Wu Wang

Ultra‐broadband high‐temperature electromagnetic (EM) ceramic absorbers are extensively desired for next‐generation radar stealth technologies; however, current absorbers are far from satisfactory. Here, we employ an entropy‐driven strategy to develop an innovative (Co, Ba, Fe, Mg, Cr, Ni, Sr, Ca, Mn)Fe ₂ O ₄ high‐entropy spinel oxide absorber, which possesses an ultrabroad effective absorption bandwidth (EAB) of 13.1 GHz at room temperature (RT), along with a wide‐temperature EAB retention of ∼100% up to 1000°C. This ultrabroad high‐temperature EM absorption performance mainly stems from the highly stable impedance matching enabled by the entropy‐driven sustenance of oxygen vacancy concentration at elevated temperatures, as well as the entropy‐driven amplification of EM dissipation via an atomic‐interface polarization loss. This work not only presents a promising EM absorber for future high‐temperature applications, but, more importantly, provides a key mechanistic insight that can be a guide for exploring high‐entropy ceramic absorbers with enhanced absorption performance.

Electromagnetic pollution from the rapid expansion of wireless and electronic systems demands advanced absorber materials. High-entropy ceramics offer a promising platform for broadband electromagnetic wave attenuation, yet their rational design remains underdeveloped. Here, we introduce a mechanism-driven strategy to enhance absorption by tailoring local chemical order via simple thermal processing. Applied to high-entropy carbides, this local chemical order-engineering approach delivers a record effective absorption bandwidth of 11.2 GHz. Atomic-resolution chemical mapping paired with theoretical simulations reveals that local chemical order, rather than atomic vacancies, governs the dominant electromagnetic wave absorption mechanisms. We further demonstrate the universality of this principle across diverse high-entropy ceramic families (borides, oxides, sulfides, silicides, and selenides), each exhibiting substantial performance gains. This work establishes a clear, structure-guided framework for designing high-performance single-phase absorbers and offers a versatile route to mitigate electromagnetic pollution through targeted control of atomic-scale chemical order.

Vertical-cavity surface-emitting lasers (VCSELs) are key light sources for short-reach optical interconnects, sensing, and three-dimensional imaging, where device performance and reliability critically depend on the structural integrity of multilayer heterostructures at the atomic scale. Here, we present a comprehensive atomic-scale investigation of an 850 nm GaAs-based VCSEL using aberration-corrected scanning transmission electron microscopy. In the quantum well (QW) active region, we directly determine the strain distribution, lattice distortion, and elemental distributions at the atomic scale, revealing that the dominant strain is localized inside the QW interior rather than at the nominal heterointerfaces. Atomic-resolution chemical mapping further uncovers pronounced cation-site inhomogeneity, with Al concentrations varying from 2.4 to 11.8 at. % and Ga contents fluctuating between 35.9 and 46.2 at. % across individual QW pairs, corresponding to a continuous compositional modulation from Al0.24Ga0.72In0.04As and Al0.04Ga0.90In0.06As. This internal compositional disparity gives rise to the largest lattice distortion at the QW centers, accounting for the emergence of unconventional strain localization within the active region. Moreover, atomic-resolution imaging and spectroscopy of the distributed Bragg reflectors reveal graded interfaces and intrinsic cation-site compositional fluctuations that deviate from ideal homogeneous alloy models, despite the preservation of overall lattice continuity. These atomic-scale observations establish a direct correlation between local compositional modulation and unconventional strain localization in VCSEL heterostructures, providing critical insights for the rational design and optimization of next-generation laser devices.

