Incident Photon Energy Range Research Articles

Investigation of thermodynamical stability and generation of large half-metallic gap along with optical properties in N-doped YHfO3 (YHO) (Y = Ca, Sr, and Ba) perovskite materials by first principle calculations

Considerable energy gap (Eg) in insulating channel, high spin-filtering, significant mean free path, and high magnetic transition temperature (TC) escalate half-metallic (HM) ferromagnetic (FM) materials very enticing for spintronic applications. Herein, ab-initio calculations have been executed comprehensively to inquest the structural, thermodynamical, electronic, magnetic, and optical properties of pure as well as nitrogen (N)-doped YHfO3 (YHO) (Y = Ca/Sr/Ba) materials with one N atom added at one of the oxygen (O) site. First, the thermodynamical stability of both bulk and doped YHO systems has been examined by estimating the formation enthalpies (ΔHf) by Convex Hull analysis, which confirms the practical realization of these materials on experimental grounds. Moreover, mechanical stability of these systems is affirmed by estimating the necessary elastic constants and respective parameters. Strikingly, all doped systems possess complete (100%) splitting in spin↑ and spin↓ channels at Fermi level and depict HM FM character with significant Eg of 3.31, 3.49, and 3.24 eV in spin↓ channels for CaHO (CHO), SrHO (SHO), and BaHO (BHO) systems, respectively. It is also found that N 2p orbitals are totally responsible for the emergence of metatallicity and magnetic character in all these doped structures. Moreover, the ground state long range FM stability between two added N atoms in doped systems is affirmed by computing the difference of total energies of FM and anti-ferromagnetic (AFM) spin ordering (ΔE) along with estimated TC at different distances. Lastly, it is found that N-doped systems have a lower optical energy loss than pristine YHO systems in the incident photon energy range of 0-50 eV. Hence, the present study proposes that an unconventional doping approach with intrinsically non-magnetic element in a variety of YHO perovskite systems could be a useful method to alter their various physical properties and forecast their potential applications in the development of novel spintronic and optoelectronic devices.

Cascade energy reemission by the silver atom ionized by 0.01–100 keV photons. Possible application of silver-based radiosensitizing agents in photon beam radiation therapy

A method of straightforward construction and analysis of the cascade decay trees is applied to study the cascade energy reemission by silver atoms upon photoionization in the incident photon energy range of 0.01–100 keV. Cascade electrons and photons emitted during the cascade relaxation of an inner-shell vacancy carry away a significant part of the energy initially acquired by the silver atom in a photoionization act. The energies redistributed through following channels were calculated as functions of incident photon energy: energy absorbed by the silver atom itself (a), and energies carried away by the cascade electrons (b) and photons (c). Channel (a) is dominant only at small incident photon energies up to the M5 ionization threshold. Channel (b) dominates between M and K thresholds making 57–85 % of the acquired energy. Above the K threshold, the weight of channel (b) is still significant, 24 %, however, dominant is channel (c).

Cross sections of cascade production of photoions after photoionization of the silver atom in the 0.07–100 keV incident photon energy range

The formation of multiply charged Agq+ ions resulting from photoionization and subsequent cascade decay of inner-shell vacancy states is studied using the method of construction and analysis of the cascade decay trees. Cross sections for the cascade production of Agq+ ions, yields of Agq+ ions, and mean photoion charge are calculated as functions of incident photon energy in the range of 70 eV to 100 keV. The results of this study are relevant for developing the strategies of radiotherapy using Ag-based radiosensitizers.

Cross sections of cascade production of photoions after photoionization of the iodine atom in the 0.01–100 keV incident photon energy range

Ion yields upon the cascade decays of single vacancies in K to O shells of an isolated iodine atom are calculated by the method of construction and analysis of the cascade decay trees. Branching ratios needed for the simulations are calculated based on Pauli–Fock partial transition widths. Partial photoionization cross sections are calculated with accounting for the core relaxation effect and used to calculate the cross sections of I q+ photoions production in the 0.01–100 keV incident photon energy range. Accounting for the spin–orbit splitting and the splitting due to electron–electron interaction is shown to be important when calculating mean energies and probabilities of the transitions between energetically closely lying ionic configurations. On the other hand, inclusion of the additional shake-off electron ejections, in spite of complicating severely the decay trees, is found to affect little calculated cascade ions production probabilities.

