering of voids observed with increasing damage levels at 345°C, (4) the addition of 5-10wt.%W to Ta delays the evolution of a/2<111> dislocation loops with increasing damage levels, and therefore the appearance of random voids. These results expand the composition palette available for the safe selection of refractory alloys for plasma facing components with enhanced, or at least predictable, tolerance to the heat-radiation flux combinations expected in future nuclear fusion plants.
A new candidate fusion engineering material, WC-FeCr, has been irradiated with He ions at 25 and 500 °C. Ions were injected at 6 keV to a dose of ~15 dpa and 50 at. % He, simulating direct helium injection from the plasma. The microstructural evolution was continuously characterised in situ using transmission electron microscopy. In the FeCr phase, a coarse array of 3–6 nm bubbles formed. In the WC, bubbles were less prominent and smaller (~2 nm). Spherical-cap bubbles formed at hetero-phase interfaces of tertiary precipitates, indicating that enhanced processing routes to minimise precipitation could further improve irradiation tolerance.
During ion irradiation which is often used for the purposes of bandgap engineering, nanostructures can experience a phenomenon known as ion‐induced bending (IIB). The mechanisms behind this permanent deformation are the subject of debate. In this work, germanium nanowires are irradiated with 30 or 70 keV xenon ions to induce bending either away from or toward the ion beam. By comparing experimental results with Monte Carlo calculations, the direction of the bending is found to depend on the damage profile over the cross section of the nanowire. After irradiation, the nanowires are annealed at temperatures up to 440 °C triggering solid‐phase epitaxial growth (SPEG) causing further modification to the deformed nanowires. After IIB, it is observed that nanowires which had bent away from the ion beam then straighten during SPEG while those which had bent toward the ion beam bend even more. This is attributed to differences in the mechanisms responsible for the ion‐beam‐induced bending in opposite directions. Thus, the results reported here give insights into the mechanisms causing the IIB of nanowires and demonstrate how to predict the evolution of nanowires under irradiation and annealing. Finally, they show that, under certain conditions, the bending can even be removed via SPEG.
The unique ability of grain boundaries to act as effective sinks for radiation damage plays a significant role in nanocrystalline materials due to their large interfacial area per unit volume. Leveraging this mechanism in the design of tungsten as a plasma-facing material provides a potential pathway for enhancing its radiation tolerance under fusion-relevant conditions. In this study, we explore the impact of defect microstructures on the mechanical behavior of helium ion implanted nanocrystalline tungsten through nanoindentation. Softening was apparent across all implantation temperatures and attributed to bubble/cavity loaded grain boundaries suppressing the activation barrier for the onset of plasticity via grain boundary mediated dislocation nucleation. An increase in fluence placed cavity induced grain boundary softening in competition with hardening from intragranular defect loop damage, thus signaling a new transition in the mechanical behavior of helium implanted nanocrystalline tungsten.
We have monitored the thermal evolution of the proton irradiated structure of W–5 wt% Ta alloy by in-situ annealing in a transmission electron microscope at fusion reactor temperatures of 500–1300 °C. The interstitial-type a/2<111> dislocation loops emit self-interstitial atoms and glide to the free sample surface during the early stages of annealing. The resultant vacancy excess in the matrix originates vacancy-type a/2<111> dislocation loops that grow by loop and vacancy absorption in the temperature range of 600–900 °C. Voids form at 1000 °C, by either vacancy absorption or loop collapse, and grow progressively up to 1300 °C. Tantalum delays void formation by a vacancy-solute trapping mechanism.
In situ ion irradiation in a transmission electron microscope was used to investigate the effects of temperature on radiation-induced bubble lattice formation in Cu by low energy (12 keV) helium ions. Bubble lattices were observed to form between - 100 and 100 degrees C, but at 200 degrees C lattice formation was impeded by continued growth and agglomeration of bubbles. Both nucleation of bubbles, and to a lesser extent bubble lattice formation, are observed at lower fluences as temperature increases, which we suggest is due to increased point defect mobility. Previous work on point defect concentrations in irradiated copper is considered when interpreting these results.
A long-standing objective in materials research is to understand
and control the dynamic response of ceramic structures to energy deposition
from irradiation. The design of radiation tolerant materials and creation of new functional materials by ion beam modification demand a comprehensive understanding and predictive models of energy deposition
, transfer and exchange processes within and between the electronic and atomic subsystems. The exchange of energy between electrons and ions can act to dampen the ionic motion, to inhibit or enhance defect production, or to reduce damage accumulation. Understanding the materials response to both electronic and nuclear energy deposition
is a challenge of materials science in diverse fields.
4H-SiC was irradiated with 3.5 keV He+ ions using the MIAMI facility at University of Huddersfield. The evolution of microstructure and gas bubbles during the irradiation at 700°C, 800°C and 900°C was observed by in situ transmission electron microscopy. Under irradiation, isolated bubbles and bubble discs formed in the SiC matrix. Bubble discs lying on {0001} and {10-10} crystal planes were beginning to form at ion fluence above 2.3 × 1020 He+/m2 at 700°C. The density of bubble discs increased with increasing irradiation fluence. However, growth rates were different at different of the implantation periods and temperature holding periods. The nucleation and growth of the bubble discs were attributed to be coalescence of the adjacent He vacancies and combination of loop punching and trap mutation, respectively.
