Narrow Results

The FP-LAPW method is utilized to investigate the elastic, optoelectronic and thermoelectric properties of ${\mathrm{\text{XTiO}}}_3$$(\mathrm{\text{X}}=\mathrm{\text{Ca, Sr}}$ and $\mathrm{\text{Ba}})$ within the GGA. The calculated lattice constants and bulk modulus are found in agreement with previous studies. The present oxide–perovskite compounds are characterized as elastically stable and anisotropic. ${\mathrm{\text{CaTiO}}}_3$ and ${\mathrm{\text{SrTiO}}}_3$ are categorized as ductile compounds, whereas the ${\mathrm{\text{BaTiO}}}_3$ compound is in the critical region between ductile and brittle. The DOS and the band structure calculations reveal indirect $(\mathrm{\text{M}}$–$\mathrm{\Gamma })$ energy bandgap for the present compounds. The hydrostatic pressure increases the energy bandgap and the width of the valence band. The character of the band structure does not change due to this pressure. The optical parameters are calculated in different radiation regions. Beneficial optics applications are predicted as revealed from the optical spectra. The transport properties are applied as a function of the variable temperatures or carrier concentration. It is found that the compounds under study are classified as a p-type semiconductor. The majority charge carriers responsible for conduction in these calculated compounds are holes rather than electrons.

This paper presents a comprehensive study and it concludes that the resonance of forest trees with properly aligned conditions precisely working as naturally available locally resonant metamaterials that are equipped with wonderful capability of generating low frequency extremely wide bandgaps in the earthquake frequency range of interest. At the geophysical scale, the propagation of Rayleigh wave in the soft sedimentary soil basin experiences strong wave attenuation when the longitudinal resonant modes of trees are coupled with vertical component of the Rayleigh wave that mimic wave hybridization phenomena. A finite element-based numerical technique is adopted and we considered a total of 10 cases where spacing, height, thickness and mechanical properties of resonant trees are varied to study the Rayleigh wave propagation and attenuation mechanism. The trapping and/or mode conversion of Rayleigh wave by resonant trees is observed as dominant phenomena for wave attenuation. A time history analysis is conducted based on an actual earthquake record to validate the performance and efficiency of the bandgaps. The effects of ground stiffness, resonant tree mechanical and geometric properties on the bandgaps are also discussed. The study explores another peculiar characteristic of the forest trees that controls the propagation of seismic wave to protect a region from earthquake hazards. Our study may motivate the relevant organizations, authorities and global communities on the needs of forestation to reduce the earthquake catastrophe.

We have performed ab initio investigation of some physical properties of the perovskite TlMnX₃ (X = F, Cl) compounds using the full-potential linearized augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) is employed as exchange-correlation potential. The calculated lattice constant and bulk modulus agree with previous studies. Both compounds are found to be elastically stable. TlMnF₃ and TlMnCl₃ are classified as anisotropic and ductile compounds. The calculations of the band structure of the studied compounds showed the semiconductor behavior with the indirect (M–X) energy gap. Both compounds are classified as a ferromagnetic due to the integer value of the total magnetic moment of the compounds. The different optical spectra are calculated from the real and the imaginary parts of the dielectric function and connected to the electronic structure of the compounds. The static refractive index $n(0)$ is inversely proportional to the energy bandgap of the two compounds. Beneficial optics technology applications are predicted based on the optical spectra.

The regularities of the formation of thin Mn/Si (111) nanofilms during solid-phase deposition of Mn on Si under conditions of ultrahigh vacuum ($P=10^{-7}$Pa) and thin Mn₄Si₇/Si (111) nanofilms during annealing of the Mn/Si system have been studied. It has been established that silicon atoms diffuse into the Mn film up to a thickness of $\mathrm{\Theta }=10$–12 monolayers, and Mn in Si up to $\mathrm{\Theta }=8$–10 monolayers, therefore, a transition layer of nonstoichiometric Mn_xSi_y silicide is formed at the Mn–Si interface. After heating at $T=1050$K, the higher manganese silicide (HMS) Mn₄Si₇ is formed. In particular, it was found that the bandgap of Mn₄Si₇is $E_g\approx 0.72$eV, and the electron affinity is $\chi \approx 3$eV and in the work, the optimal thermal diffusion conditions for the formation of stoichiometric Mn₄Si₇ silicide are determined. It is shown that at $T\le 1000$K, a partial formation of a chemical bond between manganese and silicon atoms occurs. At 1100K, a thin Mn₄Si₇ film with a good stoichiometric composition is formed.

