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Nanoscale dislocation loops formed by irradiation can significantly contribute to both irradiation hardening and embrittlement of materials when subjected to extreme nuclear reactor environments. This study explores the application of weak-beam dark-field (WBDF) scanning transmission electron microscopy (STEM) methods for quantitative irradiation-induced defect analysis in crystalline materials, with a specific focus on dislocation loop imaging and analysis. A high-purity Fe-5 wt% Cr model alloy was irradiated with 8 MeV Fe2+ ions at 450°C to a fluence of 8.8 × 1019 m-2, inducing dislocation loops for analysis. While transmission electron microscopy (TEM) has traditionally been the primary tool for dislocation imaging, recent advancements in STEM technology have reignited interest in using STEM for defect imaging. This study introduces and compares three WBDF STEM methods, demonstrating their effectiveness in suppressing background contrasts, isolating defect information for dislocation loop type classification, providing finer dislocation line images for small loop analysis, and presenting inside-outside contrast for identifying loop nature. Experimental findings indicate that WBDF STEM methods surpass traditional TEM approaches, yielding clearer and more detailed images of dislocation loops. The study concludes by discussing the potential applications of WBDF STEM techniques in defect analysis, emphasizing their adaptability across various material systems beyond nuclear materials., Competing Interests: Conflict of Interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Oxford University Press on behalf of the Microscopy Society of America 2024.)

A novel spectroscopy diagnostic for measuring internal magnetic fields in high temperature magnetized plasmas has been developed. It involves spectrally resolving the Balmer-α (656 nm) neutral beam radiation split by the motional Stark effect with a spatial heterodyne spectrometer (SHS). The unique combination of high optical throughput (3.7 mm 2 sr) and spectral resolution (δλ ∼ 0.1 nm) allows these measurements to be made with time resolution ≪1 ms. The high throughput is effectively utilized by incorporating a novel geometric Doppler broadening compensation technique in the spectrometer. The technique significantly reduces the spectral resolution penalty inherent to using large area, high-throughput optics while still collecting the large photon flux provided by such optics. In this work, fluxes of order 10 10  s -1 support the measurement of deviations of <5 mT (Δλ Stark ∼ 10 -4 nm) in the local magnetic field with 50 µs time resolution. Example high time resolution measurements of the pedestal magnetic field throughout the ELM cycle of a DIII-D tokamak plasma are presented. Local magnetic field measurements give access to the dynamics of the edge current density, which is essential to understanding stability limits, edge localized mode generation and suppression, and predicting performance of H-mode tokamaks.

The transformation of unstable austenite to ferrite or α′ martensite as a result of exposure to Xe+ or Ga+ ions at room temperature was studied in a 304 stainless steel casting alloy. Controlled Xe+ and Ga+ ion beam exposures of the 304 were carried out at a variety of beam/sample geometries. It was found that both Ga+ and Xe+ ion irradiation resulted in the transformation of the austenite to either ferrite or α′ martensite. In this paper, we will refer to the transformation product as a BCC phase. The crystallographic orientation of the transformed area was controlled by the orientation of the austenite grain and was consistent with either the Nishiyama–Wasserman or the Kurdjumov–Sachs orientation relationships. On the basis of the Xe+ and Ga+ ion beam exposures, the transformation is not controlled by the chemical stabilization of the BCC phase by the ion species, but is a result of the disorder caused by the ion-induced recoil motion and subsequent return of the disordered region to a more energetically favorable phase.

High resolution luminosity product measurements of neutral beam emission in magnetized plasmas are severely limited by the artificial Doppler broadening inherent to the use of large diameter collection optics. In this paper, a broadening compensation method is developed for the spatial heterodyne spectroscopy interferometric technique. The compensation technique greatly reduces the artificial broadening, thereby enabling high resolution measurements at a significantly higher photon flux than previously available. Compensated and uncompensated measurements of emission generated by impact excitation of 61 keV deuterium neutrals in a tokamak plasma at the DIII-D National Fusion Facility are presented. The spectral width of the compensated measurement is ${\sim}0.13 \;{\rm{nm}}$, which is comparable to the instrument resolution. This width is ${\sim}4 \times$ smaller than the uncompensated width, which for the 20 cm diameter collection lens system utilized in this study is ${\sim}0.5 \;{\rm{nm}}$.

