Search Results (316)

Three-dimensional (3D) graphene foams are attractive as lightweight conductive scaffolds with large surface area and broadband light absorption but achieving reproducible porosity and preserving the architecture after metal-template removal remain challenging. Here we report a stepwise route to freestanding 3D multilayer graphene foams based on (i) hydrogen-bubble-assisted electrodeposition of porous Ni on Cu foils, (ii) time-controlled pre-annealing at 1000 °C to drive Cu diffusion and form porous Ni-Cu alloy templates, (iii) in situ graphene CVD at 1000 °C under fixed growth conditions, and (iv) wet etching to remove the metal scaffold without a polymer support. The influence of pre-annealing (0, 1, 3, and 7 h) on template evolution, graphene growth, and foam stability was systematically investigated via SEM, EDS, XRD and Raman studies. Before etching, Raman spectroscopy indicates low-defect graphenic coatings with locally heterogeneous few-layer-like to multilayer-like signatures. Only samples pre-annealed for at least 3 h preserved the porous 3D architecture after metal removal, indicating the formation of self-supporting graphenic networks with improved post-etch morphological stability. Raman and XRD analyses further revealed a progressive reduction in structural degradation, residual strain, and stacking disorder with increasing pre-annealing time. Among the investigated samples, the foams obtained after 3 and 7 h of template pre-annealing combined preserved 3D morphology with low sheet resistance (10–20 Ω/□), negligible optical transmittance (<5%), and strong broadband visible-light absorption (75–90%). Full article

This review presents a current understanding of the relationship between the structure of multicomponent metallic melts and the processes of amorphization and nanocrystallization. Particular attention is paid to the thermal-temporal treatment (TTT) of melts as a precision method for monitoring the nonequilibrium state of the liquid phase, the relaxation kinetics of cluster associations, and liquid–liquid transitions (LLT). The mechanisms by which precrystallization melt treatment affects the homogeneity of the amorphous precursor, the size of nanograins (7–15 nm), the phase composition (Fe₃Si, Fe₂B), and the resulting magnetic characteristics of toroidal cores (μ_max > 600,000, H_c < 0.5 A/m) are investigated. Based on an analysis of structural models of metallic melts (cybotactic, quasicrystalline, and quasichemical), it is shown that critical temperatures, viscosity hysteresis, and oscillatory relaxation serve as indicators of melt equilibrium. It is noted that the optimized TTT protocols combined with controlled annealing at 542–572 °C enable the formation of Fe₃Si nanograins with exceptional magnetic softness. The results open the possibility of discussing the prospects for integrating TTT with in situ diagnostics, CALPHAD modeling, and the potential of machine learning for the design of next-generation soft magnetic nanomaterials with tailored frequency characteristics for high-frequency power electronics and their use in electromagnetic shielding. Full article

Binder-free NiMn₂O₄@NiCo₂O₄ nanocomposites with NiMn₂O₄ nanoparticle (NP) surface coverage on NiCo₂O₄ nanosheets (NSs) are fabricated on nickel foam (NF) via a two-step microwave-assisted hydrothermal (MAH) method combined with annealing treatment, which can be used as a high-performance electrode material for supercapacitors. Specifically, a tulle-like NiCo₂O₄ nanosheet framework is first in situ grown on NF, followed by the growth of NiMn₂O₄ NPs on the surface of NiCo₂O₄ NSs via a secondary MAH process. To investigate the effect of the second-step holding time (HT) of MAH on material performance, a series of experiments were carried out with an HT of 15, 30, 45, and 60 min, and the microstructures and electrochemical properties of the products were analyzed. Structural characterization results confirm the successful synthesis of well-defined NiMn₂O₄-NPs@NiCo₂O₄-NSs composites. Electrochemical tests demonstrate that the product at an HT of 30 min has the best electrochemical performance with a higher specific capacitance of 441.56 F·cm⁻² at 1 A·cm⁻² and cycling stability (75% capacitance retention after 5000 cycles at 15 A·cm⁻²). The superior electrochemical properties are mainly attributed to the unique porous tulle-like NS structure with the largest specific surface area of the 30 min product. This distinctive structure affords abundant electrochemical active sites, effectively prevents structural collapse during long-term cycling, and shortens the transmission and diffusion pathways of electrons and electrolyte ions. The optimized NiMn₂O₄@NiCo₂O₄ electrode material presents extensive application prospects for high-performance supercapacitors. Full article

