Brazilian Journal of Physics最新文献

We investigate the influence of electron-phonon interactions on the thermodynamic properties of Bernal-stacked bilayer graphene under external magnetic fields, employing the Holstein model and Green’s function approach. By calculating the one-loop electronic self-energy within a full-band framework, we derive the interacting Green’s function to analyze the temperature-dependent behavior of specific heat and Pauli spin susceptibility, alongside the energy-dependent density of states (DOS). Our results reveal that increasing electron-phonon coupling reduces the peak height of specific heat while shifting its characteristic temperature to higher values. Similarly, stronger magnetic fields elevate the DOS at the Fermi level and induce Zeeman splitting, enhancing metallic behavior. Bias voltage variations widen the band gap, reinforcing semiconducting characteristics. These findings highlight the critical role of electron-phonon interactions and external fields in tailoring the electronic and thermodynamic properties of bilayer graphene, offering insights for advanced material applications.

In the present study, Ba₂SnO₄ nanostructures were synthesized via the hydrothermal method at 180 °C for 24 h, using 1 M BaCl₂ as the barium source and varying concentrations of SnCl₄ (0.1, 0.3, 0.5, and 0.7 M) as the tin precursor. Thick films of the resulting Ba₂SnO₄ nanomaterials were fabricated using the screen printing technique. The corresponding film thicknesses obtained for each SnCl₄ concentration were approximately 65, 58, 53 and 47 μm, respectively. The structural properties of Ba₂SnO₄ were confirmed by X-Ray diffraction and the formation of nano Ba₂SnO₄ where confirmed by transmission electron microscopy (TEM). The surface morphology and surface characteristics of fabricated material analyzed using scanning electron microscopy (SEM) while the energy dispersive spectroscopy analysis (EDS) shows the chemical composition of the prepared thick film. The fabricated thick films of various compositions were tested for different hazardous gases like Nitrogen dioxide (NO₂), Ammonia (NH₃), Hydrogen Sulphide (H₂S), Ethanol (C₂H₆O), and Methanol (CH₃OH). The thick film of Ba₂SnO₄ thick film prepared at molar concentration Ba (1 M): Sn (0.1 M) (Sample 1) shows the maximum sensitivity 69.88% to NO₂ gas at an operating temperature of 200 °C and concentration of 400 ppm. The rapid response and recovery were recorded for Ba₂SnO₄ thick film gas sensor.

The objective of this work is to create innovative nanocomposite films by integrating nanostructures (bismuth oxide Bi₂O₃ and silicon dioxide SiO₂) into polystyrene (PS). The primary objective of this study was to examine the structural and optical characteristics of nanostructures made up of PS-Bi₂O₃-SiO₂. The FTIR spectra indicate the existence of a physical contact between the original polymer and nanoparticles. At a concentration of 6 wt.%, optical microscope findings indicate the formation of a cohesive network of (Bi₂O₃-SiO₂) nanoparticles inside the polymer matrix, which is different from the pure (PS) film. The optical properties of pure PS, such as extinction coefficient (K), absorption index (α), absorbance (A), refractive index (n), and optical conductivity(σ_op), showed a positive correlation with the higher concentration of (Bi₂O₃-SiO₂) nanoparticles. Thus, these findings indicate that the material may be appropriate for various optoelectronic devices, including solar cells, transistors, electronic gates, photovoltaic cells, lasers, diodes, and other related applications. The integration of nanoparticles leads to an increase in the third-order nonlinear susceptibility (χ⁽³⁾), linear susceptibility (χ⁽¹⁾), Urbach energy (E_u), average oscillator wavelength (λ_o), nonlinear refractive index (n₂), and static refractive index (n_o). Conversely, there is a noticeable reduction in the average oscillator strength (S_o), dispersion energy (E_d), and single-oscillator energy (E_osc). The analysis of the dielectric properties of (PS-Bi₂O₃-SiO₂) nanocomposites revealed that an increase in the concentration of (Bi₂O₃-SiO₂) nanoparticles resulted in a corresponding rise in the ε', ε", and σ_a.c of pure PS. The PS-Bi₂O₃-SiO₂ nanocomposites show considerable gamma ray attenuation coefficients, according to the study. This paper suggests that these nanocomposites can be used in optoelectronic nanodevices and gamma radiation shielding.

