Interface Reconstruction Research Articles

Electron-Beam Writing of Atomic-Scale Reconstructions at Oxide Interfaces.

The epitaxial growth of complex oxides enables the production of high-quality films, yet substrate choice is restricted to certain symmetry and lattice parameters, thereby limiting the technological applications of epitaxial oxides. In comparison, the development of free-standing oxide membranes gives opportunities to create novel heterostructures by nonepitaxial stacking of membranes, opening new possibilities for materials design. Here, we introduce a method for writing, with atomic precision, ionically bonded crystalline materials across the gap between an oxide membrane and a carrier substrate. The process involves a thermal pretreatment, followed by localized exposure to the raster scan of a scanning transmission electron microscopy (STEM) beam. STEM imaging and electron energy-loss spectroscopy show that we achieve atomically sharp interface reconstructions between a 30-nm-thick SrTiO3 membrane and a niobium-doped SrTiO3(001)-oriented carrier substrate. These findings indicate new strategies for fabricating synthetic heterostructures with novel structural and electronic properties.

Identifying Rare Events in Quantum Molecular Dynamics of Nanomaterials with Outlier Detection Indices.

Nanoscale and condensed matter systems evolve on multiple length- and time-scales, and rare events such as local phase transformation, ion segregation, defect migration, interface reconstruction, and grain boundary sliding can have a profound influence on material properties. We demonstrate how outlier detection indices can be used to identify rare events in machine-learning based, high-dimensional molecular dynamics (MD) simulations. Designed to order data-points from typical to untypical, the indices enable one to capture atomic events that are hard to detect otherwise. We demonstrate the approach with a nanosecond MD simulation of a grain boundary in a metal halide perovskite that is extensively studied for solar energy and optoelectronic applications. The method captures the initial grain boundary sliding and a spontaneous fluctuation half a nanosecond later, both events giving rise to persistent deep electronic trap states that impact charge carrier lifetime and transport and material performance. The approach offers a generalizable and simple method for identifying outlier events in complex condensed matter, molecular, and nanoscale systems.

A three-dimensional curve interface reconstruction algorithm for two-phase fluid flow

The curve interface reconstruction algorithm has received significant attention in the context of two-dimensional two-phase flow. However, it remains absent in the three-dimensional scenario. This paper proposes a novel three-dimensional curve interface reconstruction (CIR) algorithm to address this challenge within structured meshes for the first time. Specifically, a portion of the spherical surface is employed to reconstruct the three-dimensional curve interface segment, with the radius and center coordinates determined by curvature and mass conservation constraints, respectively. To enhance curvature accuracy, a sphere-based iterative reconstruction (SIR) algorithm is proposed to calculate the reconstructed distance function (RDF) for the three-dimensional curve interface. Various tests involving the interface reconstruction of spherical, ellipsoidal, and cubic objects demonstrate that the coupled SIR and CIR (SIR-CIR, simplified by SCIR) method achieves higher accuracy than many popular methods, particularly with coarse mesh resolutions. Additionally, the SCIR method offers the advantages of straightforward implementation and coding for interface reconstruction in two-phase flow research. This advantage results in reduced computational costs compared to the coupled volume-of-fluid and level set (VOSET) method, which also utilizes an iterative method to solve RDF.

Enhancement of Catalytic Activity via Inevitable Reconstruction of the Ni-Mo Interface for Alkaline Hydrogen Oxidation.

The inevitable oxidation of nickel-metal-based catalysts exposed to the air will lead to instability and poor reproducibility of a catalytic interface, which is usually ignored and greatly hinders their application for the catalysis of alkaline hydrogen oxidation. The details on the formation of a world-class nickel-based HOR catalyst Ni3-MoOx/C-500 are reported via an interfacial reconstruction triggered by passive oxidation upon air exposure. Interfacial reconstruction, initiated with various Ni-Mo metal ratios and annealing temperature, can fine-tune the Ni-Mo interface with an increased work function and a reduced d-band center. The optimized Ni3-MoOx/C exhibits a record high mass activity of 102.8mA mgNi -1, a top-level exchange current density of 76.5µA cmNi -2, and exceptional resistance to CO poisoning at 1000ppm CO for hours. The catalyzed alkaline exchange membrane fuel cell exhibits a maximum power output of 600mW cm-2 and excellent stability, ranking it as one of the most active non-precious metals HOR catalysts to date.

