The European Physical Journal B最新文献

The first-principles calculation method is performed to explore the monolayer 2H-MoS₂:Fe semiconductors with intrinsic ferromagnetism and strong ferromagnetic coupling by strain-modulation. In this study, we demonstrate that the biaxial strain can effectively regulate the distribution of local magnetic moment, magnetic coupling ground state types and strength. The studied results indicate that one Fe_Mo dopant will bring 2 (mu_{{text{B}}}) local magnetic moment, which is not affected by strains in range of − 6~6%. However, electronic configuration, occupation and magnetic moment distribution are closely related to strains. Moreover, smaller compressive strain can effectively strengthen ferromagnetic interactions between two Fe_Mo substitutions, and the most energy gains of ferromagnetic coupling reach to 153.9 meV under − 2% strain. However, the ferromagnetic ground state translates into antiferromagnetic one as strain in the range of − 6~ − 2.5%. The changes in magnetic moment and magnetic interaction originate from the competition between crystal-filed splitting and spin splitting under different strains. The theoretical results presented here predict that modulating the biaxial strain could be a very significant avenue to obtain intrinsic ferromagnetic 2H-MoS₂:Fe semiconductors.

Graphical abstract

The effect of strain on the electronic structures and magnetic properties of Fe doped monolayer 2H-MoS₂ were studied by first-principles calculations. We found that electronic configuration, occupancy and magnetic moment distribution are closely related to strains. Smaller compressive strain can effectively strengthen FM interactions between two Fe_Mo substitutions, and the most energy gains of FM coupling up to 153.9 meV under − 2% strain. However, the FM ground state translate into AFM one as strain in the range of − 6~− 2.5%. Our theoretical predictions highlight the important contribution of strain to electronic structures and magnetic properties, and present a valid avenue for the future design of high T_C material in monolayer MoS₂: Fe system.

Models for resident infectious diseases, like the SIRS model, may settle into an endemic state with constant numbers of susceptible (S), infected (I) and recovered (R) individuals, where recovered individuals attain a temporary immunity to reinfection. For many infectious pathogens, infection dynamics may also show periodic outbreaks corresponding to a limit cycle in phase space. One way to reproduce oscillations in SIRS models is to include a non-exponential dwell-time distribution in the recovered state. Here, we study a SIRS model with a step-function-like kernel for the immunity time, mapping out the model’s full phase diagram. Using the kernel series framework, we are able to identify the onset of periodic outbreaks when successively broadening the step-width. We further investigate the shape of the outbreaks, finding that broader steps cause more sinusoidal oscillations while more uniform immunity time distributions are related to sharper outbreaks occurring after extended periods of low infection activity. Our main results concern recovery distributions characterized by a single dominant timescale. We also consider recovery distributions with two timescales, which may be observed when two or more distinct recovery processes co-exist. Surprisingly, two qualitatively different limit cycles are found to be stable in this case, with only one of the two limit cycles emerging via a standard supercritical Hopf bifurcation.

Cadmium oxide (CdO) nanoparticles (NP) were prepared using mechanical milling and annealing. The CdO powders were grinded for 16 h using Agate mortar and Pestle and subjected to air annealing at 400 °C, 500 °C, 600 °C and 700 °C for one hour. The powder samples annealed at different temperatures were subjected to various characterization techniques such as XRD, UV–Vis-NIR spectroscopy, FT-IR spectroscopy, Raman spectroscopy, photoluminescence spectrophotometer and electrical measurements. The XRD results confirmed the polycrystalline cubic structure of the CdO nanoparticles. Rietveld analysis from XRD revealed the structural formation of CdO nanoparticles. The crystallite size decreased from 33 to 24 nm with an increase in annealing temperature. The chemical bonds in FT-IR spectra confirmed the formation of CdO nanoparticles. Raman spectra of the CdO nanparticles were recorded at room temperature and observed two distinct peaks at 269 cm⁻¹ and 956 cm⁻¹. Optical absorbance and reflectance spectra were recorded using UV–Vis-NIR spectrophotometer and the optical band gap of the nanoparticles were calculated using Tauc’s relation and Cody’ method. A decrease in the band gap was observed in both methods. The PL spectra of the CdO nanoparticles were recorded at room temperature with an excitation wavelength of 380 nm and observed emission peaks at 423 nm, 485 nm, 532 nm, and 606 nm. The electrical resistivity of the CdO nanoparticles was studied using two-probe method using the Keithley source meter and observed decrease in resistivity with annealing temperature.

