Subsurface Material Research Articles

Photothermal AFM-IR Depth Sensitivity: An Original Pathway to Tomographic Reconstruction.

Photothermal atomic force microscopy-infrared (AFM-IR) enables label-free chemical imaging and spectroscopy with nanometer-scale spatial resolution through the integration of atomic force microscopy (AFM) and infrared radiation. The capability for subsurface and three-dimensional (3D) tomographic material analysis remains, however, largely unexplored. Here, we establish a simple and robust empirical relationship between the probing depth and laser repetition rate for three important modes of AFM-IR operation: resonance-enhanced, tapping, and surface-sensitive AFM-IR. Using this empirical relationship, we demonstrate, based on the example of resonance-enhanced operation, how photothermal AFM-IR of thin surface/subsurface layers of polystyrene domains in the poly(methyl methacrylate) matrix can result in 3D representations revealing the size and thickness of small polystyrene domains in the poly(methyl methacrylate) matrix with nanometer-scale resolution. Experimental findings are confirmed by analytical models.

Multichannel Analysis of Surface Waves based on Common Virtual Source Gathers of Seismic Ambient Noise Cross-Correlations: A Case Study at an Earth Dam in Brazil

The S-wave velocity (Vs) is a valuable parameter for assessing the mechanical properties of subsurface materials for geotechnical purposes. Seismic surface wave methods have become prominent for estimating near-surface Vs models. Researchers have proposed methods based on passive seismic signals as efficient alternatives to enhance depth of investigation, lateral resolution and reduce field effort. This study presents the Multichannel Analysis of Surface Waves (MASW) utilizing Common Virtual Source Gathers (CVSGs) derived from seismic ambient noise cross-correlations, based on Ambient Noise Seismic Interferometry concepts. The method is applied to passive data acquired with an array of receivers at the Paranoá earth dam in Brasília, Brazil, to construct a pseudo-2D Vs image of the massif for interpretation. Our findings showcase the adopted processing flow and combination of methods as an effective approach for near-surface Vs estimation, demonstrating its usability also for large earth dam embankments.

Unraveling the Subsurface Damage and Material Removal Mechanism of Multi-Principal-Element Alloy FeCrNi Coatings During the Scratching Process

Multi-principal-element alloys (MPEAs) exhibit superior strength and good ductility. However, tribological properties of FeCrNi MPEAs remain unknown at nanoscale and complex environments. Here, we investigate the effects of scratching speed, depth, and temperature on microstructural and tribological characteristics of FeCrNi using molecular dynamics simulations combined with an elevated temperature tribological experiment. The scratching force experiences the increase stage, the undulated stage, and the stable stage due to chip formation. Compared to traditional alloy coatings, low force enhances the useful life. With increased speed, the friction coefficient decreases, agreeing with previous work. High speed impacting includes severe local plastic deformation, from dislocation to amorphization. As the scratching depth increases, the average scratch force and friction coefficient increases owing to material accumulation in front of the abrasive particles. The surface morphology and dislocation behavior are significantly different during the scratching process. In addition, we revealed a temperature-dependent friction mechanism. FeCrNi MPEAs have excellent wear resistance at an intermediate temperature, which is attributed to the high Cr content promoting the formation of the compact oxide layer. This work provides atomic-scale mechanistic insights into the tribological behavior of FeCrNi, and would be applied to the design of MPEAs with high performance.

Cross‐equalization for time‐lapse sparker seismic data

AbstractTime‐lapse seismic data processing is an important technique for observing subsurface changes over time. The conventional time‐lapse seismic exploration has been conducted using a large‐scale exploration system. However, for efficient monitoring of shallow subsurface, time‐lapse monitoring based on the small‐scale exploration system is required. Small‐scale exploration system using a sparker source offers high vertical resolution and cost efficiency, but it faces challenges, such as inconsistent waveforms of sparker sources, inaccurate positioning information and a low signal‐to‐noise ratio. Therefore, this study proposes a data processing workflow to preserve the signal and enhance the repeatability of small‐scale time‐lapse seismic data acquired using a sparker source. The proposed workflow has three stages: pre‐stack, post‐stack and machine learning–based data processing. Conventional seismic data processing methods were applied to enhance the quality of the sparker seismic data during the pre‐stack data processing stage. In the post‐stack processing stage, the positions and energy correction were performed, and the machine learning–based data processing stage attenuated random noise and applied a matched filter. The data processing was performed using only the seismic signals recorded near the seafloor, and the results confirmed the improvement in the repeatability of the entire seismic profile, including that of the target area. According to the repeatability quantification results, the predictability increased and the normalized root mean square decreased during data processing, indicating improved repeatability. In particular, the repeatability of the data was greatly improved through vertical correction, energy correction and matched filtering approaches. The processing results demonstrate that the data processing method proposed in this study can effectively enhance the repeatability of high‐resolution time‐lapse seismic data. Consequently, this approach could contribute to a more accurate understanding of temporal changes in subsurface structure and material properties.