Resolving subgrid-scale structures for multiphase flows using a filament moment-of-fluid method

Multiphase flows are present in many industrial and engineering applications as well as in some physical phenomena. Capturing the interface between the phases for complex flows is challenging and requires an accurate method, especially to resolve fine-scale structures. The moment-of-fluid (MOF) method improves drastically the accuracy of interface reconstruction compared to previous geometrical methods. Instead of refining the mesh to capture increased levels of detail, the MOF method, which uses zeroth and first moments as well as a conglomeration algorithm, enables subgrid structures such as filaments to be captured at a small extra cost. Coupled to a finite volume Navier–Stokes solver, the MOF method has been tested on a fixed grid and validated using well-known benchmark problems such as the dam break flows, the Rayleigh–Taylor and Kelvin–Helmholtz instability problems, and a rising bubble. The ability of the novel filament MOF method to capture the filamentary structures that eventually form for the Rayleigh–Taylor instability and rising bubble problems is assessed. Good agreement has been found with other numerical results and experimental measurements available in the literature.

Capturing thin structures in VOF simulations with two-plane reconstruction

A novel interface reconstruction strategy for volume of fluid (VOF) methods is introduced that represents the liquid-gas interface as two planes that co-exist within a single computational cell. In comparison to the piecewise linear interface calculation (PLIC), this new algorithm greatly improves the accuracy of the reconstruction, in particular when dealing with thin structures such as films. The placement of the two planes requires the solution of a non-linear optimization problem in six dimensions, which has the potential to be overly expensive. An efficient solution to this optimization problem is presented here that exploits two key ideas: an algorithm for extracting multiple plane orientations from transported surface data, and an efficient and mass-conserving distance-finding algorithm that accounts for two planes with arbitrary orientation. Additionally, a simple and robust strategy is presented to accurately represent the surface tension forces produced at the interface of subgrid-thickness films. The performance of this new VOF reconstruction is demonstrated on several test cases that illustrate the capability to handle arbitrarily thin films.

Unraveling the Fluoride-Induced Interface Reconstruction Across Lead-Based Hierarchical MnO2 Anode in Zinc Electrowinning.

Although the hierarchical manganese dioxide film electrode shows promise as a durable and catalytically active anode for zinc electrowinning, it often fails and deactivates when it is exposed to fluoride-rich environments. The lack of understanding regarding the mechanism behind fluoride-induced irreversible interface reconstruction hinders their practical application in large-scale energy-saving and pollution-reduction efforts. Here, we conducted multidimensional operando investigations to gain insights into the dynamic evolution across the film electrode interface with temporal and spatial resolution. Our findings reveal that electroosmosis of F- initially triggers structural collapse and subsequent reconstruction of [MnO6] units, followed by interaction with the spontaneous oxide film at the surface of lead substrate. Experimental studies and theoretical calculations indicate that F- facilitates the irreversible transformation of γ-MnO2 into more stable yet protective catalytic dual-defective α-MnO2. Additionally, lower levels of F- at the interface promote a change in microenvironmental pH within porous PbSO4, triggering the development of microporous corrosion-resistant β-PbO2 as the dominant phase. The combined effects of MnO2 and interphase evolution effectively explain the abnormally elevated oxygen evolution overpotential. Then, the proposed appropriate application scenarios based on the corrosion behavior will serve as a practical guide for the implementation of the hierarchical manganese dioxide film electrode.