Graphical abstract

This study offers a comprehensive exploration of the thermal characteristics of cadmium chalcogenide (CdX, X = Te, Se, S) compounds. The CdXs are synthesized by mixing high purity precursor elements at elevated temperature under vacuum. The crystalline phases of the samples are investigated through X-ray diffraction (XRD) analysis. The XRD revealed that CdTe exhibits cubic, while CdSe and CdS possess a hexagonal crystalline phase. The thermal properties of CdTe, CdSe, and CdS compounds are determined from the acquired thermogravimetric (TG) and differential thermogravimetric (DTG) analysis. The TG and DTG curves are synchronously acquired for heating rate of 5 K·min⁻¹ in an inert nitrogen atmosphere, for temperature range of ambient to 1248 K. The results of TG analysis reveal that CdTe remains stable up to 965 K, whereas CdSe and CdS exhibit stability beyond 965 K upto 1125 K. The solitary peak in DTG analysis for each samples evident degradation of the samples in one step. The thermal degradation kinetics of all samples is assessed through the application of non-isoconversional Broido, Coats–Redfern, and Piloyan–Novikova relations. The findings from the kinetic parameters corroborate the observed trends in the thermocurves. The outcomes suggest that CdTe undergoes more pronounced weight loss with degradation initiated earlier than CdS and CdSe. The experimental findings about the thermal stability of CdX compounds are reinforced through theoretical investigation into phonon dynamics employing DFT simulations, offering requisite insights into their thermal behaviour.

Graphical abstract

The electronic structure and optical properties of Cd_2-xY_xSnO₄ are studied using the first-principle calculation within the generalized-gradient approximation and the Coulomb repulsion effect. Three defect models are constructed by Y atom occupying Cd sites. The energy band shows that the 4d electrons of Y atom mainly affect the bottom of conduction band. The density of state reveals that the 4d state of Y atom hybridizes with the O 2p and Cd 5s states at the bottom of conduction band. With the increment of the substitution numbers, Y 4d states increases gradually to enhance the hybrid intensity. The average effective mass of Cd_1.875Y_0.125SnO₄ model attains 0.352m₀, which is lower than 0.484m₀ of Cd₂SnO₄. It indicates that the conductivity of Cd₂SnO₄ is improved by Y occupying Cd site. Moreover, the absorption edges of Cd_1.9375Y_0.0625SnO₄ and Cd_1.875Y_0.125SnO₄ models blueshift to induce optical transmittance reaching about 90% in the visible light region. Therefore, Cd_1.875Y_0.125SnO₄ can be applied to prepare a short wavelength optical device in future.

Graphical abstract

As the substitution concentration increases, both the conduction band and the valence band move to the low energy direction. The band gap value of Cd_1.9375Y_0.0625SnO₄ is 2.19 eV, which is the closest to the band gap value of Cd₂SnO₄. The band gap value decreases slightly with increasing substitution concentration of Y at Cd site. Compared with the effective mass m* of Cd₂SnO₄, the effective mass m* decreases after the entry of Y atoms. It indicates that Y atoms substitution has a certain improvement for the conductivity of Cd₂SnO₄. The transmittance of Cd_1.9375Y_0.0625SnO₄ and Cd_1.875Y_0.125SnO₄ models can attain 90%, which is somewhat higher than that of Cd₂SnO₄.

Tin-based perovskite represents a highly promising alternative to lead-based perovskite, offering a number of significant advantages. These include non-toxicity, high absorbance, and excellent photovoltaic properties. The use of the toxic anti-solvent chlorobenzene (CBZ) in the preparation of tin-based perovskite thin films has the dual disadvantage of increasing the environmental hazards and the cost of subsequent treatment. The use of acetic acid (HAc) as a green anti-solvent has been demonstrated to effectively regulate the crystallization process of tin-based perovskite FASnI₃, resulting in the preparation of perovskite films of superior quality. To further enhance the performance of tin-based perovskite, Zhao et al., organic cation mixing was used to add MAI to the FASnI₃ system and optimize the ratio, resulting in an optimal ratio of FA (0.75) MA (0.25) (FA = NH₂CH = NH₂⁺, MA = CH₃NH₃⁺) (Zhao et al. Adv Sci 4(11):1700204, 2024). In this study, we choose the crystallization process during the preparation of binary FA_0.75MA_0.25SnI₃ perovskite using a green anti-solvent HAc. The findings demonstrated that HAc was capable of influencing the crystallization of binary tin-based perovskite, facilitating the formation of perovskite films with minimal pinholes and enhanced uniformity and crystallinity. Additionally, the resulting perovskite exhibits a band gap of 1.35 eV, which is in close alignment with the predicted ideal band gap as postulated by Schottky's theory. Furthermore, it displays enhanced hydrophobic properties. In the binary perovskite photovoltaic device prepared using the anti-solvent HAc, the maximum device efficiency reached 3.62%. The findings of this study will contribute to the understanding of the crystallization process of diverse perovskite materials in the presence of a green anti-solvent.

Graphical Abstract