Driven by the “Dual Carbon” goals, supercapacitors have become critical energy storage devices for new energy electric vehicles. In this paper, a ZnFe₂O₄@ZnCo₂O₄ core–shell cathode was prepared by a hydrothermal method followed by high-temperature annealing, and an AC@PANI composite anode was synthesized through in situ polymerization. The materials were characterized by SEM, TEM, XRD, XPS, nitrogen adsorption–desorption and electrochemical tests. The ZnFe₂O₄ rod-like core provides mechanical stability, whereas the ZnCo₂O₄ nanosheet shell increases the specific surface area and exposes more active sites. The cathode delivers 2133 F/g at 1 A/g with 94.4% retention after 10,000 cycles. The anode reaches 398 F/g at 1 A/g. The cathode delivers 2133 F/g at 1 A/g with 94.4% retention after 10,000 cycles. The anode reaches 398 F/g at 1 A/g. The assembled ZnFe₂O₄@ZnCo₂O₄//AC@PANI hybrid supercapacitor works in a wide voltage range of 0–1.6 V. It exhibits a specific capacitance of 157 F/g at 1 A/g and a high energy density of 54.7 Wh/kg at a power density of 1600 W/kg. The device retains 91.4% of its initial capacity after 10,000 charge–discharge cycles. This study offers a promising strategy for high-performance automotive supercapacitors. Full article

The high-temperature operating requirements and the issues in the packaging process of wide-bandgap power semiconductors have positioned pressureless sinter-bonding using Ag nanoparticle paste as the most promising die-attach technology. However, under pressureless conditions, where externally applied pressure-driven particle rearrangement is absent, achieving sufficient densification and suppressing residual porosity during short-duration annealing at 250 °C remain significant challenges for conventional single-composition Ag pastes. In this study, a hybrid filler paste composed of Ag nanoparticles and a Ag complex solution was developed to implement an active mass supply strategy, in which additional Ag atoms were directly introduced into interparticle voids through in situ reduction during sinter-bonding. Mono-dispersed Ag nanoparticles with a mean diameter of 75.26 nm were synthesized via H₂O₂-mediated wet-chemical reduction, and the Ag complex solution was prepared using a Ag salt–complexing agent–formic acid system dispersed in an ethylene glycol medium. TG-DTA analysis of the hybrid paste revealed four sequential thermal stages, consisting of solvent evaporation, Ag ion reduction, organic decomposition, and interparticle sintering, accompanied by approximately 16 wt% out-gassing. Based on these results, a three-step temperature profile was designed to initiate sintering after complete out-gassing. When chip/paste/substrate assemblies, pre-dried at 50 °C for 90 s and pre-compressed at 5 MPa for 60 s, were subjected to the three-step profile with a peak temperature of 250 °C, the in situ reduced Ag effectively bridged adjacent nanoparticles and filled fine interparticle voids, leading to pronounced densification of the bond line. As a result, the hybrid paste achieved an average shear strength of 19.1 MPa, exceeding the minimum requirement for sinter-bonding applications. These findings demonstrate that the proposed hybrid filler approach provides an effective pathway for enhancing pressureless Ag sinter-bonding performance. Full article

This study investigates the formation mechanism of non-doped cubic lithium lanthanum zirconium oxide (c-LLZO) nanofibers using in situ synchrotron X-ray scattering techniques. Electrospun polymer precursor nanofibers were annealed at temperatures up to 800 °C, enabling real-time tracking of phase transitions via simultaneous small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and evolved CO₂ gas analysis. The results reveal a three-step transformation pathway: polymer decomposition, formation of La₂Zr₂O₇ (LZO), and direct conversion of LZO to c-LLZO without intermediate tetragonal phases detected within the sensitivity of our in situ WAXS measurement. Cryo-electron energy loss spectroscopy (EELS) further elucidates the role of lithium diffusion, showing Li enrichment at fiber surfaces and Li deficiency in the interior, which stabilizes the cubic phase. This Li segregation effect in nanostructured LLZO materials extends beyond the previously reported size effect. This work advances the understanding of c-LLZO formation mechanisms and provides practical insights for optimizing synthesis routes to achieve phase-pure c-LLZO for solid-state battery applications. Full article

