Journal of Materials Chemistry C最新文献

As chips become more densely integrated and the surface heat flux increases, there is a growing demand for thermal interface materials (TIMs) that exhibit both high thermal conductivity and long-term reliability. In this study, CuGa₂ microparticles were synthesized via melt atomization and then incorporated into a gallium-based liquid metal to prepare composite TIMs. Experimental results demonstrate that when the CuGa₂ mass fraction reaches 50%, the composite achieves a maximum thermal conductivity of 74.92 ± 1.04 W (m K)⁻¹, approximately 3 times higher than that of a conventional gallium-based liquid metal. This improvement is primarily due to metallic bonding at the interface between liquid gallium and the CuGa₂ intermetallic compound, where free electrons serve as the main heat carriers across the interface. Furthermore, the addition of CuGa₂ improves the TIM's coating ability while reducing its fluidity, thereby reducing the risk of leakage. Long-term testing over 35 days revealed no compositional changes or segregation hardening, confirming the excellent stability of the composite. Overall, Ga/CuGa₂ TIMs strengthened by metallic bonding present a promising solution for reliable heat dissipation applications involving high heat fluxes.

Chameleon-inspired mechanochromic photonic crystals (MPCs) are receiving growing attention owing to their unique ability to alter structural colors under external forces. Although MPCs have been extensively prepared, the low reflectance, small strain sensing range (<60%), limited wavelength tuning range (<200 nm), and lack of adhesive functions significantly limit their potential toward advanced applications. Here, a new type of MPC with a high reflectance (∼70%), a broad wavelength tuning range (305 nm), excellent adhesive properties, and capability to sense a large strain (180%) has been successfully fabricated by simply non-close-assembling polystyrene-silica core–shell particles into di(ethylene glycol)ethyl ether acrylate. The unique material and structural design, including the large refractive index contrast between the particles and acrylate, the large lattice distance, and the intense interactions between MPCs and substrates, is key to the above characteristics. By rationally combining these characteristics, bilayer MPC-based optical reflectors capable of outputting dual and dynamic photonic bandgaps have been realized, showing their potential for application in optical reflectors, photonic coatings, and wearable devices.

Unsupervised spiking neural networks (SNNs) that operate based on the spike-timing-dependent plasticity (STDP) learning rule have high biological plausibility and are considered the next generation of artificial neural networks. The development of artificial synapse devices with excellent STDP conductance update characteristics is the foundation for achieving high-performance SNNs. This work constructs a TaO_x/TiO_x memristive material featuring three distinct oxygen-vacancy concentration regimes, achieving optimized bidirectional STDP conductance updates (LTP and LTD processes) in memristive synapses. Compared with the single-layer TaO_x-based memristor synapse, the LTP part of the STDP performance of the double-layer TaO_x/TiO_x device has an increased conductance range by 110%, while the LTD part has an increased conductance range by 61%. The factor ratio of the forward and reverse conductance ranges, A₊/A₋, is closer to 1. Analysis shows that the slower forgetting rate of the tri-level oxygen defect concentration profile in the TaO_x/TiO_x based memristive synapse is the main reason for the optimized STDP performance. The simulation results show that the optimized STDP characteristics can increase the network recognition rate. This paper presents a device structure and process that can effectively regulate the bidirectional conductance update characteristics of STDP in an oxide based memristor, which is conducive to promoting the development of high-performance memristor-based neural morphological devices.