Direct numerical simulation of a subcritical coaxial injection in fiber regime using sharp interface reconstruction

The numerical simulation of space launchers combustion chambers is a topic of increasing interest, as it may help the development of safer and more efficient designs. Understanding fuel injection is a particularly severe challenge. The liquid oxygen is injected by a round orifice surrounded by an annular gaseous stream of fuel, leading in subcritical conditions to a two-phase assisted atomization process. The result of this process is a very dense and polydisperse two-phase flow, which strongly influences the behavior of the chamber. Experimental investigation of this flow is difficult due to the axisymmetric geometry and the dense characteristic of the spray. Neither RANS nor Large Eddy Simulation (LES) possess reliable models able to reproduce the smallest scales of atomization, one of the reasons being the lack of relevant experimental data. Therefore, this work aims to provide detailed information on the atomization process using Direct Numerical Simulation. This paper presents a Direct Numerical Simulation (DNS) of a coaxial liquid–gas assisted atomization in the typical fiber regime encountered in cryogenic injectors. This study aims to better understand the evolution of liquid topology and extract relevant information that may help develop larger-scale models. The flow was first analyzed in terms of topology statistical data, using a dedicated detection and classification algorithm that could characterize the individual liquid structures. These include the central liquid core, the ligament created during primary atomization, and the spherical droplet obtained at the end of the atomization process. Subsequently, a more global statistical topology indicator was investigated, namely the interface area density distribution. This quantity is used in larger-scale RANS or LES models to predict the smallest scales of atomization. Therefore, understanding its behavior in a realistic case is of utmost importance. The interface area density distribution was correlated to the global jet behavior and the liquid topology data obtained by the detection algorithm. The results showed, in particular, a strong correlation between the initial increase of liquid–gas interface area density with the generation of ligaments and between the continuous decrease of the interface area density during droplet formation and stabilization.

Subgrid scale modeling of droplet bag breakup in VOF simulations

The mesh-dependency of the breakup of liquid films, including their breakup length scales and resulting drop size distributions, has long been an obstacle inhibiting the computational modeling of large-scale spray systems. With the aim of overcoming this barrier, this work presents a framework for the prediction and modeling of subgrid-thickness liquid film formation and breakup within two-phase simulations using the volume of fluid method. A two-plane interface reconstruction is used to capture the development of liquid films as their thickness decreases below the mesh size. The breakup of the film is predicted with a semi-analytical model that incorporates the film geometry captured through the two-plane reconstruction. The framework is validated against experiments of the bag breakup of a liquid drop at We=13.8 through the comparison of the resulting drop size and velocity distributions. The generated distributions show good agreement with experimental results for drop resolutions as low as 25.6 cells across the initial diameter. The presented framework enables these drop breakup simulations to be performed at a computational cost three orders of magnitude lower than the cost of simulations utilizing adaptive mesh refinement.

A level set approach to modelling diffusional phase transformations under finite strains with application to the formation of [formula omitted]

This paper presents a sharp interface formulation for modelling diffusional phase transformations. Grain boundary motion is, in accordance with diffusional phase transformation kinetics, determined by the amount of flux towards the interface and is formulated in a level set framework. This approach enables a computational efficiency that can be expected to be higher than what can be achieved with conventional phase field methods. Compatibility of the interfaces is obtained through an interface reconstruction process, in which the locations of triple junction points are also determined. To ensure local equilibrium and a continuous chemical potential across the interfaces, the chemical composition is prescribed at the phase interfaces. The presented model is used to study the growth of the intermetallic compound (IMC) Cu6Sn5 for a system with Sn electroplated on a Cu substrate. A finite strain formulation is incorporated into the model to investigate the effects of the volume change resulting from the IMC formation. In this formulation, the Cu and Sn phases are allowed to deform plastically. The numerical simulations demonstrate IMC growth rates in agreement with experimental measurements. Moreover, the IMC evolves into a scallop-like morphology, consistent with experimental observations.