Rapid solidification by melt-spinning produces aluminum alloys with extremely refined microstructures but also introduces strong structural gradients across the ribbon thickness. In this work, the microstructural evolution of a rapidly solidified Al-Cu-Li-Mg-Sc-Zr alloy was investigated during model homogenization using in situ STEM heating experiments and correlated with bulk electrical-resistivity measurements. The as-cast ribbons exhibit two distinct solidification zones: a near-contact region consisting of columnar cells containing fine Cu-rich spherical precipitates, and a central region composed of larger eutectic cells enriched in Al₂Cu and Al₇Cu₂Fe phases. Stepwise in situ STEM annealing between 200 °C and 500 °C reveals a sequence of transformations, including matrix depletion due to precipitation of strengthening phases, coarsening of primary phases, and formation of Al₃(Sc,Zr) dispersoids. Above 500 °C, rapid dissolution of Cu-rich primary phases occurs, leaving only a limited number of stable grain-boundary particles of the Al₇Cu₂Fe phase, eliminating the original two-zone structure, and resulting in a fully homogenized ribbon. Ex situ annealing confirms that the resulting microstructure is uniform across the ribbon thickness and enables consistent precipitation strengthening during artificial aging. The proposed annealing treatment is based on numerical models for homogenization of eutectic systems. The final annealing step combines homogenization and solution treatment at 530 °C for periods close to 5 min—two orders of magnitude shorter than standard holding times. Microhardness measurements from both ribbon surfaces reveal an identical peak-aged hardness of 135 HV, validating the effectiveness of the short-time homogenization strategy for rapidly solidified Al-Cu-Li-Mg-based alloys. Full article

The practical application of inorganic ferroelectric fillers in flexible piezoelectric composites is critically constrained by low polarization efficiency and severe interfacial incompatibility with polymer matrices. Herein, we report a multi-level in situ surface modification strategy that simultaneously addresses both limitations. High-purity one-dimensional tetragonal barium titanate nanofibers (BTO NFs) are first synthesized via sol–gel electrospinning combined with a two-step gradient annealing process, which precisely controls phase evolution and preserves structural continuity. To overcome the detrimental acid-induced degradation of BTO NFs during functionalization, a polydopamine (PDA) buffer layer is first conformally coated, followed by the liquid-phase deposition of a conductive polypyrrole (PPy) shell, forming a robust core–shell PPy@PBT NFs architecture. Incorporating only 4 wt% of these multifunctional fillers into a poly(vinylidene fluoride) (PVDF) matrix yields a dramatic enhancement in electromechanical performance. The resulting flexible piezoelectric energy harvesters achieve a piezoelectric coefficient (d₃₃) of 28.7 pC/N, an output voltage of 13 V, and an output current of 0.7 μA, representing substantial improvements over unmodified filler systems. This synergistic enhancement originates from the PDA-mediated interfacial stress transfer and the PPy-induced Maxwell–Wagner polarization intensification, establishing a robust and generalizable paradigm for high-performance flexible piezoelectric composites in self-powered wearable electronics. Full article

The photoelectrochemical water-splitting process for hydrogen production is limited by the large bandgap of semiconductor titanium dioxide (TiO₂) and by interfacial recombination at particle interfaces. The technique used in this paper is that of electrochemical anodization to produce robust, ordered TiO₂ nanotube arrays (TiO₂ nanorod arrays denoted as TNTAs). Using the immersion-annealing method, Nd₂O₃ nanoparticles can be immobilized in situ, and Nd₂O₃/TNTAs composite photoanodes are fabricated. The heterointerface caused between the Nd₂O₃ nanoparticles and TiO₂ results in the alignment of the Fermi levels and the formation of band bending and an internal electric field at the interface. It allows rapid photo-generated electron-hole (e⁻/h⁺) separation at the interface and, simultaneously, introduces novel localized electron states of Nd³⁺ within the TiO₂ bandgap. This triggers hybridisation between the 3d orbitals of Ti and the 2p orbitals of O, thereby altering the band structure of TiO₂. The best-performing Nd₂O₃/TNTAs photoelectrode outperforms pure TNTAs, with a photocurrent density of 1.59 mA·cm⁻² at 1.23 V vs. RHE. It produces 162.6 μmol·cm⁻² of hydrogen in a 3 h photocatalytic hydrogen production experiment, which is about 12.2 times that of pure TNTAs. This approach highlights the unique benefits and creative opportunities of applying rare-earth elements to address the critical issues of photocatalysts, such as significant band gaps and rapid recombination. Full article