Radiation effects in materials for fission and fusion reactors are caused by fast neutrons which produce cascade damage, which has been known to be considerably different from simple Frenkel pairs produced by relativistic electrons. In-situ observation of radiation damage using a combined facility of electron microscope and heavy-ion accelerators has been a powerful tool to investigate the nature of the cascade damage. In this overview, brief historical survey of this experimental technique will be given, followed by the results and discussions on cascade damage mainly in gold will be reviewed. Careful considerations will be required to generalize the results to other metals as well as to other experimental conditions. Finally, there are a number of points to be developed for better understanding of cascade damage and for extending the “in-situ” techniques to other materials as non-metallic solids and to other intriguing phenomena.
Transmission electron microscopy with in situ ion irradiation has been used to examine the ion-beam-induced amorphisation of crystalline silicon under irradiation with light (He) and heavy (Xe) ions at room temperature. Analysis of the electron diffraction data reveal the heterogeneous amorphisation mechanism to be dominant in both cases. The differences in the amorphisation curves are discussed in terms of intra-cascade dynamic recovery, and the role of electronic and nuclear loss mechanisms.
The macroscopic properties of materials exposed to irradiation are determined by radiation damage effects which occur on the nanoscale. These phenomena are complex dynamic processes in which many competing mechanisms contribute to the evolution of the microstructure and thus to its end-state. To explore and understand the behavior of existing materials and to develop new technologies, it is highly advantageous to be able to observe the microstructural effects of irradiation as they occur. Transmission electron microscopy with in situ ion irradiation is ideally suited to this kind of study. This review focuses on some of the important factors in designing this type of experiment including sample preparation and ion beam selection. Also presented are a brief history of the development of this technique and an overview of the instruments in operation today including the latest additions.
Graphite is used as a moderator and structural component in the United Kingdom’s fleet of Advanced Gas-Cooled Reactors (AGRs) and features in two Generation IV reactor concepts: the Very High Temperature Reactor (VHTR) and the Molten Salt Reactor (MSR). Under the temperature and neutron irradiation conditions of an AGR, nuclear-grade graphite demonstrates significant changes to it mechanical, thermal and electrical properties. These changes include considerable dimensional change with expansion in the c-direction and contraction in the a/b-directions. As the United Kingdom’s AGRs approach their scheduled decommissioning dates, it is essential that this behaviour be understood in order to determine under what reactor conditions their operating lifetimes can be safely extended.
Two models have been proposed for the dimensional change in graphite due to displacing radiation: the “Standard Model” and “Ruck and Tuck”. The Standard Model draws on a conventional model of Frenkel pair production, point defect migration and agglomeration but fails to explain several key experimental observations. The Ruck and Tuck model has been proposed by M.I. Heggie et al. and is based upon the movement of basal dislocation to create folds in the “graphene” sheets and seeks not only to account for the dimension change but also the other phenomena not explained by the Standard Model.
In order to test the validity of these models, work is underway to gather experimental evidence of the microstructural evolution of graphite under displacing radiation. One of the primary techniques for this is transmission electron microscopy with in situ ion irradiation. This paper presents the results of electron irradiation at a range of energies (performed in order to separate the effects of the electron and ion beams) and of combined electron and ion beam irradiation.
The effects of displacing radiation in graphitic materials are important for technologies including nuclear power, graphitic-based nanocomposites and hybrid graphenesilicon high-speed integrated electronics. These applications expose graphitic materials to displacing irradiation either during manufacture and/or involve the deployment of these materials into irradiating environments. One of the most interesting phenomena in the response of graphite to irradiation is the formation of kink bands on the surface of the material. Here we apply the technique of transmission electron microscopy with in situ ion irradiation to observe the dynamic formation of these features. Kink bands were created at both 100 and 298K with doming of the samples also observed due to radiation induced dimensional change leading to mechanical deformation. Probably at 298 K, but certainly at 100 K, there should be no point defect mobility in graphite according to the latest theoretical calculations. However, some of the theories of dimensional change in graphite require point defect motion and agglomeration in order to operate. The implications of the experimental results for existing theories and the possibility of thermal effects due to the ion irradiation are discussed.
In this work, ion implantations with in situ transmission electron microscopy observations followed by different rates of temperature ramp were performed in (001)-Si to follow the evolution of He-plates under the influence of hydrogen. The JANNUS and MIAMI facilities were used to study the first stages of growth as well as the interactions between co-planar plates. Results showed that under a limited amount of H, the growth of He-plates resulting from a subcritical stress-corrosion mechanism can be fully described by the kinetic model of Johnson-Mehl-Avrami-Kolmogorov with effective activation energy of 0.9 eV. Elastic calculations showed that the sudden and nonisotropic coalescence of close He-plates occurs when the out-of-plane tensile stress between them is close to the yield strength of silicon. After hydrogen absorption, surface minimization of final structure occurs.
