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

In this paper, a wideband Graphene-inspired dielectric resonator THz MIMO antenna is designed. The antenna has dimensions of 56 × 56 × 3.6 μm³ and is designed on a Rogers RO3035 substrate with a relative permittivity of 3.6 and loss tangent of 0.0015. This antenna works in the range of 6.0 THz-12.5 THz (70.76 %) with a peak gain of 7.68 dBi and radiation efficiency (>70 %) is suitable for use in medical imaging and THz wireless near-field applications. A CSRR is loaded to obtain band notch characteristic for avoiding interference between nearby wireless devices in the range of 10.6–10.8 THz. EBG was also introduced with a patch antenna to reduce surface wave loss and improve isolation, resulting in a high front-to-back ratio (FBR) in the range of 10–12.5 THz. Without the graphene disk, the silicon-based DRA did not achieve significant gain. At a chemical potential of 0.5 eV and a relaxation time of 0.1 ps, the proposed DRA demonstrated good antenna properties. By varying the chemical potential and relaxation time, frequency agility was easily achieved. A Graphene disk having a height of 3 μm is placed on a Silicon (ε_r = 11.1) based cylindrical DRA to provide high gain and improve the impedance bandwidth, achieving wide bandwidth from 6.0 THz to 12.5 THz. The proposed two element antenna performance is evaluated by parameters such as gain, return loss, isolation between two antenna elements, and diversity parameters like Envelope correlation coefficient ECC<0.1, Directive Gain >9.5 dB, Total Active reflection Coefficient >10 dB and Avg. Channel capacity loss <0.35bps/Hz so that the proposed antenna is suitable for wideband nano/optical communication in IoT-6G. Furthermore, the antenna is suitable for biological sensing applications due to its average sensitivity and FOM for hemoglobin and urine of 805.33GHz/RIU and 805.55GHz/RIU, respectively, and 3.37 and 10.55.

Inverted structure perovskite solar cells have attracted much attention in recent years due to their reliable operational stability, low residual, and low-temperature fabrication process. In the past few years, to accelerate their commercialization, the focus of research on the inverted structure perovskite solar cells was on the power conversion efficiency increasing. In this study nanoparticles of Cu₂ZnSnS₄ (CZTS) were doped into the PEDOT:PSS film as the hole transport layer (HTL) and then the interface carrier recombination quenching was observed. Consequently, it leads the s to charge carrier's collection enhancement of the Inverted perovskite solar cells. Compared to other types of HTLs, the use of CZTS HTL reduces the amount of interaction of the HTL film and the perovskite film, which results in an increment of the stability of the solar cell over time.

Transition metal halides are promising for use in photovoltaics and optoelectronics. This research systematically investigated the composition-dependent electronic and optical properties of all-inorganic TiX₃ (X = Cl/Br/I) transition metal halide nanowires using first-principles density functional theory (DFT) and time-dependent DFT calculations. The findings emphasize the significant impact of the specific halide type on the electronic and optical characteristics of TiX₃ nanowires. Particularly, the type of halide significantly influences the electronic states near the Fermi level and the infrared photoabsorption properties. An important discovery is the exceptional photoabsorption strength observed in the TiCl₃ nanowire, reaching an impressive value of 26000 cm⁻¹. The study also offers insights into exciton generation, aided by Transition Contribution Maps. Apart from its theoretical implications, we expect that the insights gained from this research will contribute to the advancement of active optical devices utilizing all-inorganic halide perovskites.

Carbon nanotubes (CNTs) were grown in a horizontal reactor by chemical vapor deposition, and it was found in the experiments that different heating temperatures and the position of the porcelain boat affect the morphology and yield of CNTs. Computational fluid dynamics (CFD) software is used to simulate the gas flow field distribution in the horizontal reactor under different operating parameters, and the results revealed that the gas flow in the horizontal reactor was advancing with vortex, and this gas circulation is induced by the difference in density due to the existence of temperature difference between the gas streams. As the heating temperature and nitrogen gas velocity increase, this vortex distorts the laminar flow, which in turn weakens the growth of CNTs.

High-quality MoS${}_2$ nanostructures were fabricated via chemical vapor deposition technique on SiO₂/Si substrate. In this paper, the effect of temperature on the photoluminescence behavior of MoS${}_2$ dendritic flake is addressed. We scrutinized the photoluminescence spectra of monolayer and multilayer regions of MoS${}_2$ in the temperature range 300 K–680 K. Monolayer and multilayer behavior of MoS${}_2$ flakes are confirmed by Raman and Photoluminescence spectroscopy. The excitonic peaks from the multilayer regime become less intense and show a red shift compared to the monolayer PL spectra. Thermally-induced bandgap modulation of MoS${}_2$ is demonstrated. The excitonic intensity and peak positions reveal pronounced temperature-dependent changes. These changes are explicable through the increased electron–phonon interaction and lattice rearrangements. Furthermore, first principle calculations are employed to glean insight into the impact of atomic rearrangements on the band gap behavior of MoS${}_2$. Our research presents a detailed understanding of thermally driven band gap modulation of monolayer and multilayer MoS${}_2$, which is essential for designing optoelectronic devices.

