Low Interfacial Energy Research Articles

Heat Transport at Silicon Grain Boundaries

AbstractEngineering microstructural defects, like grain boundaries, offers superior control over transport properties in energy materials. However, technological advancement requires establishing microstructure‐property relations at the micron or finer scales, where most of these defects operate. Here, the first experimental evidence of thermal resistance for individual silicon grain boundaries, estimated with a Gibbs excess approach, is provided. Coincident site lattice boundaries exhibit uniform excess thermal resistance along the same boundary, but notable variations from one boundary to another. Boundaries associated with low interface energy generally exhibit lower resistances, aligning with theoretical expectations and previous simulations, but several exceptions are observed. Transmission electron microscopy reveals that factors like interface roughness and presence of nanotwinning can significantly alter the observed resistance, which ranges from ∼0 to up to ∼2.3 m2K/GW. In stark contrast, significantly larger and less uniform values ‐ from 5 to 30 m2K/GW ‐ are found for high‐angle boundaries in spark‐plasma‐sintered polycrystalline silicon. Further, finite element analysis suggests that boundary planes that strongly deviate from the sample vertical (beyond ∼45°) can show up to 3‐times larger excess resistance. Direct correlations of properties with individual defects enable the design of materials with superior thermal performance for applications in energy harvesting and heat management.

Atomistic study of intermetallics of Fe–Al–Zn system and their interfacial properties

Galvanizing is an important industrial process to improve the corrosion resistance of advanced high strength steels (AHSSs) that are vital for automotive industries. During galvanizing, nanoscale intermetallic phases with complex crystal structures are formed at the interface between the steel substrate and the zinc overlay. To better understand the nanoscale structures and the interfacial properties between the intermetallics, in this work, we develop a second nearest neighbor (2NN) Fe–Al–Zn ternary Modified Embedded Atom Method (MEAM) potential to describe the crystal structures of the intermetallics, i.e. Fe3Al8, Fe4Zn9 and FeZn13 and to calculate the interfacial structure and energy between them. The developed MEAM potential describes well the complex crystal structures and can be used to investigate the interfacial properties that are difficult to obtain from experiments. The Fe4Zn9, FeZn13 surface energies; the Fe–Fe4Zn9, Fe–FeZn13, Fe3Al8–FeZn13 interfacial energies; and the work of adhesion are calculated with the developed MEAM potential. The results show that FeZn13 crystal orientation has an insignificant effect on the FeZn13 surface energy and the Fe–FeZn13 interfacial energy. A negative interfacial energy is obtained for the Fe–Fe4Zn9 and the Fe–FeZn13 interface. The lowest interfacial energy is obtained in the {100}Fe case. The interfacial energy of Fe3Al8–FeZn13 depends on the surface termination of Fe3Al8 and FeZn13. A low interfacial energy is obtained when the surface termination of Fe3Al8 and FeZn13 are both Fe rich. In contrast, when the surface termination of Fe3Al8 is Al rich or the surface termination of FeZn13 is Zn rich, no low energy, stable interface can be formed between the two phases.

Unraveling the Correlation between the Interface Structures and Tunable Magnetic Properties of La1-xSrxCoO3-δ/La1-xSrxMnO3-δ Bilayers Using Deep Learning Models.