Recently, the dual beam Xe + plasma focused ion beam (Xe + pFIB) instrument has attracted increasing interest for site-specific transmission electron microscopy (TEM) sample preparation for a local region of interest as it shows several potential benefits compared to conventional Ga + FIB milling. Nevertheless, challenges and questions remain especially in terms of FIB-induced artefacts, which hinder reliable S/TEM microstructural and compositional analysis. Here we examine the efficacy of using Xe + pFIB as compared with conventional Ga + FIB for TEM sample preparation of Al alloys. Three potential source of specimen preparation artefacts were examined, namely: (1) implantation-induced defects such as amophisation, dislocations, or 'bubble' formation in the near-surface region resulting from ion bombardment of the sample by the incident beam; (2) compositional artefacts due to implantation of the source ions and (3) material redeposition due to the milling process. It is shown that Xe + pFIB milling is able to produce improved STEM/TEM samples compared to those produced by Ga + milling, and is therefore the preferred specimen preparation route. Strategies for minimising the artefacts induced by Xe + pFIB and Ga + FIB are also proposed. LAY DESCRIPTION: FIB (focused ion beam) instruments have become one of the most important systems in the preparation of site-specific TEM specimens, which are typically 50-100 nm in thickness. TEM specimen preparation of Al alloys is particularly challenging, as convention Ga-ion FIB produces artefacts in these materials that make microstructural analysis difficult or impossible. Recently, the use of noble gas ion sources, such as Xe, has markedly improved milling speeds and is being used for the preparation of various materials. Hence, it is necessary to investigate the structural defects formed during FIB milling and assess the ion-induced chemical contamination in these TEM samples. Here we explore the feasibility and efficiency of using Xe + PFIB as a TEM sample preparation route for Al alloys in comparison with the conventional Ga+FIB., (© 2020 The Authors. Journal of Microscopy published by John Wiley & Sons Ltd on behalf of Royal Microscopical Society.)

Although there is substantial literature on the impact of smoking laws, the number of studies that investigate the impact of such policies on college campuses is sparse. Using a rich data set from various waves of the American College Health Association National College Health Assessment survey for a mid-sized public university in the southern United States, we investigate a possible causal link between a limited smoking policy and smoking behaviours, health and academic outcomes among college students. We employ propensity score matching methods to control for endogeneity of unobservable characteristics. Our results show a significant reduction in the propensity to smoke cigarettes and cigars following the introduction of the policy. Further, we find that the policy has increased academic outcomes; however, it has no significant effect on student health. These findings have important policy implications for schools that are considering instituting comprehensive smoking bans on college.

Pigment distributions have a critical role in the corrosion protection properties of organic paint coatings, but they are difficult to image in 3D over statistically significant volumes and at sufficiently high spatial resolutions required for detailed analysis. Here we report, for the first time, large volume analytical serial sectioning tomography of an organic composite coating using a xenon Plasma Focused Ion Beam (PFIB) combined with secondary electron imaging, energy dispersive X-ray (EDX) spectrum imaging (SI) and electron backscattered diffraction (EBSD). Together these techniques provide a comprehensive quantitative description of the physical orientation and distribution of the pigments within a model marine ballast tank coating, as well as their crystallographic and elemental characterisation. Polymers and organic materials are challenging because of their propensity for ion beam damage and possible beam heating effects. Our novel, optimised block preparation technique permits automated data acquisition with minimal operator intervention, and can have significant applications for the structural and chemical characterisation of a wide range of organic materials. Our results revealed that the paint contained 7.5 vol% aluminium flakes and 25 vol% quartz particles. The aluminium flakes were oriented parallel to the substrate surface, which is beneficial in terms of the corrosion protection capability of the coating., (Copyright © 2018. Published by Elsevier B.V.)