Vanadium pentoxide (V₂O₅) flakes were synthesized via a hydrothermal method by varying the amount of lemon juice (5 mL for sample-1 and 10 mL for sample-2) as a natural chelating agent. Structural and morphological analyses were performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM), confirming crystalline V₂O₅ with flake-like morphologies influenced by chelating agent concentration. Electrochemical performance was evaluated using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) in a 3 M KOH electrolyte. Sample-2 exhibited a Significantly higher Specific capacitance of 1536 F g⁻¹ (CV at 1 mV s⁻¹) and 212.37 F g⁻¹ (GCD at 1 A g⁻¹) compared to sample-1, demonstrating that increasing lemon juice concentration enhances the capacitive behavior of V₂O₅ flakes by improving ion diffusion and electroactive surface area.

In this paper, we present first-principles DFT calculations of the structural, elastic, mechanical, thermoelastic, optical, and electronic properties of mixed halide perovskites CsGeCl_3-xBr_x (x = 0, 1, 2, 3). CsGeCl_3-xBr_x crystallizes in a cubic (Pm-3m) structure at (x = 0, 3) and in a tetragonal (P4/mmm) when (x = 1, 2). CsGeCl_3-xBr_x are mechanically stable with intrinsic ductility and a Debye temperature ({theta }_{D}) above 97.4 ± 300 K. Using DFT with GGA-PBE and TB-mBJ functionals, we predict that semiconductor compounds CsGeCl_3-xBr_x are stable structures with direct band gap ({E}_{g}), suitable for solar cells, photovoltaics, and related optoelectronic applications. The direct band gaps of CsGeCl_3-xBr_x are ({E}_{g}) = 1.105–1.431 eV (PBE) and ({E}_{g}) = 1.260–1.762 eV (mBJ). Also, the optical properties study reveals that the original peaks of CsGeCl_3-xBr_x materials lie in the visible light spectrum, confirming their candidate as a good absorber for solar cells. The results of this study confirm that through band gap tuning, we can obtain higher optical absorption ranges and greater efficiency for halide perovskite-based optoelectronics.

Using the Douglas-Kroll-Hess level of theory, we calculated bond lengths, binding energies, vertical ionization potentials, HOMO-LUMO energy gaps, second-order differences of total energies, dissociation energies, and spin magnetic moments of small cobalt clusters with the B1B95 functional and the DZP+1d-DKH all-electron basis set. There is good agreement between our results and the experimental data found in the literature. The spin magnetic moments computed in this study are among the most accurate theoretical values published to date. These findings lend credibility to our predicted ground state geometric structures since they do not always coincide with previously found structures. Co₃ and Co₆ are the most stable clusters, while Co₁₁ is the most reactive. To help elucidate the electronic structures of cobalt clusters, we computed the static mean dipole polarizabilities and polarizability anisotropies for the first time in the literature.

Based on the Boltzmann distribution in local thermodynamic equilibrium, the partition functions for N I, N II, N III, and N IV and O I, O II, O III, and O IV were investigated by including highly excited energy levels. Through adding the Debye corrections into the Saha equation, the particle number density for air plasma was studied for various electron temperature ((T_e)) and electron density ((n_e)) by about 10,000–40,000 K and 5(times )10(^{15})–10(^{21}) cm(^{-3}). Then, the corresponding abundance for air plasma was gained. Moreover, the changing tendency of particle number density and abundance in air plasma were applied to a lightning plasma when combined with its spectral diagnosis on (T_e) and (n_e). The measured particle number density for N I, N II, N III, O I, and O II, separately, are 1.20(times )10(^{16}), 4.08(times )10(^{17}), 6.74(times )10(^{15}), 4.72(times )10(^{15}), and (8.82times 10^{16}; text {cm}^{-3}) together with their measured abundance by about 2.31%, 78.46%, 1.29%, 0.91%, and 16.96%, respectively. Good consistency can be found in the comparison with other experiments.

