Minimization Of Interfacial Energy Research Articles

Assessment of the potential structure and nucleation efficacy of multi-component heterogeneous substrate

In recent years, nucleation of multi-component heterogeneous interface structures has attracted increasing attention due to their excellent grain refinement and anti-poisoning capabilities in Al-Si alloy. In this research, a general methodology was proposed to predict the surface structure and meanwhile evaluate the grain refinement efficacy of the multi-component boride nucleants based on a comprehensive experimental and theoretical study of a novel Al-Si alloy refiner, i.e., Al-3.5Nb-1V-1B. By using high-resolution electron microscopy, the (Nb, V)B2 particle with a characteristic “core-shell” surface structure was observed, attributed to V adsorption driven by interfacial energy minimization, validated by ab initio calculations. A general interfacial energy-based model was then proposed which predicts the multi-component boride substrate structure, well consistent with the experimental findings. The nucleation potency of different substrates was analyzed in atomic scale and only if the interfacial atomic vibration was considered together with the nucleation-influencing factors (i.e., the lattice mismatch and the anti Si-poisoning effect), the predicted nucleation potency order can agree well with the experimental results. A thermodynamics-kinetics combined analytic model was summarized by coupling the lattice mismatch parameter, the interfacial Si adsorption energy and the interfacial atomic vibration amplitude, which accurately evaluates the multi-component boride grain refiners for the Al-Si alloys.

First principles investigation of in-situ NiAl(110)/Ag(111) and NiAl(110)/MoO3(010) heterogeneous interfaces behavior in composite coatings

The interface properties of in-situ NiAl(110)/Ag(111) and NiAl(110)/MoO3(010) heterogeneous interfaces were systematically studied by first-principles calculation method. The interfacial adhesion work, interfacial energy, Mulliken bond population and partial density of states were analyzed, and the bonding mechanism were revealed from the atomic and electronic perspective. The results show that the NiAl(110)/Ag(111) heterogeneous interfaces with OB-NiAl stacking site and the NiAl(110)/MoO3(010) heterogeneous interfaces with OT-Al stacking site are the most stable interface structures with maximum interfacial adhesion work (1.602 J/m2 and 2.833 J/m2, respectively) and minimum interfacial energy (0.7391 J/m2 and −0.8154∼0.7796 J/m2, respectively). Furthermore, charge density differences, partial density of states and Mulliken bond population analysis indicates that the interface bonding mechanism of NiAl (110)/Ag(111) heterogeneous interface is dominated by Al-Ag covalent bonds, and the bonding mechanism of NiAl(110)/MoO3(010) heterogeneous interface is mainly the combination of Al-O ionic bonds and Al-Mo covalent bonds.

Nanomolding of Two-Dimensional Materials.

Lateral confinement of layered, two-dimensional (2D) materials has uniquely enabled the exploration of several topological phenomena in electron transport due to the well-defined nanoscale cross-sections and perimeters. At present, research on laterally confined 2D materials is constrained by the lack of synthesis methods that can reliably and controllably produce nanostructures with narrow widths and high aspect ratios. We demonstrate the use of thermomechanical nanomolding (TMNM) to fabricate nanowires of six layered materials (Te, In2Se3, Bi2Te3, Bi2Se3, GaSe, and Sb2Te3) with widths of 40 nm and aspect ratios above 100. During molding, the van der Waals (vdW) layers rotate by 90° from the horizontal direction in the bulk feedstock to the vertical direction in the molded nanowire, such that the layers are aligned along the nanowire length. We find that interfacial diffusion and surface energy minimization drive nanowire formation during TMNM, often resulting in single-crystalline nanowires with consistent crystallographic orientation.