Polycrystalline semiconductors are central to modern optoelectronic and energy devices, yet their performance is governed by the chemistry and electrostatics of grain boundaries (GBs). Unlike single crystals, polycrystalline systems exhibit potential barriers, trap states, and compositional inhomogeneities that critically shape carrier mobility, lifetime, and recombination. This review unifies theoretical and experimental perspectives on major transport pathways—drift–diffusion, thermionic emission, tunneling, hopping, and conduction through threading crystallites—across representative materials including Si, CdTe, CIGS, PbSe, Sb₂Se₃, Bi₂Te₃, Mg₃Sb₂, and halide perovskites. Particular emphasis is placed on how nanoscale probes such as Kelvin probe and conductive AFM, cathodoluminescence, and DLTS elucidate barrier heights, trap energetics, and boundary passivation effects. Chemical and structural strategies—such as halogen or alkali–fluoride treatments, dopant redistribution, anti-barrier engineering, and twin-boundary engineering—are demonstrated to transform recombination-active interfaces into conductive channels. By correlating microscopic boundary chemistry with macroscopic transport and device metrics, this review formulates general design guidelines for programmable grain architectures. The analysis establishes grain boundaries not as fixed defects but as tunable electronic interfaces, offering a roadmap for next-generation polycrystalline semiconductors optimized for high-mobility, high-stability optoelectronic and thermoelectric applications.

The utilization of Cu micropowder as an auxiliary material presents a promising strategy to enhance the efficiency of heavy rare earth elements in grain boundary diffusion (GBD) processes. This study systematically investigates the composite addition strategies of Cu and a TbH₃ diffusion source (including mixed diffusion and stepwise diffusion) and their effects on the diffusion behavior of Tb. Compared to the original magnet, the coercivity of the TbH₃ GBD (T GBD), Cu + TbH₃ mixed diffusion (C + T GBD), and Cu–TbH₃ stepwise diffusion (C−T GBD) magnets increases by 6.67 kOe, 12.33 kOe, and 13.16 kOe, respectively. Notably, the Tb utilization efficiency in the C−T GBD magnet reaches 146% of that in the T-GBD magnet under Cu-auxiliary diffusion. Microstructural characterization and elemental distribution analysis reveal that the C−T GBD magnet exhibits the deepest Tb diffusion depth and highest Tb content distribution, forming extensive core(Nd₂Fe₁₄B)–shell[(Nd, Tb)₂Fe₁₄B] structures that effectively enhance the reverse domain nucleation field. Temperature stability testing shows superior high-temperature performance of stepwise diffusion magnets, with a coercivity temperature coefficient of −0.51%/°C and an irreversible magnetic flux loss of only 0.5% at 150 °C. This work provides theoretical and technical insights into high-efficiency GBD based on cooperative diffusion strategies of Cu and Tb.

The polymorphic transition in TaS₂ has demonstrated rich tunability in physical properties, including modulated charge density wave (CDW) orders and superconductivity (SC), which is crucial for the development of new-concept and functional devices. Although phase engineering of TaS₂ has been explored through alkali metal intercalation and strain engineering, achieving precise control over the transition among its polytypes remains highly desirable, and in-depth investigations into the physical mechanisms triggering these structural transitions are still limited. Here, we systematically explored the phase transition behaviors of TaS₂ polytypes (2H, 4Hb, 6R, and 1T phases) under high-pressure and high-temperature (HPHT) conditions. We constructed a detailed phase diagram of TaS₂ across a pressure range of 0–6 GPa and a temperature range of 800–2000 K. Our findings indicate that high pressure effectively destabilizes the T layer of TaS₂, while high temperature exerts the opposite effect. Theoretical calculations reveal that the interaction strength between the planar Ta–Ta atoms, modulated by HPHT conditions, is a critical factor driving the T-to-H transition. Specifically, variations in the electrostatic repulsion between the lone pair electrons of S atoms and interstitial electrons from Ta atoms effectively alter the bond angles of S–Ta–S in both T and H layers, leading to the distinct deviations from their ideal geometrical configuration. Our results suggest that the deviation degree of the bond angles of S–Ta–S serves as a reliable metric correlating with the preferred phase in the competition between 1T and 2H phases. Moreover, this principle extends to other transition metal dichalcogenides (TMDs) with varying d-electron numbers, from which we established volcano curves for their preferred phases based on the interactions among transition metal atoms. Our work not only provides a novel approach for modulating the phase preference of TaS₂ but also elucidates a general phase transition mechanism for tuning TMDs.