Perovskite oxides are gaining significant attention for use in next-generation magnetic and ferroelectric devices due to their exceptional charge transport properties and the opportunity to tune the charge, spin, lattice, and orbital degrees of freedom. Interfaces between perovskite oxides, exemplified by La1-xSrxCoO3-δ/La1-xSrxMnO3-δ (LSCO/LSMO) bilayers, exhibit unconventional magnetic exchange switching behavior, offering a pathway for innovative designs in perovskite oxide-based devices. However, the precise atomic-level stoichiometric compositions and chemophysical properties of these interfaces remain elusive, hindering the establishment of surrogate design principles. We leverage first-principles simulations, evolutionary algorithms, and neural network searches with on-the-fly uncertainty quantification to design deep learning model ensembles to investigate over 50,000 LSCO/LSMO bilayer structures as a function of oxygen deficiency (δ) and strontium concentration (x). Structural analysis of the low-energy interface structures reveals that preferential segregation of oxygen vacancies toward the interfacial La0.7Sr0.3CoO3-δ layers causes distortion of the CoOx polyhedra and the emergence of magnetically active Co2+ ions. At the same time, an increase in the Sr concentration and a decrease in oxygen vacancies in the La0.7Sr0.3MnO3-δ layers tend to retain MnO6 octahedra and promote the formation of Mn4+ ions. Electronic structure analysis reveals that the nonuniform distributions of Sr ions and oxygen vacancies on both sides of the interface can alter the local magnetization at the interface, showing a transition from ferromagnetic (FM) to local antiferromagnetic (AFM) or ferrimagnetic regions. Therefore, the exotic properties of La1-xSrxCoO3-δ/La1-xSrxMnO3-δ are strongly coupled to the presence of hard/soft magnetic layers, as well as the FM to AFM transition at the interface, and can be tuned by changing the Sr concentration and oxygen partial pressure during growth. These insights provide valuable guidance for the precise design of perovskite oxide multilayers, enabling tailoring of their functional properties to meet specific requirements for various device applications.

Interfacial Chemistry Design for Hybrid Lithium‐Ion/Metal Batteries Under Extreme Conditions

AbstractThe storage behavior of Li ions in the anode limits the energy density of full cell. Storing entirely as Li ions sacrifices energy density while storing entirely as Li metal shortens cycle life. The hybrid behavior maximizes both energy density and lifespan through good anode candidate and interface engineering. In this work, Li ions storage is tailored in carbon film (CF) as a hybrid Li‐ion/metal to reduce Li metal consumption at low N/P ratios. A series of weakly solvating electrolytes are screened to enhance the Li intercalation ability of the CF anode while inducing highly reversible Li metal plating/stripping. Among them, 1 m LiFSI‐THF‐0.5 wt.%LiNO3 electrolyte achieves a low interfacial energy barrier, allowing the CF anode not only to have the highest intercalation capacity of 236.5 mAh g−1, but also to exhibit excellent cycling stability and high Coulombic efficiency, even at fast charging and low temperature. The NCM811||CF full cell with a low N/P ratio of 0.5 delivers a capacity of 527.3 mAh g−1 at 25 °C, and 381.5 mAh g−1 at −20 °C, achieving energy densities of 312.6 and 223.7 Wh kg−1, respectively. 100 mAh pouch cell can be cycled stably over 500 cycles, with a capacity retention of 83.0%.

Improving long-term thermal stability in twin-roll cast Al-Mg-Si-Cu alloys by optimizing Mg/Si ratios

Achieving high thermal stability in the 6xxx series alloys remains a challenging task, which limits their engineering application. Herein, Al-Mg-Si-Cu alloys with various Mg/Si ratios (0.5, 1, 2, and 4) were fabricated by twin-roll casting (TRC), and the microstructure evolution and mechanical properties during long-term thermal exposure of 150 °C/1000 h were studied. The results disclosed that alloys with a high Mg/Si ratio exhibited better thermal stability. The alloys with the Mg/Si ratio of 2 (Mg/Si∼2) achieved a stable high yield strength of ∼330 MPa and meanwhile maintained a satisfactory fracture elongation (> 10 %) throughout the thermal exposure process. This excellent thermal stability can be attributed to the microstructure consisting of high-density L phases and fine α-AlFeSi phases, which was related to the optimized Mg/Si ratio. Specifically, L phases were dominated in peak-aged Mg/Si∼2 alloys, while the counterparts in alloys with the Mg/Si ratio of 1 (Mg/Si∼1) were β'' and Q' phases. During the thermal exposure process, the L phases remained stable without coarsening, which was mainly due to the high coherence and low interfacial energy of the L-matrix interface. Meanwhile, the main Fe-containing phases in Mg/Si∼2 and Mg/Si∼1 alloys were fine near-spheroidal α-AlFeSi and large-size needle-like β-AlFeSi, respectively, which lead to a better ductility of Mg/Si∼2 alloys. This work may provide a strategy for the preparation of 6xxx series alloys with high thermal stability.

