Ion Beam Scanning Electron Microscopy Research Articles

Segmentation of cellular ultrastructures on sparsely labeled 3D electron microscopy images using deep learning.

Focused ion beam-scanning electron microscopy (FIB-SEM) images can provide a detailed view of the cellular ultrastructure of tumor cells. A deeper understanding of their organization and interactions can shed light on cancer mechanisms and progression. However, the bottleneck in the analysis is the delineation of the cellular structures to enable quantitative measurements and analysis. We mitigated this limitation using deep learning to segment cells and subcellular ultrastructure in 3D FIB-SEM images of tumor biopsies obtained from patients with metastatic breast and pancreatic cancers. The ultrastructures, such as nuclei, nucleoli, mitochondria, endosomes, and lysosomes, are relatively better defined than their surroundings and can be segmented with high accuracy using a neural network trained with sparse manual labels. Cell segmentation, on the other hand, is much more challenging due to the lack of clear boundaries separating cells in the tissue. We adopted a multi-pronged approach combining detection, boundary propagation, and tracking for cell segmentation. Specifically, a neural network was employed to detect the intracellular space; optical flow was used to propagate cell boundaries across the z-stack from the nearest ground truth image in order to facilitate the separation of individual cells; finally, the filopodium-like protrusions were tracked to the main cells by calculating the intersection over union measure for all regions detected in consecutive images along z-stack and connecting regions with maximum overlap. The proposed cell segmentation methodology resulted in an average Dice score of 0.93. For nuclei, nucleoli, and mitochondria, the segmentation achieved Dice scores of 0.99, 0.98, and 0.86, respectively. The segmentation of FIB-SEM images will enable interpretative rendering and provide quantitative image features to be associated with relevant clinical variables.

Detection of atmospheric aerosols and terrestrial nanoparticles collected in a populous city in southern Brazil.

The main objective of this study is to analyze hazardous elements in nanoparticles (NPs) (smaller than 100nm) and ultrafine particles (smaller than 1µm) in Porto Alegre City, southern Brazil using a self-made passive sampler and Sentinel-3B SYN satellite images in 32 collection points. The Aerosol Optical Thickness proportion (T550) identification was conducted using images of the Sentinel-3B SYN satellite at 634 points sampled in 2019, 2020, 2021, and 2022. Focused ion beam scanning electron microscopy analyses were performed to identify chemical elements present in NPs and ultrafine particles, followed by single-stage cascade impactor to be processed by high-resolution transmission electron microscopy. This process was coupled with energy-dispersive X-ray spectroscopy and later analysis via secondary ion mass spectrometry. Data was acquired from Sentinel-3B SYN images, normalized to a standard mean of 0.83µg/mg, at moderate spatial resolution (260m), and modeled in the Sentinel Application Platform (SNAP) software v.8.0. Statistical matrix data was generated in the JASP software (Jeffreys's Amazing Statistics Program) v.0.14.1.0 followed by a K-means cluster analysis. The results demonstrate the presence of between 1 and 100nm particles of the following chemical elements: Si, Al, K, Mg, P, and Ti. Many people go through these areas daily and may inhale or absorb these elements that can harm human health. In the Sentinel-3B SYN satellite images, the sum of squares in cluster 6 is 168,265 and in cluster 7 a total of 21,583. The use of images from the Sentinel-3B SYN satellite to obtain T550 levels is of great importance as it reveals that atmospheric pollution can move through air currents contaminating large areas on a global scale.

Bundling of collagen fibrils influences osteocyte network formation during bone modeling

Osteocytes form a cellular network by gap junctions between their cell processes. This network is important since intercellular communication via the network is essential for bone metabolism. However, the factors that influence the formation of this osteocyte network remain unknown. As the early stage of osteocyte network formation occurs on the bone surface, we observed a newly formed trabecular bone surface by orthogonal focused ion beam-scanning electron microscopy. The embedding late osteoblast processes tended to avoid bundled collagen fibrils and elongate into sparse collagen fibrils. Then, we examined whether the inhibition of bundling of collagen fibrils using a potent lysyl oxidase inhibitor, β-aminopropionitrile (BAPN) changed the cellular network of the chick calvaria. The osteocyte shape of the control group was spindle-shape, while that of the BAPN group was sphere-shaped. In addition, the osteocyte processes of the control group were elongated vertically to the long axis of the cell body, whereas the osteocyte processes of the BAPN group were elongated radially. Therefore, it was suggested that the bundling of collagen fibrils influences normal osteocyte network formation during bone modeling.

