Nanomaterials最新文献

Despite efforts to produce scalable, substrate-independent, low-defect-density, and high-quality MoS₂, this continues to be a critical challenge for industrial-scale applications. This work aims to present a chemical vapor deposition (CVD) method for growing high-quality and potentially large-area mono- to few-layer MoS₂ films via proximity between the Mo nanofilm substrate and the target substrates. By using stoichiometry-guided knowledge of Mo-S and Mo-O-S phase diagrams, Mo nanofilms are oxidized and then sulfurized under optimized conditions to grow high-quality, millimeter-scale mono- to few-layer MoS₂ films in proximity to the target substrate. We have achieved millimeter-scale continuous growth of MoS₂ revealed via optical microscopy. Two-dimensional Raman maps of Full Width at Half Maximum show high-quality growth, and photoluminescence-based B/A exciton amplitude ratio shows high crystalline and optical quality with low defect density.

The interaction between water and metallic interfaces is crucial in many fields, and accurate modeling requires good parametrizations using reference data. In classical molecular dynamics (MD), an important part of this interaction is described using the Lennard-Jones (LJ) potential. However, previously reported LJ parameters are not always optimal for capturing the metal/water interactions observed in ab initio descriptions such as density functional theory (DFT). Therefore, well-tailored LJ parameters are necessary to improve the description of water structuring metals in classical MD. The usual route for obtaining LJ parameters involves energetic analysis, where the energies of various structures are obtained via DFT calculations and then matched with the energies obtained using the LJ potentials by varying the sigma/epsilon parameters. Here, we show a different approach to fit LJ parameters for metal/water interactions, based on structural analysis. We report several classical MD simulations for gold/water, varying the sigma/epsilon parameters, comparing the resulting water structuring with that obtained using DFT. Additionally, we test these parameters in quantum mechanics/molecular mechanics (QM/MM) MD simulations, where electrostatic interactions are enabled. Our results demonstrate that the proposed approach can improve the LJ parameters reported in the literature and potentially develop parameters for more complex systems where the water structure above metallic surfaces plays a significant role. Finally, within this proposed approach, the water density profile obtained in hybrid QM/MM calculations, where water is treated as MM at a substantially reduced cost, closely matches the description it would have if treated as QM.

Surface nanocrystallization is a critical approach for improving mechanical and functional properties of materials. Beyond conventional mechanical routes, chemical loading presents a promising pathway for nanocrystallization via interstitial-driven phase transformation. However, the characteristics and mechanisms underlying chemical load-induced nanostructuring remain insufficiently elucidated. This work investigates the surface nanocrystallization of 17-4 PH martensitic stainless steel during low-temperature plasma nitriding at 350 °C. Microstructural characterization combining XRD, EPMA, and TEM revealed a nitrogen-saturated layer with a maximum hardness of 13.5 GPa. The modified layer consists of nanoscale domains formed via a diffusionless martensite-to-austenite transformation, as evidenced by broadened FCC peaks, dark-field images, and the absence of elemental partitioning in EDX maps. This process is driven by the cyclic accumulation of chemical and elastic-strain energy at the advancing nitrogen diffusion front, triggering a self-sustaining, periodic transformation. This study introduces a chemical-driven nanocrystallization mechanism for novel design of surface-nanostructured steels via controlled thermochemical processing.

Dislocation reduction in gallium nitride (GaN) epitaxial layers remains a critical challenge for high-performance GaN-based electronic devices. In this study, GaN epitaxial growth on newly-developed 4H-Silicon Carbide (SiC) meta-substrates was systematically investigated to elucidate the role of surface pattern geometry in modulating dislocation propagation. A series of truncated-hexagonal-pyramid meta-structures with a fixed array period and varying pattern ratios (R) were designed and fabricated to enable controlled tuning of the effective surface morphology. Atomic force microscopy confirmed comparable surface flatness for all samples after epitaxial growth. Cathodoluminescence analysis revealed a non-monotonic dependence of defect density on R, indicating the existence of an optimal pattern geometry. Among all configurations, the outstanding sample exhibited the lowest defect density, achieving a 54.96% reduction in threading dislocations (edge + mixed) compared with a planar reference. Cross-sectional transmission electron microscopy further confirmed a substantially reduced dislocation density and clear evidence of dislocation bending and termination near the meta-structured regions. These results demonstrate that geometry-engineered 4H-SiC meta-substrates provide an effective and scalable strategy for dislocation modulation in GaN epitaxy on SiC meta-substrates, offering a promising pathway toward advanced GaN power and RF devices.

This study, for the first time, investigates and simulates ballistic-transport-induced avalanche behavior in two-dimensional materials. Using a technology computer-aided design simulation platform, a device model for ballistic avalanche transport is systematically established. By accurately calibrating the material parameters of two-dimensional materials and selecting appropriate physical models, the key features of the ballistic avalanche effect are successfully reproduced, including low threshold voltage and high gain. The simulation results show good agreement with experimental data. Furthermore, mechanism-based analysis is performed to clarify the influence of critical design parameters on the avalanche threshold and multiplication gain. Finally, based on the same physical models and mechanistic understanding, the operational paradigm and performance of ballistic-transport avalanche photodetectors based on two-dimensional materials are predicted. This work provides a reliable theoretical foundation and a robust simulation framework for the optimized design of high-performance and low-power avalanche photon devices.

