Submicron Scale Research Articles

3D Topological Toron‐Like Domains in Magnetic Nanoparticles: A Micromagnetic Simulation

Abstract3D topological textures have attracted significant attention from researchers due to their distinctive spatial arrangements and intriguing physical properties. However, investigating their topological domain structures at the submicron scale (<1000 nm) proves exceedingly elusive and under‐explored. Here, the size‐dependent behaviors of non‐uniform magnetic domain structures within submicron‐sized FeNi magnetic nanoparticles by micromagnetic simulations are systematically explored. Notably, the existence of magnetic toron‐like structures at the submicron scale and discuss their spatial arrangement and topological properties are identified. Furthermore, critical transition sizes are calculated under various aspect ratios, and the domain structure phase diagram based on nanoparticle size and aspect ratio is constructed. Through visualizations of domain flipping processes and dynamic energy changes, the stable existence of toron‐like magnetic configuration resulting from the competition among demagnetization energy, magnetic anisotropy energy, and magnetic exchange energy are unveiled. Finally, the utilization of core‐shell structures to achieve the stable existence of 3D topological textures are proposed. This work provides important theoretical insights for understanding and designing multi‐domain structures of FeNi nanoparticles at the submicron scale, as well as for constructing topological textures.

Microstructure Morphology of Chemical and Structural Phase Separation in Thermally Treated KxFe2-ySe2 Superconductor.

The iron-based KxFe2-ySe2 superconductor displays chemical, structural and electronic phase separation at nanoscale to microscale, leading to the coexisting metallic phase embedded in an antiferromagnetic host matrix. The metallic character of the system is believed to arise from a percolative granular network affecting its transport in the normal as well as in the superconducting state. This percolative network can be manipulated and controlled through thermal treatments. In this study, we have used scanning X-ray micro-fluorescence to visualize morphology of the chemical phase separation coupled to the percolation in KxFe2-ySe2, manipulated by two distinct thermal treatments, i. e., fast quenching and slow cooling. We find a differing spatial correlation between Fe and K distributions in the two samples, ascribed to a different degree of Fe vacancy ordering. We have also identified an intermediate phase that acts as an interface between the two main phases. The high temperature quenching produces directionally oriented clustered microstructure in which the percolation threshold is lower and hence a more effective transport networks. Instead, the slow cooling results in larger interfaces around the percolation threshold that seems to affect the superconducting properties of the system. The results provide a quantitative characterization of microstructural morphology of differently grown KxFe2-ySe2 showing potential for the design of electronic devices based on sub-micron scale chemical phase separation, thus opening avenues for further studies of complex heterogeneous functional structures.

Dual Photonics Probing of Nano- to Submicron-Scale Structural Alterations in Human Brain Tissues/Cells and Chromatin/DNA with the Progression of Alzheimer's Disease.

Understanding alterations in structural disorders in tissue/cells/building blocks, such as DNA/chromatin in the human brain, at the nano to submicron level provides us with efficient biomarkers for Alzheimer's detection. Here, we report a dual photonics technique to detect nano- to submicron-scale alterations in brain tissues/cells and DNA/chromatin due to the early to late progression of Alzheimer's disease in humans. Using a recently developed mesoscopic light transport technique, fine-focused nano-sensitive partial wave spectroscopy (PWS), we measure the degree of structural disorder in tissues. Furthermore, the chemical-specific inverse participation ratio technique (IPR) was used to measure the DNA/chromatin structural alterations. The results of the PWS and IPR experiments showed a significant increase in the degree of structural disorder at the nano to submicron scale at different stages of AD relative to their controls for both the tissue/cell and DNA cellular levels. The increase in the structural disorder in cells/tissues and DNA/chromatin in the nuclei can be attributed to higher mass density fluctuations in the tissue and DNA/chromatin damage in the nuclei caused by the rearrangements of macromolecules due to the deposition of the amyloid beta protein and damage in DNA/chromatin with the progress of AD.