Measurement of electrostatic potential, or local electric field, turbulence is a critical missing component in validating nonlinear turbulence and transport simulations of fusion plasmas. A novel diagnostic is being developed for measuring local electric field fluctuations, E ̃ ( r , t ) , via high-speed measurements of the light emitted from a hydrogenic neutral beam. It exploits the proportionality of the spectral line splitting from the Motional Stark Effect to the total electric field experienced by the neutral atom at the excitation site. The measurement is localized by the usual cross-beam geometry of beam-spectroscopy measurements. The corner stone of the diagnostic is a high spectral resolution, high etendue spatial heterodyne spectrometer (SHS). A SHS design with high etendue (∼5 mm 2 sr) and resolution (∼0.14 nm) meets the formidable spectrometer requirements. Field tests of the spectrometer at the DIII-D tokamak demonstrate that the beam emission spectrum produced by the SHS agrees with that of a traditional spectrometer and that the measured flux is adequate for turbulence studies.

Uranium is typically the most abundant radionuclide by mass in radioactive wastes and is a significant component of effluent streams at nuclear facilities. Actinide(IV) (An(IV)) colloids formed via various pathways, including corrosion of spent nuclear fuel, have the potential to greatly enhance the mobility of poorly soluble An(IV) forms, including uranium. This is particularly important in conditions relevant to decommissioning of nuclear facilities and the geological disposal of radioactive waste. Previous studies have suggested that silicate could stabilize U(IV) colloids. Here the formation, composition, and structure of U(IV)-silicate colloids under the alkaline conditions relevant to spent nuclear fuel storage and disposal were investigated using a range of state of the art techniques. The colloids are formed across a range of pH conditions (9-10.5) and silicate concentrations (2-4 mM) and have a primary particle size 1-10 nm, also forming suspended aggregates <220 nm. X-ray absorption spectroscopy, ultrafiltration, and scanning transmission electron microscopy confirm the particles are U(IV)-silicates. Additional evidence from X-ray diffraction and pair distribution function data suggests the primary particles are composed of a UO 2 -rich core and a U-silicate shell. U(IV)-silicate colloids formation correlates with the formation of U(OH) 3 (H 3 SiO 4 ) 3 2- complexes in solution indicating they are likely particle precursors. Finally, these colloids form under a range of conditions relevant to nuclear fuel storage and geological disposal of radioactive waste and represent a potential pathway for U mobility in these systems.

We have developed a new experimental platform for in situ scanning transmission electron microscope (STEM) energy dispersive X-ray spectroscopy (EDS) which allows real time, nanoscale, elemental and structural changes to be studied at elevated temperature (up to 1000 °C) and pressure (up to 1 atm). Here we demonstrate the first application of this approach to understand complex structural changes occurring during reduction of a bimetallic catalyst, PdCu supported on TiO 2 , synthesized by wet impregnation. We reveal a heterogeneous evolution of nanoparticle size, distribution, and composition with large differences in reduction behavior for the two metals. We show that the data obtained is complementary to in situ STEM electron energy loss spectroscopy (EELS) and when combined with in situ X-ray absorption spectroscopy (XAS) allows correlation of bulk chemical state with nanoscale changes in elemental distribution during reduction, facilitating new understanding of the catalytic behavior for this important class of materials., (© 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Creep cavitation in an ex-service nuclear steam header Type 316 stainless steel sample is investigated through a multiscale tomography workflow spanning eight orders of magnitude, combining X-ray computed tomography (CT), plasma focused ion beam (FIB) scanning electron microscope (SEM) imaging and scanning transmission electron microscope (STEM) tomography. Guided by microscale X-ray CT, nanoscale X-ray CT is used to investigate the size and morphology of cavities at a triple point of grain boundaries. In order to understand the factors affecting the extent of cavitation, the orientation and crystallographic misorientation of each boundary is characterised using electron backscatter diffraction (EBSD). Additionally, in order to better understand boundary phase growth, the chemistry of a single boundary and its associated secondary phase precipitates is probed through STEM energy dispersive X-ray (EDX) tomography. The difference in cavitation of the three grain boundaries investigated suggests that the orientation of grain boundaries with respect to the direction of principal stress is important in the promotion of cavity formation.

