Physica E-low-dimensional Systems & Nanostructures最新文献

The focus of this work is to develop a sensitive and reliable acetone gas sensor using the Pt-modified Co₃O₄/CoMoO₄ heterojunction derived from metal-organic frameworks (MOFs). Pt-loaded Co₃O₄/CoMoO₄ heterojunction was successfully prepared by the surface redox method, and the composites exhibited high sensitivity and selectivity for acetone with a low detection limit. By modifying the Co₃O₄/CoMoO₄ material with platinum loading, the sensor achieved a response of 24.12 to 20 ppm acetone, which was significantly better than that of the pure Co₃O₄/CoMoO₄ heterojunction. This work not only improves acetone detection strategies, but also enhances the potential for industrial and medical VOC monitoring applications.

The optoelectronic bionic synapse, as a new memory device with integrated storage and calculation, can respond to light stimulation, for use in the bio-visual system. These also have the advantages of large bandwidth, low crosstalk, and low power consumption. In this study, amorphous silicon (Si) films were annealed at 200 °C, 300 °C, 400 °C, and 500 °C, respectively. SiO_x defects were introduced at their interfaces and optoelectronic synapses, resulting in the formation of SiO_x/a-Si/P⁺⁺-Si. X-ray photoelectron spectroscopy was used to characterize the effect of different annealing temperatures on the composition of SiO_x. The devices successfully simulated a series of important synaptic functions, including excitatory postsynaptic currents, paired-pulse facilitation, short-term to long-term memory conversion, learning-experience behaviors, etc. The devices prepared under different annealing processes had different memory effects. Based on this, a 3 × 3 array of image memory optoelectronic synapse was prepared to simulate the human brain short-term, long-term, and after-repeated memory state, of human beings. Finally, based on the changes in the mode of Si and oxygen binding and the activation energy of oxygen, the reason for the differences in the memory properties of synaptic devices prepared at different annealing temperatures could be explained.

Mode coupling can not only effectively control the frequency, amplitude and linewidth of the transmission spectrum, but also improve the Q-factor of the spectrum. Herein, we propose a H-shaped metamaterial, in which the dipole mode, LC mode and lattice mode can be excited selectively, and each mode frequency can be independently tuned by changing the polarization of incident THz wave as well as the lattice constant of the metamaterial structure, thus allowing greater degrees of freedom to customize the polarization components of different properties in the system. Under different polarization directions, the strong coupling between the lattice mode and the inductance-capacitance (LC) mode as well as the lattice mode and the dipole mode is realized, which makes the transmission resonance Q-factor of the hybrid state increase to 8 times that of the single resonance state, and the obvious anti-crossing phenomenon is observed. In addition, the LC mode and the dipole mode can be excited simultaneously, and the coupling between these two modes successfully excites a bound states in the continuum with an infinite Q-factor.

The design of the photocathode is crucial for generating high-quality electron beam in electron sources. In this study, InGaN/GaN heterojunction nanowire photocathodes were proposed, and the photoemission theoretical model was developed. The results demonstrate that the built-in electric field along the axis enables the heterojunction nanowire photocathode to achieve higher collection efficiency across the response spectrum compared to In_0.5Ga_0.5N nanowire photocathodes. The variation of incidence angle results in distinct peaks in quantum efficiency and collection efficiency for the heterojunction nanowire photocathode. Meanwhile, the “additional electric field” has the potential to decrease the number of laterally emitted electrons from the nanowires, consequently reducing the shielding effect of adjacent nanowires. With an incidence angle of 15° and an “additional electric field” of 2 V/μm, the collection efficiency of photoelectrons at the collection end can be maximized to 47.6 %. This indicates that the heterojunction nanowire array photocathode has potential for use in high-performance vacuum electron sources.

In recent years, the influence of size-dependent effect on elastic wave propagation in viscoelastic single-walled carbon nanotubes (SWCNTs) has been considerably investigated. Due to the excellent thermal conductivity of viscoelastic SWCNTs, it is very meaningful to study the influence of size-dependent effect on thermoelastic wave propagation properties in viscoelastic SWCNTs under thermal environment. Nevertheless, few theoretical investigations have been carried out to predict the thermoelastic wave propagation properties of viscoelastic SWCNTs in the existing literatures. To fill this gap, the present work aims to establish the thermoelastic coupling model for viscoelastic SWCNTs based on the Euler-Bernoulli beam theory by combining the nonlocal elasticity theory and the G-N theory, taking the surface effect into account. By assuming the wave type solutions, the dispersion relationship between frequency (or phase velocity) and wave number is determined. The influences of the nonlocal parameter, the surface effect and the damping coefficient on the thermoelastic wave dispersion relation of viscoelastic SWCNTs at two different diameters are examined and the thermoelastic wave propagation properties are presented graphically.