Effect of grain size on mechanical properties and aging of yttria-stabilized tetragonal zirconia polycrystal fabricated by stereolithography-based additive manufacturing

The objective of this investigation was to comprehensively assess the impact of grain size on the mechanical properties and low-temperature degradation (LTD) of yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) fabricated by stereolithography-based additive manufacturing at the submicron scale. Four 3Y-TZP ceramics with high relative density (>98%), ranging in grain size from 0.2 μm to 1 μm, were successfully prepared and validated for studying mechanical properties (including Vickers hardness, fracture toughness, and flexural strength) as well as LTD progression. This study elucidates the mechanical behavior of zirconia ceramics at the submicron scale, focusing on fracture micromechanisms and the grain size dependence of transformation toughening. Additionally, it examines the influence of grain size on the hydrothermal aging behavior of zirconia ceramics at the submicron scale using Raman spectroscopy.

Graphite Made from Coal by High-Temperature Treatment: An Insight into the Nanometric Carbon Structural Evolution

Graphite made from coal will not only widen the graphite mineral resource, but also significantly improve the value of coal utilization. In this study, anthracite coal was heated in the temperature range of 500 to 2900 °C to study the size increase of nanometric graphite crystallites from anthracite to real graphite. The carbon content rapidly increases to 99.2% when heated from room temperature to 1600 °C, and then gradually increases to 100% when the treated temperature increases to 2900 °C. The FTIR results show that methyl, methylene, and aromatic hydrocarbon, preexisting in the raw anthracite, were preserved in the JZS-500 sample, but that when the treated temperature ≥ 1000 °C, these C-H bonds almost disappear. The basic structural units (nano graphitic carbon) grow into distorted columns, and the basic structural units and micro-columns re-oriented and coalesced to form local molecular oriented domains with the temperature increase from anthracite to JZS-1500. When the temperature ≥ 1600 °C, amorphous carbon, onion-like carbon, turbostratic layers, and graphitic carbon co-occur within the graphitized coals. At the sub-micron scale, carbonization is a homogenous process, whereas graphitization is a heterogenous process. The average graphite crystalline size (La, lateral extension; Lc, stacking height) rapidly increases as the treatment temperature increases from 1600 to 2300 °C. Three coal structural transformation stages were classified according to the nanometric carbon structural evolution with temperature. This study will contribute to the efficient and value-added utilization of coal to make graphite materials.

Soft X-ray spectromicroscopic proof of a reversible oxidation/reduction of microbial biofilm structures using a novel microfluidic in situ electrochemical device

In situ electrochemistry on micron and submicron-sized individual particles and thin layers is a valuable, emerging tool for process understanding and optimization in a variety of scientific and technological fields such as material science, process technology, analytical chemistry, and environmental sciences. Electrochemical characterization and manipulation coupled with soft X-ray spectromicroscopy helps identify, quantify, and optimize processes in complex systems such as those with high heterogeneity in the spatial and/or temporal domain. Here we present a novel platform optimized for in situ electrochemistry with variable liquid electrolyte flow in soft X-ray scanning transmission X-ray microscopes (STXM). With four channels for fluid control and a modular design, it is suited for a wealth of experimental conditions. We demonstrate its capabilities by proving the reversible oxidation and reduction of individual microbial biofilm structures formed by microaerophilic Fe(II)-oxidizing bacteria, also known as twisted stalks. We show spectromicroscopically the heterogeneity of the redox activity on the submicron scale. Examples are also provided of electrochemical modification of liquid electrolyte species (Fe(II) and Fe(III) cyanides), and in situ studies of electrodeposited copper nanoparticles as CO2 reduction electrocatalysts under reaction conditions.

An integrated hybrid wire-arc directed energy deposition, friction stir processing, and milling system for multi-track, multi-layer part manufacturing

Wire-based Directed Energy Deposition (DED) is a widely-used manufacturing method due to its high productivity and large part fabrication capability. Meanwhile, Friction Stir Processing (FSP) is a solid-state joining process that can modify microstructure and weld lightweight alloys. Additionally, wire-based DED printed parts need machining process to achieve the desired dimensional accuracy. To take advantage of all these three processes, this work proposes an integrated hybrid system by combining the wire-arc DED, FSP, and milling processes into a standalone system which can fabricate superior materials in a multi-track, multi-layer manner for the first time. The integrated system can improve dimensional accuracy and productivity by processing the workpiece without the need to move it between different systems. It is demonstrated that a 150 × 40 × 21 mm3 block of aluminum alloy AA5183 can be fabricated using the hybrid wire-DED/FSP/milling process from wire feedstock. Material characterization shows that the hybrid process is able to refine the grain size by two orders of magnitude to sub-micron scale, while eliminating all the pores and microcracks produced by the DED process. These enhancements result in significantly improved mechanical properties including Young's modulus (15 %), yield strength (161 %), ultimate strength (33 %), and hardness (55 %) without compromising ductility.