Spinel ferrite ${\text{Ni}}_{0.08}$${\text{Mn}}_{0.90}$${\text{Zn}}_{0.02}$Fe₂O₄ was prepared by a conventional ceramic process followed by sintering at three different temperatures (1050${}^{\circ }$ C, 1100${}^{\circ }$ C and 1150${}^{\circ }$ C). X-ray diffraction (XRD) investigations stated the single-phase cubic spinel structure and the FTIR spectra revealed two prominent bands within the wavenumber region from 600 cm${}^{-1}$ to 400 cm${}^{-1}$. Surface morphology showed highly crystalline grain development with sizes ranging from 0.27 $\mu$m to 0.88 $\mu$m. The magnetic hysteresis curve at ambient temperature revealed a significant effect of sintering temperature on both coercivity ($H_c)$ and saturation magnetization ($M_s)$. Temperature caused a decrease in DC electrical resistivity, while the electron transport increased, suggesting the semiconducting nature of all samples and that they well followed the Arrhenius law from which their activation energies were determined. The values of Curie temperature ($T_c)$ and activation energy were influenced by the sintering temperature. Frequency-dependent dielectric behavior (100 Hz–1 MHz) was also analyzed, which may be interpreted by the Maxwell–Wagner-type polarization. The UV–vis–NIR reflectance curve was analyzed to calculate the bandgap of ferrites, which showed a decreasing trend with increasing sintering temperature.

Material scientists have stepped up their search for efficient materials in low-cost, high-stability, nontoxic energy conversion devices. In this paper, emerging materials inspire us to study one of the perovskite chalcogens made from alkaline-earth metals (Barelium). Therefore, we determined some fundamental properties with some application-based properties, which explained their applicability in energy conversion device fabrication by first-principles calculation within the WIEN2K Code. Structure stability has been verified by Birch–Murnaghan fits and thermal stability at different temperatures and pressure ranges is explained by Gibbs function in thermodynamic properties. By using modified Becke–Johnson (mBJ) potential, electronic and optical characteristics of these materials provide insight into their nature: they were revealed to be direct bandgap semiconductors with the calculated values of 1.77eV (1.25eV) for BaZrS₃(BaZrSe₃), respectively. Both materials exhibit transparency on low-energy striking photons and demonstrate absorption and optical conduction in the UV region.

Both materials exhibit transparency on low-energy striking photons and demonstrate absorption and optical conduction in the UV region. In the thermoelectric parameter, the figure of merit (ZT) is unity at room temperature and decreases up to 0.98 with temperature increment which reveals that these materials will be helpful in thermoelectric devices. As per the application part, we carried out the calculation of the spectroscopic limited maximum efficiency (SLME) and found that efficiency increases from 6.5% to 27.1% (8.1% to 31.9%) for BaZrS₃ (BaZrSe₃), respectively. The film thickness increased from 100nm to 1$\mu$m at room temperature and then stabilized. This emerging study shows that these materials can be used as an alert substance in energy conversion device fabrications and the proposed outcomes are in good acceptance with the experimental and other theoretical data. As per the optical and thermoelectric parameters of these materials, we infer that both are promising candidates in energy conversion device fabrication.

The invention of novel light-harvesting materials is one of the primary reasons behind the acceleration of current scientific advancement and technological innovation in the solar sector. Organometal halide perovskite (OHP) has recently attracted a great deal of interest because of the high-energy conversion efficiency that has reached within a few years of its discovery and development. Modern machine learning (ML) technology is quickly advancing in a variety of fields, providing blueprints for the discovery and rational design of new and improved material properties. In this paper, we apply ML to optimize the material composition of OHPs, propose design methods and forecast their performance. Our ML model is built using 285 datasets that were taken from about 700 experimental articles. We have developed two different ML models to predict the bandgap and performance parameters of solar cell. In the first model, we employed three ML algorithms to investigate the relationship between bandgap and perovskite material composition. We estimated the performance characteristics using projected and actual bandgap. Second, ML models are used to predict the performance parameters employing the bandgap of perovskite and energy difference between electron transport layer (ETL) and hole transport layer (HTL) with perovskite as an input parameter. Simulation results suggest that the artificial neural network (ANN) technique, which predicts the bandgap by taking into consideration how cations and halide ions interact with one another, demonstrates a better degree of accuracy (with a Pearson coefficient of 0.91 and root mean square error of 0.059). The constructed ML model closely fits the theoretical prediction made by Shockley and Queisser, and that is almost hard for a person to discover from an aggregation of datasets.