Size and shape analysis of micro- to nano-particles of quartz powders using advanced electron microscopy and laser diffraction methods

The paper deals with particle analysis and the evaluation of the shape and size distribution of micro- to nano-sized quartz particles as a key parameter for the evaluation of quality in many industrial fields, particularly for high-purity applications. Samples are analyzed by laser diffraction, the most commonly used method for determining the size of the particles; for precise measurement with the possibility of high-resolution imaging of particles, scanning electron microscopy was applied. For morphological and size analysis of electrically non-conductive micro- to nano-particles under environmentally compatible conditions of elevated gas pressure and humidity, environmental scanning electron microscopy was selected as the most suitable. Moreover, the high-end methods of focused ion beam scanning electron microscopy and serial block-face scanning electron microscopy enabled the analysis of particles in the epoxy resin volume including spatial imaging. The application of image post-processing as an important part of the electron microscopy workflow is also discussed.

Characterization for 3D pore-fracture systems in Hot-Dry-Rock samples from Gonghe Basin, China

As a new type of renewable energy, Hot-Dry-Rock (HDR) is gaining increasing attention. The physical properties of rock influenced by the pore-fracture structure are vital for the hydraulic and chemical characteristics of HDR reservoirs. However, the natural pore-fracture structure in HDR has not been sufficiently studied. To fulfill this gap, we used focused ion beam-scanning electron microscopy (FIB-SEM) to construct three-dimensional (3D) digital models for four granite samples from the deep HDR reservoir in Gonghe Basin, Qinghai Province, China, and obtained the nanoscale structure of the pores and fractures in HDR reservoir for the first time. Our analysis based on the 3D models indicates that the heat transfer area in the HDR reservoir is mainly from fractures and crack-like pores, but a large amount of small but regular pores could be neglected when heat transfer in HDR is considered. The permeability of HDR reservoirs at nanoscale varies from 9.414 nD to 0.082 mD, and the high permeability in this study is accompanied by throughgoing fractures. The variation of porosity and permeability of deep HDR at nanoscale in this study is much more severe than that of shallow granites previously studied at microscale. The performance of geothermal field is significantly influenced by the size of throats and the average size and tortuosity of the interconnected pore-fracture network in HDR. The hydraulic aperture could be 32-58% lower than the mechanical aperture of the natural fractures in HDR reservoirs, which is a vital clue for the numerical simulation associated with enhanced geothermal systems.

CDK2 inhibition disorders centrosome stoichiometry and alters cellular outcomes in aneuploid cancer cells

ABSTRACT Cyclin-dependent Kinase 2 (CDK2) inhibition prevents supernumerary centrosome clustering. This causes multipolarity, anaphase catastrophe and apoptotic death of aneuploid cancers. This study elucidated how CDK2 antagonism affected centrosome stoichiometry. Focused ion beam scanning electron microscopy (FIB-SEM) and immunofluorescent imaging were used. Studies interrogated multipolar mitosis after pharmacologic or genetic repression of CDK2. CDK2/9 antagonism with CYC065 (Fadraciclib)-treatment disordered centrosome stoichiometry in aneuploid cancer cells, preventing centrosome clustering. This caused ring-like chromosomes or multipolar cancer cells to form before onset of cell death. Intriguingly, CDK2 inhibition caused a statistically significant increase in single centrioles rather than intact centrosomes with two centrioles in cancer cells having chromosome rings or multipolarity. Statistically significant alterations in centrosome stoichiometry were undetected in other mitotic cancer cells. To confirm this pharmacodynamic effect, CDK2 but not CDK9 siRNA-mediated knockdown augmented cancer cells with chromosome ring or multipolarity formation. Notably, engineered gain of CDK2, but not CDK9 expression, reversed emergence of cancer cells with chromosome rings or multipolarity, despite CYC065-treatment. In marked contrast, CDK2 inhibition of primary human alveolar epithelial cells did not confer statistically significant increases of cells with ring-like chromosomes or multipolarity. Hence, CDK2 antagonism caused differential effects in malignant versus normal alveolar epithelial cells. Translational relevance was confirmed by CYC065-treatment of syngeneic lung cancers in mice. Mitotic figures in tumors exhibited chromosome rings or multipolarity. Thus, CDK2 inhibition preferentially disorders centrosome stoichiometry in cancer cells. Engaging this disruption is a strategy to explore against aneuploid cancers in future clinical trials.

Visualizing the Structure, Composition and Activity of Single Catalyst Particles for Olefin Polymerization and Polyolefin Decomposition.