Two-stage annealing-induced secondary grain growth for enhanced efficiency in CdTe solar cells on flexible polyimide foils

Flexible CdTe solar cells integrated onto polyimide foils are a promising renewable power generation technology. Optimizing crystal structure and reducing grain boundary recombination by CdCl2 annealing are the key approaches to increase carrier concentration and improve device performance. However, the inherent thermal constraints of polyimide substrates limit the feasibility of achieving full annealing. In response, we introduce a novel two-stage annealing process: a primary recrystallization at 350 °C followed by a secondary recrystallization at 380 °C. Employing a rigorous investigation of surface and interface energy minimization, strain energy minimization, and the growth kinetics of Cl drag phenomena, this method induces significant secondary grain growth, surpassing the film thickness itself. The culmination of these efforts yields an extraordinary power conversion efficiency (PCE) of 12.2 %, marking a historic achievement for sputtered CdTe solar cells on polyimide substrates. This study not only unveils a pioneering approach to grain boundary engineering but also offers insights into optimizing the CdCl2 annealing process for CdTe absorbers, ultimately facilitating the realization of high-efficiency, flexible CdTe solar cells.

Achieving superior pyroresistive reproducibility at HDPE/PVDF composites with tailored conductive phase size

AbstractCommercial conductive polymer composites (CPCs) with positive temperature coefficient (PTC) behavior usually suffer from inherent poor reproducibility of pyroresistive property. Herein, a conductive carbon black (CB)/high density polyethylene (HDPE)/polyvinylidene fluoride (PVDF) composite with outstanding PTC reproducibility were prepared through introducing cellulose nanocrystals (CNCs) grafted with methyl methacrylate (CNC‐g‐PMMA). Following the minimum interfacial energy mechanism, the CNC‐g‐PMMA tends to locate in PVDF of binary polymer composites. A much finer morphology of conductive CB/HDPE phase is hence obtained owing to the increasement of PVDF/HDPE viscosity ratio by introducing CNC‐g‐PMMA. Undergoing multiple repeated temperature cycles, the room temperature resistance and PTC intensity of as‐prepared material keep almost unchanged, which demonstrates superior PTC reproducibility. The improving mechanism of PTC reproducibility has also been illustrated in detail. This research provides a facile and valid strategy to enhance the PTC reproducibility and will vastly expand the application of PTC composites in the field of intelligent temperature management.Highlights Assembling binary polymer‐based PTC materials with cocontinuous structure Nanocrystals enables conductive HDPE phase with finer morphology. The precise ranges of viscosity ratio ensure the co‐continuous morphology. Small conductive phase size enhances P reproducibility. Narrow spatial domain restricts the self‐aggregation of conductive fillers.

Excellent thermal stability of nanostructured Al2O3–Y3Al5O12–ZrO2 eutectic ceramic composites by high-speed directional solidification

The contradiction between the nanostructure and thermal stability is the major obstacle on the way of the practical applications of nanomaterials. Here we demonstrated a simple solution for reconciling this contradiction, i.e., the high-speed directional solidification of a ternary eutectic ceramic composite. Its highly textured lamellar and rod-like nanostructures and low-energy interfaces contributed to an outstanding thermal stability that the nanostructure was maintained after being heated at 1573 K for 100 h. It was uncovered that the high solidification rate of 1080 mm/h had an evident restriction on the growth orientation of the faceted crystals during the solidification process, forming a highly textured nanostructure. Combining with the interface energy minimization mechanism, the low-energy interfaces were simultaneously obtained. The evolution of microstructure and interface characteristics during the coarsening process at the higher temperature was further studied. The lamellar structure presented a better thermal stability than that of the rod-like structure since the former had a constraint on the diffusion dimensions. Moreover, a novel structural evolution pattern in the coarsening process was revealed, which was completely different from that of traditional sintered ceramics. The solidified specimens could further keep stable in density, homogeneity of structure and size of internal pores during heat treatment, contributing to a better stability in hardness than that of traditional sintered specimens.

