Nanotechnology最新文献

A high-performance optical modulator based on three graphene (Gr) layers integrated with a dual elliptic-shaped silicon waveguide is proposed and investigated. The device is optimized for transverse electric mode operation, where the elliptic geometry is engineered to enhance modulation efficiency and compactness. The key performance indicators-including propagation loss (Lp), modulation depth (MD), bandwidth, energy consumption, and device footprint-are comprehensively analyzed through numerical simulations employing the finite element method. Simulation results reveal that the proposed modulator achieves a MD of 0.745 dBμm^-1, a compact cross-sectional area of 1.08μm², and a low Lp of 0.045 dBμm^-1at the telecommunication wavelength of 1550 nm. Further geometry optimization demonstrates enhanced modulation capability and reduced energy consumption. These results highlight the potential of the proposed structure as an energy-efficient and scalable candidate for future photonic integrated circuits and for advancing active nanophotonic devices incorporating two-dimensional materials.

The formation mechanism of porous anodic alumina has traditionally been attributed to field-assisted dissolution (FAD), a theory necessitating a dynamic equilibrium between electrochemical oxide growth and FAD. However, direct experimental verification of dissolution rates matching pore growth rates remains elusive. This study quantitatively decouples the contribution of corrosive dissolution from pore propagation kinetics by anodizing aluminum in phosphoric acid electrolytes (1-4 wt%) modified with polyethylene glycol (PEG). Crucially, the experimental results contradict the fundamental prediction of FAD theory: the addition of 50 wt% PEG unexpectedly accelerated the pore growth rate from 152 nm min^-1(in pure aqueous solution) to 250 nm min^-1, despite significantly reducing the electrolyte's corrosive power. Furthermore, immersion tests without electric field reveal a maximum chemical corrosion rate of only ∼2.73 nm min^-1at up to 60 °C, representing a two-order-of-magnitude discrepancy compared to the 300 nm min^-1growth rate required by FAD models. These findings demonstrate that chemical corrosion is kinetically insufficient to drive rapid pore channel extension. Consequently, this work challenges the validity of the FAD theory and provides robust evidence supporting the oxygen bubble model, wherein pore growth is governed by the plastic flow of barrier oxide around oxygen gas molds generated by electronic current.

Nanophotonic metamaterials exhibit application potential in micro/nano-optics owing to their unique optical properties. However, achieving dual-band perfect absorption with high quality factor remains a challenge. This study proposes a metamaterial featuring symmetry-broken silicon nanodisk arrays, which enables dual-band high-Qperfect absorption by transforming bound states in the continuum (BIC) into quasi-BIC and exciting an anapole mode. Numerical simulations demonstrate that the structure achieves absorption rates of 99.19% and 99.76% at wavelengths of 1068.55 nm and 1106.17 nm, respectively, with narrow linewidths of 1.08 nm and 0.84 nm, corresponding toQ-factors as high as 989 and 1316. Due to the polarization sensitivity of BIC, the absorption peaks can be switched on and off by adjusting the incident light polarization angle, offering a novel strategy for optical switching. Furthermore, as a dual-channel refractive index sensor, the metamaterial exhibits excellent sensing performance, with sensitivities of 81.9 nmRIU-1and 139.5 nmRIU-1, and figures of merit of 75.83RIU-1and 166.1RIU-1. This work not only provides a new design route for ultra-high-Qdual-band perfect absorbers, but also offers technical support for cutting-edge applications such as dual-frequency channel sensor and photonic switching.

All-inorganic cesium lead halide perovskite quantum dots, CsPbX₃(X = Cl, Br, I), exhibit exceptional potential in nonlinear optical (NLO) applications. This is due to their outstanding optoelectronic properties, including high photoluminescence quantum yield, tunable band gaps, and strong absorption coefficients. However, their practical utility is severely limited by their environmental instability against ambient air and moisture. In this study, CsPbBr₃QDs were encapsulated in a SiO₂matrix using a sol-gel method to fabricate CsPbBr₃/SiO₂gel-glass composites. Structural characterization (transmission electron microscopy, x-ray diffraction, and Fourier transform infrared) confirmed the uniform dispersion and complete encapsulation of the QDs within the amorphous SiO₂network. Optical analyses revealed that the composites retained the intrinsic absorption and emission characteristics of the CsPbBr₃QDs (bandgap: 2.29 eV; fluorescence peak: 510 nm), while exhibiting tunable linear transmittance (50%-82%).Z-scan measurements under 532 nm picosecond pulsed laser excitation revealed significant nonlinear absorption coefficients (β) of up to 0.85 cm GW^-1and a low optical limiting threshold (OL) of 0.22 J cm^-2. Importantly, SiO₂encapsulation markedly enhanced the environmental stability of the CsPbBr₃QDs, and their NLO properties remained stable after 365 d of storage under ambient air conditions. This work provides a viable strategy for realizing halide perovskite-based OL devices and establishes a promising platform for further development. Future device-level integration and cycling tests will be essential for practical deployment.