A theoretical comprehensive implementing of the structural, elastic, electronic and optical properties of CsSnX₃ (X = Br and I) perovskite compounds under pressures 0 and 20 GPa is performed by ab-initio calculations included within the density functional theory (DFT). The structure of crystal perovskite compounds is found to be stable under induced pressure. The compounds have shown a decrease in the structural properties such as lattice constant and interatomic bond length when the pressure was induced. Whereas, there was an increase in the thermodynamic properties such as Debye temperature and average velocities of sound when pressure was induced. Moreover, the values of mechanical parameters, such as the elastic constant, increased under applied pressure. The electronic parameters indicate that the compounds can be classified as semiconductor materials with a direct (M-M) gap. The induced pressure is found to enhance the optical parameters in the different energy regions. Our calculation predicts that the studied compounds can be the relevant candidates in optical, thermoelectric and mechanical applications.

In the present paper, the surface modification of low-density polyethylene (LDPE) polymer is done by plasma-etching to tune its surface structure, wettability and optical behavior to make it useful for technical applications. For this purpose, two gasses (N${}_2)$ and (O${}_2)$ are used as the discharge precursors in a home-built plasma reactor. The plasma-treated LDPE surface etch-rate (control other surface properties) is high at the beginning and slows down as the treatment time increases due to surface restructuring. The etched surfaces are analyzed by scanning electron microscopy (SEM), which indicate greater surface changes due to O₂ plasma compared to that of N₂. Also, the surface hardness is slightly low at the first treatment time and increases rapidly at higher exposure durations. Besides, the friction coefficient is significantly changed by plasma treatment, suggesting the formation of cohesive surface skin. The obtained X-ray diffraction (XRD) patterns show that the plasma-treated LDPE samples suffer disordering and structural changes which increase with raising the treatment duration. Surface restructuring is attributed to the combined effects of active species (from plasma) bombardments and surface oxidation. Also, the surface chemistry changes are evaluated using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy which reveals chain scission after N₂ plasma treatment. Whereas, the O₂ plasma-treated samples suffer surface oxidation and formation of polar groups which offer some surface oxidation coatings. Furthermore, the surface wettability has been determined by the sessile drop method and shows enhancement upon plasma treatment due to the combined influence of surface chemistry and morphology. Also, the surface free energy (SFE) and adhesion are found to increase with the plasma exposure time due to surface activation. The optical behavior of LDPE is studied using ultraviolet–visible (UV–Vis) spectrophotometer which indicates that the optical bandgap performance depends on the amorphous or crystalline nature of the polymer. Also, the conjugated carbon atoms were examined and correlated to the reduced bandgap. In conclusion, the studied home-built glow discharge plasma reactor could be utilized efficiently to tune polymer surface properties to be used in high technology applications.

By employing the first principles method within the generalized gradient approximation for the exchange and correlation potential, the electronic, optical and magnetic properties of pure and Fe-doped zinc-blende ZnSe are investigated. According to the obtained band structure, density of state and optical spectrum the electronic origin of the maxima in the optical spectrum has been observed. The optical spectrum peak is generated mainly from the charge transfer between the Se(4$p)$ and Zn(3$p)$ states. Our results reveal that the strong spin polarization of the 3$d$ states of the Fe atoms is the origin of antiferromagnetism in Zn${}_{1-x}$Fe${}_x$Se. A decrease in the concentration of iron atoms in the supercell does not affect the stability of the AFM phase.