Exploring the dielectric loss of Martian regolith in the frequency domain using Zhurong radar data

Martian regolith is one of the primary science objectives of Mars exploration missions. The Rover Penetrating Radar carried by Zhurong rover allows for high-resolution subsurface imaging and in-situ measurements of Martian regolith dielectric properties, which are crucial to advance our understanding of Martian geology and hydrological evolution. While earlier studies have derived dielectric constants for the shallow subsurface, further characterization of subsurface materials requires the determination of attenuation properties. In this study, we applied the centroid-frequency shift method to explore the attenuation property of the Martian regolith in the frequency domain. Lateral attenuation variation was analyzed in detail by integrating subsurface radargram and navigation terrain images. The results show that, within a depth of ∼4 m, the attenuation of radar signal for Zhurong subsurface material is equal to a loss tangent of 0.0079, with a standard deviation of 0.001. Based on the loss tangent value, dielectric permittivity and ground characterization, we preclude the possibility that the regolith is predominantly igneous materials. The lateral variation of the attenuation property could likely be attributed to changes in the proportion of duricrusts, which are heterogeneously distributed along the rover traverse. Our findings offer valuable information for understanding the Martian regolith and its evolution, serving as a important reference for future Mars sample return missions.

Advanced petrographic thin section segmentation through deep learning-integrated adaptive GLFIF

In geological research, precise segmentation of sandstone thin sections is crucial for detailed subsurface material analysis. Traditional methods often fall short in accurately capturing the complexities of these samples. This study presents an innovative segmentation approach that integrates an adaptive Global and Local Fuzzy Image Fitting (GLFIF) algorithm with Otsu's thresholding, significantly enhancing segmentation accuracy and efficiency. Our method combines deep learning and traditional image processing techniques. The adaptive GLFIF algorithm, powered by deep learning, automates parameter tuning, thereby reducing manual intervention and improving precision. Unlike conventional methods that learn fixed parameters, our model dynamically adjusts the segmentation process to achieve accurate results. The dual-phase segmentation strategy effectively isolates small features and handles intricate boundaries, ensuring high-quality outcomes. Experimental results demonstrate that our approach improves segmentation accuracy by 11.2% (from 82.6% to 93.8%), the Jaccard index by 15.4% (from 76.8% to 92.2%), and the Dice coefficient by 9% (from 86.9% to 95.9%) compared to traditional methods. This technique bridges the gap between conventional image analysis and deep learning, combining precise segmentation with the automation and computational power of advanced algorithms. Our segmentation algorithm represents a significant advancement in automated petrographic thin section analysis. Traditional image processing methods, such as thresholding and level sets, excel in handling small objects and complex boundaries but require significant manual intervention and cannot achieve full automation. Recent deep learning methods, particularly semantic segmentation, offer end-to-end automation but struggle with small targets and intricate boundaries. Our approach effectively combines the strengths of both methodologies, providing a comprehensive and efficient solution for geological image analysis that ensures both high accuracy and full automation.

Analysis of a large buried impact crater and vertical mineral composition at the Chang'E-4 landing site by multi-source remote sensing data

Exploring the concealed subsurface structures and materials beneath the lunar surface can reveal significant insights into geological history. This study offers a comprehensive analysis of the stratigraphic interpretation and subsurface material composition at the Chang'E-4 landing site, integrating both in-situ and orbital radar with multispectral datasets. We report the identification of a subsurface structure, which resembles a buried impact crater (∼420 m in diameter) under the Yutu-2 rover's path. This crater could degrade over a period of 0.42 to 0.53 Ga, with an initial diameter of 293 to 323 m and an initial depth of 45.9 to 51.4 m. Surface material above the buried crater, evaluated by the in-situ visible and near-infrared imaging spectrometer (VNIS) detector, shows a higher abundance of clinopyroxene compared to surrounding areas, where a near-equal mix of clinopyroxene and orthopyroxene is observed. Assessment of crater diameters in proximity to the Chang'E-4 landing site, along with the mineral compositions at their epicenters, reveals a decrease in the abundance of clinopyroxene and plagioclase with depth. Conversely, the quantities of orthopyroxene and olivine increase, implying that orthopyroxene-rich Finsen ejecta significantly influenced the Chang'E-4 landing site's geological composition. Two potential stratigraphic boundary depths are identified at 13.5 and 22 m, based on pronounced variations in mineral abundance, offering fresh insights into subsurface delineation beyond radar data. Considering the VNIS and vertical mineral composition, we propose the buried crater's formation resulted from Finsen crater's ejecta. Also, we identify eight potential historical impacts by comparing subsurface relief variations with mineral composition ratios between clinopyroxene and orthopyroxene. The integration of subsurface structure, along with surface and subsurface mineral composition, enables a more robust stratigraphic interpretation, facilitates shallow material source analysis, and allows for historical impact tracing.