Deciphering the Intricate Control of Minerals on Deep Soil Carbon Stability and Persistence in Alaskan Permafrost.

Understanding the fate of organic carbon in thawed permafrost is crucial for predicting climate feedback. While minerals and microbial necromass are known to play crucial roles in the long-term stability of organic carbon in subsoils, their exact influence on carbon persistence in Arctic permafrost remains uncertain. Our study, combining radiocarbon dating and biomarker analyses, showed that soil organic carbon in Alaskan permafrost had millennial-scale radiocarbon ages and contained only 10%-15% microbial necromass carbon, significantly lower than the global average of ~30%-60%. This ancient carbon exhibited a weak correlation with reactive minerals but a stronger correlation with mineral weathering (reactive iron to total iron ratio). Peroxidase activity displayed a high correlation coefficient (p < 10-6) with Δ14C and δ13C, indicating its strong predictive power for carbon persistence. Further, a positive correlation between peroxidase activity and polysaccharides indicates that increased peroxidase activity may promote the protection of plant residues, potentially by fostering the formation of mineral-organic associations. This protective role of mineral surfaces on biopolymers was further supported by examining 1451 synchrotron radiation infrared spectra from soil aggregates, which revealed a strong correlation between mineral OH groups and organic functional groups at the submicron scale. An incubation experiment revealed that increased moisture contents, particularly within the 0%-40% range, significantly elevated peroxidase activity, suggesting that ancient carbon in permafrost soils is vulnerable to moisture-induced destabilization. Collectively, this study offers mechanistic insights into the persistence of carbon in thawed permafrost soils, essential for refining permafrost carbon-climate feedbacks.

Investigation the Impact of Different Injection Agents on Tight Oil Reservoirs of Recovery Performance

Abstract Objectives/Scope: Due to strong water sensitivity and extremely low permeability, conventional water flooding method is not suitable for the Mahu Conglomerate reservoir. In response to the complex reservoir physical properties, different injection agents such as CO2, N2, water and air huff and puff injection were carried out in order to optimize injection parameters for enhanced oil recovery in tight conglomerate reservoirs. Methods, Procedures, Process: By means of NMR, scanning electron microscopy, energy spectrum, pore fluids state in different media after different agents displacement were studied. Displacement and CT testing on different media and post fracturing state were conducted. Through experiments on on-site cores from two different layers, three different injection media (H2O, N2, CO2 and air with different O2 concentration) were tested for enhanced oil recovery. Then, the injection process was performed under different injection pressures. Finally, multiple cycles of enhanced oil recovery tests were conducted corresponding optimal injection pressures. Results, Observations, Conclusions: The remaining oil in the pores is mainly in free and bound states, with a free state of approximately 58% and a bound state of approximately 42%. Four pressures were selected for this test based on the minimum miscibility pressure of CO2 with crude oil: 15MPa, 20MPa, 23MPa, and 25MPa. The recovery factor under different pressures is 6.44%, 8.14%, 10.31%, and 10.38%, respectively. As the huff and puff pressure increases, the recovery of CO2 huff and puff gradually increases, and the increase of recovery is insignificant when the mixture pressure is reached. The gas flooding process involves oil production from large and submicron pores first. As the displacement pressure difference increases, oil production from large pores decreases, with medium pores becoming the main force of oil production, while oil production from nanoscale micropores shows an increasing trend. The increase in oxygen content results in significant development of sub-micron micron scale pores. The gas breakthrough time is long, the capillary force decreases, and air can undergo low-temperature oxidation with crude oil, resulting in an overall oil displacement efficiency of 65.81%. Novel/Additive Information: At present, there is few research on the pore fluid flow and status of oil displacement in tight conglomerate reservoirs with different injection media. This study provides a good understanding of the submicron to nanoscale pore throat structure characteristics of tight oil reservoirs, revealing the state of pore fluids in gravel after displacement by different injection media, and providing support for on-site application of CO2 enhanced oil recovery in tight conglomerate oil reservoirs.