Electrodeposition of CoSx-graphene nanoplatelets on Ni(OH)2 nanosheets for improving the pseudocapacitance performance

In the present work, binder-free CoSx–graphene nanoplatelets porous structures were coated on Ni(OH)2 nanosheets using a one-step electrodeposition process. The graphene was produced from the electroreduction of CO2∗ intermediates during the electrodeposition of CoSx. The surface morphology and interfacial bonding states of CoSx–graphene@Ni(OH)2 were sensitive to the deposition time and Co–to–thiourea molar ratio (Mr). The interface reconstruction between CoSx–graphene NCs and Ni(OH)2 nanosheets improved the pseudocapacitance performance, which was investigated at different Mr and varying deposition times. Raman spectra verified the presence of graphene and CoSx mixed phases in all heterostructure electrodes, where CoS2 was dominant at Mr = 0.2. An XPS analysis indicated the evolution of various interfacial bonding states (CO, CO, CoONi, and SO) between Ni(OH)2 nanosheets and CoSx-graphene nanoplatelets, revealing the improvement in the interfacial synergy and concentration of electroactive sites. The hybrid CoSx-graphene@Ni(OH)2 NCs at Mr = 0.2 exhibited the highest capacitance of 2116 F∙g−1 at 2 mV∙s−1 and 1618 F∙g−1 at 1 A∙g−1 compared with bare Ni(OH)2, which achieved 1212 F∙g−1 at 2 mV∙s−1 and 882.88 F∙g−1 at 1 A∙g−1, and other NCs. Bare Ni(OH)2 nanosheets retained only capacitance retention of 25 % after 2000 cycles, which improved to 70 % in all CoSx-graphene@Ni(OH)2 nanoplatelets.

Boosting All-Perovskite Tandem Solar Cells by Revitalizing the Buried Tin-Lead Perovskite Interface.

Narrow-bandgap (NBG) mixed tin-lead (Sn-Pb) perovskite solar cells (PSCs) serve as crucial top subcells in all-perovskite tandem solar cells (TSCs). However, the prevalent use of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) hole transport layers (HTLs) in NBG PSCs compromises device efficiency and stability. To address this, the study proposes a revitalizing strategy for the buried interface of Sn-Pb perovskites by directly immersing acetylcholine chloride (ACh) into PEDOT: PSS. ACh acts as a proficient "diver," not only modulating the bottom PEDOT: PSS HTLs but also facilitating the reconstruction of the buried interface and significantly enhancing the quality of the top perovskite layers. This intervention with ACh prevents Sn2+ oxidation, mitigates buried defects, and encourages the growth of large, densely packed grains within Sn-Pb perovskites. Consequently, the optimized NBG PSCs exhibit significantly improved hole transport and reduced carrier recombination, achieving a steady-state efficiency of 22.98% with enhanced stability. Furthermore, these optimized NBG Sn-Pb cells enable highly efficient two-terminal and four-terminal all-perovskite TSCs, boasting steady-state efficiencies of 27.54% (certified at 26.41%) and 28.01%, respectively. This study emphasizes the importance of optimizing NBG PSCs through buried interface reconstruction, propelling the advancement of all-perovskite TSCs.

Interface reconstruction of NiCoP@NiMoP self-supported electrodes for highly efficient alkaline water/seawater electrolysis

Electrocatalytic water splitting is considered a feasible hydrogen generation technique. However, their sluggish kinetics and poor stability remains a huge challenge for alkaline water electrolysis. Herein, we report a corrosion-resistant NiCoP@NiMoP micro-pillar arrays for catalysts. It indicates that a layer of amorphous film on the surface of catalysts exposes many active sites and accelerates the species reconstruction. The prepared hybrid catalysts present an overpotential of 76 mV at −10 mA cm−2 for hydrogen evolution reaction (HER) and 268 mV@100 mA cm−2 for oxygen evolution reaction (OER). Furthermore, the assembled cell realizes a stable and high-efficiency water splitting with cycling life of 100 h in seawater media. This work provides a universal approach toward highly active and durable electrocatalysts.