The structural and morphological characterization of individual catalyst particles for olefin polymerization, as well as for the reverse process of polyolefin decomposition, can provide an improved understanding for how these catalyst materials operate under relevant reaction conditions. In this review, we discuss an emerging analytical toolbox of 2D and 3D chemical imaging techniques that is suitable for investigating the chemistry and reactivity of related catalyst systems. While synchrotron-based X-ray microscopy still provides unparalleled spatial resolutions in 2D and 3D, a number of laboratory-based techniques, most notably focused ion beam-scanning electron microscopy, confocal fluorescence microscopy, infrared photoinduced force microscopy and laboratory-based X-ray nano-computed tomography, have helped to significantly expand the arsenal of analytical tools available to scientists in heterogeneous catalysis and polymer science. In terms of future research, the review outlines the role and impact of in situ and operando (spectro-)microscopy experiments, involving sophisticated reactors as well as online reactant and product analysis, to obtain real-time information on the formation, decomposition, and mobility of polymer phases within single catalyst particles. Furthermore, the potential of fluorescence microscopy, X-ray microscopy and optical microscopy is highlighted for the high-throughput characterization of olefin polymerization and polyolefin decomposition catalysts. By combining these chemical imaging techniques with, for example, chemical staining methodologies, selective probe molecules as well as particle sorting approaches, representative structure-activity relationships can be derived at the level of single catalyst particles.

How sintering temperature affects the electrochemical performance of ultra-high nickel (Ni > 0.9) cathode material

The burgeoning demand for electric vehicles with extended driving ranges has propelled ongoing development efforts for ultra-high nickel (Ni > 0.9) cathode materials. Despite significant ongoing research focused on Ni-rich cathode materials, a more comprehensive foundational understanding of ultra-high nickel cathode materials is essential. In our research, we employed LiNi0.94Co0.06O2 as a model ultra-high nickel cathode material to systematically delve into the interplay between sintering temperature, structural features, and electrochemical behavior. Within a sintering temperature spectrum of 660–720 °C, we discerned that specimens produced at diminished temperatures manifest a reduced initial discharge capacity yet excel in cycling endurance. In stark contrast, their counterparts produced at augmented temperatures behave inversely. Identifying a singular sintering temperature that achieves equilibrium between initial discharge capacity and cycling performance proves elusive. Through X-ray diffraction and high-resolution transmission electron microscopy, it became evident that samples synthesized at lower temperatures exhibit pronounced lithium-nickel mixing and develop a thicker NiO layer on the surface, leading to compromised initial discharge performance and capacity. Utilizing focused ion beam scanning electron microscopy, differential capacity analysis, and in-situ X-ray diffraction, we confirm that samples synthesized at lower temperatures possess smaller particle sizes, enabling them to withstand volumetric expansion stress during cycling, resulting in enhanced cycling performance. In the realm of ultra-high nickel cathode materials, elevating the sintering temperature is a conduit to superior initial discharge efficiency and capacity. Yet, the imperative of preserving diminutive particle dimensions, as a stratagem to bolster cycling performance, stands out as a pivotal research frontier.

Local Structural Modifications in Metallic Micropillars Induced by Plasma Focused Ion Beam Processing.

A focused ion beam scanning electron microscope (FIB-SEM) is a powerful tool that is routinely used for scale imaging from the micro- to nanometer scales, micromachining, prototyping, and metrology. In spite of the significant capabilities of a FIB-SEM, there are inherent artefacts (e.g., structural defects, chemical interactions and phase changes, ion implantation, and material redeposition) that are produced due to the interaction of Ga+ or other types of ions (e.g., Xe+, Ar+, O+, etc.) with the sample. In this study, we analyzed lattice distortion and ion implantation and subsequent material redeposition in metallic micropillars which were prepared using plasma focus ion beam (PFIB) milling. We utilized non-destructive synchrotron techniques such as X-ray fluorescence (XRF) and X-ray nanodiffraction to examine the micropillars prepared using Xe+ ion energies of 10 keV and 30 keV. Our results demonstrate that higher Xe ion energy leads to higher density of implanted ions within the redeposited and milled material. The mixing of ions in the redeposited material significantly influences the lattice structure, causing deformation in regions with higher ion concentrations. Through an X-ray nanodiffraction analysis, we obtained numerical measurements of the strain fields induced in the regions, which revealed up to 0.2% lattice distortion in the ion bombardment direction.

