Nanotechnology最新文献

This paper proposes substrate nitridation as an effective method to reduce radio-frequency (RF) loss in Si-based GaN epitaxial wafers. By optimizing the process, an amorphous SiN_xlayer was formed, which effectively blocks the downward diffusion of Al atoms and suppresses the formation of a parasitic conductive channel, thereby leading to a significant reduction in RF loss. Four distinct pre-flow conditions were specifically designed to decouple and modulate the properties of the AlN/Si interface. A detailed analysis of the initial dislocation evolution behavior was conducted, comparing the nitridated substrate with conventional pre-deposited Al processes. Although the nitridation process leads to a moderate increase in threading dislocation density by promoting their parallel propagation, the proposed dislocation coalescence mechanism, supported by our experimental design and analysis, indicates that the spatial extent of individual dislocations and defects is effectively constrained. This results in a substantial improvement in the overall RF electrical characteristics. Based on this proposed process, a coplanar waveguide (CPW) transmission line was fabricated, demonstrating a low RF loss of only -0.6 dB at 40 GHz. These results underscore that the nitridation process is a highly promising pathway for enhancing the RF performance of Si-based GaN materials; more importantly, this study reveals that the advantage of an initially optimized interface must be synergistically integrated and stabilized with subsequent epitaxial processes to achieve low-loss performance in final high-electron-mobility transistor devices, which holds significant implications for the development of high-performance RF devices.

Self-powered solar-blind photodetector offers irreplaceable advantages for applications such as wearable electronics and ultra-low power systems, but their performance is often limited due to the absence of an external bias. In this work, we demonstrate a high-performance self-powered photodetector based on a well-designed NiO/Ga₂O₃ p-i-n heterostructure that requires no complex pre-treatment methods. The photodetector exhibits a high photo-to-dark current ratio of 378, a high responsivity of 137 mA W^-1, and fast response times of 27 ms/650 ms. Furthermore, we quantitatively elucidated the physical origin of the self-powered behavior. The analysis of the p⁺-n^-one-sided abrupt junction, based on repeatable capacitance-voltage characterization, confirmed the presence of a strong built-in electric field with a calculated maximum field strength of 136 kV cm^-1. It is the fundamental driving force for the photodetector's excellent self-powered performance.

The efficiency of green hydrogen production via water splitting is typically hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Here we investigate the performance of various nickel nanoclusters, deposited via a binder-free gas-phase method, as OER catalysts on two distinct porous platforms: commercial gas diffusion layers (GDLs) for electrocatalysis and mesoporousTiO2thin films for photoelectrocatalysis. For dark electrocatalysis on GDL, we find a non-linear relationship between catalyst loading and activity, where the lowest Ni loadings exhibited the highest specific activity. Trace iron impurities in the electrolyte dramatically enhanced the performance, leading to a 120-fold increase in specific current for the lowest loading samples through thein situformation of highly active NiFe oxyhydroxide species. When integrated as co-catalysts on mesoporous TiO_₂photoanodes, Ni nanoclusters significantly improved photocurrents, with an optimal loading of 0.27-0.89μg cm^-2. While Fe impurities also boosted photoelectrochemical performance at low Ni coverages, the effect was less pronounced and became detrimental at higher loadings. These findings underscore that the precise control of the catalyst loading and composition is decisive for designing scalable and highly efficient systems for water oxidation.

Electron beam-induced current (EBIC) is a vital characterization technique for promising semiconducting single-walled carbon nanotube (CNT) devices, yet its underlying imaging mechanism remains poorly understood. This study elucidates the EBIC imaging mechanism in CNTs. By simultaneously analyzing secondary electron (SE) and EBIC signals at landing energies of 1 keV and 10 keV in scanning electron microscopy (SEM), it is demonstrated that the EBIC signal is strongly correlated with SE emission intensity. This finding indicates that, unlike traditional three-dimensional semiconductor materials where EBIC imaging is dominated by built-in potential, the Pd-CNT system is governed by substrate charging polarity and electron dose. Moreover, the signal intensity distribution is determined by the resistance gradient along the CNT. This fundamental clarification of the physical origin of EBIC in CNTs provides the essential mechanistic foundation required for the reliable quantitative analysis of electrical properties at nanoscale interfaces in low-dimensional electronics.

A nano-inscribing technique was tested as a method of cost-effective replication of blazed diffraction gratings for x-rays. A saw-tooth mold for the nano-inscribing was fabricated by a double-replication process from a master blazed grating. The nano-inscribing was performed using a UV-curable resist of low viscosity to provide a small thickness of the resist replicas, required for a following transfer process. The nano-inscribing process was optimized to minimize surface relaxation and preserve the saw-tooth shape of the grooves, required for high diffraction efficiency. The quality of the replica gratings was evaluated via diffraction efficiency simulations. The simulations demonstrated that near theoretical efficiency can be achieved for the x-ray gratings made by the nano-inscribing approach.

