Tinghong Gao

Epitaxial growth of GaN on AlN templates is considered an effective method for fabricating high-quality GaN films, but the atomic-scale mechanism underlying the growth process remains unclear. Specifically, the effects of AlN crystal orientation on the structural evolution and heterointerface roughness during growth have not yet been fully elucidated. This work examines the variations in GaN film growth induced by AlN crystals with distinct orientations through molecular dynamics simulations. The findings demonstrate that the crystal quality of GaN films is affected by the crystallographic orientation of AlN. The films developed along the [1 1 −2 0] and [−1 1 0 0] orientations have a hexagonal diamond single-crystal structure with reduced interface roughness, whereas the GaN film on the polar [0 0 0 1] template exhibits an alternating cubic-hexagonal diamond structure with the greatest interface roughness. Tensile tests indicate that fracture preferentially occurs in the GaN region. The mechanical performance of the [0 0 0 1] template heterostructure is suboptimal. The study elucidated the growth mechanism and defect evolution of GaN films on AlN templates at the atomic level, providing a theoretical foundation for modulating the heterointerface and GaN film phase structure and delivering significant practical insights for the epitaxial design and process optimization of high-performance GaN-based devices.

Aqueous sodium-ion batteries (ASIBs) are considered promising candidates for large-scale energy storage due to the natural abundance and low cost of sodium. However, the practical application of NASICON-type Na3V2(PO4)3 (NVP) cathodes in aqueous electrolytes is severely hindered by structural degradation and material dissolution, leading to rapid capacity fading. Herein, we propose a multi-metal substitution strategy to address these challenges by successfully synthesizing a Ti, Cr, and Al co-substituted Na3V1Ti1/3Cr1/3Al1/3(PO4)3 (NVTCAP) cathode material via a sol-gel method. The synergistic effect of the incorporated metal ions optimally tunes the crystal lattice, enhancing structural stability and mitigating volume expansion during cycling. This multi-metal substitution effectively suppresses active material dissolution, as revealed by in-situ X-ray diffraction (XRD), and enables the structural evolution of crystals during charging and discharging to exhibit the characteristics of quasi-solid-solution reactions. Quantitatively, the NVTCAP electrode undergoes a continuous structural evolution during Na+ extraction/insertion, with the unit cell volume recovering to within just 0.31% of its initial value after a full cycle. Consequently, the optimized NVTCAP electrode exhibits significantly improved electrochemical kinetics, delivering a high reversible capacity, outstanding rate capability (retaining 86.7% of its initial capacity from 0.1 to 5 A g–1), and exceptional long-term cycling stability (88.6% capacity retention after 3000 cycles at 5 A g–1). When coupled with an activated carbon anode, the NVTCAP cathode maintains superior performance, with 62.1% capacity retention after 5000 cycles. This work demonstrates that multi-metal synergistic substitution is a highly effective strategy for developing high-performance NVP-based cathodes, paving the way for advanced ASIBs with enhanced durability and rate capability.

Sodium‐ion batteries (SIBs) are promising for large‐scale energy storage, but the large ionic radius of Na ⁺ restricts their transport kinetics. Polyanionic K ₃ V ₃ (PO ₄ ) ₄ (KVP) is an attractive cathode material owing to its stable crystal structure and excellent cycling performance, yet it suffers from metal ion segregation, particle agglomeration, and poor pore structure regulation during synthesis. Herein, a sol–gel method was employed to optimize KVP preparation. Adjusting the stoichiometric ratio of citric acid suppressed ion segregation, while optimizing the sintering temperature balanced crystallinity and porosity. Prepared with 2 mmol citric acid and sintered at 800°C, the optimized KVP2 exhibits excellent crystallinity, a uniform porous structure, and homogeneously distributed K, V, and P elements. Electrochemical tests reveal a pseudocapacitance‐dominated charge storage mechanism (81% pseudocapacitive contribution at 1 mV s ⁻¹ ). KVP2 delivers an initial discharge capacity of 64.7 mAh g ⁻¹ at 10 mA g ⁻¹ and retains 82.3% capacity after 500 cycles at 100 mA g ⁻¹ . This work effectively enhances the kinetics and structural stability of KVP via citric acid regulation and sintering optimization, providing a novel strategy for designing high‐performance polyanionic cathodes and promoting SIB industrialization.

Magnetic skyrmions hosted in two-dimensional (2D) magnets offer exciting prospects for next-generation spintronic information storage and processing. Nevertheless, progress on skyrmions in 2D systems has been limited, mainly owing to the inversion symmetry of most 2D magnets, which in turn leads to the lack of the key factor Dzyaloshinskii–Moriya interaction (DMI) for generating topological magnetic structures. In this study, 2D half-metallic MoX2 (X = S, Se) monolayers are investigated by first-principles calculations and atomic spin simulations, which reveal their high Curie temperatures, strong DMI, and intrinsic chiral spin textures. Crucially, both MoS2 and MoSe2 can host stable skyrmion states over a wide range of external magnetic fields. Moreover, a dimensionless criterion is used to clarify the relationship between magnetic parameters and spin textures. The findings highlight that MoX2 monolayers are promising candidates for developing spintronic devices based on topological spin textures.