Optimal design and characteristic analysis of CsPbBr3 nanocrystals hybridized with 2,5-diphenyloxazole molecules for UV and X-ray detection

Scintillation is a flash of light produced in a material by the passage of a high-energy particle or photon. Desirable properties of scintillators, such as high quantum yield, low afterglow, and radiation hardness, are determined by their physical and optoelectronic properties. Metal halide perovskite (CsPbX3, X = Cl, Br, I) nanocrystals (NCs) have gained increasing attention as materials for optical and X-ray scintillators across a wide range of incident photon energies owing to their outstanding luminescent properties. In this study, we demonstrate the dependence of scintillation yield (SY) on incident photon energy ranging from ultraviolet (UV) light to X-rays in colloidal CsPbBr3 NCs hybridized with organic molecules (2,5-diphenyloxazole: PPO). The measured SY varied with the changing concentration ratio of NCs and PPO molecules. Experimental and theoretical analyses suggested that the SY is associated with the competition between photoluminescence quenching (reabsorption) and photoelectric effect enhanced by X-ray photon induced charge transfer from the organic molecules to the NCs. The optimally engineered hybrid nanomaterial scintillator exhibits excellent X-ray imaging with sharp image contrast (i.e., super-resolved edge spread function (ESF)), under X-ray irradiation commonly used for diagnosis.

Electronic, optical and thermoelectric properties of Cs2XInCl6 (X = Ag, Na) halide double perovskites

Herein, the optoelectronic, structural, thermoelectric and elastic features of halide double perovskites (HDPs) Cs2XInCl6(X=Ag, Na) are examined by using full‐potential linearized augmented plane wave (FP‐LAPW) technique. The Generalized Gradient Approximation (GGA) and Tran‐Blaha modified Becke‐Johnson (TB‐mBJ) potential is employed to figure out the features of mentioned compounds. The computed values of direct band‐gaps (Eg) for Cs2AgInCl6 and Cs2NaInCl6 compounds are 2.52 and 5.24 eV, correspondingly. The stability of perovskites is confirmed in terms of formation energy ΔHf, tolerance factor (τ) and octahedral factor. Furthermore, optical properties analysis demonstrates that studied compound exhibit conductivity and absorptivity across a broad range of incident photon energy with minimum R(ω). Moreover, outcomes of elastic parameters display isotropic and ductile nature for both materials. Thermoelectric (TE) properties like thermal conductivity (k/τ), power factor (PF), electrical conductivity (σ/τ) and Seebeck coefficient (S) are also calculated by utilizing BoltzTrap code. Cs2NaInCl6 attained the maximum value of ZT (0.76) with PF of 0.42. Computed TE and optical parameters indicate that Cs2XInCl6(X=Ag, Na) are promising for usages in solar absorbing and energy conversion devices.This article is protected by copyright. All rights reserved.

A DFT investigation of mechanical, optical and thermoelectric properties of double perovskites K2AgAsX6 (X = Cl, Br) halides

Focusing on renewable energy device applications, we explored double perovskites K2AgAsX6 (X = Cl, Br) halides for the first time. We used WIEN2k (all-electron method) and BoltzTrap code to investigate optoelectronic and thermoelectric properties for renewable energy device applications. For structural and elastic calculations, we employed PBEsol generalized gradient approximations and found that both halides in the cubic phase are structurally stable. Further, Pugh's and Poisson's predicted values indicate that both halides are ductile. Furthermore, we also calculate the formation energy to check the thermodynamical stability of both halides. For accurate calculations of optoelectronic properties, we applied Tran-Bhala modified Becke and Johnson potential (TB-mBJ). Electronic band structure calculations indicate both halides are indirect bandgap nature having values of 2.1 eV and 1.6 eV, respectively, and might be potential candidates for solar cell applications. We also discussed the optical parameters within the incident photon energy range of 0–12 eV. We found strong absorption in the visible region for K2AgAsX6 (X = Cl, Br) halides indicating both halides are appropriate solar cell devices. Lastly, we calculate thermoelectric parameters against temperature and chemical potential. A probing figure of merit shows halides is also potential candidates for thermoelectric device applications.