Metal-organic frameworks (MOFs) have emerged as promising microwave absorbers owing to their tunable composition, structural diversity, and high porosity. However, their low intrinsic permittivity leads to impedance mismatch and inadequate attenuation capacity. To address this limitation, we developed a series of polypyrrole (PPy)/MOFs composites through ultrasonic integration of high-permittivity PPy nanoparticles with hydrothermally synthesized [(CH₃)₂NH₂]Mn(HCOO)₃(Mn-MOF). The optimal composite with a PPy-Mn mass ratio of 4:1 (50 wt% filler in paraffin) achieved a minimum reflection loss (RL) of -63.4 dB at 17.67 GHz with an ultrathin thickness of 1.7 mm. Its maximum effective absorption bandwidth (EAB, RL⩽ -10 dB) reached 5.44 GHz (10.60-16.04 GHz) at a thickness of 2.2 mm. Unlike typical PPy-based absorbers limited to medium frequencies and greater thicknesses, this work achieves the integration of strong absorption, high-frequency, and an ultrathin profile (~2 mm). Enhanced performance stemmed from synergistic interfacial polarization, dipole relaxation, and optimized impedance matching. This study presented an effective strategy to design MOF-based as the promising microwave absorber.

The static and dynamic properties of meron-like magnetic textures stabilised by anisotropic Dzyaloshinskii-Moriya interaction (A-DMI) are examined in nanodots across hosting geometries. By considering a circular magnetic nanoring, we use micromagnetic simulations to identify geometric conditions that minimise the total energy and favour the stabilisation of vortex or antivortex textures as a function of the ring hole. For each texture, we find an optimal geometry that maximises stability. We further map the spin-wave spectra under in-plane and out-of-plane field pulses. For antivortices, out-of-plane excitation yields a single well-defined mode, whereas vortices exhibit a richer modal structure arising from the competition between A-DMI and geometry. Under in-plane excitation, vortices and antivortices support the same number of low-frequency modes with similar spatial profiles. These results highlight the interplay between meron cores and chiral interactions, with implications for spintronic and magnonic devices that rely on stabilising magnetic textures or tailoring spin-wave modes.

A number of ecological stressors negatively impact on rice yield, drastically lowering crop productivity. Among these, arsenic stress is considered a major abiotic factor that affects number of processes in plants, ultimately leading to reduced productivity. Nano-hormonal interactions have garnered allure as a possible way to lessen arsenic toxicity in plants. In this work, the synergistic effects of zinc oxide nanoparticles (ZnO-NPs) and epibrassinolide (EBL) on rice (Oryza sativa) with arsenic stress were examined. A fully randomized block design (CRD) was used in a pot experiment. Exposure to arsenic (150μm) impaired growth (length and biomass), photosynthetic performance, soluble sugars, starch, and sucrose (primary metabolites), phenolics and flavonoids (secondary metabolites), as well as key mineral nutrients. However, foliar application of ZnO-NPs (100 mg l^-1) and EBL (0.01μm) alleviated arsenic-induced toxicity by promoting enzymes activity and promoting the involvement of secondary metabolites in defense. These improvements in the biochemical and physiological matrices of rice plants effectively mitigated growth losses under arsenic stress. Overall, this work concludes the interactions between ZnO-NPs and EBL in modulating development and growth in rice, thereby contributing to global food security.

Metal halide perovskites generally present functional properties such as ferroelectricity and ferroelasticity, forming nano domains which dictate most of their physical properties. Crystalline changes in the nanoscale, including heat-induced domain rearrangements, are generally responsible for the appearance of structural defects. This is valid for bulk and surface but is especially relevant in nanomaterials, where charge traps lead to degradation in perovskites, reducing the lifetime and compromising their use in solar cells. The growth of oriented nano domains, on the other hand, does not only improve perovskite-based solar cells efficiency and lifetime, but can be potentially used to tailor conductivity and optical emission, opening new possibilities for applications in optoelectronic devices. Studying phase transitions, defect formation and nano domain dynamics in perovskites is challenging, requiring techniques capable of probing crystals with high strain sensitivity and good spatial resolution.In situandoperandoexperiments, for instance, are difficult to perform using traditional techniques which require severe sample preparation. Recent developments in synchrotron x-ray sources, with the emergence of instruments able to offer small x-ray beams with improved photon flux and coherence, can bring new insights into the field. This review focuses on x-ray methods for the study of perovskite basic properties, enlightening possible multi-technique experiments which are currently available in large scale facilities.

The intrinsic strong bonding network limits controlled two-dimensional (2D) nanosheet exfoliation of non-van der Waals materials. We report here the successful stabilization and 2D nanosheet exfoliation of 2Dγ-Fe_₂O_₃(maghemite) nanosheets through the application of ultrasound-assisted liquid-phase exfoliation with the aid of cetyltrimethylammonium bromide (CTAB) as the stabilizing agent. Atomic force microscopy (AFM) confirms the existence of ultrathin nanosheets of thickness ∼0.5-2 nm corresponding to the monolayer and few-layer structures. X-ray diffraction verifies the broadening of the peaks and the characteristic shifting of the peaks of compressive strain in the nanosheets of the exfoliated structure. X-ray photoelectron spectroscopy corroborates the existence of hydroxyl (-OH) functional groups on the nanosheet surfaces and the existence of the CTAB molecules that achieve stabilization through electrostatic and steric interactions. A prominent peak in the 200-250 nm region with the extended broad absorption to the visible region is observed through the application of UV-Vis spectroscopy and it is assigned to defect states formed during the process of exfoliation. Such structural and surface modifications are expected to modify the 2Dγ-Fe_₂O_₃'s physical and chemical properties, making it a promising material for a wide range of applications in materials science, nanotechnology, and environmental or energy-related technologies. We demonstrate here an effective route to the production of processable and stable 2Dγ-Fe_₂O_₃nanoparticle nanosheets and shed light on the structural transformation during the exfoliation process.