Phase field modeling of hyperelastic material interfaces –Theory, implementation and application to phase transformations

Interface mechanics can significantly govern the evolution of multiple phases on smaller scales, e.g., determining the properties of TWIP- and TRIP-steels, geopolymers or Li-ion batteries. The present contribution is specifically centered around the influence of interface elasticity on mechanically induced phase transformations. A geometrically exact finite element framework is developed for this purpose based on incremental energy minimization. It is set up in three-dimensional space and comprises an Allen-Cahn type phase field formulation based on a Modica-Mortola double-well functional, as well as a Ginzburg-Landau type viscosity formulation. The phase field approximation of the interface deformation gradient is derived by means of homogenization theory. A monolithic solver is employed for the resulting set of non-linear coupled equations. The example of coalescing spheres shows that larger interface energies can amplify and accelerate coalescence. Lower interface energies, in contrast, allow for distinct spreading of the energetically favorable bulk phase. Deformation-dependent interface energies particularly add stress peaks to this process that are localized at the phase transition zone. The relaxation of a stepped interface shape showed that deformation-dependent interface energies favor a plane partition of the bulk phases. Yet, they also delay breakup events compared to simple constant interface energies. This peculiarity can be beneficial for calibration purposes. Strain dependence moreover causes an additional elastic stiffness in the direction of the interface tangent plane and constitutes thus another origin for anisotropy of the overall structure.

Room-temperature quantum emission from interface excitons in mixed-dimensional heterostructures

The development of van der Waals heterostructures has introduced unconventional phenomena that emerge at atomically precise interfaces. For example, interlayer excitons in two-dimensional transition metal dichalcogenides show intriguing optical properties at low temperatures. Here we report on room-temperature observation of interface excitons in mixed-dimensional heterostructures consisting of two-dimensional tungsten diselenide and one-dimensional carbon nanotubes. Bright emission peaks originating from the interface are identified, spanning a broad energy range within the telecommunication wavelengths. The effect of band alignment is investigated by systematically varying the nanotube bandgap, and we assign the new peaks to interface excitons as they only appear in type-II heterostructures. Room-temperature localization of low-energy interface excitons is indicated by extended lifetimes as well as small excitation saturation powers, and photon correlation measurements confirm antibunching. With mixed-dimensional van der Waals heterostructures where band alignment can be engineered, new opportunities for quantum photonics are envisioned.

Rapid thermal process for fabricating α-alumina tight ultrafiltration membrane with narrow pore size distribution

The development of tight ceramic ultrafiltration membranes for water purification facilitates is challenging because of high fabrication costs and low permeate flux. In this study, a low-energy rapid thermal process (RTP) was comprehensively investigated for fabricating of high-precision, permeable α-alumina tight ultrafiltration membranes. Compared to the conventional thermal process (CTP), RTP offers an ultra-fast heating rate and shorter holding time, effectively mitigating grain growth and pore aggregation. Moreover, the decomposition of organic matter is delayed during RTP, providing a lower interfacial energy that enables direct formation of α-alumina at a low temperature of 750 °C. During a secondary subsequent RTP, the residual phase is fully converted to α-alumina by the in-situ seeding effect. By utilizing RTP, we successfully prepared α-alumina ultrafiltration membranes within 30 min by calcination, with an average pore size of approximately 6 nm, a narrow pore distribution coefficient of 1.12, and high permeance of 219 L−1·m−2·h−1·bar−1.

