Physics of the Solid State最新文献

Transparent semiconducting silver sulfide (Ag₂S) thin films were deposited by chemical bath deposition technique on glass substrates. The effect of different deposition temperatures (10, 20, and 30°C) on the structural and optical properties of silver sulfide films was studied. The XRD spectra showed that the structure of the films was monoclinic and polycrystalline, and the predominant growth of crystals was at the plane (022). The intensity of the peaks increases with increasing preparation temperature, becoming narrower and clearer. The best-structured films with the least crystalline defects were that prepared at 30°C. UV-VIS spectroscopic scanning showed that all films had a minimum transmittance and maximum absorbance at the ultraviolet field within the range 300–350 nm. The transmittance decreased and absorbance increased with increasing wavelength and temperature. The energy gap values changed within the range 2.105–2.242 eV, which clearly increased with increasing preparation temperature.

We conducted first-principles calculations using density functional theory (DFT) to explore the structural, electronic, and optical characteristics of gallium arsenide (GaAs) in its wurtzite (WZ), zinc-blende (ZB), and rock-salt (RS) crystalline forms. These studies were carried out employing the full potential-linearized augmented plane wave (FP-LAPW) approach within the Wien2k computational framework. For the exchange-correlation (XC) potentials, we utilized various functionals including the local density approximation (LDA), generalized gradient approximation (PBE), Perdew–Burke–Ernzerhof for solids (PBEsol), modified Becke–Johnson (MBJ), and the strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation (meta-GGA). These functionals were applied to determine key physical properties such as equilibrium lattice constants, cell volume, bulk modulus, pressure derivatives, and energy band gaps. Additionally, we assessed optical features including dielectric and loss functions, refractive and extinction indices, and optical conductivity across the WZ, ZB, and RS phases. Our findings indicate that the structural and optical parameters derived from the SCAN meta-GGA functional show remarkable consistency with experimental observations, although it tends to underestimate the energy band gap. The most accurate predictions for the energy gap were achieved using the MBJ-PBEsol approach, aligning closely with experimental data.

Two different methods (chemical and biological) are used to synthesize silver nanoparticles in this study. Silver nitrate was reduced using NaOH in a chemical method, while in a biological approach, Ag ions were reduced with an aqueous leaf extract of Tridax procumbens. Both types of synthesized nanoparticles were characterized using FT-IR, UV-Visible, XRD, PL, DLS, ZE, and SEM with EDAX. The X-ray diffraction (XRD) patterns established the incidence of a crystalline face centred cubic (FCC) structure in both nanoparticles samples. The average nanoparticles sizes were 29 nm for the chemically produced nanoparticles and 18 nm for the biologically synthesized ones. SEM analysis revealed a spherical shape for both types of nanoparticles, with average sizes of 36 nm for the chemically produced and 25 nm for the biologically synthesized nanoparticles. The surface plasmon resonance (SPR) peaks were observed at 384 nm for the chemically synthesized nanoparticles and at 424 nm for the biologically synthesized ones. FT-IR analysis indicated that O–H, C=O, and C–O–C functional groups were involved in the formation of Ag nanoparticles, with a zeta potential of –27.83 eV, exhibited long-term stability and resistance to agglomeration compared to the chemically synthesized nanoparticles, which had a zeta potential of –9.46 eV. Photoluminescence (PL) analysis demonstrated an enhanced visible spectrum for the nanoparticles. Additionally, the antibacterial activity tests showed that the biosynthesized Ag nanoparticles were more effective than the chemically synthesized ones. This enhanced activity was attributed to the protein capping and the mode of entry into bacterial cells, making the biosynthesized nanoparticles more potent. The study concluded that biosynthesized Ag nanoparticles exhibit a smaller crystalline size, better morphology, and more significant antimicrobial activity compared to their chemically synthesized counterparts.

Double perovskite halides (DPHs), specifically Cs₂CuSbH₆ (where H = Cl, Br, and I), serve as key components in the fabrication of flexible electronic devices, including solar cells, wearable biodevices, and optoelectronics. Utilizing QuantumATK NanoLab Software Tool, an investigation into the mechanical, electrical, optical, and structural properties of these halide perovskites was undertaken. Structural stability was validated by optimizing the structure and tolerance factors of these compounds, demonstrating positive values of C₁₁, C₁₂, and C₄₄. These double perovskite halides (DPHs) align with the Born–Huang stability criterion following the trend C₁₁ > C₁₂ > C₄₄. Electronic characteristics were determined by assessing band structures, density of states (DOS), and projected density of states (PDOS). The investigated Cs₂CuSbCl₆, Cs₂CuSbBr₆, and Cs₂CuSbI₆ compounds exhibited indirect band gaps of 0.95, 0.60, and 0.20 eV, respectively, indicative of their semiconducting nature. In our research, the optical properties, including dielectric functions, refractive indices, reflectivity, extinction losses, and absorption coefficients, have been computed. Calculations revealed static dielectric function values Re(ε) for Cs₂CuSbCl₆, Cs₂CuSbBr₆, and Cs₂CuSbI₆ as 3.716, 4.6033, and 6.133, respectively. Notably, absorption bands for these materials were identified within the visible range spanning wavelengths from 378 to 632 nm, 356 to 688 nm, and 373 to 720 nm for Cl, Br, and I, respectively. Furthermore, the refractive indices of Cs₂CuSbCl₆, Cs₂CuSbBr₆, and Cs₂CuSbI₆ demonstrated values below 2.0 for higher energy spectra, elucidating the propagation of light within these materials. In conclusion, the findings suggest promising applications for DPHs, specifically Cs₂CuSbH₆ (H = Cl, Br, and I), in future solar cells, optoelectronic devices, and various other flexible electronic applications.