Three-dimensional architecture of granulosa cell derived from oocyte cumulus complex, revealed by FIB-SEM

The oocyte cumulus complex is mainly composed of an oocyte, the perivitelline space, zona pellucida and numerous granulosa cells. The cumulus granulosa cells (cGCs) provide a particularly important microenvironment for oocyte development, regulating its growth, maturation and meiosis. In this study, we studied the internal structures and cell-to-cell connections of mouse cGCs using focused ion beam scanning electron microscopy (FIB-SEM). We reconstructed three-dimensional models to display characteristic connections between the oocyte and cGCs, and to illustrate various main organelles in cGCs together with their interaction relationship. A special form of cilium identified in granulosa cell was never reported in previous literature.

Ultrastructure of noise-induced cochlear synaptopathy

Acoustic overexposure can eliminate synapses between inner hair cells (IHCs) and auditory nerve fibers (ANFs), even if hair-cell function recovers. This synaptopathy has been extensively studied by confocal microscopy, however, understanding the nature and sequence of damage requires ultrastructural analysis. Here, we used focused ion-beam scanning electron microscopy to mill, image, segment and reconstruct ANF terminals in mice, 1 day and 1 week after synaptopathic exposure (8–16 kHz, 98 dB SPL). At both survivals, ANF terminals were normal in number, but 62% and 53%, respectively, lacked normal synaptic specializations. Most non-synapsing fibers (57% and 48% at 1 day and 1 week) remained in contact with an IHC and contained healthy-looking organelles. ANFs showed a transient increase in mitochondrial content (51%) and efferent innervation (34%) at 1 day. Fibers maintaining synaptic connections showed hypertrophy of pre-synaptic ribbons at both 1 day and 1 week. Non-synaptic fibers were lower in mitochondrial content and typically on the modiolar side of the IHC, where ANFs with high-thresholds and low spontaneous rates are normally found. Even 1 week post-exposure, many ANF terminals remained in IHC contact despite loss of synaptic specializations, thus, regeneration efforts at early post-exposure times should concentrate on synaptogenesis rather than neurite extension.

Solid electrolyte cracking due to lithium filament growth and concept of mechanical reinforcement – An operando study

Lithium metal solid state batteries (LMSSB) attract great interest in academia and industry due to their projected high energy density and safety. However, hard short circuits due to the penetration of lithium filaments through the solid electrolyte impede their development for practical application. Here, multi-characterization methods ranging from operando and in situ scanning electron microscopy to ex situ focused ion beam scanning electron microscopy are employed for comprehensive understanding of the cell failure. The rapid failure is attributed to coupled crack propagation and subsequent lithium filament growth during the plating process which is demonstrated in a Li6PS5Cl (lithium argyrodite) based LMSSB. Cracking initiates at current constriction spots and voids, where inhomogeneous lithium plating/stripping causes high local stress fields that trigger continuous crack propagation. Lithium filament growth finally leads to a hard short circuit. Considering the low fracture toughness of ceramic electrolytes, strengthening with Al2O3 fibers is shown to be effective in significantly improving the critical current density and cycling stability. Our results clearly show that cracks can have a detrimental effect on LMSSB and we suggest focusing on strategies to improve the fracture toughness of thiophosphate electrolytes in order to suppress lithium filament growth.

Automatic pore structure analysis in organic-rich shale using FIB-SEM and attention U-Net

The pore structure is an important factor in determining the productivity of shale, which can help us make better operational decisions. Shale formations have an extremely complex pore structure with a wide range of pore sizes, shapes, orientations, and connectivity. Advanced imaging techniques, such as focused ion beam scanning electron microscopes (FIB-SEM), contribute significantly to the analysis and understanding of complex pore networks in shale, but they are time-consuming. Developing new methods and techniques to capture the spatial distribution and connectivity of pores at various scales is essential to understanding pore structure and its impact on fluid flow. This study aims to analyze the pore characteristics of shale reservoirs by using artificial intelligence (AI) and FIB-SEM. We applied a novel attention gate (AG) model to FIB-SEM images that automatically learns to focus on target structures of varying pores’ shape and size. AG can be fully incorporated into the U-Net model with minimal computational impact. The AG improved prediction accuracy by making the U-Net model more sensitive to essential features in the input images and achieved a precision of 97%, recall of 71%, and F1 score of 81% at a confidence threshold of 1. Experimental results show that Attention U-Net outperformed in predicting the pore structures in shale samples from Longmaxi Formation, Qingshankou Formation, Cambrian Niutitang Formation, Yanchang shale oil, and Bakken shale while obtaining optimal performance without requiring multiple convolutional neural network (CNN) models. Additionally, Attention U-Net addresses some of the limitations of the Edge-Threshold Automatic Processing (ETAP) method, including the limited ability to obtain a complete description of the pore space as well as the low segmentation accuracy and sensitivity. The proposed workflow offers a promising solution for optimizing the automatic processing of microscopic images for pores and microfractures identification. Researchers and industry professionals can improve their understanding of shale properties and applications in various fields by maximizing the benefits of our workflow.