The first-principles and ab initio molecular dynamics simulations revealing the interface energy of the NbC/α-Fe

The low index interfacial configuration, interface energy and electronic properties of NbC/α-Fe are calculated using the first-principles method based on density functional theory and ab initio molecular dynamics simulation. Additionally, the NbC/α-Fe interface with the low index interfacial configuration is calculated by two-dimensional disregistry method. It is demonstrated that the Fe-C type has an interface energy of -1.553 J/m2 , the smallest interface energy and the most stable structure, therefore the Fe-C type is the most stable conformation of the NbC(001) /α-Fe(001). Strong orbital resonance phenomenon exists between Fe-3d, Nb-4d and C-2p, producing strong metallic and covalent bonds. The results of disregistry calculation by different interfacial structures of NbC/α-Fe shows that the disregistry of NbC(001)/α-Fe(001) crystalline surface is the smallest at 10.19%, which corresponds to the results of interface energy calculation. It can be shown that the α-Fe(001) is the optimal orientation surface of the NbC(001) . Herein, we have revealed the site-oriented and stable bonding mode relationship of NbC/α-Fe interface in steel, which provides important theoretical guidance to explore the mechanism of grain refinement of NbC particles in shipbuilding steels.

Dipolar Chemical Bridge Induced CsPbI3 Perovskite Solar Cells with 21.86 % Efficiency.

CsPbI3 perovskite receives tremendous attention for photovoltaic applications due to its ideal band gap and good thermal stability. However, CsPbI3 perovskite solar cells (PSCs) significantly suffer from photovoltage deficits because of serious interfacial energy losses within the PSCs, which to a large extent affects the photovoltaic performance of PSCs. Herein, a dipolar chemical bridge (DCB) is constructed between the perovskite and TiO2 layers to lower interfacial energy losses and thus improve the charge extraction of PSCs. The results reveal that the DCB could form a beneficial interfacial dipole between the perovskite and TiO2 layers, which could optimize the interfacial energetics of perovskite/TiO2 layers and thus improve the energy level alignment within the PSCs. Meanwhile, the constructed DCB could also simultaneously passivate the surface defects of perovskite and TiO2 layers, greatly lowering interfacial recombination. Consequently, the photovoltage deficit of CsPbI3 PSCs is largely reduced, leading to a record efficiency of 21.86 % being realized. Meanwhile, the operation stability of PSCs is also largely improved due to the high-quality perovskite films with released interfacial tensile strain being obtained after forming the DCB within the PSCs.

Dipolar Chemical Bridge Induced CsPbI3 Perovskite Solar Cells with 21.86 % Efficiency

AbstractCsPbI3 perovskite receives tremendous attention for photovoltaic applications due to its ideal band gap and good thermal stability. However, CsPbI3 perovskite solar cells (PSCs) significantly suffer from photovoltage deficits because of serious interfacial energy losses within the PSCs, which to a large extent affects the photovoltaic performance of PSCs. Herein, a dipolar chemical bridge (DCB) is constructed between the perovskite and TiO2 layers to lower interfacial energy losses and thus improve the charge extraction of PSCs. The results reveal that the DCB could form a beneficial interfacial dipole between the perovskite and TiO2 layers, which could optimize the interfacial energetics of perovskite/TiO2 layers and thus improve the energy level alignment within the PSCs. Meanwhile, the constructed DCB could also simultaneously passivate the surface defects of perovskite and TiO2 layers, greatly lowering interfacial recombination. Consequently, the photovoltage deficit of CsPbI3 PSCs is largely reduced, leading to a record efficiency of 21.86 % being realized. Meanwhile, the operation stability of PSCs is also largely improved due to the high‐quality perovskite films with released interfacial tensile strain being obtained after forming the DCB within the PSCs.

Tuning the Crystallization Mechanism by Composition Vacancy in Phase Change Materials.