Electronic properties of CdGa₂S₄ single crystals are studied experimentally by the spectral ellipsometry and also theoretically from the first principles using the density functional theory (DFT). From the ellipsometric studies in the energy range 0.7–6.5 eV, the imaginary and real parts of the dielectric function and the optical conductivity along and perpendicularly to the axis, the dispersion of the refractive index, extinction ratio, absorption factor, etc., have been determined. The estimations are performed for the direct energy gap width. The band structure, the origin of energy states, optical functions, and partial densities of states (PDOS) projected onto atoms are determined by calculations from the first principles. The results obtained by theoretical calculations are compared with the experimental data obtained in this work by the spectral ellipsometry method.

In this paper, we investigated the surface states of the chiral semimetal under the three-dimensional (3D) vector external field. Firstly, we introduced a Lorentz rotation transformation to transform the 3D vector field into a one-dimensional scalar field to calculate the surface state of the system. We found that there were two types of surface states as drumhead surface state and coexistence surface state of Z₂ and Chern. And the topological invariant of the coexistence state with mirror symmetry breaking was calculated by a mirror Chern number. Then, by theoretical analysis and numerical calculation of the zero mode under the 3D external field we found that the coexistence surface state still existed when the emergent symmetries were broken, which demonstrated the coexistence is robust to the emergent symmetries. This work provided a convenient method for the experimental study of 3D vector external field. As well as the calculation of the precise control of surface states by a 3D vector field can be a feasible method for field measurement in the surface engineering field.

The present work reports the performance of nitrogen-doped Ag/ZnO/MWCNT nanocomposites, leveraging a microwave-assisted hydrothermal approach to modulate the bandgap via silver (Ag) doping variations. Employing transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL), field emission scanning electron microscopy (FE-SEM), UV-visible-NIR spectrophotometry, X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX), the study characterizes the nanocomposites’ optical and structural properties. Notably, the bandgap narrows from 3.18 to 2.52 eV with increasing Ag content, enhancing photocatalytic degradation of methylene blue and congo red dyes by up to 97 and 89%, respectively. These findings reveal the potential of Ag/ZnO/MWCNT nanocomposites in environmental and optoelectronic applications.

Iron-based amorphous alloys have garnered significant attention because of their superior soft magnetic properties (SMPs).The effect of Fe content on the glass forming ability (GFA), thermal stability, and SMPs of Fe-rich Fe_83+xSi₁B₁₄C_2–x (x = 0, 0.5, 1.0, 1.5) amorphous alloys was investigated. It was observed that as the Fe content increases, the GFA and thermal stability of FeSiBC amorphous alloys decrease. When x = 0.5 and 1.0, the alloys approach the critical composition and the crystallization peak shifts from a single peak to double peaks. After annealed at 340°C for 30 min, the Fe_83.5Si₁B₁₄C_1.5 amorphous alloy exhibited superior SMPs, with saturation magnetic induction (Bs) and coercivity (Hc) values of approximately 1.68 T and 4.9 A/m, respectively.

CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x, hybrid perovskites thin films were grown on glass substrates employing spin-coating technique at different rotational speeds varying from 1000 to 2000 rpm. All the films exhibited a polycrystalline tetragonal structure with a preferred (110) orientation. For each rotational speed, the CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x films had approximately the same order of the absorbance in the visible region of solar spectrum. The current–voltage measurements of the CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x films showed a ferroelectric hysteresis behavior in the dark which it becomes Ohmic under the illumination indicating the microstructural improvement. The all samples were strongly resistive in the dark, and their electrical conductivity improving thousands of times under the illumination; it had varied in the ranges 25.5 × 10^–3‒206.61 (Ω cm)^–1 and 82.81 × 10^–3‒689.47 (Ω cm)^–1 for CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x, respectively. Our results demonstrated that the 1000 and 2000 rpm were optimal parameters for CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x films preparation, respectively. Moreover, the addition of the chlorine in CH₃NH₃PbI₃ films improves their physico-chemical properties. Indeed, compared to the CH₃NH₃PbI₃ prepared at 1000 rpm, the CH₃NH₃PbI_3–xCl_x film synthesized at 2000 rpm had the thinner thickness 571.58 nm, largest crystallite size 204.81 nm, lesser dislocation density 2.38 × 10^–5 lines nm^–2, superior quality of surface morphology, higher band gap 1.53 eV, lower Urbach energy 276.23 meV, higher refractive index 2.96, higher electrical conductivity in the dark 82.81 × 10^–3 (Ω cm)^–1 and under the illumination 689.47 (Ω cm)^–1. CH₃NH₃PbI_3–xCl_x thin film synthesized at 2000 rpm has better quality that might be more suitable as a light absorbers films for photovoltaic cells and optoelectronic devices.

This study investigates the potential of Ca(Hf_1–xTi_x)S₃ chalcogenide perovskite alloys (orthorhombic phase) for optoelectronic applications. Density functional theory (DFT) calculations explore the influence of titanium (Ti) doping (x = 0, 0.25, 0.50, 0.75, 1.00) on the material’s structural, thermodynamic, electronic, and optical properties. The calculations confirm the structural and thermodynamic stability of the alloys through tolerance factor and formation energy calculations. Interestingly, Ti doping is found to influence the bulk modulus and its derivative, affecting the material’s compressibility and hardness. A crucial finding is the decrease in bandgap with increasing Ti concentration, falling within the optimal range for efficient light absorption (1.0–1.6 eV). This suggests that Ti doping can enhance the optoelectronic properties of Ca(Hf_1–xTi_x)S₃. Furthermore, all studied compositions (x = 0, 0.25, 0.50, 0.75, 1.00) exhibit favorable light absorption across the visible to ultraviolet spectrum, making them promising candidates for solar cells and other optoelectronic devices.