Tracking the dynamics of catalytic Pt/CeO2 active sites during water-gas-shift reaction

Understanding the atomistic structure of the active site during catalytic reactions is of paramount importance in both fundamental studies and practical applications, but such studies are challenging due to the complexity of heterogeneous systems. Here, we use Pt/CeO2 as an example to study the dynamic nature of active sites during the water-gas-shift reaction (WGSR) by combining multiple in situ characterization tools. We show that the different concentrations of interfacial Ptδ+ – O – Ce4+ moieties at Pt/CeO2 interfaces are responsible for the rank of catalytic performance of Pt/CeO2 catalysts: Pt/CeO2-rod > Pt/CeO2-cube > Pt/CeO2-oct. For all the catalysts, metallic Pt is formed during the WGSR, leading to the transformation of the active sites to Pt0 – Ov – Ce3+ and interface reconstruction. These findings shed light on the nature of the active site for the WGSR on Pt/CeO2 and highlight the importance of combining complementary in situ techniques for establishing structure-performance relationships.

ECM-Mimicking Strontium-Doped Nanofibrous Microspheres for Periodontal Tissue Regeneration in Osteoporosis.

Regenerating periodontal defects in osteoporosis patients presents a significant clinical challenge. Unlike the relatively straightforward regeneration of homogeneous bone tissue, periodontal regeneration requires the intricate reconstruction of the cementum-periodontal ligament-alveolar bone interface. Strontium (Sr)-doped biomaterials have been extensively utilized in bone tissue engineering due to their remarkable pro-osteogenic attributes. However, their application in periodontal tissue regeneration has been scarcely explored. In this study, we synthesized an innovative injectable Sr-BGN/GNM scaffold by integrating Sr-doped bioactive glass nanospheres (Sr-BGNs) into the nanofiber architecture of gelatin nanofiber microspheres (GNMs). This design, mimicking the natural bone extracellular matrix (ECM), enhanced the scaffold's mechanical properties and effectively controlled the sustained release of Sr ions (Sr2+), thereby promoting the proliferation, osteogenic differentiation, and ECM secretion of PDLSCs and BMSCs, as well as enhancing vascularization in endothelial cells. In vivo experiments further indicated that the Sr-BGNs/GNMs significantly promoted osteogenesis and angiogenesis. Moreover, the scaffold's tunable degradation kinetics optimized the prolonged release and pro-regenerative effects of Sr2+ in vivo, matching the pace of periodontal regeneration and thereby facilitating the regeneration of functional periodontal tissues under osteoporotic conditions. Therefore, Sr-BGNs/GNMs emerge as a promising candidate for advancing periodontal regeneration strategies.

A hybrid marching cubes based IsoAlpha method for interface reconstruction

SummaryIn modelling two‐phase flows, accurate representation of interfaces is crucial. A class of methods for interface reconstruction are based on isosurface extraction, which involves a non‐iterative, interpolation based approach. These approaches have been shown to be faster by an order of magnitude than the conventional PLIC schemes. In this work, we present a new isosurface extraction based interface reconstruction scheme based on the Marching Cubes algorithm (MC), which is commonly used in computer graphics for visualizing isosurfaces. The MC algorithm apriori lists and categorizes all possible interface configurations in a single grid cell into a Look Up Table (LUT), which makes this approach fast and robust. We also show that for certain interface configurations, the inverse problem of obtaining the isovalue from the cell volume fraction is not surjective, and a special treatment is required while handling these cases. We then demonstrate the capabilities of the method through benchmark cases for 2D and 3D static/dynamic interface reconstruction.

Interface reconstruction of MXene-Ti3C2 doped CeO2 nanorods for remarked photocatalytic ammonia synthesis

Prospective photocatalytic ammonia synthesis process has received more attentions but quite challenging with the low visible light utilization and weak N2 molecule absorption ability around the photocatalysts. Herein, interface reconstruction of MXene-Ti3C2/CeO2 composites with high-concentration active sites through the carbon-doped process are presented firstly, and obvious transition zones with the three-phase reaction interface are formed in the as-prepared catalysts. The optimal co-doped sample demonstrates an excellent photo response in the visible light region, the strongest chemisorption activity and the most active sites. Moreover, much more in-situ extra oxygen defects are also produced under light irradiation. It is expected that the double decorated catalyst shows a remarked ammonia production rate of above 0.76 mmol gcal−1·h−1 under visible-light illumination and a higher apparent quantum efficiency of 1.08 % at 420 nm, which is one of the most completive properties for the photocatalytic N2 fixation at present.

