Conventional Scanning Electron Microscopy Research Articles

A soft touch with electron beams: Digging out structural information of nanomaterials with advanced scanning low energy electron microscopy coupled with deep learning

Nanostructured materials continue to find applications in various electronic and sensing devices, chromatography, separations, drug delivery, renewable energy, and catalysis. While major advancements on the synthesis and characterization of these materials have already been made, getting information about their structures at sub-nanometer resolution remains challenging. It is also unfortunate to find that many emerging or already available powerful analytical methods take time to be fully adopted for characterization of various nanomaterials. The scanning low energy electron microscopy (SLEEM) is a good example to this. In this report, we show how clearer structural and surface information at nanoscale can be obtained by SLEEM, coupled with deep learning. The method is demonstrated using Au nanoparticles-loaded mesoporous silica as a model system. Moreover, unlike conventional scanning electron microscopy (SEM), SLEEM does not require the samples to be coated with conductive films for analysis; thus, not only it is convenient to use but it also does not give artifacts. The results further reveal that SLEEM and deep learning can serve as great tools to analyze materials at nanoscale well. The biggest advantage of the presented method is its availability, as most modern SEMs are able to operate at low energies and deep learning methods are already being widely used in many fields.

Non‐Destructive Tomographic Nanoscale Imaging of Ferroelectric Domain Walls

AbstractExtraordinary physical properties arise at polar interfaces in oxide materials, including the emergence of 2D electron gases, sheet‐superconductivity, and multiferroicity. A special type of polar interface is ferroelectric domain walls, where electronic reconstruction phenomena can be driven by bound charges. Great progress has been achieved in the characterization of such domain walls and, over the last decade, their potential for next‐generation nanotechnology has become clear. Established tomography techniques, however, are either destructive or offer insufficient spatial resolution, creating a pressing demand for 3D imaging compatible with future fabrication processes. Here, non‐destructive tomographic imaging of ferroelectric domain walls is demonstrated using secondary electrons. Utilizing conventional scanning electron microscopy (SEM), the position, orientation, and charge state of hidden domain walls are reconstructed at distances up to several hundreds of nanometers away from the surface. A mathematical model is derived that links the SEM intensity variations at the surface to the local domain wall properties, enabling non‐destructive tomography with good noise tolerance on the timescale of seconds. The SEM‐based approach facilitates high‐throughput screening of materials with functional domain walls and domain‐wall‐based devices, which is essential for monitoring during the production of device architectures and quality control in real‐time.

High‐resolution strain mapping in a thermionic LaB6 scanning electron microscope

AbstractThe high source stability and brightness of field emission gun equipped scanning electron microscopes (SEM) makes them ideal for high‐resolution digital image correlation (HRDIC). However, their high initial capital cost can be prohibitive for research organisations and groups. Conventional thermionic SEMs using either a tungsten hairpin or LaB6 filament are far more widespread due to their lower cost. Whilst it is understood that overall performance and ultimate resolution are lower than field emission SEMs, we propose that there is no fundamental reason why these instruments are unsuitable for HRDIC. We investigate the use of a LaB6 SEM as a viable tool for HRDIC. We detail the subtleties of performing HRDIC using a LaB6 thermionic source SEM, providing technical recommendations for best practices in using these instruments for strain mapping. The effects of instrument parameters on strain measurement noise are examined, with a focus on parameters of key relevance to in situ and ex situ mechanical testing. Errors in focus and image pixel size are found to be the primary contributors to the strain noise floor values, with stage accuracy being of secondary importance. We present a case study in oxygen‐free high‐conductivity copper, OFHC‐Cu, which is used in the designs of nuclear fusion components as a heat sink interlayer. Heterogeneous strain patterns are observed in this material, with high levels of strain localisation at grain boundaries. Active slip systems are identified using the relative displacement ratio method, demonstrating the quality of these data and the suitability of LaB6 instruments for HRDIC strain mapping, achieving performance approaching that expected of a field emission SEM.

