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

In this study, we examine the electronic and optical properties of ABBA-stacked tetralayer graphene (4LG), emphasizing its unique characteristics in contrast to its counterparts. The full tight-binding model elucidates the significance of interlayer couplings in the system. We investigate the influence of gate voltage on the system and uncover alterations in the band structure, the emergence of edge states, and the formation of band gaps. The analysis of the density of states reveals the existence of van Hove singularities, which dynamically evolve with the changing gate voltage, resulting in a transition from semimetallic to semiconductor properties. The optical absorption spectrum demonstrates asymmetrical peaks and step-like structures, further affected by a potential difference. Under a finite electric field, optical excitations in gated 4LG reveal triangular isoenergy loops with significant interaction-induced distortions of up to 100 meV. This study anticipates the potential for tuning optical properties in ABBA-stacked 4LG through external electric fields, offering opportunities for experimental exploration.

Mid-infrared (MIR) region includes many important fingerprint signals about of particular chemical molecules and functional groups, which is an important band for compact optical sensing system. Controlling the localized surface plasmons (LSPs) and surface plasmon polariton (SPP) modes is an effective approach to achieving perfect absorption in plasmonic metasurfaces. In this work, we systematically investigate the interaction between LSP and SPP within a composite plasmonic metasurface absorber, as well as the impact of this interaction on its absorption characteristics. The absorber achieves absorptivity 99.2 % at 2.39 μm and 98.8 % at 3.61 μm. The detailed absorption mechanism and tunability of the absorber are discussed associated with a physical model based on quantum electron dynamics (QED) theory. Our analysis also explores the effect of incident angle, identifying a Rabi splitting at 40° and 3.61 μm due to the interaction between cavity modes and LSPs, while the absorption peak at 2.39 μm experiences a redshift with an increasing angle. These peaks show minimal dependence on the polarization angles of incident light. Furthermore, we investigate the impact of the SiO₂ spacer's refractive index using an admittance model, observing a redshift in the absorption peaks with an increase in refractive index. Our findings not only introduce a metasurface absorber for the MIR spectrum, applicable in sensing and detection, but also establish a foundation for further research.

Controlling the quantum interference in nanoscaled systems has potential application for the realization of high-performance functional devices. In this work, the quantum interference of a T-shaped double-quantum-dot system is studied in detail by evaluation of differential conductance by means of nonequilibrium Green’s function method. The factors of Coulomb interaction in Luttinger liquid leads, electron–phonon interaction, interdot tunneling, and dot-lead coupling are taken into account. In the differential conductance curve, there appear a series of antiresonance dips due to phonon-assisted destructive interference when the interdot tunneling is weak, and they can coexist with zero-bias antiresonance dip. When the dot-lead couplings are asymmetric, both the antiresonance dip and Fano line shape dip can occur for strong dot-lead coupling. Our results also show the coexistence of low-bias negative differential conductance and Fano antiresonance, as a manifestation of the interplay between strong intralead Coulomb interaction and weak dot-lead coupling. These interference phenomena emerged in a relatively simple model promises helpful guidance for controlling over the electrical performance of interference-based molecular devices.

A Janus monolayer can be described as a two-dimensional material with distinct anions on either side of each layer. Two of these distinct chalcogen atoms are situated in the mirror-symmetric lattice positions of the transition metal atoms and are referred to as Janus transition metal dichalcogenides (TMDs). This material breaks the out-of-plane mirror symmetry and thus has excellent properties not found in conventional TMDs. However, during material synthesis, it can generate a number of defects that can substantially alter its properties. Therefore, in this article, the changes in the electronic structure and optical properties of Janus WSeTe when generating single vacancy defects, double vacancy defects and antisite defects have been investigated using first principles study. Assess the stability of the material through computations of its phonon spectrum, AIMD simulation and defect formation energy. Analyse its bandstructure, projected density of states, and optical absorption coefficient to present the change in its properties. The results show that the easiest and most stable form of defect is the substitution of Se atom for Te atom. These defect types change the bandgap value in different ways in Janus WSeTe, which further changes the peak optical absorption coefficient. The lattice constants undergo alterations during the defect generation process. For this purpose, we also investigated the changes in the properties of Janus WSeTe and its defects when subjected to biaxial tensile and compressive strains ranging from −9% to 9 %. As the tensile and compressive strains increase, a gradual decrease in the band gap value is observed. Our findings may serve as a theoretical basis for experiments in the synthesis of Janus WSeTe and the development of electronic devices using monolayer Janus WSeTe.

The unique electronic structure of layered black phosphorus (BP) makes it an ideal candidate material for electrocatalytic oxygen evolution reaction (OER). Charge doping effectively improves the environmental stability and catalytic activity of BP by providing electron transfer channels and reducing charge transfer barrier. Therefore, based on the first principles calculation, this paper theoretically discusses how the intrinsic charge doping without introducing impurities changes the electronic structure and improves the catalytic activity of BP. It is found that charge engineering can effectively regulate and change the electronic structure and work function by stimulating the hybridization between different P-p orbitals, while maintaining the direct bandgap semiconductor characteristics of monolayer BP system. More importantly, in the catalytic process of OER, electrons and hole doping as free charges provide different donor and acceptor energy levels for the system depending on the doping concentration, and affect the adsorption capacity of monolayer BP to different reaction intermediates. At a certain doping concentration, the carrier mobility increases significantly, and the optimal Gibbs free energy and overpotential can be achieved in monolayer BP. These results provide new opportunities and possibilities for designing charge-engineered BP catalysts with adjustable electronic structure and excellent OER activity.