Tuning the potential drop at graphene/protic ionic liquid interface by molecular structure engineering

Ionic liquids (ILs) have been extensively employed in many applications involving interfaces with carbon-based electrodes, such as energy storage devices (batteries or supercapacitors) or electrocatalytic devices, where the way each ion of the IL interacts with the electrode has a strong impact on the overall performance of the device. For instance, the amount of potential difference between the electrode and the bulk of the IL is highly sensitive to the IL composition and it is directly related to the device capacitance. The selection of the most suited pair of ions often proceeds by time-consuming and costly trial-and-error approaches. It is necessary to understand the atomistic features of the interface to determine the effect of each ion on the potential drop. By classical molecular dynamics simulations, we show that it is possible to quickly infer the interface potential arising at the carbon electrode by carefully inspecting the molecular structure of the IL. The ion orientation at the interface is, in fact, determined by the distribution of charges within the molecules. Depending on where charges are located, ions can either lie flat or perpendicular to the interface to minimize the surface energy. The interface potential is found to be mainly determined by ion–ion interactions dictating the interface energy minimization process, whereas ion–electrode interactions are found to enforce higher ordering and charge layers stacking but not to induce selective adsorption of an ion over the other.

Contact Angle on Rough Curved Surfaces and Its Implications in Porous Media

The equilibrium contact angle depends on both the chemistry of the two fluids and solid base and the microstructure on the solid surface. Actual surface of the pore wall in porous media is typically rough and curved, which has not been well-considered in related applications. This work uses a free interfacial energy minimization approach to theoretically derive the equilibrium contact angle on two specific surface structures on flat surfaces and extends the derivation considering the surface curvatures in porous media. Results reveal that the equilibrium contact angle is not dependent on the curvature of spherical surfaces, and we further prove that this conclusion applies to any point along the apparent common line at solid surfaces with any arbitrary curvature. The fundamental physics is the local mechanical balance of a composite contact among three interfacial tensions. Furthermore, the contacting mode can shift from non-wetting to wetting when the pressure difference between two fluids exceeds the entry pressure of the microstructures, which should be considered in relative dynamic scenarios such as rain droplet impact and fluid displacement in porous media. Note that these conclusions are from pure theoretical analysis based on idealistic assumptions, and real circumstances may deviate from these assumptions.

A Leaky Integrate-and-Fire Neuron Based on Hexagonal Boron Nitride (h-BN) Monocrystalline Memristor

As a competitive candidate for artificial neurons, memristors have become the focus of intense research owing to their intrinsic ion migration tunability, enabling an authentic implementation of biomimicry. However, they still suffer from variability issues due to 3-D uncontrollable filament dynamics in an amorphous medium and modeling of switching dynamics underlying filament growth and rupture is still under investigation. In this work, we present volatile memristors that exhibit desired characteristics for neuromorphic computing with low performance variations utilizing a hexagonal boron nitride (h-BN) monocrystalline as a switching medium. Theoretical investigations assisted by the Monte Carlo simulation combined with experimentally detected <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> characteristics described that the electric field dominates the set process, whereas the Gibbs–Thomson interfacial energy minimization and heat dissipation influence the relaxation process mostly. Additionally, h-BN memristors with high switching uniformity provide an ideal hardware platform for credible neuron emulation and software identification of digital images.

Strain‐Driven Thermal and Optical Instability in Silver/Amorphous‐Silicon Hyperbolic Metamaterials

AbstractHyperbolic metamaterials show exceptional optical properties, such as near‐perfect broadband absorption, due to their geometrically‐engineered optical anisotropy. Many of their proposed applications, such as thermophotovoltaics or radiative cooling, require high‐temperature stability. In this work, Ag/a‐Si multilayers are examined as a model system for the thermal stability of hyperbolic metamaterials. Using a combination of nanotomography, finite element simulations, and optical spectroscopy, the thermal and optical instability of the metamaterials is mapped. Although the thermal instability initiates at 300 °C, the hyperbolic dispersion persists up to 500 °C. Direct finite element simulations on tomographical data provide a route to decouple and evaluate interfacial and elastic strain energy contributions to the instability. Depending on stacking order the instability's driving force is either dominated by changes in anisotropic elastic strain energy due thermal expansion mismatch or by minimization of interfacial energy. These findings open new avenues to understand multilayer instability and pave the way to design hyperbolic metamaterials able to withstand high temperatures.

Facile Fabrication of Starch-Based Microrods by Shear-Assisted Antisolvent-Induced Nanoprecipitation and Solidification.