In this work, we present a theoretical investigation of the elasticity properties of new exotic carbon allotropes studied recently, called Irida-graphene and Sun-graphene. Despite being theoretically studied in single-layer (2D), a study of the elastic properties of Irida-CNTs and Sun-CNTs has not yet been performed. Thus, we seek to investigate the elastic properties of nanotubes of these new exotic allotropes of carbon in quasi-one-dimensional geometry (1D), nanotubes for different chiralities, diameters, and lengths at room temperature. Our theoretical results obtained in the computational simulation show that the values of Young’s modulus for Irida-CNTs are in a slightly larger range (640.34 GPa - 825.00 GPa), while the Young’s modulus range of Sun-CNTs is 200.44 GPa - 472.84 GPa, lower values than those presented for conventional carbon nanotubes (CNTs). Our results also show the magnitude of Poisson’s ratio for Irida-CNTs and Sun-CNTs from the relative of nanotube bending and stretch, where the Poisson’s ratios are positive. For Irida-CNT, (nu = 0.86-0.98), and for Sun-CNT, (nu = 1.34-1.64). This tunability of Poisson’s ratio can be exploited in the design of nanotube-derived composites, artificial muscles, gaskets, and chemical and mechanical sensors. These findings provide insights into the nanomechanical behavior of Irida-CNTs and Sun-CNTs and their potential applications in nanoscale devices.

The energy density functional (EDF) theory is an essential microscopic approach used in theoretical nuclear physics to study the nuclear structure of heavy nuclei on a large scale. In this research, density functional theory (DFT) solvers were utilized to solve self-consistent equations for both spherical and deformed shapes. The effects of spin–orbit density, energy, and charge radius of Sn isotopes were analyzed using the Skyrme Hartree Fock (SHF) and Skyrme Hartree Fock Bogolyubov (SHFB) methods, which take into account pairing interactions that vary with density. The calculated radius for both spherical and deformed states was compared to experimental data to evaluate the influence of deformation. These comparisons are usually performed using the Hartree Fock Bogolyubov (HFB) or the Hartree Fock BCS (HFBCS) method. The consistency of our findings with those obtained from the spherical RMF(Relativistic Mean-Field)-PC code strengthens the reliability of our conclusions. These results are significant as they allow for an accurate assessment of the force distribution within uniform spherical Nuclei.

Organic–inorganic hybrid perovskites (OIHP) are currently the subject of rigorous study due to their promising utility in optoelectronics and photovoltaics. Therefore, in this work, we perform an in-depth analysis of OIHP perovskites, in particular [NH₃(CH₂)₄NH₃]MCl₄ (M = Co, Cd). We focus on structural, electronic, and optical properties and present information on this subject for the first time. Our study revealed the stable triclinic phase structure of the hybrid [NH₃-(CH₂)₄-NH₃]CoCl₄ and monoclinic of the hybrid [NH₃-(CH₂)₄-NH₃]CdCl₄ perovskites, with calculated free energies of − 10522.91 eV and − 10520.13 eV, corresponding to a relative stability difference of approximately 2.78 eV, respectively indicating their structural robustness. The semiconducting characteristics of [NH₃(CH₂)₄NH₃]CoCl₄ and [NH₃(CH₂)₄NH₃]CdCl₄ are highlighted by their wide indirect band gaps of 1.84 eV and 0.88 eV, respectively. We then examine the optical parameters, including the dielectric function, absorption coefficient, optical conductivity, refractive index, and energy loss function. Our results highlight the exceptional ability of these materials to absorb ultraviolet radiation in the electromagnetic spectrum, making them promising candidates for optoelectronic applications. The outcomes of our research catalyze deeper inquiry into the application of these materials in technologically significant contexts. Calculations were performed using a first-principles approach based on density functional theory (DFT). The electronic properties of the system were examined using the HSE06 hybrid exchange–correlation function and the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) within the CASTEP framework. Within this framework, Kramers–Kronig relations are used to obtain crucial optical parameters.