Can rubberized-asphalt comprising tire-derived aggregates produced through dry process be an alternative subsurface road material?

The major objective of this study was to investigate the suitability of utilizing tire-derived aggregates (TDA) at varying contents for the design of rubberized-asphalt base / subsurface layers through the dry process, along with (i) understanding the cracking potential and mechanical stress-strain response of the different materials under cyclic and confining stresses through triaxial resilient modulus (MR), dynamic modulus |E*|, and static semi-circular bend test, and (ii) assessing bonding strength of TDA with binder-aggregate matrix through moisture susceptibility test. The scope encompassed preparation of ten base course mixtures: one unbound granular base (UGB), three cement treated base (CTB), two asphalt treated base (ATB), and four rubberized-asphalt treated base (RATB) and obtaining mechanical performance at varying temperature-frequency combinations totaling 2636 data points. Triaxial MR tests indicated that CTB mix displayed highest modulus followed by ATB and RATB mixes, which was then followed by the UGB mix mainly ascribed to cement / asphalt treatment of the unmodified control subsurface material. Further, a finite element modeling study helped optimize the confinement levels to obtain realistic |E*| of ATB and RATB mixes. |E*| test results depicted that RATB mixtures would be rut-resistant at higher temperatures as they performed similar to the ATB mixes as well as crack-resistant at low to intermediate temperatures with significantly lower |E*| than ATB mixes, attributed to slower rate of change of viscosity with changing temperature in conjunction with enduring viscoelastic property (1.5–3 times higher phase angle than ATB) ascribed to high asphalt binder content and resilient nature of the rubber particles. Albeit the fracture toughness of ATB was twice higher than RATB, the latter had higher fracture energies, mainly due to the resiliency rendered by the rubber inclusions in concert with the extra viscous effect provided by the rubber-asphalt binder conglomerate. Based on the performance-based ranking, RATB mixes performed better than control mixes, and thus were adjudged as the most suitable alternative subsurface / base course materials in a pavement system. It is envisioned that this research will advance the current understanding of utilizing TDA in asphalt base / subbase courses using the dry process, and further assist in judging the viability of using rubberized-asphalt as potential sustainable alternatives to conventional systems to develop futuristic resilient pavement infrastructures with a strong emphasis on recycling of end-of-life tires, conservation of materials, and circular economy.

Integrated geochemical and geophysical monitoring for the assessment of natural pollutant mitigation in heavy metal-contaminated areas of South Korea, Deagu.

The evaluation and monitoring of sites contaminated with heavy metals are essential for pollution remediation and prevention. In this study, we conducted geophysical and geochemical investigations at a site exhibiting heavy metal contamination downstream from an abandoned mine, with the aim of analyzing the extent of contamination and its temporal variation. We employed geophysical survey methods including electrical resistivity and induced polarization surveys of areas contaminated with heavy metals. Repeated surveys were conducted over time using the electrical resistivity method. Numerical simulations were employed to mitigate and eliminate electrical noise stemming from topography on the site. Additionally, time-lapse inversion was conducted on the resistivity data sets to analyze the changes in resistivity caused by variations in heavy metal contaminants. In the geochemical survey, soil samples were collected from the same locations as the geophysical survey, and chemical properties including pH, water content, electrical conductivity, and cation exchange capacity were analyzed. Our results showed that with the reduction of major sources of As and Zn contamination by 50%, the time-lapse electrical resistivity inversion results indicated that the resistivity of the subsurface materials increased by a factor of two. This paper demonstrated the natural reduction of the heavy metal contaminants at the site due to rainfall, aiming to comprehensively analyze the resultant alteration of both geochemical and geophysical properties.