The local structure and chemical environment critically govern transport properties in quantum and energy materials, but their atomic-scale manifestations remain elusive. Here we uncovered the atomic characteristics, intrinsic origin, and thermoelectric implications of chemical inhomogeneity in Bi 2 Te 3 -based materials with varying Se alloying. Using aberration-corrected electron microscopy, chemical bonding analysis, and thermodynamic modeling, we revealed pronounced Se enrichment in the central layer of a quintuple structure and constructed precise atomic models for this intrinsic inhomogeneity. Atomic-scale charge-density and valence-state measurements provided direct experimental evidence for chemical bonding disparity in Bi 2 Te 3 , with more covalent bonding in central layers and greater ionic bonding in outer layers. We also showed that this bonding disparity, coupled with entropy-enthalpy competition, drove the observed site preference and local chemical segregation in Bi 2 Te 3 − x Se x ( x = 0.5 , 1.0, 1.5, 2.0, and 2.5). The site-resolved bonding analyses further demonstrated that selective Se occupation tuned both ionic and covalent components of Bi– X bonds in Bi 2 Te 3 − x Se x . Therefore, this intrinsic chemical inhomogeneity modulated bonding polarity, the electronic band gap, and the Seebeck coefficient, serving as a fundamental determinant of thermoelectric performance. Our findings highlight atomic-scale chemical inhomogeneity as a key factor in tailoring functional properties of layered quantum materials beyond thermoelectrics.

We present an 850 nm vertical-cavity surface-emitting laser (VCSEL) featuring enhanced thermal stability and >30 GHz modulation bandwidth. The device maintains stable performance with bandwidths of 30.30 GHz at 25°C and 30.54 GHz at 55°C under 5 mA bias, showing minimal change. Notably, the bandwidth remains nearly constant across a wide current range (3-7 mA). The VCSEL exhibits excellent signal integrity, with relative intensity noise (RIN) consistently below -140 dB/Hz even at elevated temperatures. Advanced thermal management techniques, including polyimide integration and a double-mesa structure, effectively mitigate thermal impedance increase and carrier dynamics degradation. Furthermore, the device successfully achieves 106 Gbit/s PAM4 transmission, as evidenced by clear eye diagrams. These results demonstrate that our co-optimized thermal and carrier design represents a promising approach for developing robust optoelectronic devices capable of reliable high-temperature operation.

Thin-film β tungsten (β-W), a metastable phase of tungsten, holds significant potential in the fabrication of superconducting and spin-memory devices. However, due to the rapid surface passivation of tungsten in oxygen and moisture, the synthesis of nanosized metastable β-W with the intrinsic atomic surface is still difficult, and their magnetic properties remain rather unexplored. Inspired by the strong host-guest interaction-induced stabilization, we reported the synthesis of atomically thin (1.0-1.3 nm) metastable β-W nanowires within single-walled carbon nanotubes (SWCNTs) through an oxygen-assisted transformation of starting W₂C, with 85% of β-W nanowires along the anisotropic ⟨010⟩ direction. Atomically resolved electron microscopy directly unveils the dynamic evolutions of W₂C-to-β-W and further β-to-α-W within SWCNTs, depending on the H₂-annealing time. Detailed mechanistic studies by theoretical calculations and experiments reveal that oxygen diffused within the W₂C lattice governs the formation and stabilization of ultrathin β-W nanowires within the SWCNTs. Additionally, the nanoconfinement of SWCNTs, restricting the thickness of W nanowires down to 2 nm, also benefits the thermodynamically favorable nucleation of β-W than α-W. With the protection of a single graphene layer against water erosion, β-W@SWCNTs exhibit a ferromagnetic response at ∼130 K, with higher chemical stability than fully exposed thin-film β-W. This work may provide a feasible way to design the ferromagnetic nanowire metamaterials based on aligned SWCNT arrays that have the potential to fabricate microwave and spin devices.

In high-entropy materials, local chemical fluctuation from multiple elements inhabiting the same crystallographic site plays a crucial role in their unique properties. Using atomic-resolution chemical mapping, we identified the respective contributions of different element characteristics on the local chemical fluctuation of high-entropy structures in thermoelectric materials. Electronegativity and mass had a comparable influence on the fluctuations of constituent elements, while the radius made a slight contribution. The local chemical fluctuation was further tailored by selecting specific elements to induce large lattice distortion and strong strain fluctuation to lower lattice thermal conductivity independent of increased entropy. The chemical bond fluctuation induced by the electronegativity difference had a noticeable contribution to the composition-dependent lattice thermal conductivity in addition to the known fluctuations of mass and strain field. Our findings provide a fundamental principle for tuning local chemical fluctuation and lattice thermal conductivity in high-entropy thermoelectric materials.