This study demonstrates drift-assisted positron annihilation lifetime spectroscopy on a p-type (100) silicon substrate in a MOS capacitor, using an applied electric field to control the spatial positron distribution prior to annihilation. The device was operated under accumulation, depletion, and inversion conditions, revealing that the internal electric field can drift-transport positrons either toward or away from the SiO₂/Si interface, acting as a diffusion barrier or support, respectively. Key positron drift-transport parameters were derived from lifetime data, and the influence of the non-linear electric field on positron trapping was analyzed. The comparison of the presented results to our previous oxide-side drift experiment on the same metal-oxide-silicon capacitor indicates that the interface exhibits two distinct sides, with different types of defects: void-like and vacancy-like (Pb centers). The positron data also suggest that the charge state of the Pb centers likely varies with the operation mode of the MOS, which affects their positron trapping behavior.

Oxide transistors have attracted significant interest in the field of integrated circuits (ICs). Among various oxide semiconductors, InAlZnO (IAZO) stands out as a promising candidate due to its potential for high mobility and excellent stability. In this work, we fabricate high-performance IAZO transistors with a field-effect mobility of 56.60 cm²/V·s, a subthreshold swing of 82.59 mV/decade, an on-to-off current ratio over 10⁷, and a small threshold voltage shift of 0.09 V and -0.03 V under positive and negative bias stress, respectively. Based on these transistors, Pseudo-Enhancement-Load (PEL) inverters were constructed. An adjustable bias voltage (V_BIAS) was also introduced as an additional control parameter, which allows for flexible control of the trade-off between circuit performance and power consumption. The resulting inverters achieve a balance between static and dynamic performance, exhibiting a voltage gain of 1.83 V/V and a relatively low power consumption of 2.58 × 10^-6 W (V_BIAS = 1.0 V). Our work demonstrates the potential of IAZO transistor-based PEL inverters for high-performance, low-power oxide IC applications.

This study examines how both the nature of the carbon support and the palladium precursor influence catalytic performance in acetylene hydrogenation. Six Pd-based catalysts were prepared on four carbon materials-high-heat-treated fibers (HHTs), carbon nanotubes, activated carbon and high surface area graphite-using either sulfate or chloride precursors. Catalytic tests performed in a continuous fixed-bed reactor reveal that HHT-supported catalysts achieve the highest ethylene selectivity and long-term stability, while in general catalysts derived from sulfate precursors exhibit enhanced selectivity compared to their chloride-derived counterparts. These improvements are consistent with the formation of sulfur, which may be incorporated as sub-stoichiometric sulfide species (S^2-) interacting with metallic Pd, as revealed by the XPS results, rather than to palladium dispersion alone. The role of the carbon support in stabilizing these sites was further assessed by complementary characterization techniques, including transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The combined results indicate that highly graphitic supports such as HHT fibers favor sulfur retention at the catalyst surface, thereby promoting the stability and catalytic performance of Pd-S active motifs during acetylene hydrogenation.

To tackle challenges including excessive initial boiling superheat and low heat transfer coefficients inherent in conventional working fluids, hydrophobic-modified TiO₂@carbon nanotube (MWCNT) composite nanofluids were fabricated. Subsequently, the boiling heat transfer mechanisms were systematically investigated and visually verified. Hydrophobic TiO₂ nanofluids exhibit enhanced stability, whereas hydrophobic TiO₂@MWCNTs composite nanofluids demonstrate improved thermal conductivity. At a mass ratio of hydrophobic-modified TiO₂ to MWCNTs of 2:1, the optimal heat transfer performance was attained, with a 31.6% increase in heat transfer coefficient (HTC) and a 46.5% increase in critical heat flux (CHF) density relative to hydrophobic-modified TiO₂ nanofluids. Composite nanofluids exert effective regulation over bubble kinetic parameters: hydrophobic nanoparticles increase vaporization core density, reduce bubble nucleation energy barriers, and mitigate initial boiling superheat. Benefiting from the superior thermal conductivity and mechanical properties, MWCNTs remarkably promote heat transfer efficiency. The synergistic effect between the two components enables the concurrent enhancement of HTC and CHF, thus highlighting the promising application potential of hydrophobic-modified TiO₂@MWCNTs composite nanofluids in intensifying pool boiling heat transfer.

Optimizing efficient electrode materials that combine high energy density, rapid charge transport, and excellent cycling stability remains a challenge for advanced supercapacitors. Here, we report the synthesis of an innovative copper(I)-based metal-organic framework (MOF), Cu₃(NDI)₃, prepared via a simple solvothermal method using N,N'-bis(3,5-dimethylpyrazol-4-yl)-naphthalene diimide (H₂NDI-H) as a linker. Structural analyses (XRD, FTIR, SEM, EDX, and BET) confirmed the formation of a highly crystalline, porous MOF. Integration of this MOF into laser-induced graphene (LIG) matrices yielded hybrid electrodes with enhanced structural characteristics and electrochemical activity, compared to its only-LIG counterpart. Electrochemical studies (CV, CD, EIS) revealed that the LIG-MOF electrode exhibited the highest performance, delivering a specific capacitance of 4.6 mF cm^-2 at 0.05 mA cm^-2, and an areal energy density of 60.03 μWh cm^-2 at a power density of 1292.17 μW cm^-2, outperforming both LIG and MOF-LIG configurations. This enhancement arises from the synergetic interaction between the conductive LIG network and the redox-active Cu₃(NDI)₃ framework, highlighting the potential of LIG-MOF hybrids as next-generation materials for high-performance supercapacitors.