Confocal Scanning Laser Microscopic (CSLM) characterization of volcanic rocks

Optical and microscopical analyses of surficial and internal textures are key elements of volcanic rock characterization. Yet conventional methods for textural analyses often pose challenges and difficulties in terms of sample preparation and/or time and resources consumption, beside their inherent limitations. Here, we performed Confocal Scanning Laser Microscopy (CSLM) to characterize vesicles in volcanic rocks and their experimental analogs and to compare the results to those of conventional Scanning Electron Microscopy (SEM) investigations. Further, we discuss surface roughness analysis as a possible parameter to analyze different vesicle textures. CSLM obviates the need for sample impregnation (using fluorescent resin) and polishing, it enables fast and automated analyses of samples surfaces at lower costs than conventional techniques. Calculated vesicle size distributions and vesicle number densities of the analyzed samples were compared in order to determine the potential and precision of volume and area information directly obtainable from CSLM measurements in 3D. Monodisperse samples with homogeneous vesicle texture show remarkable similarities in vesicle size and volume distribution, when compared directly with the two methods. For all experimental and natural samples, roughly half of them show VNDs and porosity show the same range, which can be explained by vesicle coalescence. After de-coalescing the images of CSLM for FOAMS analysis, these differences vanish almost entirely for most of the sample types. Combining our textural data and our numerical modeling, we present a universal scaling model to link surface roughness with vesicle number density, porosity, and polydispersivity. These results indicate that CSLM can be a powerful tool to investigate vesicle structures from the millimetric to micrometric scale. The resulting data is both quantitatively and qualitatively equivalent to SEM-derived data for a variety of volcanic rock types. This, combined with the simple sample preparation and handling make CSLM a valid alternative to SEM investigations to characterize vesicles, particles, and any sort of rock property that reflects on topography. Surface roughness can become a new key parameter to interpret porous networks in volcanic rocks and can be applied to other geological fields.

An enhanced visualization image acquisition method for samples with poor conductivity under a conventional scanning electron microscope.

The low-vacuum and low-accelerating-voltage modes are the most simple and practical ways to directly analyze poorly conductive samples in conventional scanning electron microscopy (SEM). However, structural feature information may disappear or be obscured in these imaging modes, making it challenging to identify and analyze some local microstructures of poorly conductive samples. To overcome this challenge, an enhanced visualization image acquisition method for samples with poor conductivity is proposed based on the image registration and multi-sensor fusion technology. Experiments demonstrate that the proposed method can effectively obtain enhanced visualization images containing clearer terrain information than the SEM source images, thereby providing new references for measuring and analyzing microstructures.

Deep learning image segmentation for the reliable porosity measurement of high-capacity Ni-based oxide cathode secondary particles

The optimization of geometrical pore control in high-capacity Ni-based cathode materials is required to enhance the cyclic performance of lithium-ion batteries. Enhanced porosity improves lithium-ion mobility by increasing the electrode–electrolyte contact area and reducing the number of ion diffusion pathways. However, excessive porosity can diminish capacity, thus necessitating optimizing pore distribution to compromise the trade-off relation. Accordingly, a statistically meaningful porosity estimation of electrode materials is required to engineer the local pore distribution inside the electrode particles. Conventional scanning electron microscopy (SEM) image-based porosity measurement can be used for this purpose. However, it is labor-intensive and subjected to human bias for low-contrast pore images, thereby potentially lowering measurement accuracy. To mitigate these difficulties, we propose an automated image segmentation method for the reliable porosity measurement of cathode materials using deep convolutional neural networks specifically trained for the analysis of porous cathode materials. Combined with the preprocessed SEM image datasets, the model trained for 100 epochs exhibits an accuracy of > 97% for feature segmentation with regard to pore detection on the input datasets. This automated method considerably reduces manual effort and human bias related to the digitization of pore features in serial section SEM image datasets used in 3D electron tomography.Graphical abstract

Supergene phases from ferruginous duricrusts: non-destructive microsampling and mineralogy prior to (U–Th) ∕ He geochronological analysis