Interface-influenced crystallization is crucial to understanding the nucleation- and growth-dominated crystallization mechanisms in phase-change materials (PCMs), but little is known. Here, we find that composition vacancy can reduce the interface energy by decreasing the coordinate number (CN) at the interface. Compared to growth-dominated GeTe, nucleation-dominated Ge2Sb2Te5 (GST) exhibits composition vacancies in the (111) interface to saturate or stabilize the Te-terminated plane. Together, the experimental and computational results provide evidence that GST prefers (111) with reduced CN. Furthermore, the (8 - n) bonding rule, rather than CN6, in the nuclei of both GeTe and GST results in lower interface energy, allowing crystallization to be observed at the simulation time in general PCMs. In comparison to GeTe, the reduced CN in the GST nuclei further decreases the interface energy, promoting faster nucleation. Our findings provide an approach to designing ultrafast phase-change memory through vacancy-stabilized interfaces.

Achieving superior grain refinement efficiency for Al–Si casting alloys through a novel Al–La–B grain refiner

Conventional Al–Ti–B and Al–Ti–C refiners fail to refine Al–Si casting alloys with high Si content due to the well-known “Si-poisoning” effect. Developing a novel grain refiner with superior grain refinement efficiency for Al–Si casting alloys is the research focus in recent years. In this work, a superior anti Si-poisoning α-Al grain refiner Al–2La–1B alloy with fine LaB6 particles was successfully fabricated via the aluminum melt reaction method. The microstructural evolution, grain refinement performance and refinement mechanisms of the Al–2La–1B alloy were comprehensively investigated based on the experiment results and first-principles calculations. The currently designed Al–2La–1B refiner presents supreme grain refinement efficiency on Al–Si casting alloys. The average grain size of Al–7Si alloy inoculated with 0.5% Al–2La–1B alloy can be refined to 67 ± 5 μm. The superior grain refinement performance can be attributed to the presence of fine LaB6 particles in the refiner. These particles are highly stable in Al–Si alloy melt and can directly act as the potent nucleation sites for α-Al due to the small lattice misfit and low interfacial energy. Moreover, the nucleation potency of the LaB6 particles will not be influenced by the solute Si element. Our work provides an effective strategy for designing a superior α-Al grain refiner for Al–Si casting alloys.

The use of biomimetic surfaces to reduce single- and dual-species biofilms of Escherichia coli and Pseudomonas putida

The ability of bacteria to adhere to and form biofilms on food contact surfaces poses serious challenges, as these may lead to the cross-contamination of food products. Biomimetic topographic surface modifications have been explored to enhance the antifouling performance of materials. In this study, the topography of two plant leaves, Brassica oleracea var. botrytis (cauliflower, CF) and Brassica oleracea capitate (white cabbage, WC), was replicated through wax moulding, and their antibiofilm potential was tested against single- and dual-species biofilms of Escherichia coli and Pseudomonas putida. Biomimetic surfaces exhibited higher roughness values (SaWC = 4.0 ± 1.0 μm and SaCF = 3.3 ± 1.0 μm) than the flat control (SaF = 0.6 ± 0.2 μm), whilst the CF surface demonstrated a lower interfacial free energy (ΔGiwi) than the WC surface (−100.08 mJ m−2 and −71.98 mJ m−2, respectively). The CF and WC surfaces had similar antibiofilm effects against single-species biofilms, achieving cell reductions of approximately 50% and 60% for E. coli and P. putida, respectively, compared to the control. Additionally, the biomimetic surfaces led to reductions of up to 60% in biovolume, 45% in thickness, and 60% in the surface coverage of single-species biofilms. For dual-species biofilms, only the E. coli strain growing on the WC surface exhibited a significant decrease in the cell count. However, confocal microscopy analysis revealed a 60% reduction in the total biovolume and surface coverage of mixed biofilms developed on both biomimetic surfaces. Furthermore, dual-species biofilms were mainly composed of P. putida, which reduced E. coli growth. Altogether, these results demonstrate that the surface properties of CF and WC biomimetic surfaces have the potential for reducing biofilm formation.

Selective Isolation of Mono- to Quadlayered 2D Materials via Sonication-Assisted Micromechanical Exfoliation.