Graphene-bioactive glass composites: Structural, Vickers hardness, and gamma-ray attenuation characteristics

Introduction: Graphene-based materials have gained increasing attention for use in radiation attenuation applications. In this study, pristine graphene nanoplatelet-containing (1, 3, 5, and 10 wt%) borate-based bioactive glass composites were prepared.Methods: Structural properties, Vickers microhardness, and gamma-ray radiation shielding properties of the fabricated composites were examined in detail.Results and Discussion: Results revealed that the inclusion of the graphene in the glass matrix led to a decrease in the bulk density of the glass-based composites from 2.41 to 2.31 g/cm3. Similarly, a decrease in Vickers hardness was obtained as the graphene concentration was increased due to a convoluted effect of the non-uniform distribution of graphene nanoplatelets in the bioactive glass matrix and the higher residual porosity. Vickers hardness of the bare and the 10 wt% graphene-containing bioactive glass discs were measured to be 5.03 ± 0.28 GPa and 1.87 ± 0.56 GPa, respectively. On the other hand, the incorporation of graphene starting from 3 wt% decreased the crack propagation after indentation which may be attributed to an increase in fracture toughness. In the study, fundamental gamma ray absorption properties of graphene-containing bioactive glasses were examined in the 0.015–15 MeV incident photon energy range. For this purpose, the Py-MLBUF code was employed to determine gamma ray absorption parameters. Results showed that linear attenuation coefficients of the glass-based composites decreased due to a decrease in the density of the samples. On the other hand, as graphene was incorporated into the bioactive glass structure, exposure buildup factor and energy absorption buildup factor values increased. The growing graphene ratio in the glass structure contributed negatively to the photon’s tendency to interact with the material.

Cascade energy reemission after inner-shell ionization of atomic gold. Role of photo- and cascade-produced electrons in radiosensitization using gold-containing agents

A method of straightforward construction and analysis of the cascade decay trees is applied to calculate photon and electron spectra emitted upon the cascade de-excitation of single inner-shell vacancies in the gold atom produced by photoionization. The energy acquired by the gold atom upon photoionization is split into the following channels: i) energy absorbed by the gold atom itself, ii) energy carried away by the cascade electrons, and iii) energy carried away by the cascade photons. The energies absorbed through channels i–iii are analyzed for the cascade decay of each single vacancy in O to K shells, and presented as functions of incident photon energies based on calculated partial photoionization cross sections. Energy reemitted through channels ii and iii in the cases of O-, N-, M-, L-, and K-ionization make, respectively, 47–60%, 55–69%, 85–89%, 94–96%, and 99% of the initially acquired energy. Cascade-produced electrons and photons eventually transfer their energy to the medium which lays the base for using gold-containing compounds and gold nanoparticles as radiosensitizing agents in radiotherapy. Cascade-produced electrons, as well as photoelectrons, are found to be the principal transmitters of energy to atoms of the environment in the vicinity of the sites of initial ionization. Their relative role in possible radiosensitizing effect is analyzed on the incident photon energy range of 0.01–1000 keV.