The real-space renormalisation group method can be applied to the Chalker–Coddington model of the quantum Hall transition to provide a convenient numerical estimation of the localisation critical exponent, $\nu$. Previous such studies found $\nu \sim 2.39$ which falls considerably short of the current best estimates by transfer matrix ($\nu =2.593\frac{+0.005}{-0.006}$) and exact-diagonalisation studies ($\nu =2.58\left(3\right)$). By increasing the amount of data 500 fold we can now measure closer to the critical point and find an improved estimate $\nu =2.51\frac{+0.11}{-0.11}$. This deviates only $\sim$3% from the previous two values and is already better than the $\sim$7% accuracy of the classical small-cell renormalisation approach from which our method is adapted. We also study a previously proposed mixing of the Chalker–Coddington model with a classical scattering model which is meant to provide a route to understanding why experimental estimates give a lower $\nu \sim 2.3$. Upon implementing this mixing into our RG unit, we find only further increases to the value of $\nu$.

Carbon, being the most common element on Earth, exhibits a diverse range of allotropic phases, hence contributing to its intricate physical characteristics. In recent times, a number of carbon allotropes near the Fermi surfaces have been predicted from first principles with rich topological phases. In this study, we present body-centered tetragonal C₄ (bct C₄), a new form of crystalline sp³ carbon, is a potential candidate for both an obstructed atomic insulator (OAI) and a real Chern insulator (RCI). It is noteworthy that bct C₄ demonstrates an unconventional bulk-boundary correspondence due to its manifestation of hinges boundary states. Our current work reveals that bct C₄ is a viable carbon phase platform for investigating the real topology and second-order bulk-boundary correspondence. It is hoped that our work can serve as a good starting point for future studies on three-dimensional (3D) real Chern insulators.

We investigated the photoluminescence (PL) properties of a GaAs/AlAs asymmetric seven-folded quantum well (ASFQW) superlattices (SLs) with thin separating barriers within the ASFQW period. The linearly blue-shifted PL was proportional to the applied bias voltage. By performing a numerical analysis of the electric-field dependence of subband energies in the ASFQW, we concluded that this PL originated from consecutive Γ-X mixings between spatially long-range-separated Γ-subband states and an X-state in this ASFQW. These results indicate that various phenomena appear in ASFQW-SLs due to the increased degree of freedom of carrier transport paths, but a precise analysis of the electric field dependence of subband resonances is required. Therefore, the integrated study of AMQW-SLs definitely reveals new physical properties and leads to the development of new devices.

Compared to single two-dimensional (2D) materials, stacking layered 2D materials with van der Waals (vdW) heterostructures offers novel opportunities to achieve desired exotic properties. Herein, 2D Sb/SnSe vdW heterostructure is constructed by vertically stacking the antimonene (Sb) monolayer on the tin selenide (SnSe) monolayer. We have conducted a theoretical study by using the first-principles calculations to comprehensively examine the electronic, optical, and mechanical properties. Phonon dispersion and ab initio molecular dynamics simulations have demonstrated that the Sb/SnSe vdW heterostructure possesses remarkable stability, ensuring its robustness up to $900$ K. The Sb/SnSe vdW heterostructure is characterized as a semiconducting material with a direct band gap of $0.24$ eV, calculated by the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional method. Compared to the pristine Sb and SnSe monolayers, the Sb/SnSe vdW heterostructure exhibits a lower work function value of $3.82$ eV. Furthermore, the carrier mobility of the heterostructure demonstrates anisotropic characteristics with a notable improvement in hole-mobility (12.05 × 10³ cm²V⁻¹s⁻¹) along the y-direction. The Sb/SnSe vdW heterostructure shows enhanced broadband absorption spectra, especially in the visible to near-infrared ranges. Our findings underscore the potential of the Sb/SnSe vdW heterostructure for future nano-electronic and optoelectronic technologies.

The Kagome lattice is rich in unique electronic and magnetic properties, such as flat band, superconductivity, charge density waves, and so on. In this paper, the magnetic properties, flat and Dirac bands of monolayer Mn₃Sn₃Se₂ with Kagome lattice are investigated based on first-principles calculations. A total of four magnetic configurations are considered, and the intrinsic ground state of Mn₃Sn₃Se₂ is identified as the ferromagnetic state. Strain has a significant effect on its magnetic ground state, which changes to an in-plane AFM state when the tensile strain exceeds 5 %. Monolayer Mn₃Sn₃Se₂ has an out-of-plane magnetic anisotropy of up to 0.777 meV, and the Curie temperature is 528 K. The band structure of the FM state is shown to be metallic, and spin polarized flat and Dirac bands appear near the Fermi level, which are degenerate. Monolayer Mn₃Sn₃Se₂ changes to half-metallic when a strain of 1%–2% is applied. Strain and correlation effects can significantly alter the flatness of flat band and the relative energy with Dirac bands. These results not only enrich the family of two-dimensional ferromagnets, but also provide a reference for studying the regulation of flat and Dirac bands.