The controllable growth of in-plane Ge nanowires provides alternative material foundations for the scalability of Ge-based semiconductor qubit devices. Here, ordered in-plane Ge hut wires with controllable size are grown on the trench-patterned Si substrate by molecular beam epitaxy. By tuning the thickness of the SiGe alloy layer, which acts as strain buffered layer, GeSi mounds with controllable size are achieved. Subsequently, through the deposition of a Ge layer followed by in situ annealing, we realize the size-controllable growth of the Ge nanowire with a height from 1.8 nm to 4.0 nm, as characterized by AFM and TEM techniques. These size-tunable and catalyst-free Ge hut wires provide a promising pathway toward the fabrication of integrated nanowire-based quantum devices. Full article

Satellite remote sensing offers a cost-effective solution for the continuous monitoring of black and odorous water bodies (BOWs). However, limitations in spatial and spectral resolution hinder the quantitative inversion of water quality parameters and the precise assessment of risk levels using satellite data alone. To address this challenge, this study proposes a synergistic approach combining satellite and Unmanned Aerial Vehicle (UAV) remote sensing to rapidly identify potentially polluted water bodies and quantitatively assess their risk levels. First, a Black and Odorous Water Index (MBOWI) was constructed based on reflectance characteristics in the visible to near-infrared bands to screen for potential black and odorous water bodies using satellite imagery. Subsequently, high-resolution multispectral UAV imagery, integrated with in situ sampling data, was employed to develop machine learning models for inverting key water quality parameters, including Chemical Oxygen Demand (COD), Dissolved Oxygen (DO), Total Phosphorus (TP) and Ammonia Nitrogen (NH₃-N). Comparative analysis of Polynomial Regression (PR), Random Forest (RF), and Simulated Annealing-optimized Support Vector Regression (SA-SVR) revealed that RF and SA-SVR exhibited superior performance in inverting four non-optically active water quality parameters due to their robust nonlinear fitting capabilities, with the mean Adjusted Coefficient of Determination ($R_{adj}^2$) ranging from 0.57 to 0.69. Water quality classification based on the single-factor worst-case method achieved an overall accuracy of 0.70 across validation samples. Notably, for Class V (heavily polluted) water bodies, both classification accuracy and recall rate reached 0.89, demonstrating the model’s high precision in identifying high-risk waters. Finally, the proposed framework was applied to northern Zhejiang Province to assess seven potential black and odorous water bodies, successfully identifying four as high-risk and one as low-risk. This study validates satellite and UAV synergistic remote sensing for the hierarchical risk management of black and odorous water bodies. Full article

Selective laser melting (SLM), a pivotal additive manufacturing (AM) technology for titanium alloys, enables near-net-shape forming of complex structures with relative densities of up to 99.9%, making it indispensable in aerospace, biomedical, and marine engineering. This review comprehensively updates the state of the art on SLM-fabricated TC4 (Ti-6Al-4V) alloy, addressing critical gaps in previous studies by integrating novel research progress, in-depth mechanistic analyses, and multi-dimensional comparisons. The core focus is on the unique thermal cycle (10⁶–10⁸ °C/s heating/cooling rates) of SLM, which induces a predominant needle-like martensitic α′ phase (99.7%) and minimal β phase (0.3%), leading to intrinsic anisotropy and low ductility. Room-temperature tensile strength reaches 1315.32 MPa with 9.6% elongation, and high-cycle fatigue limits the range from 417 to 829 MPa, strongly dependent on process parameters and post-treatment. Corrosion anisotropy is systematically analyzed: the XY plane (parallel to scanning direction) exhibits superior corrosion resistance in 1 M HCl (fewer pits and lower corrosion current density) and 3.5% NaCl (more stable passive film) compared to the XZ plane (deposition direction). Novel insights include: (1) synergistic effects of SLM process parameters (laser power–scanning speed–hatch spacing) on defect evolution and microstructure uniformity; (2) atomistic mechanisms of α′→α + β phase transformation during post-heat treatment; and (3) corrosion–mechanical coupling behavior in harsh environments (e.g., marine and biomedical). Post-treatment strategies are refined: annealing at 800 °C for 2 h achieves 1099 MPa tensile strength and 17.4% elongation, while hot isostatic pressing (HIP) reduces porosity from 0.08% to 0.01% and weakens fatigue anisotropy. This review also identifies unresolved challenges (e.g., in situ defect monitoring and multi-field regulated performance) and proposes future directions (e.g., AI-driven process optimization and functional gradient structures). Full article