In this study, the stability, electronic, structural, and fracture toughness, and mechanical properties of the Half-Heusler(HH) alloys MnCoSb, MnCoAs, MnCoP, and MnNiSb were comprehensively investigated using first-principles calculations based on density functional theory (DFT). The calculated results reveal that all four alloys exhibit half-metallic characteristics, characterized by the presence of a substantial band gap in the spin-down channel. The phonon spectra and negative formation energies confirm that these alloys possess both dynamic and thermodynamic stability. The Born criteria further validate the structural stability in terms of mechanical properties. Three-dimensional representations of the Young’s modulus, bulk modulus, and shear modulus for the four alloys indicate that MnCoP exhibits the most pronounced anisotropy. The overall fracture toughness of the alloys ranges from 1.58 MPa·m^1/2 to 2.63 MPa·m^1/2, which falls within the typical range for half-metallic materials, albeit at the lower end, attributable to the relatively ductile nature of the four alloys. Although the two methods yield different absolute values, the explicit crack model (Method I) is considered more reliable for anisotropic systems because it directly simulates crack propagation and accounts for local relaxations, while the empirical formula (Method II) provides a useful reference for high-throughput screening. Among the alloys, MnCoSb demonstrates a superior mechanical performance, with K_IC values of 2.63 MPa·m^1/2 and 1.58 MPa·m^1/2 and brittleness indices M of 8.97 and 14.94, indicating excellent damage tolerance compared to the other three alloys. In contrast, MnCoP exhibits higher brittleness and lower mechanical reliability, with K_IC values of 2.00 MPa·m^1/2 and 1.63 MPa·m^1/2 and higher M values of 13.83 and 16.99. This study provides quantitative predictions of fracture toughness and establishes a relationship between microscopic and mechanical properties. These findings offer a theoretical foundation for the application of damage-tolerant HH alloys in fields such as spintronics and magnetism.

Heterogeneous high-entropy alloy (HEA) nanocomposites have garnered considerable scholarly attention due to their remarkable mechanical properties. However, their atomic deformation mechanisms during nanoindentation remain ambiguous. This study employs molecular dynamics simulation to perform indentation testing under three loading modes (Ni phase, Ni/HEA heterogeneous interface, and HEA phase). The results show that the indentation response is significantly influenced by the loading mode. The heterogeneous interface loading exhibits the most stable characteristics, whereas direct loading on the Ni phase induces significant force fluctuations and the highest hardness. These fluctuations arise from complex dislocation reactions, wherein dislocations generated in the Ni phase can traverse the heterogeneous interface and propagate throughout the whole nanocomposite. The HEA phase is essential for stabilizing the mechanical response. The Ni/HEA interface and HEA loading modes demonstrate significantly diminished force fluctuations and progressively declining hardness values. The surface roughness under HEA loading is the highest. The heterogeneous interface effectively blocks dislocation propagation from the HEA phase, confining dislocation activity to localized regions within the HEA. Sessile dislocations persist at the interface, impeding the propagation of dislocations. At a low temperature of 77 K, the nanocomposite demonstrates increased hardness and fewer variations in indentation force. The nanocomposite exhibits diminishing hardness values with increasing indenter size. Nonetheless, a larger indenter causes localized amorphization in the HEA region, hence increasing material hardness. The study thoroughly elucidates the mechanical property response to loading modes in heterogeneous HEA nanocomposites, providing guidance for the design of HEA nanocomposites with adjustable mechanical characteristics.

Gallium arsenide (GaAs), as a key semiconductor material, plays an important role in the electronics and aerospace industries. However, existing processing technologies still face limitations in improving the mechanical performance and machining quality of GaAs. To address these challenges, this study proposes a laser-rotation-assisted grinding method that combines laser heating with abrasive rotation. Through molecular dynamics (MD) simulations, the effects of laser assistance and rotational assistance on material removal behavior, stress distribution, dislocation evolution, and atomic-scale structural transformations are systematically investigated. Compared with conventional grinding and single-assisted methods, laser-rotation-assisted grinding significantly reduces the grinding force, decreasing the average grinding force from 181 nN to 74 nN, while reducing the subsurface damage depth from 50.64 Å to 42.10 Å. The spatial extent of high-stress regions is markedly reduced, and the onset of initial dislocation nucleation is delayed to approximately 6.8 nm, indicating enhanced resistance to defect formation and thereby further improving surface quality and structural stability. These findings provide deeper insight into the material removal mechanisms in coupled machining fields and offer important theoretical guidance for the development of high-precision semiconductor machining technologies.