Analysis of the Impact of Electrochemical Properties of Copper-Doped Electrode Membranes on the Output Force of Biomimetic Artificial Muscles.

In this study, a biomimetic artificial muscle electroactive actuator was fabricated using environmentally friendly sodium alginate extract. Ultrasonic agitation was employed to embed ultrafine copper powder within a mesh-like structure formed by multi-walled carbon nanotubes (MWCNTs), aimed at reducing the internal resistance of the composite electrode membrane and enhancing its output force performance. Focused gallium ion beam-scanning electron microscopy observations, energy-dispersive X-ray spectroscopy (EDS) analysis, and surface morphology imaging confirmed the successful incorporation of the ultrafine copper powder into the MWCNT network. Additionally, we designed and constructed an output force measurement apparatus to assess the output performance of biomimetic artificial muscles (BMAMs) doped with varying quantities of ultrafine copper powder. Electrochemical testing results demonstrated that the artificial muscles exhibited optimal performance when doped with a mass of 1.5 g, yielding a maximum output force of 6.96 mN, an output force density of 30.64 mN/g, and a peak average rate of 0.059 mN/s. These values represented improvements of 224%, 189%, and 222% compared to the electrode membrane without the addition of ultrafine copper powder, respectively.

The influence of microstructure on corrosion mechanism for brazed sheet of AA4045/AA3003mod/AA4045 laminated composites at different depths

The depth profiling of the element content and precipitation phase distribution of the AA4045/AA3003mod (Al-1.5Mn-0.35Cu alloy)/AA4045 brazed sheets were investigated by optical microscope observation, electron probe microanalysis (EPMA), focused ion beam-scanning transmission electron microscopy (FIB-STEM). The electrochemical test and sea water acetic acid test (SWAAT) were performed to obtain the evolution of electrochemical responses and corrosion forms of brazed sheet. EPMA results showed that a diffusion layer with the thickness of approximately 50 μm existed between the clad layer and core layer, where the Cu diffused from the core layer and Si diffused from the clad layer. It was found that brazing led to a significant low elements solid solution area at the end of the Si diffusion path, where the open circuit potential was lower by 25 mV comparing to the unaffected region. Thus the diffusion zone can provide effective cathodic protection to the unaffected region as sacrificial anode by the potential gradient. The SWAAT analysis revealed the corrosion mechanism of the residual cladding was pitting and intergranular corrosion. This area with high density of intermetallic compounds and Si particles increased sensitivity to localized attacks. These results demonstrated the successful application of the FIB-STEM system in illustrating the electrochemical responses and corrosion propagation by an accurate in-depth characterization of intermetallic particles and the matrix solid solution.

Bone Hierarchical Structure: Heterogeneity and Uniformity

AbstractBone has a complex hierarchical structure with structural integration from nm to cm. The understanding of bone structure is developing rapidly due to improvements in available methodologies that allow unravelling structures across several length scales. These methods include advances in electron microscopy, in particular, focused ion beam scanning electron microscopy (FIB‐SEM), confocal laser scanning microscopy techniques, X‐ray imaging, X‐ray diffraction tomography (XRD‐CT), and tensor tomography (small angle X‐ray scattering tensor tomgraphy, SAXS‐TT and wide angle X‐ray scattering tensor tomgraphy, WAXS‐TT). Special emphasis is placed on the latter X‐ray techniques that are emerging into powerful tools. Through a review of selected recent results on the structure of the bone matrix as well as the lacuno‐canalicular network housing the osteocyte cells of bone, it is proposed that bone is more heterogeneous than typically described and that local variation in composition and crystallography may play a significant role in bone biology in health and disease.