Numerical study on migration and solidification behavior of molten droplets on structure surface and in debris voids during debris bed melting process

The melt migration and solidification behavior on the surface of metal structure and in the debris voids is a key phenomenon of debris bed melting, which has an important impact on the assessment of reactor pressure vessel damage and melt leakage. In this study, the moving particle semi-implicit (MPS) method with high-order discretization scheme was coupled with a surface tension model that was established based on interface reconstruction. The migration and solidification behavior of UO2–ZrO2 and Fe–Zr melts on the metal structure surface and in the debris voids were investigated with the improved MPS method. The effects of temperature, velocity, contact angle and droplet diameter on the melt migration and solidification were analyzed. The results showed that the molten UO2–ZrO2 droplet on the metal structure surface presented three stages with solidification rate decreasing, while the solidification rate of molten Fe–Zr droplet had little change. The maximum spread factor and solidification rate increased with the increase of droplet falling velocity, but the spread factor was independent of the melt type at the same velocity. The high-temperature molten droplet penetrated the voids formed by the debris with diameter of 5 mm more easily compared to the voids formed by the debris with diameter of 3 mm. The influence of contact angle on the migration of molten droplet with initial velocity was small, and the maximum difference in droplet mass fraction was about 6%. Three groups of molten droplets with different diameters penetrated the voids, and the average increments of penetration mass fraction were 2.3%, 2.7% and 5.8%, respectively, with the increase of velocity. Near the bottom of the debris bed, the molten droplet without initial velocity solidified and blocked the flow channel, but the molten droplet with initial velocity of 0.5 m/s penetrated through the debris voids. The droplet with initial velocity of 0.5 m/s had a faster solidification rate in the voids compared to the droplet without initial velocity, and the droplet solidification mass fraction was 96.27% when the initial melt temperature was 1410 K.

A horizontal refined piecewise curve interface reconstruction (HOPCIR) algorithm for reconstructing the vapor-liquid interface

The vapor-liquid interface can be characterized as a circle or sphere affected by surface tension. However, linearization or planarization processing is commonly employed to simplify the reconstruction of the vapor-liquid interface within a grid cell, introducing errors in numerical simulations of two-phase flow. Therefore, this paper proposes a straightforward and accurate Horizontal Refined Piecewise Curve Interface Reconstruction (HOPCIR) algorithm to reconstruct the curve vapor-liquid interface for the two-dimensional structured grid. In this method, a standardized circle segment is employed to represent the vapor-liquid interface segment within each mixed grid cell, uniquely defined by its radius and center. The radius of this circle is determined by the curvature of the interface segment, and an iterative procedure is employed to calculate the circle's center using the known fluid volume fraction and initial interface obtained by linear reconstruction. Another integral aspect of the HOPCIR algorithm involves solving the reconstructed distance function to enhance the accuracy of curve reconstruction. Comparative analysis with the coupled volume-of-fluid and level set (VOSET) method demonstrates the superior performance of the HOPCIR algorithm in reconstructing vapor-liquid interfaces and solving the reconstructed distance function, interface curvature, surface tension, and fluid volume fraction.

A consistent methodology to transport a passive scalar with the geometric Volume-of-Fluid method isoAdvector

This paper presents a new methodology allowing the discretisation of phase specific transport equations within the Volume-of-Fluid interface capturing method framework. The method uses a sharp interface algorithm to compute the transport of species concentration. The interface reconstruction and advection is provided by the geometric advection scheme isoAdvector[1] implemented in the OpenFOAM® library. When discretising the transport equation for species, lack of consistency with the free surface advection scheme can lead to numerical errors, causing conservation or boundedness issues. This work addresses the issue of consistency in convective transport of species and is divided in two parts. First, a new interpolation procedure is used to compute face values from cell-centered values. Then, the diffusive operator of the transport equation is corrected. Finally, a set of test cases are presented to validate the transport equation's consistency with the free surface advection. Species transport across the interface is not part of the scope of this article, however, this methodology can further be used to study mass transfer at the gas-liquid interface using additional mass source terms that are not discussed here.