Estimation of site-specific amplification function from quarter-wavelength velocity profile and its application to obtain local amplification maps

Quarter-wavelength (QWL) velocity refers to the S-wave velocity at a depth equal to one-fourth of the wavelength of the seismic waves. It provides valuable information about the characteristics of the subsurface material properties affecting seismic waves propagation. The Swiss Seismological Service (SED) network, with over 200 stations across different lithologies, offers a rich dataset to implement correlation between site properties and site amplification factors. The current study is based on a subset of 113 selected SED seismic stations for which shear-wave velocity (Vs) profiles from geophysical measurements are available. We first meticulously analyzed and adjusted them to accurately determine the bedrock depth of the sites they are located on. Using empirical spectral modelling (ESM), we computed amplification functions from recorded earthquakes, referenced to the Swiss standard rock profile with a VS30 of 1100 m/s. Then we performed a bivariate analysis between empirical amplification functions, QWL velocity and QWL velocity contrast. The resulting coefficients are used to predict elastic amplification at frequencies between 0.5 and 10 Hz, with predictions generally being within 20–28% of observed values. We also developed an empirical equation relating VS30 (time-averaged Vs to 30 m depth) and κ0 (high-frequency attenuation parameter), to incorporate the anelastic term in the amplification. Applying our method to a 3D geophysical model of Visp, a high seismic hazard zone in Switzerland, we found it effective in predicting 1D site amplification, but noted caution in areas susceptible of 2D/3D resonance effects. A calibration function based on observed vs. predicted amplification and the frequencies of estimation normalized by the expected 2D resonance frequency improved predictions for Visp. Our study demonstrates that QWL velocity profiles offer a straightforward approach for characterizing site effects, which can be used in seismic hazard assessment to evaluate the potential amplification of ground motions.

Effects of surface and subsurface water/ice on spatial distributions of impact crater ejecta on Mars

Ejecta blankets around craters on a km-scale show stark differences in the ejecta mobility (maximal extent of ejecta divided by the crater radius) with latitude and types of plains on Mars, which has been known for a long time (Barlow and Pollak, 2002; Li et al., 2015) but is not well-understood. Our main goal is to explore the idea that the subsurface rheology drives ejecta dynamics and leaves characteristic, observable imprints in the spatial distributions of ejecta. We conduct numerical simulations of impact cratering into a variety of subsurface models and study the impact of varied subsurface material (porous basalt, water ice, water), as well as structure and layering on impact sites and properties of impact ejecta. Our models consider variations in the depth of water or ice covering basalt; the thickness of buried ice; and the depth of burial of ice. We find that ejection angles and velocities depend on these quantities and configurations, e.g. velocities decrease and angles of ejection increase with increasing water layer thickness, buried ice thickness, or thickness of basaltic debris over an ice sheet. As a result, several ejecta characteristics derived from ejecta thickness profiles carry information about the underlying rheology. Specifically, the ejecta mobility, as well as the radial position of the maximum and the slope of the ejecta thickness profiles are diagnostic. The power-law function of the thickness profile of the ejecta blanket right after formation is a good indicator of ejecta from water- or ice-covered targets but not from more complex multi-layered structures, hence we caution against using scaling relations to describe ejecta from such targets. As any surface water/ice volatile mass is unstable on Mars, we also consider the geomorphology of craters and ejecta after the loss of volatiles. Our main findings include the observation that after the loss of surface volatiles, craters which formed in water-covered targets would appear shallower than those formed in basalt. The ejecta mobilities observed today would also be smaller if craters formed in volatile-covered targets than in basalt. Our findings can aid the interpretation of data returned from cameras onboard multiple spacecraft orbiting Mars such as HiRISE, CaSSIS, or CTX, and constitute a proof of concept of the hypothesis that information on the subsurface, including where ice is or was present, is encoded in the ejecta profile and spatial distribution.

The Estimation of Shear Wave Velocity for Shallow Underground Structures in the Central Himalaya Region of Nepal

A subsurface investigation was conducted to assess the suitability of a site for potential tunnel construction, focusing on the determination of shear wave velocities (Vs) in subsurface materials. This study employed three distinct methods to analyze Vs in weathered soft rock: drilling mechanism, multichannel analysis of surface waves (MASW), and microtremor array measurement (MAM). Through the utilization of MASW and MAM, empirical relationships were established, enabling the determination of Vs based solely on soil type and depth, offering a practical alternative to the limitations of SPT N-Value, particularly when exceeding 50 blows. The comparison of Vs values obtained from these methods revealed a close alignment between empirical techniques and MASW/MAM, which proved to be cost-effective and an efficient alternative to drilling for comprehensive underground structure assessments. The reliability of MASW was further underscored through its comparison with existing empirical methods. Moreover, the empirical approach demonstrated its efficacy in predicting velocities in weathered soft rock within the Central Himalayan region of Nepal, thus enhancing the feasibility study of underground structures. Lastly, this study proposed a Vs-Depth correlation specifically tailored for highly weathered meta-sandstone bedrock resulting in clay and sandy soils.