Abstract. Interpreting the ages of supergene mineralogical phases in laterite is complex because they consist of polycrystalline mixtures of different phases at the microscopic scale that could be crystalized at different epochs. Among the geochronometers, the (U-Th)/He method on hematite and goethite is more often used, but ages can be difficult to interpret due to phases mixing. To resolve this issue, this study proposes a methodology for performing detailed mineralogical analysis of hematite and goethite single grains prior to their dating using the (U-Th)/He method. Strictly non-destructive mineralogy of single grains is not achievable by classical tools, such as conventional powder XRD (X-ray diffraction; requiring at least some milligrams of powder) or SEM (scanning electron microscopy; that can contaminate the grain by coating or fixing). Therefore, we performed X-ray diffraction patterns of single grains using high-flux X-ray beams from both a rotating anode (XRD_rotat) laboratory diffractometer and a synchrotron beamline (XRD_synch) and compared the results in order to design a method based on XRD_rotat only. For this purpose, two samples from the pisolitic facies of a Brazilian ferruginous duricrust (Alto Paranaíba region, Minas Gerais State, Brazil) were chosen because they presented a usual heterogeneity. Rietveld refinements of the XRD patterns obtained from both XRD_rotat and XRD_synch yielded similar results for the weight percentage ratio of the main phases and mean coherent domain sizes and less similar results for Al substitution rates, thus validating the XRD_rotat approach. No beam damage was observed when increasing X-ray exposure time, neither on XRD patterns nor on (U-Th)/He ages. Hence, sub-millimeter, undisturbed grains can be used to analyze the mineralogy of ferruginous duricrusts by XRD_rotat with a short exposure, and the same grains can subsequently be dated by (U-Th)/He geochronology analysis. The (U-Th)/He dating of pisolitic core and cortex grains also provided meaningful ages: they revealed two evolution phases of the ferruginous duricrust, which occurred at or before the Oligocene for the pisolitic core and middle Miocene for the pisolitic cortex, agreeing with the previous model for the development of pisolites. The mineralogy of single grains selected for dating is helpful for discussing the crystallization ages, and the high-flux XRD approach may be applied to other supergene mineral parageneses used for absolute dating.

Robust Local Thickness Estimation of Sub-Micrometer Specimen by 4D-STEM.

A quantitative four-dimensional scanning transmission electron microscopy (4D-STEM) imaging technique (q4STEM) for local thickness estimation across amorphous specimen such as obtained by focused ion beam (FIB)-milling of lamellae for (cryo-)TEM analysis is presented. This study is based on measuring spatially resolved diffraction patterns to obtain the angular distribution of electron scattering, or the ratio of integrated virtual dark and bright field STEM signals, and their quantitative evaluation using Monte Carlo simulations. The method is independent of signal intensity calibrations and only requires knowledge of the detector geometry, which is invariant for a given instrument. This study demonstrates that the method yields robust thickness estimates for sub-micrometer amorphous specimen using both direct detection and light conversion 2D-STEM detectors in a coincident FIB-SEM and a conventional SEM. Due to its facile implementation and minimal dose reauirements, it is anticipated that this method will find applications for in situ thickness monitoring during lamella fabrication of beam-sensitive materials.

Mineral Assemblage of Olivine-Hosted Melt Inclusions in a Mantle Xenolith from the V. Grib Kimberlite Pipe: Direct Evidence for the Presence of an Alkali-Rich Carbonate Melt in the Mantle Beneath the Baltic Super-Craton