The novel pyramidal-shaped ternary molybdenum nickel selenide (MoNiSe4) nanomaterial was successfully synthesized using a solvothermal technique for the first time.The structural, optical and electrochemical properties of the synthesized sample were analysed through XRD, UV-visible spectroscopy, FTIR, FESEM, EDX and XPS analyses.The XRD pattern revealed a distinct shift of the main diffraction peaks toward a lower angle compared to pure MoSe3, validating the effective incorporation of nickel and the formation of the MoNiSe4 phase with an average crystallite size of 44 nm. The optical band gap of the material was estimated as 1.41 eV. FTIR spectra confirmed the presence of relevant metalselenide bonds and its functional groups. Morphological analysis by FESEM revealed a pyramidal shape with triangular surfaces featuring sharp edges and distinct facets that reflect its high crystallinity. Elemental analysis through EDS validated the stoichiometric composition of Mo, Ni and Se, whereas XPS confirmed the oxidation states of Mo⁶⁺, Ni 2 ⁺ and Se²⁻, further supporting the formation of the MoNiSe4 phase. Electrochemical analysis demonstrated superior supercapacitive characteristics of the MoNiSe4 electrode. Cyclic voltammetry exhibited a pseudocapacitive nature with specific capacitances of 304 F/g and 161 F/g at the scan rates of 50 and 100 mV/s respectively. Galvanostatic charge-discharge studies showed remarkable cycling stability with good capacitance retention even after 1500 cycles. The calculated specific capacitance, energy density and power density after 1500 cycles were 5695×10 -5 F g⁻¹, 285×10 -9 Wh kg⁻¹ and 24×10 -3 W kg⁻¹ respectively. The Nyquist and Bode plots indicated ideal capacitive and pseudocapacitive behavior, confirming the efficient charge storage performance of the electrode. Overall, the MoNiSe4 nanomaterial demonstrates strong potential as a highly effective electrode material for advanced supercapacitor applications.

High-speed atomic force microscopy enables real-time visualization of molecular dynamics using small cantilevers with high resonance frequencies. To further enhance temporal resolution, cantilevers must be scaled down to achieve higher resonance frequencies while maintaining low spring constants to minimize tip-sample interaction forces and preserve sample integrity. As cantilevers shrink, conventional piezo-based actuation, relying on external actuators to drive the cantilever, becomes less effective due to limited bandwidth and the appearance of spurious resonances in the cantilever spectrum in liquid environments. Photothermal actuation offers clean, high-frequency excitation but often requires high laser powers which can impose a significant thermal load on delicate samples. In this work, we present a wafer-scale microfabrication process for producing ultra-small bimorph cantilevers that combine sub-10µm lengths, resonance frequencies up to 10.5 MHz, and low spring constants suitable for biological applications. To enhance photothermal actuation efficiency, we substitute the conventional gold coating with palladium, enabling suitable cantilever oscillation at a reduced laser power. We validated the functionality of these cantilevers by imaging a self-assembled DNA lattice of blunt-end stacked DNA three-point stars in buffer.

CsPbBr₃nanoparticles were synthesized by hot-injection using the pair of reagents MnBr₂-SbCl₃and MnBr₂-SbBr₃as doping precursors. Said nanoparticles were green-luminescent (λ_em= 515 nm) with an average particle size of ∼12 nm and with monoclinic and orthorhombic crystal structure lasting longer than 80 d at ambient conditions. Additionally, a 54% photoluminescence quantum yield was maintained for at least 60 d when using MnBr₂-SbBr₃as precursors for doping. Transmission electron microscopy and selected area electron diffraction (SAED) revealed a reduced interplanar distance for the (110) planes for such condition (d_hkl= 0.57 nm-0.56 nm), suggesting heterogeneous doping into the analyzed nanoparticles, along with chemical analysis. On the other hand, Cl was detected through energy dispersive x-ray spectroscopy in the CsPbBr₃nanoparticles synthesized with the MnBr_2-SbCl₃doping precursor; as a consequence, these nanoparticles displayed a slight blue-shift in their luminescence (λ_em= 508 nm). Meanwhile, undoped CsPbBr₃nanoparticles decomposed into non-luminescent Cs₄PbBr₆with rhombohedral crystal structure before 80 d at ambient condition, as was evidenced by the SAED analysis. Finally, a green-luminescent LED (λ_em= 519 nm) was fabricated using the doped CsPbBr₃nanoparticles. The achieved stability points to an improvement in the passivation of CsPbBr₃'s crystal structure through Sb³⁺and Mn²⁺doping.