Use of Heat-killed Aspergillus ochraceus NRRL 3174 Discs as Biosorbent for petroleum Removal

The purpose of this work was to evaluate the petroleum sorption capacity of heat-killed fungal discs obtained from Aspergillus ochraceus strain. Effect of various parameters such as biosorbent dose (0.5g-2.5g/100mL), petroleum concentration (0.5-5%), pH (4.0-8.0), contact time (1-12h) and re-usability of biosorbent (1-6) were investigated. Accordingly, the highest biosorption capacity was obtained with 1% petroleum concentration, 1.5 g/100mL heat-killed fungal discs, 10h contact time at pH: 5.0 and room temperature. Additionally, each disc was able to actively use for at least 6 more cycles in biosorption experiments. The specific removal rate was calculated as 0.114 day−1, the rate constant and half-life period were also 1.609 day-1, t1/2 = 0.431, respectively. The kinetic study was described by the pseudo-second order model and the equilibrium modeling was found to be well fitted with Langmuir isotherm. The biosorbent(s) were characterized by Focused Ion Beam Scanning Electron Microscopy (FIB-SEM). Over 80% removal of long-chain n-alkanes by the heat-killed fungal discs was confirmed by GC-MS analysis. Since there has been no similar study investigating the sorption of petroleum with heat-killed Aspergillus ochraceous discs, this novel bio-based sorbent with its low cost, environmentally friendly and easy-to-apply properties can be used in advanced biosorption studies.

Revealing the aging process of solid electrolyte interphase on SiOx anode

As one of the most promising alternatives to graphite negative electrodes, silicon oxide (SiOx) has been hindered by its fast capacity fading. Solid electrolyte interphase (SEI) aging on silicon SiOx has been recognized as the most critical yet least understood facet. Herein, leveraging 3D focused ion beam-scanning electron microscopy (FIB-SEM) tomographic imaging, we reveal an exceptionally characteristic SEI microstructure with an incompact inner region and a dense outer region, which overturns the prevailing belief that SEIs are homogeneous structure and reveals the SEI evolution process. Through combining nanoprobe and electron energy loss spectroscopy (EELS), it is also discovered that the electronic conductivity of thick SEI relies on the percolation network within composed of conductive agents (e.g., carbon black particles), which are embedded into the SEI upon its growth. Therefore, the free growth of SEI will gradually attenuate this electron percolation network, thereby causing capacity decay of SiOx. Based on these findings, a proof-of-concept strategy is adopted to mechanically restrict the SEI growth via applying a confining layer on top of the electrode. Through shedding light on the fundamental understanding of SEI aging for SiOx anodes, this work could potentially inspire viable improving strategies in the future.

3D architecture and a bicellular mechanism of touch detection in mechanosensory corpuscle.

Mechanosensory corpuscles detect transient touch and vibration in the skin of vertebrates, enabling precise sensation of the physical environment. The corpuscle contains a mechanoreceptor afferent surrounded by lamellar cells (LCs), but corpuscular ultrastructure and the role of LCs in touch detection are unknown. We report the three-dimensional architecture of the avian Meissner (Grandry) corpuscle acquired using enhanced focused ion beam scanning electron microscopy and machine learning-based segmentation. The corpuscle comprises a stack of LCs interdigitated with terminal endings from two afferents. Simultaneous electrophysiological recordings from both cell types revealed that mechanosensitive LCs use calcium influx to trigger action potentials in the afferent and thus serve as physiological touch sensors in the skin. The elaborate architecture and bicellular sensory mechanism in the corpuscles, which comprises the afferents and LCs, create the capacity for nuanced encoding of the submodalities of touch.

Porosity evolution in proton irradiated microfine-grained POCO graphite

This work investigated the porosity evolution of POCO ZXF-5Q graphite that has been irradiated by 340 kW, 120 GeV protons inside NT02 target system in Fermilab's NuMI beamline. This POCO graphite has undergone direct bulk dimensional swelling at low dose irradiation and its local microstructural change is still not well-understood during this process. In this work, the (sub-) micrometre scale porosity from six locations across proton beam fluence and temperature gradients have been studied using focused ion beam-scanning electron microscopy (FIB-SEM) tomography. A deep learning-based tomographic image segmentation technique has been established and implemented for porosity segmentation and quantification. It has been found that there is a decrease in the total volumetric percentage of the porosity at proton beam centre (∼ 8 – 8.4 vol.%), by comparing to un-irradiated POCO (∼ 12 – 13 vol.%) and to beam 2σ and 5σ radii (∼ 12 vol.%). This decrease in porosity volume percentage was found to be caused by the reduction in pores with volumes > 0.1 μm3 induced by material bulk dimensional swelling at proton beam centre area. The porosity reduction in relation to dimensional change and irradiation creep was discussed among with other contributing factors, and further investigations through well-controlled irradiation experiment are still needed.