This report deals with the first mineralogical examination of secondary crystallized melt inclusions (CMIs) in healed cracks within olivine in a mantle peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province). In contrast to micro/nano-inclusions in diamonds, the studied CMIs are quite large (up to 50 µm), so that the mineral composition of the CMIs can be determined via conventional analytical approaches, e.g., Raman spectroscopy and scanning electron microscopy. Garnet peridotite is a coarse-grained mantle rock that equilibrates at 3.3 GPa and 750 °C (corresponding to a depth of ~100 km). The CMIs are therefore tiny snapshots of melt that existed in the shallow lithospheric mantle and were entrapped in olivine. In total, nineteen mineral species were identified among the daughter magmatic minerals of the CMIs. Various Na-K-Ca-, Na-Ca-, Na-Mg-, Ca-Mg-, Mg- and Ca-carbonates; Na-Mg-carbonates with the additional anions Cl−, SO42− and PO43−; alkali sulfates; chlorides; phosphates; sulfides; oxides; and silicates were established. Within the mineral assemblage, carbonates were predominant, with their abundance being more than 62 vol.%. The CMIs contained twelve alkali-rich minerals; nine of them were Na-bearing and showed bulk molar (Na + K)/Ca ≥ 1. The CMIs’ parental melt was an alkali-rich carbonate liquid that contained low amounts of SiO2 (≤9.6 wt%) and H2O (≤2.6 wt%). According to our estimates, the time of complete equilibration between olivine within the healed cracks and host olivine in the mantle at the calculated P-T parameters for the studied xenolith should be no more than several years. Based on this geologically short time span, a genetic link between the studied CMIs and the magmatism that formed the V. Grib kimberlite pipe is suggested.

Rock Physical Properties of Longmaxi Shale Gas Formation in South Sichuan Province, China

Deep shale gas (burial depth > 3500 m) in the Longmaxi Formation of southern Sichuan Province will be the primary target for exploration and development in China for a relatively long period. However, the lack of a physical basis for the “sweet-spots” seismic and well-logging prediction is caused by uncertainty in the rock physical properties of deep shale gas in the research area. Acoustic and hardness measurements were performed on shale samples from a deep layer of the Longmaxi Formation in southern Sichuan. Microtextural characteristics of the shale samples were also analyzed by conventional optical microscopy and scanning electron microscopy. Based on these measurements, the rock physical properties of the shale samples and control factors are discussed. It is shown that the deep shale samples have similar properties to the shallow shale in mineral composition, microtexture, and pore type. However, the organic pore in deep shale samples is relatively undeveloped, while the dissolved pores are more developed. For high-quality shale samples (total organic content > 2%), crystal quartz of biological origin forms the framework of rock samples, resulting in effective dynamic and static properties, reflecting the elastic behavior of rigid quartz aggregates. For organic-lean samples (total organic content < 2%), orientated detrital clay particles take the role of load-bearing grains. Therefore, these shale samples’ overall rock physical properties are mainly controlled by the elastic properties of “soft” clay. The load-bearing grain variation from organic-rich shale samples to organic-lean samples results in an overturned “V”-type change in terms of velocity versus content. Organic-rich shale samples also show an apparent low Poisson’s ratio. Organic-rich shale has a slight velocity–porosity trend, while organic-lean shale shows a significant velocity–porosity trend. In addition, due to the difference in rock microtexture between organic-rich and organic-lean shale, these two kinds of reservoir rocks can be discriminated in cross plots of P-wave impedance versus Poisson’s ratio and Young’s modulus versus Poisson’s ratio. Change in hardness also reflects the control of microtexture, and shale samples with biological-origin quartz as load-bearing grains show higher hardness and brittleness. However, the variation in quartz content has less of an impact on hardness and brittleness in shale samples with clay as the load-bearing grain. Our results provide an experimental basis for the geophysical identification and prediction of deep shale gas layers.

Pluronic-123 Assisted Synthesis of Cobalt Vanadate Microparticles (µ-CoV MPs) for Durable Electrochemical Oxygen Evolution Reaction in Seawater and Connate Water