Nanomechanical behavior of impulse atomized Al-Ce eutectic particles

Al – 20 wt% Ce alloy particles with varying eutectic morphologies and sizes were fabricated using high cooling rate impulse atomization. Nanoindentation and in situ compression in a scanning electron microscope were used to evaluate the hardness, flow strength and plastic deformability of individual phases (Al and Al11Ce3) and various Al11Ce3/α-Al eutectic morphologies. The mechanisms that determine compressive strengths, plastic deformability and fracture of the intermetallic phase are interpreted in terms of the eutectic morphology and spacing. Fine, degenerate eutectic structure facilitated significant strain hardening and delayed onset of cracking, making it highly resilient under compression, while the fine and regular eutectic structure showed relatively lower strengthening and early crack nucleation compared to coarser lamellar eutectic structure. This study reveals the significant effects of microstructure morphology as well as size, specifically focusing on the degenerate eutectic microstructures at submicron scale, in controlling the flow strength and plastic deformability of fine-scale metallic eutectic microstructures containing hard, intermetallic phases.

Spatiotemporal dynamics of fast electron heating in solid-density matter via XFEL

High-intensity, short-pulse lasers are crucial for generating energetic electrons that produce high-energy-density (HED) states in matter, offering potential applications in igniting dense fusion fuels for fast ignition laser fusion. High-density targets heated by these electrons exhibit spatially non-uniform and highly transient conditions, which have been challenging to characterize due to limitations in diagnostics that provide simultaneous high spatial and temporal resolution. Here, we employ an X-ray Free Electron Laser (XFEL) to achieve spatiotemporally resolved measurements at sub-micron and femtosecond scales on a solid-density copper foil heated by laser-driven fast electrons. Our X-ray transmission imaging reveals the formation of a solid-density hot plasma localized to the laser spot size, surrounded by Fermi degenerate, warm dense matter within a picosecond, and the energy relaxation occurring within the hot plasma over tens of picoseconds. These results validate 2D particle-in-cell simulations incorporating atomic processes and provide insights into the energy transfer mechanisms beyond current simulation capabilities. This work significantly advances our understanding of rapid fast electron heating and energy relaxation in solid-density matter, serving as a key stepping stone towards efficient high-density plasma heating and furthering the fields of HED science and inertial fusion energy research using intense, short-pulse lasers.

Integrated textural and geochemical analysis of igneous zircon by atom probe tomography

Mechanisms relating to growth and/or compositional modification of zircon occur at the atomic scale. For felsic igneous systems, processes responsible for growth patterns in zircon have previously remained elusive as the volume of material needed to analyze these compositional features using traditional in-situ methods is considerably larger than the typical sub-micron scale distribution of trace elements. To illuminate some of these driving forces, we characterize and quantify minor and trace element concentrations in igneous zircon grains by combining methods of cathodoluminescence (CL) imaging, electron microprobe microanalysis (EMPA) elemental maps for Hf, Y, Yb and U or Th, and atom probe tomography (APT). We focus on igneous zircon from the Chon Aike Silicic Large Igneous Province (Patagonia) that provide novel insights into (1) dissolution and re-crystallization during crustal anatexis, (2) crystallization to produce oscillatory zonation patterns that are typical of igneous zircons, and (3) the incorporation of trace element impurities (e.g., P, Be, and Al) at the nanoscale. Significantly, these APT volumes provide nanoscale sampling of boundaries between oscillatory growth zones in an igneous zircon to reveal compositional zoning of Y and, to a lesser extent P, which appear as high-angle, planar features. These concentration boundaries measured on the order of 10 to 12 nm are difficult to reconcile with proposed mechanisms for generating fine-scaled oscillations. Lastly, we fit diffusional profiles to measured Y concentrations to provide an estimate on the maximum timescales of zircon growth prior to eruption, as a function of the temperature at which diffusion occurred. When combined with known pressure-temperature-time paths for the magmatic system considered, these extremely short diffusion profiles that are resolvable by APT provide a powerful method to constrain timescales of crystal growth.