Based on the concept of generalized phononic crystals (GPCs), a type of 1D cylindrical shell of generalized phononic crystals (CS-GPCs) where two kinds of homogeneous materials are arranged periodically along radial direction was proposed in this paper. On the basis of radial, torsional shear and axial shear vibrational equations of cylindrical shell, the total transfer matrix of mechanical state vector were set up respectively, and the bandgap phenomena of these three type waves were disclosed by using the method of transfer matrix eigenvalue of mechanical state vector instead of the previous localized factor analyses and Bloch theorem. The characteristics and forming mechanism of these bandgaps of CS-GPCs, together with the influences of several important structure and material parameters on them were investigated and discussed in detail. Our results showed that, similar to the plane wave bandgaps, 1D CS-GPCs can also possess radial, torsional shear and axial shear wave bandgaps within high frequency region that conforms to the Bragg scattering effect; moreover, the radial vibration of CS-GPCs can generate low frequency bandgap (the start frequency near 0 Hz), as a result of the double effects of wavefront expansion and Bragg scattering effect, wherein the wavefront effect can be the main factor and directly determine the existence of the low frequency bandgaps, while the Bragg scattering effect has obvious enhancement effect to the attenuation. Additionally, the geometrical and material parameters of units have significant influences on the wave bandgaps of CS-GPCs.

In this paper, we investigate theoretically the transmission properties of one-dimensional quasi-periodic photonic crystals that containing nanocomposite material in the IR wavelength regions. Our structure is particularly designed using the Fibonacci role. Here, the nanocomposite material is composed of nanoparticles of Ag that are randomly immersed in a host dielectric material of SiO₂. Numerical results are mainly investigated based on the well-known characteristic matrix method. The numerical results show the appearance of many photonic bandgaps due to the multiple periodicities of our structure. Furthermore, the effects of the parameters of the nanocomposite such as the volume fraction, the refractive index of the dielectric material and the size of the nanoparticles have distinct effects on the transmittance characteristics of our structure. Wherefore, the proposed structure could be considered the cornerstone for many applications such as multichannel filters and optical switches.

First-principles calculations of the structural, electronic, optical and thermal properties of chalcopyrite CuXTe₂ (X=Al, Ga, In) have been performed within density functional theory using the full-potential linearized augmented plane wave (FP-LAPW) method, by employing for the exchange and correlation potential the approximations WC-GGA and mBJ-GGA. The effect of X cations replacement on the structural, electronic band structure, density of states and optical properties were highlighted and explained. Our results are in good agreement with the previous theoretical and experimental data. As far as we know, for the first time we find the effects of temperature and pressure on thermal parameters of CuAlTe₂ and CuGaTe₂ compounds. Thermal properties are very useful for optimizing crystal growth, and predict photovoltaic applications on extreme thermodynamic conditions.

In this paper, we have performed a study on the optical properties of single crystals ZnGa₂S₄ by method of density functional theory (DFT) and ellipsometry measurements. The calculated results for the real ${\epsilon }_r$ and imaginary ${\epsilon }_i$ parts of the dielectric function are compared with the measured experimental spectroscopic ellipsometry (SE) spectra in the 0.7–6.5 eV spectral region. Absorption coefficient-photon energy dependency revealed the existence of direct bandgap transitions with energy 3.5 eV. This result is very close to bandgap obtained from our theoretical calculation.

In this study, zinc selenide (ZnSe) thin films were produced on glass substrate by using chemical bath deposition (CBD) method at 80${}^{\circ }$C, from aqueous solutions of zinc sulphate and sodium selenosulphide, which were produced using solid selenium as the selenium source. The optical and structural properties of ZnSe thin films were investigated at room-temperature. The pH of the chemical bath, in which ZnSe thin films were immersed, were changed between pH:8–11. Optical properties of the films, including extinction coefficient, refractive index, reflectance, absorbance, transmittance, dielectric constants and optical density values were calculated using absorbance and transmittance measurements determined using a Hach Lange 500 spectrophotometer, in 300–1100 nm wavelength range. Optical bandgap values were obtained from transmittance and absorbance spectra ranged between 2.12 and 2.49 eV. According to XRD results, it was found that the films have polycrystalline structure and they exhibited different film thicknesses depending on phase and pH changes.