BaTiO3 perovskite for optoelectronics application: A DFT study

BaTiO3 perovskite material is an attractive material for optoelectronics applications. Here, we discuss the results of our investigations using density functional theory(DFT)into the BaTiO3 structure. The computations were performed utilizing Generalized Gradient Approximation (GGA) and Local Density Approximation (LDA) through SIESTA code. In the current study, we have calculated the electronic properties such as energy band structure, density of states (DOS)/eV and optical properties of the BaTiO3 perovskite material. The band structure of this material was estimated using the Spin Orbital Coupling (SOC) effect. The band gap value for the BaTiO3 perovskite material produced by GGA is 1.54 eV and LDA is 1.67 eV, which is quite comparable with previously reported work. The calculated DOS and PDOS for this perovskite materials show that the states of Ti-3d and O-2p has a significant effect on the electronic properties. The static dielectric constant, reflectivity R(ω), absorption coefficient α(ω) and refractive index n(ω) have also been estimated in terms of optical characteristics. The results obtained on the optical properties such as the low reflectivity rate and high absorption of the incident photon energy range in GGA is 2–4 eV and LDA is 2–5 eV. This energy range suggests that BaTiO3 in perovskite solar cells has a good optical response to absorbingsolar wavelengths.

First-principle insight into the structural, electronic, elastic and optical properties of Cs-based double perovskites Cs2XCrCl6 (X = K, Na).

This study communicates the theoretical investigations on the cubic double perovskite compounds Cs2XCrCl6 (X = K or Na). Density functional theory (DFT) calculations were carried out using the TB-mBJ approximation. These compounds were found to be stable in the cubic perovskite structure having lattice constants in the range of 10.58-10.20. The stability of the investigated materials was assessed by the Gold-Schmidt tolerance method, which resulted in the tolerance factor values of 0.891 and 0.951 for Cs2KCrCl6 and Cs2NaCrCl6, respectively. The calculated values of the elastic constants C11, C12, and C44 of the cubic compounds studied by our research team confirm the elastic stability. The values of the formation energies were also calculated for both the compounds and were found in the range from -2.1 to -2.3. The electronic behavior of the presently investigated materials was examined by inspecting their band structures and the density of states. It was observed that both the materials have half-metallic nature. To check the suitability of the studied compounds in optical applications, we determined the real and imaginary parts of their respective dielectric functions, absorption coefficients, optical conductivities, refractive index, and reflectivity as a function of a wide range of incident photon energies up to 40 eV.

Probing the physical properties of M2LiCeF6 (M = Rb and Cs) double perovskite compounds for prospective high-energy applications employing the DFT framework.

Herein, the optoelectronic, structural, thermoelectric, and elastic characteristics of M2LiCeF6 (M = Rb and Cs) double perovskite compounds were investigated using ab initio modeling in the DFT framework. The Birch-Murnaghan fitting curve used for the optimization showed that these two compounds are structurally stable. The elastic properties of the M2LiCeF6 (M = Rb and Cs) double perovskite compounds were examined using the IRelast code. The results showed that these two compounds possess mechanical stability, anisotropy, and toughness, and offer resistance to plastic deformation. The precise and accurate determination of their electronic properties was achieved via the Trans-Blaha-modified Becke-Johnson (TB-mBJ) approximation. The Rb2LiCeF6 and Cs2LiCeF6 compounds are narrow band gap semiconductors with band gaps of 0.6 eV and 0.8 eV at the high symmetrical points from (Γ-M), respectively, exhibiting an indirect nature. To further understand how the various states contribute to the different band structures, total and partial density of state (DOS) computations were performed. The optical properties in the energy range of 0-40 eV for Rb2LiCeF6 and Cs2LiCeF6 were explored. The selected materials show transparency in the low incident photon energy range and have large light absorption and transmission at higher photon energies. Thus, it can be concluded that Rb2LiCeF6 and Cs2LiCeF6 can be used in high-frequency UV devices based on their optical characteristics. Both materials exhibit high electrical conductivity, power factors, and figures of merit (ZT) and act as effective thermoelectric resources. To the best of our knowledge, this is the first theoretical research on the optoelectronic, structural, thermoelectric, and elastic features of M2LiCeF6 (M = Rb and Cs).