Rod-like particles have attracted increasing attention because of their unique shape-dependent properties, which enable their superior performance compared to their isotropic counterparts. Thus, rod-like particles have potential applications in many fields, especially in biomedicine. However, the fabrication of uniform rod-like particles is challenging because of the principle of interfacial energy minimization. Herein, we present a facile, rapid, and cost-effective strategy for preparing starch-based microrods with tunable aspect ratios via shear-assisted antisolvent-induced nanoprecipitation and solidification. The preformed spherical particles swollen by the mixed solvent were elongated by the shear force and solidified in rod-like shape by antisolvent induction. The resulting starch-based microrods can encapsulate hydrophobic active substances and be modified with functional groups, indicating their potential applications as drug carriers and biologically active materials. The formation mechanism of the starch-based microrods discovered in this study provides a new perspective on the fabrication of rod-like polymer particles.

Observations of unexpected grain boundary migration in SrTiO3

High-energy x-ray diffraction microscopy (HEDM) nondestructively maps microstructures in 3D, allowing for the same grains and boundaries to be tracked over time during annealing experiments. Here, HEDM was applied to observe grain growth in strontium titanate. These results are compared to a 3D isotropic grain growth simulation that starts from the same initial microstructure to identify potentially unknown grain boundary migration mechanisms. During the simulation, grain growth behaves as expected: the change in grain volume is correlated with the number of neighbors, and the grain boundary velocity is correlated with its local curvature. Experimentally, however, flat boundaries were found to move faster than curved boundaries, and 37% of all measured boundaries move in the direction opposite to their curvature. These unexpected observations suggest that, in materials with anisotropic grain boundary properties, mechanisms other than curvature-driven boundary migration play a role in the minimization of interfacial energy.

Solution-based synthesis of wafer-scale epitaxial BiVO4 thin films exhibiting high structural and optoelectronic quality.

We demonstrate a facile approach to solution-based synthesis of wafer-scale epitaxial bismuth vanadate (BiVO4) thin films by spin-coating on yttria-stabilized zirconia. Epitaxial growth proceeds via solid-state transformation of initially formed polycrystalline films, driven by interface energy minimization. The (010)-oriented BiVO4 films are smooth and compact, possessing remarkably high structural quality across complete 2′′ wafers. Optical absorption is characterized by a sharp onset with a low sub-band gap response, confirming that the structural order of the films results in correspondingly high optoelectronic quality. This combination of structural and optoelectronic quality enables measurements that reveal a strong optical anisotropy of BiVO4, which leads to significantly increased in-plane optical constants near the fundamental band edge that are of particular importance for maximizing light harvesting in semiconductor photoanodes. Temperature-dependent transport measurements confirm a thermally activated hopping barrier of ∼570 meV, consistent with small electron polaron conduction. This simple approach for synthesis of high-quality epitaxial BiVO4, without the need for complex deposition equipment, enables a broadly accessible materials base to accelerate research aimed at understanding and optimizing photoelectrochemical energy conversion mechanisms.

Wearable healthcare smart electrochemical biosensors based on co-assembled prussian blue-graphene film for glucose sensing.

Wearable film-based smart biosensors have been developed for real-time biomolecules detection. Particularly, interfacial co-assembly of reduced graphene oxide-prussian blue (PB-RGO) film through electrostatic interaction has been systematically studied by controllable pH values, achieving optimal PB-RGO nanofilms at oil/water (O/W) phase interface driven by minimization of interfacial free energy for wearable biosensors. As a result, as-prepared wearable biosensors of PB-RGO film could be easily woven into fabrics, exhibiting excellent glucose sensing performance in amperometric detection with a sensitivity of 27.78 µA mM-1cm-2 and a detection limit of 7.94μM, as well as impressive mechanical robustness of continuously undergoing thousands of bending or twist. Moreover, integrated wearable smartsensing system could realize remotely real-time detection of biomarkers in actual samples of beverages or human sweat via cellphones. Prospectively, interfacial co-assembly engineering driven by pH-induced electrostatic interaction would provide a simple and efficient approach for acquiring functional graphene composites films, and further fabricate wearable smartsensing devices in health monitoring fields.