Morphometric Analysis Using Remote Sensing and Geographical Information System: A Case Study of Nawagarh Watershed of Chhattisgarh, India

The study highlights the suitability of a GIS-based approach for evaluating morphometric parameters. It focuses on the quantitative analysis of morphometric characteristics within thirteen sub-watersheds of the Nawagarh watershed, which originates from the Seonath river catchment in the Mahanadi basin in Chhattisgarh, India. The Nawagarh watershed spans an area of 2647.27 km2. Its outlet is located at 21°46'10" N Latitude and 81° 48’43” E Longitude. The Nawagarh watershed covers four districts in Chhattisgarh - Kabirdham, Bemetara, Baloda Bazar, and Mungeli. The analysis reveals the relative qualities of the sub-watersheds in terms of hydrological response. The Nawagarh watershed features a dendritic drainage network with 2760 streams of different orders. The slope of the land directly affects water absorption and drainage. High relief ratio 0.032 in SWD1 and SWD3 indicates rapid concentration, rapid stream flow, and greater susceptibility to erosion than other sub watersheds. The drainage density is 0.80 km-1, which is close to 1 km-1, indicating that the basin has a nearly high drainage density, which demonstrate that the location with impermeable weak subsurface material and has high relief. The elongated shape with the values of form factor (0.39), circulatory ratio (0.28) and elongation ratio (0.69), indicated that the Nawagarh watershed is more elongated with lower peak flow of long duration having low permeability. The drainage density in the basin is relatively high, suggesting a significant drainage network. The study emphasizes the need for effective erosion control methods in the Nawagarh watershed to protect the land.

Shallow subsurface structure and material composition of Martian Utopia Planitia: Constraints from SHARAD data

Shallow subsurface structure and material composition of Martian Utopia Planitia: Constraints from SHARAD data

Study on Laser Polishing of Ti6Al4V Fabricated by Selective Laser Melting.

Laser-based additive manufacturing has garnered significant attention in recent years as a promising 3D-printing method for fabricating metallic components. However, the surface roughness of additive manufactured components has been considered a challenge to achieving high performance. At present, the average surface roughness (Sa) of AM parts can reach high levels, greater than 50 μm, and a maximum distance between the high peaks and the low valleys of more than 300 μm, which requires post machining. Therefore, laser polishing is increasingly being utilized as a method of surface treatment for metal alloys, wherein the rapid remelting and resolidification during the process significantly alter both the surface quality and subsurface material properties. In this paper, the surface roughness, microstructures, microhardness, and wear resistance of the as-received, continuous wave laser polishing (CWLP), and pulsed laser polishing (PLP) processed samples were investigated systematically. The results revealed that the surface roughness (Sa) of the as-received sample was 6.29 μm, which was reduced to 0.94 μm and 0.84 μm by CWLP and PLP processing, respectively. It was also found that a hardened layer, about 200 μm, was produced on the Ti6Al4V alloy surface after laser polishing, which can improve the mechanical properties of the component. The microhardness of the laser-polished samples was increased to about 482 HV with an improvement of about 25.2% compared with the as-received Ti6Al4V alloy. Moreover, the coefficient of friction (COF) was slightly reduced by both CWLP and LPL processing, and the wear rate of the surface layer was improved to 0.790 mm3/(N∙m) and 0.714 mm3/(N∙m), respectively, under dry fraction conditions.

A rolling contact fatigue life prediction model for bearing steel considering its gradient structure due to cyclic hardening

This paper presents a rolling contact fatigue life prediction model for bearing steel. In the initial stage of rolling contact, the gradient structure appears in the subsurface region of bearing steel and the hardness shows a gradient distribution along the contact depth direction due to the roller compaction effect. This indicates that the fatigue resistance of bearing steel varies in the subsurface region. Besides, each subsurface material volume element is subject to different stress cycles. Based on Weibull theory, the survival possibility of subsurface volume elements is formulated. Then the rolling contact fatigue life is evaluated considering the stress state and anti-fatigue performance of each elementary volume of the subsurface material. According to the phenomenon and assumption, the model proposed for gradient material was applied in the rolling contact fatigue life prediction of the bearing steel GCr15 and validated with the fatigue experiment data in the open literature. Furthermore, the accuracy of the proposed model results was compared with the traditional empirical rolling contact fatigue life prediction models.