Bandgap tuning and thermoelectric characteristics of Sc-based double halide perovskites K2ScAgZ6 (Z = Cl, Br, I) for solar cells applications

Using the full-potential linearized augmented plane wave plus local orbitals method within the frame work of density functional theory, the Sc-based double halide perovskites K2ScAgZ6 (Z = Cl, Br, I) are investigated for determining their physical properties. To investigate the structural and thermodynamic stability of these Sc-based double halide perovskites we calculate tolerance factor, formation energy, and phonon dispersion curve using GGA-PBEsol approximation. The calculated values of lattice parameters using GGA-PBEsol are found to be consistent with the available data. Subsequently, the Tran-Blaha modified Becke-Johnson (mBJ-LDA) potential is used for electronic properties. Implementation of TB-mBJ potential is clearly shows that K2ScAgZ6 have indirect bandgap, which is consistent with the literature. To evaluate these double perovskites and reveal their potential use in optical devices, several optical parameters are computed for an incident photon energy range of 0–8 eV. The BoltzTraP code is also employed to investigate temperature dependent electrical characteristic of these compounds in the temperature range of 200–600 K. Investigated halide double-perovskites have been shown to display excellent physical properties for solar cells and renewable energy device applications.

Theoretical investigation of doped LiMg1-xYxN (Y = Ag, Cu, Mn, Zn) for RRAM application

With the assistance of a First Principles research based on density functional theory, electronic and optical characteristics of the LiMg1-xYxN (Y = Ag, Cu, Mn, Zn) are examined. The influence of magnetic (Mn, Zn) and non-magnetic (Ag, Cu) dopants without and with nitrogen vacancies (VN) on the electronic and optical characteristics of optimized LiMgN is investigated by determining the contribution of each atom towards charge redistribution. The isosurface charge density and integrated charge density plots depicted the development of conduction filaments. Electronic properties showed best conductivity that makes the studied composites vibrantly useful for resistive switching memory applications. The optical analysis showed that considered composite possess conductivity and absorptivity in a wide range of incident photon energies with their nominal reflectivity. The least formation energy and greatest conductivity observed in LiMgN-Mn-VN proved it to be the most stable. Entire analyses portray that considered compounds are potential candidates for applications in optoelectronic devices.

Direct Measurement of Helicoid Surface States in RhSi Using Nonlinear Optics.

Despite the fundamental nature of the edge state in topological physics, direct measurement of electronic and optical properties of the Fermi arcs of topological semimetals has posed a significant experimental challenge, as their response is often overwhelmed by the metallic bulk. However, laser-driven currents carried by surface and bulk states can propagate in different directions in nonsymmorphic crystals, allowing for the two components to be easily separated. Motivated by a recent theoretical prediction G. Chang et al., Phys. Rev. Lett. 124, 166404 (2020)PRLTAO0031-900710.1103/PhysRevLett.124.166404, we have measured the linear and circular photogalvanic effect currents deriving from the Fermi arcs of the nonsymmorphic, chiral Weyl semimetal RhSi over the 0.45-1.1eV incident photon energy range. Our data are in good agreement with the predicted spectral shape of the circular photogalvanic effect as a function of photon energy, although the direction of the surface photocurrent departed from the theoretical expectation over the energy range studied. Surface currents arising from the linear photogalvanic effect were observed as well, with the unexpected result that only two of the six allowed tensor element were required to describe the measurements, suggesting an approximate emergent mirror symmetry inconsistent with the space group of the crystal.

Optical Response of Ultrathin Periodically Aligned Single-Wall Carbon Nanotube Films

AbstractWe present a semi-analytical expression for the dielectric response function of quasi-2D ultrathin films of periodically aligned single-walled carbon nanotubes. We derive the response function in terms of the individual nanotube conductivity, plasma frequency, and the volume fraction of carbon nanotubes in the film. The real part of the dielectric response function is negative for a sufficiently wide range of the incident photon energy, indicating that the film behaves as a hyperbolic metamaterial. Inhomogeneous broadening increases the effect.

