Science and Technology of Advanced Materials最新文献

Magnetic thin films and nanostructures present a unique challenge for a range of thermal measurements, with important consequences for both fundamental physics and material science and applications. This paper reviews the unique capabilities for measurement and control of these systems using thermal gradients applied using micro- and nanofabricated silicon-nitride membrane platforms. Supporting a thin film or nanostructure removes bulk heat sinks from the tiny structure, enabling otherwise challenging or impossible measurements including thermal conductivity, Seebeck coefficient, Peltier coefficient, magnon drag, both the anomalous and planar Nernst effect, specific heat, and novel manifestations of thermally assisted spin transport. After providing some historical context and motivation and overviewing the design and fabrication of silicon-nitride membrane thermal platforms, example data for each of the measurements above is reviewed, and the paper concludes with a consideration of the outlook for measurements enabled by these techniques.

We report on various magnetic configurations including spirals and skyrmions at the surface of the magnetic insulator Cu ${ }_2$ OSeO ${ }_3$ at low temperatures with a magnetic field applied along 100 using resonant elastic X-ray scattering (REXS). We observe a well-ordered surface state referred to as a distorted tilted conical spiral (dTC) phase over a wide range of magnetic fields. The dTC phase shows characteristic higher harmonic magnetic satellites in the REXS reciprocal space maps. Skyrmions emerge following static magnetic field cycling and appear to coexist with the dTC phase. Our results indicate that this phase represents a distinct and stable surface state that does not disappear with field cycling and persists until the field strength is increased sufficiently to create the field-polarized state.

The anatase form of TiO₂ is a widely studied material due to its broad range of applications. Epitaxial anatase thin films have attracted significant attention because of their enhanced electrical and optical properties. However, fabricating anatase thin films remains challenging due to their metastability and the need for highly sophisticated fabrication techniques. On-site controlled hydrolysis is a simple, cost-effective, and rapid method for producing smooth, compact thin films on various surfaces. In this study, we demonstrate a straightforward approach to fabricating highly oriented epitaxial anatase thin films on LaAlO₃ substrates using different solvent mixtures. The epitaxial orientation and film quality were analyzed using X-ray diffraction pole figures and rocking curves, while surface morphology was characterized by Scanning electron microscopy and atomic force microscopy. Our results indicate that thin film quality and morphology are primarily influenced by the annealing temperature rather than the choice of solvent or titanium precursor, confirming the feasibility of a scalable, low-cost epitaxial fabrication technique for anatase thin films.

LiFe₆Ge₄, with a theoretically predicted saturation magnetization of 1 T, a magnetocrystalline anisotropy energy of 1.78 MJ/m³ and a Curie temperature of 620 K was suggested to be a promising permanent magnet as an outcome of a data-mining search. Magnetic measurements of the synthesized sample are reported here. Unfortunately, experiments revealed a weak ferromagnetic behaviour with magnetization values much below that predicted by theory. This discrepancy is analyzed in detail, and is attributed to the trigonal crystal symmetry that was missed in the previous characterisation of the material. The correct crystal structure is R $\bar{3}$ mH (space group 166) and it is found here to have an antiferromagnetic ground state, as opposed to a theoretically predicted ferromagnetic state of the previously reported monoclinic crystal structure. Theoretical calculations show that element substitution can stabilize a ferromagnetic state of the trigonal crystal structure, with high values of saturation magnetization and magnetocrystalline anisotropy. The best results are seen for the Al or Ga substitution for Ge of the LiFe₆ X ₄ compound.

Cerium dioxide (CeO ${ }_2$ ) is extensively studied due to its exceptional redox properties, which are closely related to oxygen vacancy formation and the associated charging of cerium atoms from Ce ${ }^{4+}$ to Ce ${ }^{3+}$ . These charged species play an important role in promoting active sites in CeO ${ }_2$ -based catalysts. The existence of Ce ${ }^{3+}$ atoms is typically characterized by means of surface spectroscopic techniques, because the direct atomic-scale observation and discrimination of Ce ${ }^{3+}$ ions from Ce ${ }^{4+}$ atoms remains challenging. Here, we use simultaneous scanning tunneling microscopy (STM) and atomic force microscopy (AFM) complemented by force spectroscopy to characterize candidates to Ce ${ }^{3+}$ atoms on partially reduced CeO ${ }_2$ (111) samples. While STM images reveal electronic modulations of the atomic contrast in the form of an inhomogeneous shading, AFM clearly differentiates these electronic features from the true topographic atomic structure. The chemical reactivity of these candidates to Ce ${ }^{3+}$ atoms is quantified against the Ce ${ }^{4+}$ counterparts by means of force spectroscopy using carbon monoxide functionalized probes. This study demonstrates that the combination of STM with AFM and force spectroscopy bears great potential to provide robust atomic-level insights into the chemistry of defects at ceria surfaces.

We developed an Ag nanowire-polyurethane (AgNW-PU) mixed electrode on a PU substrate with an optimized bilayer structure for highly stretchable and wearable strain sensors. In the AgNW-PU mixed composite, PU functioned as a stretchable matrix, preserving the high conductivity and transparency of the AgNW network even under applied mechanical stress. The AgNW-rich bottom layer (25:1) provided an effective conduction path, whereas the PU-rich top layer provided mechanical support and elasticity, improving the durability of the electrode under repeated stretching and bending cycles. With the optimized bilayer (AgNW-PU 100:1/25:1), the AgNW-PU bilayer electrode exhibited a low sheet resistance of 26.3 Ω/square and a high transparency of 86.4%. Compared with the AgNW-PU single-layer electrode, the bilayer electrode exhibited superior stretchability, as confirmed by various applications, such as heater devices, strain sensors, and interconnectors. An optimized AgNW-PU bilayer electrode exhibited heat generation of 90°C with 7 V applied even after 15% stretching. The gauge factor of the optimized electrode increased from 8 to 11.2 even as the bending degree increased from 30° to 90°. The AgNW-PU bilayer electrode also demonstrated potential as a stretchable interconnector for various next-generation electronic applications.