The field of perovskite photovoltaics has seen unprecedented developments, driving a sevenfold increase in power-conversion efficiency since 2009. This growth testifies to the broad potential impacts of these materials. While solvent polarity enhances charge separation (CS) and the rate of charge transfer (CT) leading to CS, the instability of these perovskites in polar environments hampers the realization of their potential. Focusing on interfacial CT in nonpolar environments, here we demonstrate the importance of binding a redox-active moiety to cesium tribromoplumbate(II), or cesium lead tribromide (CsPbBr₃), perovskite nanocrystals (NCs) for achieving efficient CT in hydrocarbon media. Tight-binding compounds, such as amines, etch such low-valency perovskites. At controlled concentrations, however, binding an amine derivative of a phenothiazine electron donor to NC surfaces not only provides electronic coupling for efficient CT but also eliminates sites responsible for undesired exciton deactivation. This dual benefit from “wiring” CT mediators to perovskite surfaces ensures efficient charge extraction in nonpolar media, providing a key paradigm for interfacing these optoelectronic materials with an organic phase.

The limited penetration depth of ultraviolet/visible light and the low quantum yield of upconversion nanoparticles (UCNPs) have hindered their practical application in near-infrared (NIR)-driven photocatalysis. To address this, we propose a rational design combining plasmonic, upconversion, and photocatalytic components into a composite architecture: SiO₂ sphere array@Au film@UCNPs. The plasmonic SiO₂–Au interface concentrates excitation fields within nanoscale gaps, achieving optimal spectral coupling with UCNPs. This configuration suppresses radiative losses and enhances fluorescence intensity by 10.4-fold. The amplified emission efficiently excites the adjacent Au film, generating hot carriers that drive methylene blue degradation. Mechanistic studies reveal synergistic contributions from plasmon-enhanced luminescence, localized thermal activation, and radical generation (–OH/O₂⁻), underpinning the high catalytic performance. Theoretical modeling of optical and energy-transfer properties further supports the proposed mechanisms. This work demonstrates high-efficiency photocatalysis under 980 nm NIR light, offering promising potential for rapid dye degradation and advancing environmental and water-safety applications.

Some members of the RFeSi (R = Pr, Tb, Dy, Gd) family of intermetallic compounds, with tetragonal CeFeSi-type crystalline structure, exhibit low-temperature ferromagnetic behaviour. These alloys are of particular interest for two main reasons: (i) the Fe atoms appear to carry negligible or no magnetic moment, with R being solely responsible for the spontaneous magnetization; and (ii) they display a noticeable magnetocaloric effect (MCE) below 150 K. We have successfully fabricated single-phase GdFeSi ribbons in a one-step melt-spinning process, avoiding conventional thermal treatments such as long-time (several weeks) high-temperature annealing (above 1000 °C), thereby considerably reducing production costs. The ribbons show a broad entropy change leading to a relative cooling power of 517 J kg⁻¹ (∼3.76 J cm⁻³) over 110–180 K, providing a useful working range despite a modest isothermal magnetic entropy peak value. Materials operating efficiently in this temperature window are relatively scarce compared with other intermetallic magnetocalorics. The magnetocaloric properties of GdFeSi ribbons, as shown by these results, make them promising for magnetic refrigeration technologies, including liquefaction processes for light hydrocarbons and industrial gases.

Two-dimensional van der Waals ferromagnets are attractive for their potential in novel technological applications. In this work, femtosecond transient optical spectroscopy is used to study the dynamics of photoexcited carriers and coherent optical phonons in Fe₄GeTe₂ single crystals at 10–300 K. The optical response involves exponential decay due to the relaxation of carriers and damped oscillations due to the A_1g phonon vibration. Our measurements reveal an anomalous temperature dependence of electron–phonon thermalization time around the critical temperature of the spin-reorientation transition, which can be attributed to the abrupt change of the electronic structure near the Fermi surface. We also discover a spin–lattice relaxation process showing an anomaly below the Curie temperature. Such behavior originates from the temperature dependence of the magnetic specific heat. The damped oscillations of the coherent optical phonons can be well described using the anharmonicity model including lattice thermal expansion and phonon–phonon coupling. Our findings provide valuable insight into the nonequilibrium carrier and lattice properties in Fe₄GeTe₂.