Band Offsets, Optical Conduction, and Microwave Band Filtering Characteristics of γ‐In2Se3/CuO Heterojunctions

Herein, the design and experimental characterization of γ‐In2Se3/CuO interfaces are considered. Thin films of γ‐In2Se3 are coated with thin layers of CuO at room temperature. The heterojunction device is structurally, morphologically, and optically characterized. It is observed that the coating of CuO onto γ‐In2Se3 engenders the formation of CuSe2 at the ultrathin interface. The γ‐In2Se3/CuO heterojunctions exhibit maximum possible conduction and valence band offsets of values 0.47 and 0.96 eV, respectively. The dielectric spectra display two dielectric resonance peaks at 2.96 and 1.78 eV. In addition, analyses of the optical conductivity spectra reveal accurate drift mobility and plasmon frequency values of 31.31 cm2 Vs−1 and 1.5 GHz, respectively. The ability of the device to control the signal propagation at gigahertz level is experimentally tested by the impedance spectroscopy technique which proved the ability of the device to behave as bandpass filters of notch frequency of 1.49 GHz. The γ‐In2Se3/CuO heterojunction devices are also observed to display terahertz cutoff frequency values of ≈24 THz in the infrared (IR) range of incident photon energy and ≈193 THz in the ultraviolet light range. The nonlinear optical performance of the device nominates it for use as terahertz/gigahertz band filters.

Fabrication and assessment of Mn–Co–Ni–Nb–O composite films: structural, optical, and electrical properties

Mn1.56−xCo0.96Ni0.48NbxO4 (MCNN) composite films with different Mn/Nb ratios were synthesized on a SiO2/Si substrate via the chemical solution deposition method. The film structure and morphology were investigated via X-ray diffractor (XRD), Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. The optical properties of the composite films were explored via ellipsometry. The XRD results indicated that MCNN was a composite of the Mn-based spinel oxide and the nickel/cobalt niobates. The morphology of the MCNN films improved with increasing Nb content from 0.2 to 0.4. The partial replacement of Mn into Nb significantly improved the optical properties of the composite films over the incident photon energy range of 1.0–5.0 eV. The optical absorption mechanism of the composite films has also been discussed.

Accurate atomic momentum integrals and Compton profiles

Analytical expressions for integrals involving momentum density have been developed, and an algorithm for the efficient computation of Compton profiles (CPs) based in those equations is reported. The performance of the algorithm is tested by computing the CPs of atoms from helium to xenon for a wide range of incident photon energies. Calculations have been made at Hartree–Fock level (HF), using three different Slater basis sets, showing a good agreement with the experimental results.

Advances in Analysis of Microcalorimeter Gamma-Ray Spectra

Microcalorimeters based on transition-edge sensors (TESs) have been successfully deployed in numerous spectroscopic instruments that operate over a large range of incident photon energies. TES microcalorimeter arrays combine unmatched energy resolution with broadband spectral coverage and high quantum efficiency. An important application requiring these characteristics is nondestructive isotopic analysis via gamma-ray spectroscopy of the complex mixtures of actinide isotopes found in the nuclear fuel cycle. Steady progress has been made over the last ten years to develop TES microcalorimeter instruments for this application, leading to arrays that demonstrate significantly better energy resolution than the state-of-the-art high-purity germanium (HPGe) sensors. However, further algorithm development and automation of the data analysis procedure have been required to bring these systems closer to being ready for production use. In this article, we describe recent advances in data analysis techniques for gamma-ray data acquired with microcalorimeter systems. In particular, we discuss new approaches to automated calibration of our spectra, and a new approach for quantifying the uncertainty of peak area estimation for isolated peaks. Our data analysis pipeline has also been automated, requiring minimal manual intervention for full processing of data sets, with performance that is sufficient to allow future deployment of real-time spectrum generation. We show that, using this pipeline, we are able to achieve ~0.25% statistical uncertainty in isotope ratios, which indicates that if systematic errors are controlled, microcalorimeter arrays can achieve better than 1% total uncertainty in these measurements.