The capability to perform liquid in situ transmission electron microscopy (TEM) experiments provides an unprecedented opportunity to examine the real-time processes of physical and chemical/electrochemical reactions during the interaction between metal surfaces and liquid environments. This work describes the requisite steps to make the technique fully analytical, from sample preparation, through modifications of the electrodes, characterization of electrolytes, and finally to electrochemical corrosion experiments comparing in situ TEM to conventional bulk cell and microcell configurations.

Access to and characterization of sustained, toroidally confined plasmas with a very high plasma-to-magnetic pressure ratio (β&#95;{t}), low internal inductance, high elongation, and nonsolenoidal current drive is a central goal of present tokamak plasma research. Stable access to this desirable parameter space is demonstrated in plasmas with ultralow aspect ratio and high elongation. Local helicity injection provides nonsolenoidal sustainment, low internal inductance, and ion heating. Equilibrium analyses indicate β&#95;{t} up to ∼100% with a minimum |B| well spanning up to ∼50% of the plasma volume.

In situ analytical transmission electron microscopy (TEM) can provide a unique perspective on dynamic reactions in a variety of environments, including liquids and gases. In this study, in situ analytical TEM techniques have been applied to examine the localised oxidation reactions that occur in a Ni-Cr-Fe alloy, Alloy 600, using a gas environmental cell at elevated temperatures. The initial stages of preferential intergranular oxidation, shown to be an important precursor phenomenon for intergranular stress corrosion cracking in pressurized water reactors (PWRs), have been successfully identified using the in situ approach. Furthermore, the detailed observations correspond to the ex situ results obtained from bulk specimens tested in hydrogenated steam and in high temperature PWR primary water. The excellent agreement between the in situ and ex situ oxidation studies demonstrates that this approach can be used to investigate the initial stages of preferential intergranular oxidation relevant to nuclear power systems., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The growth/coarsening kinetics of γ ″ ( Ni 3 Nb - D0 22 ) precipitates have been found by numerous researchers to show an apparent correspondence with the classical (Ostwald ripening) equation outlined by Lifshitz, Slyozov and (separately) Wagner for a diffusion controlled regime. Nevertheless, a significant disparity between the actual precipitate size distribution shape and that predicted by LSW is frequently observed in the interpretation of these results, the origin of which is unclear. Analysis of the literature indicates one likely cause for this deviation from LSW for γ ″ precipitates is the "encounter" phenomenon described by Davies et al. (Acta Metall 28(2):179-189, 1980) that is associated with secondary phases comprising a high volume fraction. Consequently, the distributions of both γ ″ precipitates described in the literature (Alloy 718) and measured in this research in Alloy 625 are analysed through employing the Lifshitz-Slyozov-Encounter-Modified (LSEM) formulation (created by Davies et al.). The results of the LSEM analysis show good far better agreement than LSW with experimental distributions after the application of a necessary correction for what is termed in this research as "directional encounter". Moreover, the activation energy for γ ″ coarsening in Alloy 625 shows conformity with literature data once the effect of heterogeneous (on dislocations) precipitate nucleation at higher temperatures is accounted for., (© The Author(s) 2017.)

In recent years, an increasing number of studies utilizing in situ liquid and/or gaseous cell scanning/transmission electron microscopy (S/TEM) have been reported. Because of the difficulty in the preparation of suitable specimens, these environmental S/TEM studies have been generally limited to studies of nanoscale structured materials such as nanoparticles, nanowires, or sputtered thin films. In this paper, we present two methodologies which have been developed to facilitate the preparation of electron-transparent samples from conventional bulk metals and alloys for in situ liquid/gaseous cell S/TEM experiments. These methods take advantage of combining sequential electrochemical jet polishing followed by focused ion beam extraction techniques to create large electron-transparent areas for site-specific observation. As an example, we illustrate the application of this methodology for the preparation of in situ specimens from a cold-rolled Type 304 austenitic stainless steel sample, which was subsequently examined in both 1 atm of air as well as fully immersed in a H2O environment in the S/TEM followed by hyperspectral imaging. These preparation techniques can be successfully applied as a general procedure for a wide range of metals and alloys, and are suitable for a variety of in situ analytical S/TEM studies in both aqueous and gaseous environments.