AlGaN/GaN based high-electron-mobility transistors utilize the excellent electronic and transport properties of Gallium Nitride and related compounds, making them highly sought after for high-power and high-frequency applications. However, threading dislocations that form during the GaN epitaxy growth on lattice mismatched Si substrates impact the device performance and reliability by causing an early breakdown and carrier trapping phenomena. For applications exceeding 1 kV, the growth of thick GaN stacks on 200 mm Si wafers introduces significant strain, compromising substrate integrity. This has triggered the development of engineered substrates for GaN epitaxy and the re-evaluation of the subsequent epitaxial growth. In this study, we have investigated the current transport properties of detrimental dislocations in AlGaN/GaN heterostructures grown on AlN engineered substrates (commonly referred to as QST®) and on conventional Si (111) substrates. This study has been achieved by developing a correlative nanoscale characterization methodology implementing conductive atomic force microscopy, cathodoluminescence microscopy, and electron channelling contrast imaging and revisiting dislocation-sensitive etching behaviour. This allowed us to observe vertical conduction paths manifesting themselves only in certain types of dislocations and to analyse the associated current transport mechanisms. Our modelling of the local current-voltage characterization on such dislocations, which are only 1% of the total dislocation density, directly associate them to the conduction mechanism via Poole-Frenkel emission in the reverse bias and variable range hopping in the forward bias.

Effective detection of dissolved acetylene is critical for diagnosing early faults in oil-immersed power transformers; however, achieving a synergy between high sensitivity and mechanical robustness presents a significant challenge in sensor design. We developed a photocurable composite film comprising copper-based benzene-1,3,5-tricarboxylate (HKUST-1) and butyl methacrylate (BMA) via ultraviolet crosslinking. HKUST-1 possesses a three-dimensional interconnected pore structure with uniform-sized nanocage windows (0.69-1.08 nm). The high density of Cu2+ sites enables rapid acetylene capture, achieving a rapid response time of 15 s. Coating the fiber tip with HKUST-1 creates a Fabry-Pérot interferometer (FPI) structure. Experimental gas adsorption tests and optical simulations validated the sensing probe's efficacy, demonstrating a sensitivity of 0.531 pm/ppm, a resolution of 0.716 ppm, and a detection limit of 2.11 ppm. The integration of MOFs' nanoscale confinement effects with photopolymerization presents a promising strategy for nano-engineered gas sensing.

This study investigates the structural and microstructural characteristics of magnetite (Fe₃O₄) and cobalt ferrite (CoFe₂O₄) nanoparticles synthesized via the sol-gel auto-combustion method using ferric nitrate and cobalt nitrate as metal precursors. X-ray diffraction (XRD) analysis confirmed the formation of single-phase crystalline nanoparticles with a cubic inverse spinel structure. Transmission electron microscopy further validated the nanocrystalline nature and morphological uniformity of the particles. To gain deeper insight into the crystallite size and lattice strain, multiple XRD-based analytical approaches Williamson-Hall, size-strain plot, and Halder-Wagner methods were employed. The novelty of this work lies in the first systematic side-by-side comparison of Fe₃O₄and CoFe₂O₄nanoparticles synthesized under identical conditions and evaluated using four complementary XRD models, ensuring cross-validated accuracy. The comparative evaluation of these models revealed slight discrepancies in size estimations, attributed to their varied assumptions regarding strain and instrumental broadening. Notably, CoFe₂O₄nanoparticles exhibited marginally larger crystallite sizes and higher lattice strain compared to Fe₃O₄, imply compositional influence on structural properties. The combined application of these analytical techniques enabled accurate estimation of crystallite size, microstrain, and energy density, providing insights into the mechanical stability and potential functional behavior of the synthesized nanoparticles.