Photothermal defect imaging in hybrid fiber metal laminates using the virtual wave concept

This study presents photothermal imaging results of subsurface material defects within fiber metal laminates utilizing the virtual wave concept. Therefore, we theoretically analyze the propagation of the virtual wave signal in a hybrid composite laminate via the method of images. For provoking local material damage, the hybrid composite sample is subjected to a defined impact loading. The results obtained from photothermal defect imaging, utilizing rectangular laser pulse excitation, are compared with results obtained from 3D x-ray computed tomography. To sum up, we demonstrate a fast, non-invasive, and easily interpretable reconstruction of defects within macroscopic hybrid composite laminates based on the virtual wave concept.

Residual stresses assessment on waterjet peening metallic biomaterials by thermoelectric magnetic sensing

The superficial treatment for metallic materials with water jet peening is oriented to improve the mechanical fixation of implants through an increase in roughness. Because of superficial plastic deformation, additional subsurface material effects occur such as grain refinement, hardening, increased compressive residual stresses and cold worked; which are generally evaluated by destructive tests. This research is focused on the analysis of these subsurface material effects by a non-destructive technique such as the non-contact thermoelectric power (TEP) inspection using a magnetic sensor to detect thermoelectric currents induced by a temperature gradient in water jet peened 316LVM austenitic stainless-steel and Ti-6Al-4 V ELI titanium alloy samples. The results obtained by magnetic TEP non-destructive test versus the X-ray diffraction technique are compared. It was found that it is possible to qualitatively characterize some of the subsurface material effects mainly residual stresses and cold working produced by deformation through surface treatment with blasting of water.

Selected Area Manipulation of MoS2 via Focused Electron Beam-Induced Etching for Nanoscale Device Editing.

We demonstrate direct-write patterning of single and multilayer MoS2 via a focused electron beam-induced etching (FEBIE) process mediated with the XeF2 precursor. MoS2 etching is performed at various currents, areal doses, on different substrates, and characterized using scanning electron and atomic force microscopies as well as Raman and photoluminescence spectroscopies. Scanning transmission electron microscopy reveals a sub-40 nm etching resolution and the progression of point defects and lateral etching of the consequent unsaturated bonds. The results confirm that the electron beam-induced etching process is minimally invasive to the underlying material in comparison to ion beam techniques, which damage the subsurface material. Single-layer MoS2 field-effect transistors are fabricated, and device characteristics are compared for channels that are edited via the selected area etching process. The source-drain current at constant gate and source-drain voltage scale linearly with the edited channel width. Moreover, the mobility of the narrowest channel width decreases, suggesting that backscattered and secondary electrons collaterally affect the periphery of the removed area. Focused electron beam doses on single-layer transistors below the etching threshold were also explored as a means to modify/thin the channel layer. The FEBIE exposures showed demonstrative effects via the transistor transfer characteristics, photoluminescence spectroscopy, and Raman spectroscopy. While strategies to minimize backscattered and secondary electron interactions outside of the scanned regions require further investigation, here, we show that FEBIE is a viable approach for selective nanoscale editing of MoS2 devices.

Characterization and Environmental Risk Assessment of Coal-based Solid Waste Towards Underground Backfilling

This study evaluated the feasibility of coal-based solid waste as a subsurface fill material based on its physicochemical properties and potential environmental risks. The results show that the special physical structure and the chemical composition of coal-based solid wastes are advantageous as filling materials. In terms of physical structure, the spheres improve the flowability and mixing homogeneity of the mixture, while lumps give stabilizing support; the special chemical compositions also improve the strength, durability and corrosion resistance of the filler. The contents of Cd, As, Cr, Cu, Ni and Co in coal-based solid waste are less directly harmful to the environment, but arsenic showed a relatively strong enrichment. Cd in coal gangue and desulfurized gypsum were medium or very high risk due to strong migration and bioavailability, respectively, while Co in desulfurized gypsum present a medium risk. Both coal gangue and desulfurized gypsum may contaminate the underground environment, the other materials pose less threat to the environmental. In engineering applications, attention should be paid to the main contaminant As, as well as Cd and Co because of their mobility and high bioactive fraction, to reduce potential environmental risk.