Water, as a most common but unique molecule, plays a key role in biological and physical processes, whose properties can be effectively modulated by electric fields. In this work, we use molecular dynamics simulations to investigate the structures and dynamics of bulk water under the influence of terahertz electric fields. The result indicates that the diffusion coefficient of water decreases almost linearly with the increase in field frequency, because the water molecules have to adjust their dipole orientation intensively at high field frequency, which impedes the water motion. Additionally, for a small field frequency the diffusion coefficient is not sensitive to the change in field strength; while at high frequencies it displays an interesting minimum behavior. The minimum translational diffusion coefficient is about one fourth of natural diffusion, suggesting a freezing state of water molecules. In addition, almost the same trend can be seen in the rotational diffusion coefficient. Subsequent analyses of the hydrogen bond number support the behaviors of diffusion coefficient, revealing the two ways that the terahertz electric fields affect the bulk water: clustering and oscillation. Then, we reveal the structural changes of water under terahertz electric field through radial distribution function (RDF), potential of mean force (PMF) and dipole angle, which show the sensitivity to the field frequency and strength. These findings demonstrate that the terahertz electric field is an effective method to modulate the structures and dynamics of water, providing significant new physical insights.

The designed nanocomposite film of self-assembled 2D Ag-doped CuO:SnO₂ nanoflakes have been successfully synthesized through facile one-step hydrothermal technique. The fabricated sensor film is developed to detect liquefied petroleum gas (LPG) at room temperature. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and UV–visible spectroscopy comprehensively characterize the film's microstructure, morphology, element composition, and optical properties. The LPG sensing outcomes reveal that the Ag-doped CuO:SnO₂ film based sensor exhibits exceptional response and excellent repeatability towards LPG at room temperature. This is predominantly due to formation of CuO: SnO₂ interface, sensitized by doping silver (Ag) that drastically increases the carrier concentration of the NC sensor film and provides superior ability to detect LPG across a range of concentrations at room temperature. The sensor response increases from 300 % for 0.5 vol% LPG to a maximum of 414 % at 2.0 vol%. Notably, the sensor demonstrates fast response and recovery times (21 s and 30 s for 0.5 vol% LPG). These promising attributes position the NC sensor film as a strong candidate for real-world LPG sensing applications. Additionally, the research proposes a comprehensive mechanism explaining the NC sensor film's detection performance.

A considerably enhanced Rashba coefficient, $\alpha$ of up to ∼1.7 $eV\AA$ in single layer graphene (SLG) on Ni(111) in bridge-top (BT) configuration is obtained using density functional theory with spin-orbit coupling calculations. This is attributed to significant proximity and exchange effects in the BT configuration of SLG/Ni arising from a direct and enhanced Ni-$d_{z^2}$ interaction with SLG-$\pi$ states. The Rashba and exchange splitting occur in the graphene bands directly above and below the E_F in the dispersion along the $M-K-M^{\prime }$ path, that is involving the Dirac point. No Rashba splitting is noted along $\Gamma -M$ direction in agreement with angle-resolved photoemission spectroscopy (ARPES). The above results reveal the specific conformation of SLG on ferromagnetic substrate different from the commonly studied top-fcc (TF) structure and paves the way for SLG for spin-orbitronics without the need for interfacing or intercalating heavy and precious metals.

In TiO₂@MAPbI₃ core-shell nanowire array solar cells, the full use of incident light, rapid transportation of carrier, and enhancement of mutual properties are realized as a whole. However, the perovskite layer is prone to defects during the growth process, and the density of deep energy level defects on the surface of polycrystalline perovskite layers is 1–2 orders of magnitude higher than that of the bulk phase, so the surface composite mainly limits the carrier lifetime of perovskite layers. To address the interfacial defects of perovskite layers, it has been shown that modification of the ETL surface using complexing agents can eliminate or improve these defects by forming ionic and coordination bonds with the perovskite surface. However, the number of ligands and the number of unliganded ions will directly affect the degree of improvement of the hybridized perovskite defects. So we investigated the effect of complexing agent concentration on the photovoltaic performance of NWs array solar cells, and when TiO₂ NWss were modified by complexing agent at a concentration of 0.3 mol/L the best performance of the devices was achieved with a PCE of 9.86 % and an increase of 37.1 %. It shows that the concentration of the complexing agent has a significant impact on the carrier transport characteristics and photovoltaic performance of the core-shell structure NWs array. This will provide some guidances for improving the photovoltaic performance of core-shell NWs array solar cells.

Within the framework of effective mass approximation and with the use of finite element method, we calculate the energy states of an electron in a double toroidal quantum ring with a Hopf link structure. The study includes the influence of externally applied static electric and magnetic fields, and considers different geometric combinations of radii and link positions. We have found that geometric manipulations have significant impact on the energy values and the distribution of electronic probability densities in either one or both linked rings. Similar effects can be achieved with the application of the electromagnetic probes.