The MIAMI* facility at the University of Huddersfield is one of a number of facilities worldwide that permit the ion irradiation of thin foils in-situ in a transmission electron microscope. MIAMI has been developed with a particular focus on enabling the in-situ implantation of helium and hydrogen into thin electron transparent foils, necessitating ion energies in the range 1 – 10 keV. In addition, however, ions of a variety of species can be provided at energies of up to 100 keV (for singly charged ions), enabling studies to focus on the build up of radiation damage in the absence or presence of implanted gas.
This paper reports on a number of ongoing studies being carried out at MIAMI, and also at JANNuS (Orsay, France) and the IVEM / Ion Accelerator Facility (Argonne National Lab, US). This includes recent work on He bubbles in SiC and Cu; the former work concerned with modification to bubble populations by ion and electron beams and the latter project concerned with the formation of bubble super-lattices in metals.
A study is also presented consisting of experiments aimed at shedding light on the origins of the dimensional changes known to occur in nuclear graphite under irradiation with either neutrons or ions. Single crystal graphite foils have been irradiated with 60 keV Xe ions in order to create a non-uniform damage profile throughout the foil thickness. This gives rise to varying basal-plane contraction throughout the foil resulting in almost macroscopic (micron scale) deformation of the graphite. These observations are presented and discussed with a view to reconciling them with current understanding of point defect behavior in graphite.
*Microscope and Ion Accelerator for Materials Investigations
Sputtering yields, enhanced by more than an order of magnitude, have been observed for 80 keV Xe ion irradiation of monocrystalline Au nanorods. Yields are in the range 100-1900 atoms/ion compared with values for a flat surface of ≈50. This enhancement results in part from the proximity of collision cascades and ensuing thermal spikes to the nanorod surfaces. Molecular dynamic modeling reveals that the range of incident angles occurring for irradiation of nanorods and the larger number of atoms in "explosively ejected" atomic clusters make a significant contribution to the enhanced yield.
The origin of small spot and-loop features observed in eleetron
micrographs of thin evaporated single-crystal gold films was investigated. It is
found that the features are introduced into the specimens while being examined in
the electron microscope. Conclusive evidence is given to show that they arise
from bombardment by energetic negative ions emitted fronm the tungsten filament
of the electron gun, although the ions were not identified The rate of ion damage
can be considerably increased by coating the tungsten filament with a standard
oxide emitter. Annealing characteristics of the damage were studied. Above
about 300350 deg C the majority of the spot features anneal out, and ion damage
above about 350 deg C consists of the formation of small tetrahedra of stacking
fault. The ion damage is assumed to be very similar in character to that
produced by primary knock-ons resulting from irradiation by other particles
(e.g., neutrons). (auth)
A JEM 200 A electron microscope has been linked to a 120 kV heavy-ion accelerator in order to observe the dynamic effects of heavy-ion bombardment of materials. The ions, produced in a sputtering ion source, are accelerated, analyzed, directed through a flight line and then deflected to strike the specimen in the electron microscope. The effects of the ion bombardment on the specimen are recorded on videotape as they occur. Details of the system and examples of its use are presented.
A simple plasma ion source which is capable of delivering beams of 1×10<sup>-6</sup> A at 200 eV and 0.1–0.2 eV energy spread is described. Gas efficiencies of the order of percents are obtained. This source was found to be very successful in experiments using low energy beams in the electron volt region.
Transmission electron microscopy (TEM) with in situ ion irradiation is unique amongst experimental techniques in allowing the direct observation of the internal microstructure of materials on the nanoscale whilst they are being subjected to bombardment with energetic particles. Invaluable insights into the underlying atomistic processes at work can be gained through direct investigation of radiation induced and enhanced effects such as: phase changes and segregation; mechanical and structural changes; atomic/layer mixing and chemical disorder; compositional changes; chemical reactions; grain growth and shrinkage; precipitation and dissolution; defect/bubble formation, growth, motion, coalescence, removal and destruction; ionisation; diffusion; and collision cascades. The experimental results obtained can be used to validate the predictions of computational models which in turn can elucidate the mechanisms behind the phenomena seen in the microscope.It is 50 years since the first TEM observations of in situ ion irradiation were made by D.W. Pashley, A.E.B. Presland and J.W. Menter at the Tube Investment Laboratories in Cambridge, United Kingdom and 40 years since the first interfacing of an ion beam system with a TEM by P.A. Thackery, R.S. Nelson and H.C. Sansom at the Atomic Energy Research Establishment at Harwell, United Kingdom. In that time the field has grown with references in the literature to around thirty examples of such facilities. This paper gives an overview of the importance of the technique, especially with regard to the current challenges faced in understanding radiation damage in nuclear environments; a description of some of the important construction elements and design considerations of TEMs with in situ ion irradiation; a brief history of the development of this type of instrument; a summary of the facilities built around the world over the last half century; and finally a focus on the instruments in operation today.
TEM imaging conditions: bright field, off zone, and underfocus. The scale marker applies to all three panels
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−2. TEM imaging conditions: bright field, off zone, and underfocus. The scale marker applies to all three panels.