Room-temperature bulk photovoltaic effect of a ferroelectric liquid crystal based on diphenylterthiophene bearing dilactate side chains is provided in this study. In the polarized smectic phase of this compound, the improved bulk photovoltaic effect was observed without electron acceptors, indicating the open-circuit voltage of 1.1 V. A time-of-flight measurement revealed that the hole and electron mobilities were retained to be over 1 × 10^-3 cm²V^-1s^-1 at room temperature. Dielectric relaxation spectra exhibited that the relaxation of dipolar fluctuation shifted from 10⁵ Hz to 10⁴ Hz in the polarized smectic phase, indicating suppression of thermal motion of the polar side chains. By doping a fullerene derivative as an electron acceptor, the performance of the bulk photovoltaic effect was also enhanced at room temperature, indicating the power conversion efficiency of 0.24 %. The double chiral structure of the dilactate side chain should restrict the conformation of the carbonyl groups in the side chains to enhance packing of the π-conjugated units and to stabilize the polarized structure of the smectic phase.

Magnetic cooling technology, based on the magnetocaloric effect (MCE), offers an energy-efficient and eco-friendly alternative to conventional gas compression, but is often hindered by large magnetic hysteresis, which limits cyclic performance. In this study, we show that the hysteresis of La_0.7Ce_0.3(Fe,Si)₁₃ hydrides - a promising material for room-temperature refrigeration - can be significantly reduced by refining the microstructure of the precursor alloy. Substituting Ce for La in (La_0.7Ce_0.3)(Fe,Si)₁₃H_x increases hysteresis losses from 12.3 J/kg to 34 J/kg. However, preparing the precursor alloy using the melt-spinning technique can almost eliminate this hysteresis. Lorentz transmission electron microscopy (Lorentz-TEM) shows that phase transition nucleation preferentially occurs at the grain boundaries. The hydrides prepared from melt-spun ribbons exhibit a much larger volume fraction of grain boundaries due to finer grains, providing a higher density of nucleation sites. This reduces the energy barrier for the phase transition and weakens the magneto-structural phase transition, as confirmed by in-situ X-ray diffraction patterns. Consequently, the reduced phase transition energy barrier leads to significantly lower hysteresis in melt-spun hydrides samples. These findings demonstrate the potential of microstructure engineering to reduce hysteresis in (La,Ce)(Fe,Si)₁₃Hₓ materials for room-temperature magnetocaloric applications.

Silicon (Si) is a promising next-generation anode material for lithium-ion batteries (LIBs) due to its exceptionally high theoretical capacity (3579 mAh g^{- 1}) and natural abundance. However, its commercialization remains challenging due to severe volume expansion (~300%) during cycling, leading to poor structural stability and rapid capacity degradation. To address this issue, we developed a novel biomass-derived binder system denoted as SCC, composed of sodium alginate (SA) and chondroitin sulfate (CS), crosslinked via a simple calcium chloride (CaCl₂) aqueous treatment. Unlike conventional synthetic polymer-based binders, this system enhances mechanical stability while maintaining an environmentally friendly, water-based fabrication process. Spectroscopic analysis confirmed strong hydrogen bonding interactions between SA and CS, as well as robust crosslinking formation through Ca²⁺. These interactions effectively enhance the mechanical strength of the SCC binder, enabling it to accommodate the severe volume changes that occur during electrochemical reactions in Si anodes. This, in turn, contributes to enhanced structural stability of Si electrode, which leads to a reduction in both solid electrolyte interphase and charge transfer resistance. As a result, the SCC electrode showed improved electrochemical cycling stability, with a 13.45% higher capacity retention after 60 cycles at a 0.2C rate compared to SA alone. This suggests its potential as a sustainable and scalable solution for next-generation high-performance Si anodes.

Lithium metal is a promising anode for high-energy batteries due to its high capacity and low density. However, issues like dendrite growth and volume expansion limit its practical use. To address these challenges, three-dimensional (3D) copper foam current collectors with porous architectures and superior electrochemical properties have emerged as a research focus. Three-dimensional copper foam current collectors have emerged as a strategic solution, leveraging their porous architecture to regulate lithium nucleation, enhance mechanical stability, and maintain electrochemical equilibrium. Despite their potential, current implementations confront four key constraints: excessively large pore sizes, uneven surface current distribution (leading to non-uniform lithium deposition, dendrite growth, and dead lithium formation), poor lithiophilicity, and weak oxidation resistance. These factors hinder the long-term suppression of lithium dendrites and degrade the oxidation resistance of copper nanostructures. This review systematically examines recent advancements in 3D copper foam engineering through three principal modification approaches: metallic/alloy coatings, surface functionalization, and structural optimization. The advantages, limitations, and critical issues of these approaches are analyzed. Furthermore, the importance of 3D copper foam current collectors in advancing lithium metal batteries is elucidated, highlighting current achievements, areas for improvement, and potential applications. Finally, recommendations and future prospects for further optimization of 3D copper foam current collectors are proposed to achieve commercially viable lithium metal batteries.