We have performed the first-principles density functional theory (DFT) and DFT$+$U calculations on the electronic and optical properties of CaO: Eu${}^{+2}$ (SrO: Eu${}^{+2}$) phosphors compounds. Herein, we have focused on the polarization of the electronic structures, i.e., the energy bandgap and the density of states. All electrons were treated within the most common exchange and correlation functional called generalized gradient approximation plus optimized effective Hubbard parameter U as GGA$+$U. GGA$+$U is a very effective tool for describing the electronic band energy upto considerable accuracy. Hence, we have opted for the arbitrary values of U as 3.0, 4.0, 5.0 and 7.0 eV to treat the strongly correlated electrons for obtaining the matching result with the experimental one. However, GGA$+$U is highly expensive in terms of computation due to interaction of d or f electrons. The result shows that the appearance of Eu-4f states at the valance band maximum of the spin-up causes a substantial impact on the electronic properties of the studied compounds. The value of energy bandgap is smaller in case of spin up as compared to spin down case. In case of majority spin, the energy gap of 2.224 (2.14) eV belongs to the Eu-4f orbitals and governs the CBM. The partial densities of states (PDOS) structure displays a strong hybridization that may be pointed to the formation of covalent bonds. The calculated and the measured values are in good agreement with each other. In the study of optical properties of the compound, the optical spectral structure shows a lossless region and uniaxial anisotropy. The value of uniaxial anisotropy is positive at static limit and its value is negative above this value.

Cobalt (Co) doped magnesium hydroxide Mg(OH)₂ nanoparticles are synthesized by a surfactant-free co-participation method. Scanning electron microscopy (SEM) images show nanometer size Mg(OH)₂ particles in spherically shaped particle-like morphology. Synthesis of these Mg(OH)₂ nanocrystals involves the formation of monomeric MgOH${}^{+}$ ions as the precursor for the Mg(OH)₂ nuclei which finally evolves in spherical particle-like morphology. X-ray diffraction (XRD) confirms the hexagonal crystal structure of the samples. With increasing Co concentration, the absorption spectra of the samples show narrowing of the bandgap from 5.47 eV (for pure Mg(OH₂)) to 5.26 eV (for 10% Co-doped Mg(OH₂)) effect is attributed to changes in the interaction potentials between Co and the host Mg(OH)₂ lattice due to dopant-induced lattice distortion and the presence of a mixed valance Co${}^{2+}$/Co${}^{3+}$ state.

${\mathrm{\text{MgTa}}}_2{\mathrm{\text{O}}}_6$ single crystals with trirutile structure have been employed as research objects in this paper. The absorbance spectra of the ${\mathrm{\text{MgTa}}}_2{\mathrm{\text{O}}}_6$ crystals are presented and the optical bandgap structures of ${\mathrm{\text{MgTa}}}_2{\mathrm{\text{O}}}_6$ are discussed. Both room temperature and temperature-dependent photoluminescence (PL) of ${\mathrm{\text{MgTa}}}_2{\mathrm{\text{O}}}_6$ single crystals are investigated. Significantly, there are two processes in the emission, and the optical phonon participated procedures are observed and described.

The two-dimensional transition-metal dichalcogenides (2D TMDs) WX₂ (S, Se, Te) have received extensive attention and research since they have excellent physical properties and have been widely used in the fields of photoelectronics. Monolayer (ML) WX₂ has excellent physical properties and can be modified by simple strain. Using the first principles based on density functional theory (DFT), this paper mainly studies the electronic properties of ML WS₂, WSe₂ and Wte₂. We also study the stabilities of three ML structures, the changes of Raman spectra and the movement of Raman peaks under biaxial tensile and compressive strains. Under the control of strain not only does the bandgap changes, but also the band properties shift between the direct bandgap and the indirect bandgap. With the increase of strain, bond length and bond angle change in the opposite trend. At the same time, we also studied the phonon dispersion relations of WX₂ under different strains. We found that three structures showed good thermodynamic stabilities under the tensile strain (1–10%). When the compressive strain is 2%, one of the acoustic modes of WS₂ or Wse₂ becomes imaginary at $\mathrm{\Gamma }$ point, which indicates the structural instability. When tensile strain Raman summit blueshifts and when compressive strains, the redshift occurs.

We have obtained the optical properties of one-dimensional defective photonic crystals containing nanocomposite materials of Ag as a defect layer in UV region; the permittivity of nanocomposite materials depends on plasmon frequency of metal nanoparticles. Our analysis is based on the fundamentals of the transfer matrix method. We have investigated the effect of many parameters such as metal thickness, volume fraction, and defected dielectric materials on the intensity of a defect layer.