Exploring different catalytic material paradigms could drive the search for the best oxygen evolution reaction (OER) catalyst to achieve industrially-feasible hydrogen fuel from water. Cobalt-based materials are considered good choices in this regard. Herein, we synthesized Pluronic-123 (P-123)-stabilized, unique, rough, globular-shaped cobalt vanadate microparticles (µ-CoV MPs) using an ultrasonic-assisted solvothermal method. The as-synthesized µ-CoV MPs were subjected to high-temperature annealing to improve the crystallinity and the surface polymer moieties were pyrolyzed. Conventional SEM, XRD, FTIR, and BET analyses evaluated the morphological and structural features. The temperature-controlled crystalline phase led to extensive OER performance in SW electrolytes. The OER onset potential (VOER) was observed at 1.557 V@10 mA/cm2 in seawater (SW) for µ-CoV MPs annealed at 400 °C compared to the VOER of 1.632 V of non-annealed µ-CoV MPs. The current density showed a steep increase beyond 1.557 V, confirming the excellent electrokinetics OER behavior of the µ-CoV MPs-deposited electrode. The chronoamperometric (I–t) OER stability comparison in SW and connate water (CW) electrolytes indicated only a <20% initial current density decrease after 8 h in the case of the SW electrolyte. However, the CW electrolyte posed serious challenges to the electrode and activity was completely lost after <2 h. The electrolytic comparison indicated that SW is highly suitable for µ-CoV MPs electrodes.

Enhancing the precision of 3D sidewall measurements of photoresist using atomic force microscopy with a tip-tilting technique

A key issue associated with advanced lithography techniques for semiconductor-device manufacturing is the reduction in the sidewall roughness of photoresist line patterns, known as line-edge roughness (LER). We have developed a technique for measuring the sidewall of the resist pattern using atomic force microscopy (AFM) that enables three-dimensional (3D), high-resolution, low-noise, and nondestructive measurements. Conventional LER measurement technology using scanning electron microscopy (SEM) causes shrinkage of the resist pattern due to electron-beam (EB) exposure, whereas our new AFM technique can in principle avoid EB-induced shrinkage. This AFM technology is capable of 3D measurements because it employs a tip-tilting mechanism that enables the sharp AFM tip to scan the vertical sidewalls, which is difficult for a conventional AFM technique. In addition, laser interferometers are equipped for the measurement of the AFM tip displacement, which yields high-resolution, high-accuracy, and low-noise results. This technology overcomes issues such as low resolution, noise, and destructive measurements that afflict conventional SEM measurements. In addition, it enables observations and quantitative analyses of the 3D sidewall roughness. For example, in the present experiment, we observed that grain shapes (several tens of nm in size) were formed randomly on the resist sidewall and that there were almost no footing shapes. By analyzing the sidewall profiles with a height resolution of 1 nm, we obtain the roughness (self-affine fractal) parameters at each height. This AFM-based resist sidewall measurement technique can, thus, provide important insights into resist patterning and related process technologies for next-generation semiconductor-device manufacturing.

Decellularization of precision-cut kidney slices—application of physical and chemical methods

The extracellular matrix (ECM) obtained by decellularization provides scaffolds with the natural complex architecture and biochemical composition of the target organ. Whole kidney decellularization by perfusion uses the vasculature to remove cells leaving a scaffold that can be recellularized with patient-specific cells. However, decellularization and recellularization are highly complex processes that require intensive optimization of various parameters. In pursuit of this, a huge number of animals must be sacrificed. Therefore, we used precision-cut kidney slices (PCKS) as a source of natural scaffolds, which were decellularized by immersion in chemical reagents allowing the examination of more parameters with less animals. However, chemical reagents have a damaging effect on the structure and components of the ECM. Therefore, this study aimed at investigating the effects of physical treatment methods on the effectiveness of PCKS decellularization by immersion in chemical reagents (CHEM). PCKS were treated physically before or during immersion in chemicals (CHEM) with high hydrostatic pressure (HHP), freezing–thawing cycles (FTC) or in an ultrasonic bath system (UBS). Biochemical and DNA quantification as well as structural evaluation with conventional histology and scanning electron microscopy (SEM) were performed. Compared to decellularization by CHEM alone, FTC treatment prior to CHEM was the most effective in reducing DNA while also preserving glycosaminoglycan (GAG) content. Moreover, while UBS resulted in a comparable reduction of DNA, it was the least effective in retaining GAGs. In contrast, despite the pretreatment with HHP with pressures up to 200 MPa, it was the least effective in DNA removal. Histological scoring showed that HHP scaffolds received the best score followed by UBS, FTC and CHEM scaffolds. However further analysis with SEM demonstrated a higher deterioration of the ultrastructure in UBS scaffolds. Altogether, pretreatment with FTC prior to CHEM resulted in a better balance between DNA removal and structural preservation.