AlGaN nanowires have plenty of applications in optoelectronic functional devices. However, the electronic characteristics and stability of AlGaN nanowires are rarely explored, especially for an actual prediction of bandgaps with varying Al components. In this work, we utilize first principles calculation with DFT + U method to study the stability, charge redistribution, band structures, density of states of Al_xGa_1-xN alloy nanowires with x spanning from 0 to 1. The results indicate that the stability of the nanowire is enhanced with increasing nanowire diameter and Al component. The bond length in the outermost layer, vertical to the specified direction, is stretched as the Al component increases. The bandgap of nanowire is larger than that of bulk phase and the bowing parameter of nanowire is relatively low. According to the analysis of density of states (DOS), the migration of band structures is attributed to N-p states at VBM and Ga-s and Al-p states at CBM. The calculation of Crystal Orbital Hamilton Population (COHP) reveals the variation of bandgap with changing Al component and diameter. According to the analysis of electron density difference and charge transfer, Al atom has a stronger electron negativity and the electron density surrounding Ga is more delocalized compared Al atom. The results obtained in this study is expected to give some guidance for the preparation of optoelectronic devices based on AlGaN nanowires.

A mid-infrared ultra-wideband tunable terahertz absorber based on bulk Dirac semimetal (BDS) is presented. It has a simple three-layer structure: a top BDS metal layer, a middle dielectric layer, and a bottom reflective metal layer. The BDS layer was designed by creating a square cavity and a long rectangular cavity in the center of the BDS rectangle. The long rectangle was then rotated by 90° to form a centrosymmetric cavity. Using CST Studio Suite software, we numerically simulate the absorption characteristics. The simulation results indicate that the absorber achieves a high absorption (>90 %) of about 47.59 THz in the range of 37.5–90 THz when the Fermi energy level is 70 meV. The average absorption exceeds 95 %. In addition, adjusting the Fermi energy level of the BDS alters the absorption bandwidth. The centrosymmetric design of the structure ensures the absorber exhibits insensitivity to different polarization modes and angles of incidence, as well as excellent absorption stability. The designed shock absorber also exhibits excellent tolerance in manufacturing, reducing fabrication challenges and enabling practical applications. In addition, our design possesses the unique ability to modulate light in the mid-infrared band. These remarkable properties position our findings with significant potential in fields such as spectral analysis, optical biosensing technology, infrared sensing, and related applications.

Half-infinitely-wide ferromagnetic stripe and nanosized Schottky-metal stripe can be experimentally assembled on surface of GaAs/Al_xGa_1-xAs heterostructure, fabricating a hybrid semiconductor nanostructure, which was recently proven to act as an electron-momentum filter (a type of emerging nanoelectronics device). With the help of atomic-layer doping technique, a tunable δ-potential can be intentionally embedded inside the device. Because the inclusion of δ-doping does not clear two-dimensional characteristic of electron motion, an obvious wave vector filtering (WVF) effect still appears. Moreover, the effective potential experienced by electron in the semiconductor nanostructure is closely related to the δ-doping, therefore, a structurally-controllable electron-momentum filter with a tunable WVF efficiency by weight or position of the δ-doping can be obtained for nanoelectronics device applications.

In this work, the electronic, photocatalytic, and spin properties of 2D Janus XMoYZ${}_2$ (X= S, Se, Te; Y=Si, Ge and Z=N, P) monolayers are studied. The electronic properties are investigated and the results indicate that all of them are semiconductor with a suitable bandgap. The band structures with spin–orbit consideration indicate Rashba spin-splitting at the $\Gamma$-valley in the valence band. The spin-splitting at the K-point in the valence band is also significant, whereas the conduction band has negligible spin-splitting. Due to the mirror asymmetry of these compounds, their potential distribution and the corresponding dipole moments are investigated. Finally, by studying the photocatalytic properties, it is found that the redox happened on both sides of SMoSiN${}_2$ and SMoGeN${}_2$ monolayers. However, in the cases of SMoSiP${}_2$ and TeMoGeN${}_2$ monolayers, each photocatalytic half-reaction occurs on one side where the generated hydrogen and oxygen molecules are separated.

The current flow through an Y junction in graphene/hexagonal boron nitride (hBN) has been investigated at room temperature. The study has revealed that an electric field normal to the current flow can induce significant dissimilarities in the two drain currents outgoing from the Y branches, allowing the implementation of an electron beam splitter with variable ratio. An unexpected hysteretic effect due to fabrication processes was also observed. The Y junctions have been fabricated at wafer scale.