Mechanical exfoliation methods of two-dimensional materials have been an essential process for advanced devices and fundamental sciences. However, the exfoliation method usually generates various thick flakes, and a bunch of thick bulk flakes usually covers an entire substrate. Here, we developed a method to selectively isolate mono- to quadlayers of transition metal dichalcogenides (TMDCs) by sonication in organic solvents. The analysis reveals the importance of low interface energies between solvents and TMDCs, leading to the effective removal of bulk flakes under sonication. Importantly, a monolayer adjacent to bulk flakes shows cleavage at the interface, and the monolayer can be selectively isolated on the substrate. This approach can extend to preparing a monolayer device with crowded 17 electrode fingers surrounding the monolayer and for the measurement of electrostatic device performance.

Industrially produced 2.4 GPa ultra-strong steel via nanoscale dual-precipitates co-configuration

An ultra-high strength martensitic steel, strengthened by the dual-precipitation of NiAl and M2C nano-particles, has been successfully developed and produced on an industrial scale. It has achieved a remarkable tensile strength of 2467 MPa and exhibited ductility approaching 10%. The precipitation configurations of NiAl and M2C nano-particles during ageing at 510 °C for durations ranging from 0.5 to 10 h were characterized using atom probe tomography. The results indicate that the preferential precipitation of NiAl, facilitated by minimal lattice misfit and low interfacial energy, promotes the uniform nucleation of M2C particles within the matrix while restricting their growth. As a result, both types of precipitates maintain a high number density. With increasing ageing time, the distribution density of the precipitates decreases, their size increases and the increase in yield strength gradually decreases. Furthermore, the addition of element cobalt effectively reduces the diffusivity of other major alloying elements, synergistically inhibiting the growth of NiAl and M2C particles. The dual precipitates co-configuration provides a substantial hardening effect (1046 MPa at 510 °C for 220 min) compared to the individual hardening effect of M2C observed in AerMet100 steel.

Developing high strength/high toughness grades steels by dual-precipitates co-configuration during aging process

Development of new ultrahigh strength steels with high strength and high toughness requires thorough comprehension of nanoscale precipitation mechanisms. In this investigation, a comprehensive array of techniques including atom probe tomography, transmission electron microscopy, scanning electron microscopy, electron backscatter diffraction, small angle x-ray Scattering and thermodynamic calculations were employed. These methods unveiled an intriguing co-precipitation mechanism involving NiAl and carbide nanoparticles in a 2.2 GPa grade strength steel. The results demonstrate that the precipitation mechanisms of NiAl and carbides at different aging temperatures have a significant impact on the strength and toughness of the steel. Sub-micron ε-carbide at the interface of martensite lath and uniformly distributed NiAl cluster in the matrix are independent nucleation during the low-temperature aging process. The high distribution density of NiAl cluster in the matrix results in an increase in the impact absorbed energy of the steel to 136 J, albeit with a slight decrease in strength. On the other hand, the NiAl with minimal lattice misfit and low interfacial energy preferentially nucleates uniformly in the matrix, inducing the nucleation of M2C and increasing the number density of M2C precipitates at the secondary hardening temperature. The homogeneous precipitation of spherical NiAl, along with needle-shaped M2C in the martensite, significantly enhances the strength of the steel, with a tensile strength reaching up to 2216 MPa and an impact absorbed energy of 21 J.

Modeling of Electrostatic and Contact Interaction between Low-Velocity Lunar Dust and Spacecraft