Study of Phase Composition in TiFe + 4 wt.% Zr Alloys by Scanning Photoemission Microscopy

The alloy TiFe is widely used as hydrogen storage material. However, the first hydrogenation is difficult. It was found that the addition of zirconium greatly improves the kinetic of first hydrogenation, but the mechanism is not well understood. In this paper, we report the use of scanning photoemission microscopy to investigate the composition and chemical state of the various phases present in this alloy and how they change upon hydrogenation/dehydrogenation. We found the presence of different oxide phases that were not seen by conventional SEM investigation. The nature of these oxides phases seems to change upon hydrogenation/dehydrogenation cycle. This indicates that oxide phases may play a more significant role in the hydrogen absorption as what was previously believed.

Palaeoebiological implications of cuticle morphology, microstructure and formation in modern and fossil Daira (Decapoda, Brachyura, Dairoidea)

The origin and function of peculiar mushroom-shaped cuticular structures in some decapod crustaceans remains unknown. This ornamentation has appeared several times in widely disparate clades (in podotreme and heterotreme crabs, and pagurids). These structures are analysed in the modern genus Daira and compared with fossil material from the Eocene of Huesca and the Miocene of Alicante and Mallorca. A morphological and petrographic study is carried out using conventional microscopy and Scanning Electron Microscopy to understand the microstructure in modern and fossil representatives. This provides a clear view of the mushroom-like structures that cover the carapace of Daira and the distribution of the different layers of the exoskeleton. The results reveal a complex morphology, which involves all layers of the cuticle, with changes in the thickness of the exocuticle in different areas, and the presence of conical structures that especially affect the outer layers. These convolutions form a network of channels connected to the outside by pores. Finally, possible anti-predatory functions of these complex structures are proposed.

Outreaching with the TEM

Thin-section transmission electron microscopy (TEM) of cells and tissues is not the technique that comes to mind when electron microscopy (EM) enthusiasts itch for outreach. Conventional scanning EM is far easier to love, and easier to do, but does that mean looking at cells down the TEM cannot inspire the public?

The chondro-osseous junction of articular cartilage

In the synovial joints the transition between the soft articular cartilage and the subchondral bone is mediated by a layer of calcified cartilage of structural and mechanical characteristics closer to those of bone. This layer, buried in the depth of articular cartilage, is not directly accessible and is mostly visualized in histological sections of decalcified tissue, where it appears as a darker strip in contact with the subchondral bone. In this study conventional histology and scanning electron microscopy (SEM) with secondary electron imaging (SE) or backscattered electron imaging (BSE) were used to discriminate the calcified and the uncalcified cartilage in high resolution on native, untreated tissue as well as in deproteinated or demineralized tissue. This approach evidenced a high heterogeneity of the calcified layer of articular cartilage. High resolution pictures revealed that the mineralization process originates by progressive accretion and confluence of individual, small mineral clusters, in a very different way from other hard tissues such as bone, dentin and mineralized tendons. Finally, selective removal of the soft matrix by thermal treatment allowed for the first time a face-on, unrestricted 3D view of the mineralization front.

Scanning electron microscope imaging by selective e-beaming using photoelectron beams from semiconductor photocathodes

Pulsed electron beams from a photocathode using an InGaN semiconductor have brought selectively scanning technology to scanning electron microscopes, where the electron beam irradiation intensity and area can be arbitrarily selected within the field of view in SEM images. The p-type InGaN semiconductor crystals grown in the metalorganic chemical vapor deposition equipment were used as the photocathode material for the electron beam source after the surface was activated to a negative electron affinity state in the electron gun under ultrahigh vacuum. The InGaN semiconductor photocathode produced a pulsed electron beam with a rise and fall time of 3 ns, consistent with the time structure of the irradiated pulsed laser used for the optical excitation of electrons. The InGaN photocathode-based electron gun achieved a total beam operation time of 1300 h at 15 μA beam current with a downtime rate of 4% and a current stability of 0.033% after 23 cycles of surface activation and continuous beam operation. The InGaN photocathode-based electron gun has been installed in the conventional scanning electron microscope by replacing the original field emission gun. SEM imaging was performed by selective electron beaming, in which the scanning signal of the SEM system was synchronized with the laser for photocathode excitation to irradiate arbitrary regions in the SEM image at arbitrary intensity. The accuracy of the selection of regions in the SEM image by the selective electron beam was pixel by pixel at the TV scan speed (80 ns/pix, 25 frame/s) of the SEM.