Redox conditions influence the chemical composition of iron-associated organic carbon in boreal lake sediments: A synchrotron-based NEXAFS study

The global carbon and iron cycles are intimately linked as redox-sensitive iron oxides readily bind organic carbon in a variety of environmental settings, including marine and lacustrine sediments. While these iron-organic carbon complexes sequester vast quantities of organic carbon, the composition of the organic matter within them remains unknown for lacustrine environments. Here we present C K1s and Fe L3,2 edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of surface sediments and authigenic iron complexes from adjacent basins of a pristine boreal lake located in Québec, Canada, with contrasting oxygen exposure regimes. We demonstrate differences in organic carbon speciation in sediments from both basins, as well as co-localization of organic carbon and iron on a sub-micron scale in 100 nm thick samples. Differences in redox cycling across these two basins allow for a direct comparison of the effect of oscillating redox conditions on the composition of organic carbon sequestered by iron. Our results suggest that reactive organic molecules, which may be polysaccharides, were found preferentially associated with iron in the perennially oxic sediments compared to more phenol rich organics in the seasonally anoxic sediments, highlighting the importance of iron oxides in the protection and preservation of labile organic compounds. Traces of aliphatic carbon were observed in sediments from the anoxic basin, alongside carboxyl and aromatic functionalities. This carboxyl-rich aliphatic material could possibly interact with the sediment mineral matrix either through a ligand exchange mechanism between the mineral phases and the carboxyl functionalities, or via non-specific hydrophobic interactions involving the aliphatic moieties. Finally, our work also shows that OC:Fe ratios should be used with caution when inferring a binding mechanism between OC and iron oxides.

3D Microporosity Characterizations in the Heterogeneous Middle Jurassic Tuwaiq Mountain Formation: Insights into an Unconventional Sweet Spot.

Carbonate microporosity can vary significantly across depositional lithofacies and cycles, owing primarily to the high degree of heterogeneity in their pore sizes, pore throat radius, geometry, and connectivity. This is further compounded by the complex diagenetic alterations during various stages of burial. In addition, the presence of micropores, which are abundant in carbonate rocks, but not visible using conventional techniques, is challenging to characterize. To address this issue, our study focused on the Middle Jurassic Tuwaiq Mountain Formation (TMF) due to its importance as an analogue to subsurface conventional and unconventional reservoirs. Here, we utilized eight samples and performed pore network modeling to quantify microporosity distribution and connectivity from high-resolution microcomputed tomography images of different microfacies (MF) in the TMF from both mud- and grain-dominated facies. These results were then validated with petrographic, SEM images, and porosity-permeability measurements. Our study revealed that, in the high-energy, grain-supported microfacies of the shallow lagoon depositional cycle, micropores dominated by interparticle and microvug types were abundant and well-connected, with mean pore and throat sizes of 7 and 4 μm. Conversely, micropores within the low-energy mud-dominated microfacies of the deep lagoon depositional cycle dominated by intraparticle and intercrystalline types were isolated and rarely connected, even at the microscale (1-4 μm in diameter, with an average of 2 μm). This result suggests that pore connectivity at the microscale is not always related to matrix porosity, and the pore connectivity is present in submicron scale, which goes against common concepts in unconventional carbonate reservoirs. Furthermore, our observations indicate that primary depositional processes play a major role in controlling the distribution and connectivity of the Tuwaiq Mountain Formation's microporosity, while diagenetic processes only have minor controls. Our study emphasizes the importance of characterizing microporosity and its connectivity in heterogeneous carbonate rocks, which may reduce the uncertainty in exploring the properties of complex carbonate reservoirs worldwide.

