Nanotechnology最新文献

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.

Recently, symmetry-broken ground states, such as correlated insulating states, magnetic order and superconductivity, have been discovered in twisted bilayer graphene (tBLG) and twisted trilayer graphene (tTLG) near the so-called magic angles. Understanding the magnetic order in these systems is challenging, however, as atomistic methods become extremely expensive near the magic angle and continuum approaches fail to capture important atomistic details. In this work, we develop an approach to incorporate short-ranged Hubbard interactions self-consistently in a continuum model. In addition, we include long-ranged Coulomb interactions which are known to be important when doping the flat bands of tBLG and tTLG. Therefore, for the first time, magnetic order in moiré graphene multilayers is self-consistently explored in a continuum model with atomistic detail. With this approach, we perform a systematic analysis of the magnetic phase diagram of tBLG as a function of doping level and twist angle, near the magic angle. Our results are consistent with previous perturbative atomistic Hartree+Ucalculations. Furthermore, we investigated magnetic order of tTLG, which were found to be similar to those in tBLG. In the future, the developed continuum model can be utilized to investigate magnetic ordering tendencies from short-range exchange interactions in other moiré graphene multilayers as a function of doping, twist angle, screening environment, among other variables.

This research outlines a simulation-based analysis of dual-gate semiconducting graphene field-effect transistors (GFETs) constructed using vertically aligned synthesized graphene via plasma-enhanced chemical vapor deposition (PECVD) technique. Using SILVACO TCAD software, the study investigates the impact of varying plasma parameters-specifically electron and ion temperatures, and densities-each associated with different graphene channel thicknesses. Distinct combinations of plasma electron/ion temperature and density were investigated; each linked to a specific graphene channel thickness. The study focused on the electrical properties of the dual gate semiconducting GFET, comparing them with the existing experimental observations and correlating these properties with the plasma processing parameters. It was seen that the values of these properties, like drain current,Ion/Ioff current ratio, transconductanceg_m, cutoff frequencyf_c, etc., increased on decreasing the plasma parameters of the PECVD process involved. The relations developed can be used to modulate the properties of plasma-grown GFETs, by scaling them down for industrial use in several concerned sectors of high-frequency circuits, solar cells, supercapacitors and biosensing technologies. These findings provide a theoretical framework to support future experimental validation and process optimization.

Non-van der Waals layered transition metal chalcogenide Cr₂Te₃ exhibits unique properties including perpendicular magnetic anisotropy, anomalous Hall effect, and non-trivial band topology. Our first principles study further reveals that, induced by the surface Cr atoms, a transition from metallicity to a half-metallicity could occur when Cr2Te3 is reduced to an ultrathin film. The synergistic effect induced by the surface termination and the thickness of the film was found to play a crucial role in this transition. Specifically, a correlation between the bonding symmetry broken on the surface Cr, the strong orbital hybridization between surface Cr and Te atoms, and the squeeze of spin-down valence bands associated with Te-5p orbitals below the Fermi level was found in such ultra-thin 2D Cr2Te3 film during this transition. Such a finding provides key insights into the tunability of Cr₂Te₃ on its spintronic properties by modulating its thickness and surface termination, making it a potential application for designing highperformance spintronic devices.

In this study, the growth of vertical graphene (VG) nanosheets on copper (Cu) substrates in a direct-current plasma-enhanced chemical vapor deposition (PECVD) system was studied. The plasma process during the VG growth was characterized using a high-speed camera and optical emission spectroscopy. Results showed that the plasma composition remained constant, but the overall plasma intensity increased with increasing substrate open area (OA). At low OAs of > 0.05, VG growth was limited to edges, and the VG height increased gradually to reach 700 nm as more reactants became readily available. Two distinctive regimes were identified: diffusion-limited growth at OAs < 0.6, and kinetic-limited growth at OAs > 0.6 for Cu meshes and screens. Under the diffusion-limited regime, VG growth occurred preferentially from the substrate edge toward the center. Therefore, the deposition time was extended to achieve uniform VG deposition. However, in the kinetic-limited regime, the increased availability of reactants did not alter the VG height, which remained at 700 nm. The kinetic-limited deposition was uniform across the substrate due to less plasma screening. This study sheds light on the growth mechanism of VG on perforated substrates, opening new avenues to control deposition on Cu substrates within plasma-screened interfaces.