Soil crusting: New insight from synchrotron 2D micro X-ray diffraction mapping of clay-particle orientation and mineralogy

Our understanding of soil crusting and its detrimental consequences is mainly based on the analysis of morphological changes occurring at the soil surface. Such changes are usually assessed at spatial scales ranging from a few millimeters to that of the field. The inner-reorganisation within the topsoil during soil crusting primarily involves the redistribution of clay particles. Their mineralogy and arrangement remain however delicate to determine by the sole use of microscope observations. To overcome these limitations, we developed an innovative methodology based on synchrotron 2D micro X-ray diffraction (2D-µXRD) to map relevant parameters related to the organisation of all types of soil clay minerals, i.e. relative diffracted intensities, degree of preferential orientation, mean deviation angle from the surface. Our methodological strategy was first validated on a laboratory-made model sample, composed of various pure clay phases with clear preferential orientations. Then, a vertical section of soil crust from long-term bare fallow (LTBF) experiment of the France's National Research Institute for Agriculture, Food and Environment (INRAE, Versailles, France) was studied. Micromorphological features of the soil crust were first described by using conventional scanning electron microscopy. Synchrotron 2D-µXRD analyses were then successfully applied on the same region of interest. The in-depth analysis provided by the synchrotron 2D-µXRD approach revealed the presence of clay microlayers that were not observed on SEM images. Additionally, clay mineralogy as well as preferred clay-particle orientation and overall alignment highlighted specific quantitative structural signatures. These signatures involved the discrimination between clay microlayers associated to the settling of clay particles in microdepressions and clayey microaggregates resulting from transportation of pre-existing soil crusts. This new technique has led to re-interpretation of the deposition mechanisms in the natural soil investigated here and opens wide perspectives for in-depth detailed characterization of clay mineralogy in soil crusts.

Morphological classification and three-dimensional pore structure reconstruction of shale oil reservoirs: A case from the second member of Paleogene Kongdian Formation in the Cangdong Sag, Bohai Bay Basin, East China

This study combines large volume three-dimensional reconstruction via focused ion beam scanning electron microscopy (FIB-SEM) with conventional scanning electron microscope (SEM) observation, automatic mineral identification and characterization system (AMICS) and large-area splicing of SEM images to characterize and classify the microscopic storage space distribution patterns and 3D pore structures of shales in the second member of the Paleogene Kongdian Formation (Kong 2) in the Cangdong Sag of the Bohai Bay Basin. It is shown that: (1) The Kong 2 Member can be divided into seven types according to the distribution patterns of reservoir spaces: felsic shale with intergranular micron pores, felsic shale with intergranular fissures, felsic shale with intergranular pores, hybrid shale with intergranular pores and fissures, hybrid shale with intergranular pores, clay-bearing dolomitic shale with intergranular pores, and clay-free dolomitic shale with intergranular pores. (2) The reservoir of the intergranular fracture type has better storage capacity than that of intergranular pore type. For reservoirs with storage space of intergranular pore type, the dolomitic shale reservoir has the best storage capacity, the hybrid shale comes second, followed by the felsic shale. (3) The felsic shale with intergranular fissures has the best storage capacity and percolation structure, making it the first target in shale oil exploration. (4) The large volume FIB-SEM 3D reconstruction method is able to characterize a large shale volume while maintaining relatively high spatial resolution, and has been demonstrated an effective method in characterizing the 3D storage space in strongly heterogeneous continental shales.