We report the electrochemical detection of the redox active cardiac biomarker myoglobin (Mb) using aptamer-functionalized black phosphorus nanostructured electrodes by measuring direct electron transfer. The as-synthesized few-layer black phosphorus nanosheets have been functionalized with poly-l-lysine (PLL) to facilitate binding with generated anti-Mb DNA aptamers on nanostructured electrodes. This aptasensor platform has a record-low detection limit (∼0.524 pg mL(-1)) and sensitivity (36 μA pg(-1) mL cm(-2)) toward Mb with a dynamic response range from 1 pg mL(-1) to 16 μg mL(-1) for Mb in serum samples. This strategy opens up avenues to bedside technologies for multiplexed diagnosis of cardiovascular diseases in complex human samples.

Tokamak experiments at near-unity aspect ratio A≲1.2 offer new insights into the self-organized H-mode plasma confinement regime. In contrast to conventional A∼3 plasmas, the L-H power threshold P&#95;{LH} is ∼15× higher than scaling predictions, and it is insensitive to magnetic topology, consistent with modeling. Edge localized mode (ELM) instabilities shift to lower toroidal mode numbers as A decreases. These ultralow-A operations enable heretofore inaccessible J&#95;{edge}(R,t) measurements through an ELM that show a complex multimodal collapse and the ejection of a current-carrying filament.

This paper presents an investigation of the limitations and optimisation of energy dispersive X-ray (EDX) tomography within the scanning transmission electron microscope, focussing on application of the technique to characterising the 3D elemental distribution of bimetallic AgAu nanoparticles. The detector collection efficiency when using a standard tomography holder is characterised using a tomographic data set from a single nanoparticle and compared to a standard low background double tilt holder. Optical depth profiling is used to investigate the angles and origin of detector shadowing as a function of specimen field of view. A novel time-varied acquisition scheme is described to compensate for variations in the intensity of spectrum images at each sample tilt. Finally, the ability of EDX spectrum images to satisfy the projection requirement for nanoparticle samples is discussed, with consideration of the effect of absorption and shadowing variations., (Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.)

Ga(+) Focused Ion Beam-Scanning Electron Microscopes (FIB-SEM) have revolutionised the level of microstructural information that can be recovered in 3D by block face serial section tomography (SST), as well as enabling the site-specific removal of smaller regions for subsequent transmission electron microscope (TEM) examination. However, Ga(+) FIB material removal rates limit the volumes and depths that can be probed to dimensions in the tens of microns range. Emerging Xe(+) Plasma Focused Ion Beam-Scanning Electron Microscope (PFIB-SEM) systems promise faster removal rates. Here we examine the potential of the method for large volume serial section tomography as applied to bainitic steel and WC-Co hard metals. Our studies demonstrate that with careful control of milling parameters precise automated serial sectioning can be achieved with low levels of milling artefacts at removal rates some 60× faster. Volumes that are hundreds of microns in dimension have been collected using fully automated SST routines in feasible timescales (<24h) showing good grain orientation contrast and capturing microstructural features at the tens of nanometres to the tens of microns scale. Accompanying electron back scattered diffraction (EBSD) maps show high indexing rates suggesting low levels of surface damage. Further, under high current Ga(+) FIB milling WC-Co is prone to amorphisation of WC surface layers and phase transformation of the Co phase, neither of which have been observed at PFIB currents as high as 60nA at 30kV. Xe(+) PFIB dual beam microscopes promise to radically extend our capability for 3D tomography, 3D EDX, 3D EBSD as well as correlative tomography., (Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.)