Plug-and-play microfluidic production of monodisperse giant unilamellar vesicles using droplet transfer across Water–Oil interface

Giant unilamellar vesicles (GUVs) are cell-sized compartments widely used in biological and chemical applications. The monodispersity of GUVs is essential for quantitative analysis and experimental reproducibility in biomimetic microreactor studies. In this study, we established a highly reproducible plug-and-play microfluidics-based method to generate monodisperse GUVs without surface treatment of the channel or precise flow-rate adjustment. In the microfluidic channel, we generated water-in-oil (W/O) droplets through hydrodynamic flow focusing and transferred across the W–O interface to form thin-shelled water-in-oil-in-water (W/O/W) droplets as precursors to GUVs. The success rate of the W/O droplet transfer reached nearly 100% by stabilizing the co-flow of oil and water and adjusting the curvature of the W–O interface. Owing to interfacial energy minimization, the thin oil layer of the W/O/W droplets dewetted and detached to form GUVs. We performed a membrane-protein insertion assay to confirm the unilamellarity of the GUVs and their shrinkage caused by osmotic action.

Morphological instability of the G-phase induced a different contribution to hardening of ferrite phase in a duplex stainless steel

G-phase plays an indispensable role in the hardening of ferrite during thermal aging process of the duplex stainless steel. Although there are many studies on quantifying the contribution of spinodal decomposition and G-phase precipitation to the hardening of ferrite, details regarding the influence of G-phase morphology transformation on hardening are lacking. These knowledge gaps hinder a deep understanding of the correlation between G-phase and ferrite hardening, and hence hinder the exploration of new techniques for repairing performance degradation. In this study, after aging at 400 °C and 475 °C, driven by the minimization of interfacial energy, the morphology of G-phase changes from sphere to cube, and consequently the contribution of G-phase to hardening increases significantly. After annealing at 550 °C, the G-phase does not dissolve, but coarsens, resulting in a further increase in the contribution to hardening. The difference from annealing is that after pulsed electric field treatment at 460 °C, the unstable spherical G-phase precipitates are almost completely dissolved, while the stable cubic G-phase is spheroidized. The behaviors of dissolution and spheroidization are driven by the intervention of the electric free energy, and as a result, the hardening caused by G-phase is eliminated or relieved due to the dissolution and refinement of G-phase. It is conceivable that this work is a decisive step to completely repair the deteriorated performance of duplex stainless steel after long-term operation.

Textural evolution of metallic phases in a convecting magma ocean: A 3D microtomography study

The textures of solid and molten metal in the presence of varying fractions of silicate melt at high temperature have been investigated to shed light on differentiation processes occurring in magma oceans formed on rocky bodies of the early solar system. Analogue experiments have been performed in a three-phase system (composed of coexisting metal, forsterite and silicate melt) in both static (1 GPa, 1723 K) and dynamic (i.e. agitated, at 1 bar, 1713 K and 1743 K) conditions. Micro-textures were analyzed with SEM and EBSD techniques, while meso-textures of the metallic phase were analyzed using ex-situ 3D microtomography.Although all samples exhibit the same micro-scale organization consistent with the minimization of local interfacial energies, their meso-scale textures differ significantly. Static conditions produce metal grains that have shapes close to spherical, corresponding to the state predicted by the grain-scale minimization of interfacial energies. In contrast, under dynamic conditions and in the presence of high silicate melt fractions (≥50 vol%), molten metal coalesces to form pools with sizes that are several orders of magnitude larger than those predicted by grain growth mechanisms. Furthermore, in agreement with expectations based upon an interfacial energy budget, images show that nickel grains, whether solid or molten, do not occur surrounded entirely by silicate melt, but rather in contact with both forsterite crystals and silicate melt, leading to the formation of composite aggregates.Assuming that a magma ocean has less than 50 vol% of crystals (the upper limit that permits convective motion), thermodynamic calculations indicate that at the necessary temperatures, the metallic subsystem (Fe-Ni-S) of the planetesimal is entirely molten and the silicate residue is only composed of olivine. Convective motions in such a body will drive agitation, promoting the formation of composite aggregates of olivine and molten iron-sulfide, their initial coalescence and subsequent fragmentation. In detail, these composite aggregates have a reduced density contrast with the surrounding silicate melt that reduces their settling velocities compared to pure metal. They also entrain olivine during the downward migration of iron-sulfide pools. Olivine grains concentrate at the surface of the metallic pools, hindering coalescence between pools or with a pre-existing core. An alternative differentiation scenario for core formation is explored in which the simple compaction of partially molten mixtures in the basal non-convecting layer of the magma ocean expels the interstitial silicate melt upward, such that the local fraction of iron-sulfide increases by mass-balance, reaching its percolation threshold and allowing core formation. This process is not only limited to early accreted planetesimals but may also occur in terrestrial bodies.