The accumulation of highly adhesive dust on spacecraft presents a serious issue to hinder long-term extravehicular activity and the establishment of a permanent station on lunar surface. In contrast to the immediate physical damage caused by hypervelocity (>1.0 km/s) impacts, this adhesion observed at low-velocity (0.01 to 100 m/s) collisions can more unobtrusively and mortally degenerate the performance of equipment. This paper proposes a theoretical model aimed at comprehensively analyzing the dynamics of adhesion and escape phenomena occurring during low-velocity impacts between charged dust particles and spacecrafts enveloped by a plasma sheath. The electrostatic force is modeled using the image multipole method, and contact force is calculated based on the adhesive–elastic–plastic theory. The results reveal that the implementation of a dielectric coating possessing both low permittivity and low interface energy can substantially reduce energy dissipation during collisions. However, the ultimate adhesion on the surface or escape from the sheath for low-velocity charged dust is dominated by the long-range electrostatic interaction rather than short-range contact interaction. Positively charged particles of smaller sizes demonstrate a greater propensity for surface adhesion in comparison to negatively charged particles of larger sizes. Counterintuitively, without additional dust removal techniques, modifying the properties of the dielectric coating does not effectively reduce the accumulation of dust, which can be merely accomplished by decreasing the spacecraft’s potential. The model presented in this study serves as a crucial step toward understanding the mechanism of lunar dust pollution.

Enhanced linear and symmetric synaptic weight update characteristics in a Pt/p-LiCoOx/p-NiO/Pt memristor through interface energy barrier modulation by Li ion redistribution.

Artificial synaptic devices have been extensively investigated for neuromorphic computing systems, which require synaptic behaviors mimicking the biological ones. In particular, a highly linear and symmetric weight update with a conductance (or resistance) change for potentiation and depression operation is one of the essential requirements for energy-efficient neuromorphic computing; however, it is not sufficiently met. In this study, a memristor with a Pt/p-LiCoOx/p-NiO/Pt structure is investigated, where a low interface energy barrier between the Pt electrode and the NiO layer makes for a more linear and symmetric conductance change. In addition, the use of voltage-driven Li+ ion redistribution in the NiO layer facilitates the analog conductance change at a low voltage. Besides the linear and symmetric potentiation and depression weight updates, the memristor exhibits various synaptic characteristics such as the dependence of weight update on the pulse amplitude and number, paired pulse facilitation, and short-term and long-term plasticity. The conductance modulation is thought to be induced by a tunable interface energy barrier at the NiO layer and Pt bottom electrode, as a result of Li+ ion diffusion in NiO supplied from the LiCoOx layer and their redistribution. Thanks to the use of Li+ ion redistribution, the conductance change could be achieved at a voltage <4 V within the time of μs range. These results verify the potential of artificial synapses with the Pt/LiCoOx/NiO/Pt memristor operated by voltage-driven Li+ ion redistribution under the low interface energy barrier conditions, realizing a highly linear and symmetric weight update at a low voltage with a high speed for energy-efficient neuromorphic computing systems.

Microstructure-armored surface and its tribological effects on ultralow-wear PEEK/PTFE composites

Reducing interfacial energy gradient can improve the anti-wear property and even achieve an ultralow wear performance of polyetheretherketone/polytetrafluoroethylene (PEEK/PTFE) composite. Previous studies have primarily focused on the tribochemical crosslinking of PTFE molecules to reduce interfacial energy gradient which resulted in poor lubricity and lengthy run-in periods of polymer-lubricating systems. Here, we propose and prepare a microstructure-armored surface (MSAS) for directly reducing the interfacial energy gradient for the ultralow-wear PEEK/PTFE composites. The morphological, chemical, and tribological characteristics of the PEEK/PTFE running against MSAS were studied. The results show that MSAS can decrease the friction coefficient of PEEK/PTFE by more than 30 %, while reducing its initial run-in time by over 80 %, accomplished with the lowest wear rate of ∼3.8 × 10−8 mm3/Nm. This represents the best performance observed in PEEK- and PTFE-based tribosystems so far. Scanning electron microscopy, infrared spectroscopy, and X-photoelectron spectroscopy revealed the low interfacial energy gradient consisting of PEEK, PTFE, and carboxylated PTFE contributes to the remarkable performance of PEEK/PTFE-on-MSAS tribosystems. This study provides a new approach to designing ultralow-wear polymer tribosystems with great lubricity and a short run-in period beyond composite design.