Enhanced mechanical properties and anti-wear performance of Cu45Mn8Ni40Sn7 medium entropy bronze alloy by multi-stage heat treatment

High/ medium entropy brass and bronze alloys exhibit considerable potential for application as structural materials. This study focuses on a Cu45Mn8Ni40Sn7 medium entropy bronze alloy that demonstrates excellent hardness, compressive strength, ductility, and wear resistance through a multi-stage heat treatment technique. The effects of heat treatment on the phase composition, microstructural evolution, mechanical properties, and tribological performance of the alloy were systematically investigated. The alloy, treated by homogenization (820 ℃/4 h)-solution (900 ℃/1 h)-aging (450 ℃/5 h), exhibits a hardness of 362 HV, yield strength of 626 MPa, ultimate strength of 1229 MPa, compressive strain of 47.2 %, fracture toughness of 20.7 MPa·m1/2, and maintains a low wear rate of 1.72×10−5 mm3·N−1·m−1. The processes of homogenization and solution treatment reduce dendrite segregation of elements and eliminate the detrimental lamellar structure at the grain boundaries. During the aging treatment of the alloy, sub-micron scale needle-like precipitates are formed, which play a significant role in enhancing its mechanical properties.

Noise Interrogation during an Induced Faradaic Reaction

Single-entity electrochemistry has emerged as a potent method that allows for examination of individual responses within a system to comprehend a bulk response. For example, utilizing electrodes on the micrometer scale or smaller provides the requisite sensitivity to discern the impact of a nanoparticle contacting the electrode surface which catalyzes a reaction. Nevertheless, the detection of nanoimpacts is limited by the presence of noise which stems from the inherent non-inert nature of electrodes.Understanding the noise level under a continuous Faradaic reaction becomes crucial for detecting catalysis at the sub-micron scale. In this presentation, I will describe how we understand and quantify the level of noise under diverse conditions. We measured noise while varying electrode size, sampling frequency, and redox-probe concentration. These results allowed us to formulate a model to predict noise at an electrode. Commonly, noise is thought to scale with the square root of current. However, our measurements reveal that the background noise level shifts from a square root dependence at the macroscale to a linear dependence at the microscale. Moreover, a chemically-coupled reaction (EC’) produces lower noise in comparison with a purely electrochemical reaction that produces the same steady-state current. In combination, these results suggest that diffusion partially dictates the amount of noise, along with the amount of redox-active species exchanging charge with the electrode. By understanding these noise sources, we may begin to control them, yielding more accurate and precise single-entity results.

Strengthening gold with dispersed nanovoids.

Materials often fail prematurely or catastrophically under load while containing voids, posing a challenge to materials manufacturing. We found that a metal (gold) containing spherical voids with a fraction of up to 10% does not fracture prematurely in tension when the voids are shrunk to the submicron or nanometer scale. Instead, the dispersed nanovoids increase the strength and ductility of the material while simultaneously reducing its weight. Apart from the suppressed stress or strain concentration, such structure provides enormous surface area and promotes surface-dislocation interactions, which enable strengthening and additional strain hardening and thus toughening. Transforming voids from crack-like detrimental defects into a beneficial "ingredient" provides an inexpensive and environmentally friendly approach for the development of a new class of lightweight, high-performance materials.

Transport Effects in Electrochemical Biochip Sensors with Redox Cycling Amplification: Computational and Experimental Analysis