Evolution of grain boundary α phase during cooling from β phase field in a α + β titanium alloy

Evolution of grain boundary α (GB α) in a α + β titanium alloy had been examined by morphology and crystallographic orientation analysis. The results indicate that GB α only retains a Burgers orientation relationship (BOR) with one of the adjacent β grains in most of the prior β/β boundaries. The colony α (single crystallographic variant of parallel α plates) tends to evolve in the adjacent β grain that maintains BOR with GB α, whereas the dendritic α (small protuberances of GB α) tends to grow in the other adjacent β grain that does not maintain BOR with GB α. Additionally, two α colonies developing into two adjacent β grains from GB α keep the same crystallographic orientation as that of GB α when GB α maintain a near BOR with both adjacent β grains in a special prior β/β boundary (60°/〈1 1 0〉). These observations are understood from the perspective of minimum interfacial energy and strain energy.

Nanoprecipitation behavior and resultant mechanical and magnetic properties in Fe–Si–Ni–Al–Mn high strength non-oriented silicon steel

Low mismatch and low energy interface between precipitates and ferrite matrix was adopted to promote the precipitation of high density of uniformly dispersed coherent NiAl phase in the silicon steel, aiming to improve strength to meet the requirement of drive motor. The precipitation mechanism of NiAl and its influence on magnetic and mechanical properties of silicon steel were studied. The theoretical lattice mismatch between precipitation and matrix was 0.72%, and a new high strength non-oriented silicon steel reinforced by B2 structure NiAl precipitation with a volume content of 1.73% and an average size of 15 nm was prepared. The uniformity of precipitation size and minimization of interface energy remarkably reduced the driving force for NiAl precipitation and hindered the Ostwald ripening. The texture of annealed silicon steel was characterized by strong α* fiber with a peak at {411}<148> and a moderate γ fiber texture with a peak at {111}<110>. With increase in aging time (from 0 h to 16 h), the strength of silicon steel increased to peak values then decreased and the magnetic properties decreased slightly. The nano-scale NiAl precipitation had little effect on coercivity and hysteresis loss of silicon steel while improving the strength of silicon steel, P10/400 and P10/1000, of silicon steel was as low as 21.7 W/kg and 93.3 W/kg, respectively in the peak-aged condition (at 550 °C for 4 h), and the yield strength was 802 MPa. Thus, it is underscored that using NiAl precipitation as strengthening phase improves the mechanical properties of silicon steel without excessively deteriorating the magnetic properties.

Tensile strain induced texture evolution in a Ni–Mo alloy with extremely fine nanotwinned columnar grains

In the present paper, plastic deformation in an electrodeposited nanotwinned columnar grained Ni–Mo film with an extremely fine columnar grain size of 8 ± 1.7 nm and a twin thickness of 1.3 ± 0.5 nm was investigated via uniaxial micro-tensile tests at room temperature. We found significant detwinning and an evident texture evolution from a randomly-oriented in-plane fiber texture to a highly-oriented out-of-plane texture in the alloy upon tensile straining when tensile direction was oriented in parallel to the twinning plane. Interface energy minimization characterized by the substitution of high angle grain boundaries by low angle grain boundaries and incoherent twin boundaries constitutes the driving force of the texture evolution. Tensile plastic deformation can be attributed to the activity of threading dislocations, which not only contributes to a high yield strength of 2.11 GPa, but also results in in-plane lattice rotation with noticeable deformability.