With the growing demand for high-performance die materials under harsh service conditions, the development of composite coatings with enhanced hardness and wear resistance has attracted significant attention. In this study, homogeneous laser cladding was employed to fabricate H13 alloy coatings reinforced with varying TiC contents (0, 10, 20, and 30 in wt.%) on H13 steel, which minimizes compositional segregation and ensures strong metallurgical bonding. TiC particles acted as heterogeneous nucleation sites during solidification, refining the microstructure and enhancing phase stability. The coatings consisted of initial TiC residues, newly formed primary and eutectic TiC, as well as austenite and martensite phases. With increasing TiC addition, TiC morphology evolved from fine particles to complex fishbone-like and polygonal structures. The coating containing 30% TiC achieved the highest hardness of 1095.9 HV_0.5, approximately five times that of the as-annealed H13 steel substrate while the 20% TiC coating exhibited optimal high-temperature wear resistance. Under the sliding conditions at 600 °C, the friction coefficient decreased from 0.467 for the substrate to 0.367 for the 20% TiC coating, accompanied by a remarkable reduction in wear rate from 27.45 × 10⁻⁴ mm³ N⁻¹ m⁻¹ to 4.32 × 10⁻⁴ mm³ N⁻¹ m⁻¹. The superior performance was attributed to the multiscale TiC reinforcement mechanism: initial TiC promoted grain refinement and strong interfacial bonding, in situ formed primary TiC induced lattice distortion and dislocation strengthening, and eutectic TiC reinforced grain boundaries, jointly enhancing hardness, thermal stability, and wear resistance. Full article

Ni@TiO₂ core–shell nanoparticles were synthesized by magnetron sputtering and their structure verified by HRTEM and EDS analysis. The thermal stability of these particles was investigated using in situ TEM annealing and compared with that of pure Ni nanoparticles. While pure Ni particles sinter at 450 °C and exhibit significant growth at 800 °C, Ni@TiO₂ nanoparticles remain stable up to 700 °C, with the sintering onset between 700 and 800 °C. A simple thermal-mismatch model was applied to explain the stabilizing effect of the TiO₂ shell, demonstrating that differences in thermal expansion between Ni and TiO₂ generate interface stresses sufficient to crack the shell after the amorphous–rutile transformation. The TiO₂ coating effectively delays Ni coalescence by 250 °C relative to bare Ni, highlighting its role as a protective shell against high-temperature sintering. Full article

To achieve an atomically clean surface of single-crystal aluminum nitride (AlN) substrates, this study systematically evaluated the effects of each step in ex situ wet chemical cleaning (solvent, piranha solution, HF, HCl) and in situ hydrogen annealing. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses revealed that while the combination of solvent and piranha solution exposed step morphology, its effectiveness in removing organic contaminants was limited. HF cleaning efficiently removed the oxide layer but introduced fluorine residues, whereas HCl cleaning left no chlorine residues but exhibited lower efficiency in oxide removal. In situ hydrogen annealing significantly reduced carbon and oxygen contamination, albeit accompanied by a transformation of the surface morphology from step to island mode. By modulating the low V/III ratio during low-temperature metal–organic chemical vapor deposition (MOCVD) growth, a controlled transition from 3D island growth to 2D step-flow growth was achieved. This research provides a basis for optimizing AlN substrate surface treatment, offering important insights for advancing nitride-based optoelectronic and power devices. Full article