In the last few decades, and especially after the COVID-19 pandemic, point-of-care diagnostics and field-deployable biosensors have attracted significant attention. Key components of these instruments are microchips that integrate microfluidics with a sensor (e.g., optical or electrochemical) to provide rapid, low-cost, real-time detection of analyte molecules in very small volumes. Next-generation electrochemical sensors have been miniaturized on solid-state platforms (e.g., arrays and vectors) where the area is limited. However, as the active surface area of the sensors decreases from a few square microns to sub-micron and nanometric scales, the measured currents drop, hence affecting the limit of detection. As the concentration of many analytes in the physiological environment is low, low signal-to-noise ratios have limited the miniaturization of standard electrochemical sensors. One way to increase signal at the sensor output is by redox amplification. To achieve amplification, a second working electrode must be incorporated close to the first working electrode and proper bias must be applied to both. Micrometer-sized interdigitated electrode arrays have been fabricated using robust and scalable processes based on optical lithography and reactive ion-etching techniques. In some cases, IDAs have been integrated into microfluidics devices. The physical and electrochemical phenomena that occur in microfluidic channels under flow have been previously evaluated and showed an increase of current under flow. The effect of redox cycling in microfluidic and nanofluidic systems has also been qualitatively demonstrated. Some studies measured the amplification in the cases with and without flow and showed that the flow itself amplifies the measured electrochemical current, though in most cases, it reduces the amplification factor.Towards a more quantitative investigation, analytical and computational modeling were used, providing meaningful insights into the physics of IDAs without requiring numerous device fabrications. In this work, we used COMSOL Multiphysics to create a full three-dimensional simulation-based model of a real device in order to study the effect of laminar flow on redox cycling, as well as a simplified one-dimensional model for the analysis of transition velocity between different amplification regimes. IDAs with 5-10 mm for both electrodes width and gap were studied numerically and experimentally. The results of the 3D and 1D simulations were consistent between themselves, and also with those of the physical experiments. The relationship between the two mass transfer methods — diffusion and convection — were analyzed at different flow velocities and for different electrode geometries.Here we report a study of transport effects on a microfluidic sensor-chip in which electrochemical sensing is amplified by redox cycling using an interdigitated electrode array (IDA). Our models indicate that there exist two dominant regimes: one which is limited by redox cycling diffusion—a unique feature of IDAs— which is dominant at relatively low flow rates, and another which is limited by convection and has dominant flow effects which are effective at high flow rates (see Figure). The transition velocity between the two sensing regimes depends on the width of the electrode and spacing. It was found to be Vflow [mm/sec]=0.335/L[μm] + 0.04 which is similar to the prediction of Vflow∝1/L obtained from the one-dimensional model.An understanding of the combined effects of redox cycling and convection flow is critical as microfluidic chips with electrochemical sensing amplified by redox cycling using IDAs are becoming widely used in diagnostic assays. The method for prediction of current under any flow rate described here will support technological development of more efficient and accurate devices. Figure 1

Sub-micron alkylated graphene oxide from coal

Sub-micron graphene oxide (GO) has emerged as a promising additive in the realms of composite films and fibers applications. Traditional GO preparation involves acid oxidation of high-purity graphite, yielding particles in micron scale. Achieving sub-micron dimensions typically demands rigorous conditions, leading to increased defects with low yield. In this study, the sp2 carbon domain from anthracite first undergoes graphitization, growing from nano to sub-micron scale, then sub-micron GO is extracted via oxidatively severing its bridging bonds. The resulting GO exhibits an average size of 800 nm, a thickness of 1-2 layers, and a yield of 107%. This methodology is applicable to bituminous and lignite as well. Furthermore, the broken bridging bonds act as alkyl danglings on sub-micron GO and serving as anchors in composites through hydrogen bonding. The reinforcing efficacy of sub-micron GO is demonstrated through the fabrication of composite films and fibers. This work pioneers cost-effective production of high-quality sub-micron GO, elevating coal’s value through advanced applications.

Effect of scandium concentration on the performances of cantilever based AlN unimorph piezoelectric energy harvester with silicon nitride substrate

Microelectromechanical systems (MEMS) offer its ability to sense, control and actuate on sub-micron scale and exhibit its effect on macro scale. To implement any specific MEMS system, small, efficient and long-lifespan micro power sources are required. Piezoelectric energy harvester (PEH) along with radioactive source is one of the most promising approaches to harness electrical energy at micro to millimeter range. In this report, a scandium (Sc) doped Aluminium Nitride (AlN) unimorph piezoelectric energy harvester has been demonstrated. Unimorph piezoelectric layer is built on Silicon Nitride (Si3N4) substrate platform that act as cantilever beam and that can be vibrated by inbuilt radioactive system. In particular, Si3N4 as cantilever material and the impact of Sc doping concentration on electrical and mechanical properties of AlN piezoelectric thin film materials have been studied in MATLAB simulation platform. Results obtained from numerical study suggests that the proposed energy harvester model composed of AlScN unimorph piezoelectric (with 10% Sc doping concentration, Sc-10%) layer and Si3N4 cantilever can yield a maximum power output of ~ 19.33 μW and overall mechanical energy conversion efficiency of ~ 91.07%. These are the maximum output power and mechanical energy conversion efficiency numerically obtained from Sc doped AlN piezoelectric energy harvester systems to the best of our knowledge.