Electronic Optical Properties Research Articles

Computational analysis of electronic structure and optical properties of monocrystalline silicon-vacancy defect system based on density functional theory

Monocrystalline silicon is an important substrate or base material for manufacturing integrated circuit chips, mirrors, etc. However, it is a typical hard and brittle material, which is very prone to produce defects during processing. This paper investigates the electronic structure and optical properties of sphalerite monocrystalline silicon with vacancy concentrations of 1.5625%, 3.125%, 4.6875%, and 6.25% using the first principles method based on density functional theory. The results demonstrate that the introduction of impurities results in the formation of impurity bands (IB) within the band structure, thereby facilitating electronic transitions. However, vacancy defects do not alter the properties of monocrystalline silicon as an indirect semiconductor. Regarding optical properties, an increase in defect concentration leads to a decrease in the macroscopic symmetry of the system, resulting in noticeable anisotropy in each property. Also found that the main spectral peaks of the defect system are red-shifted, and the vacancy defects introduce new peaks in the near-infrared region and the visible region with increasing intensity, but the peaks in the ultraviolet region gradually decrease with the increase of the defect concentration. The refractive index peak gradually decreases with the increase of defect concentration, and the calculated average refractive index is around 1.2. In the high-energy region, the refractive index takes a very small value, and the reflection of electromagnetic waves from the doped system is also weak at this time, which indicates that the system has a high transmittance property. Importantly, there is a higher intensity of energy loss at photon energies around 16.5 eV. Consequently, these calculations are deemed valuable for advancing research and applications involving monocrystalline silicon optical mirrors.

Electronic Structure and Optical Property of 2D MgPX3 (X = S and Se) Monolayer by Density Functional Theory

2D metal phosphorus trichalcogenides (MgPX3) have attracted tremendous research interests in spintronic, electrocatalytic, and photoelectronic applications due to their unique magnetic and optical properties. Herein, a systematical investigation on the electronic structures and optical properties of 2D MgPX3 (X = S and Se) monolayers is performed by density functional theory. Owing to small cleavage energy, 2D MgPX3 monolayers can be obtained by mechanical exfoliation with an excellent structure stability of 2D MgPX3 monolayers demonstrated by elastic tensor, phonon dispersion, and molecular dynamics, respectively. 2D MgPX3 behaves as a direct bandgap semiconductor with a strong optical absorption in UV range whereas a weak adsorption near the band edge, demonstrated by both single‐ and quasiparticle approximations. Upon analyses on transition dipole moment along with the wave function symmetry, the weak optical absorption is attributed to the parity‐forbidden effect where the wave functions almost show the same parity between top valence band and bottom conduction band. The findings indicate that 2D MgPX3 monolayers hold promise as candidate materials for flexible UV photoelectronics devices and provide a theoretical insight into the optical properties of 2D semiconductors.

Effects of external magnetic fields on the confined states and optical properties of conical quantum dot nanowire

In this paper, we have investigated theoretically the effect of the external magnetic fields on the electronic structuctures and optical properties of a nanosystem consisting of a conical InAs quantum dot embedded in an infinite GaAs nanowire. To this end the Schrodinger equation have been solved numerically utilizing the effective mass approximation to calculate the confined energy states and binding energies of the system. The findings demonstrate that under the effect of the magnetic fields, the energies of confined states in the Quantum Dot of +|m| and −|m| angular momentum have been separated and increased toward the energy continuum of the nanowire. It has been shown that the lower limit of energy continuum of ±m states are split which results in different binding energy for states of +|m| and −|m| angular momentum. Finally, the oscillator strength for intersubband transitions between the system's confined energy states has been explored in order to discuss the optical properties of the described system.

(Invited) Photo-Assisted Electron Emission from Silicon-Based Electron Emission Devices

Ultrafast pulsed electron sources with spatial coherence have attracted significant interest in emerging applications such as scientific instruments of ultrafast electron microscopy [1-3] and electron beam lithography [4], and also as sources of X-ray [5] and micro- and THz-waves [6-9]. In particular, high-frequency electron bunch trains generated directly from the cathode surface can not only dramatically reduce dimensions and weight through the elimination of the pre-modulation circuit, but can also provide extremely high efficiency and improve the power in the electron beam devices due to coherence effects.One solution is employing photoemission from electron sources driven by ultrashort laser pulses for such emerging applications. Metallic flat photocathodes and recently metallic nanotips have been employed. However, a low quantum efficiency (QE), typically of approximately 0.01 %, and a large work function require a high-power UV laser to generate an intense electron beam. Negative electron affinity (NEA) semiconductor photocathodes such as NEA GaAs can provide QE as high as ~ 10 % [10], operating using visible laser light irradiation. However, the NEA surface is fragile and easily damaged by residual gas adsorption or beam extraction.In this presentation, we introduce the research and development of gated Si-FEAs with a volcano structure and planar-type electron emission devices based on a MOS diode structure and discuss the potential of the devices as a photocathode of the devices operating without NEA surface treatment. We investigate the optical properties of emitted electrons from the devices under visible laser light irradiation. The results indicate that Si-based electron emission devices with a fully optimized structure hold promise as a photocathode with a high QE and a high-speed response for generating a train of ultrashort electron bunches, operating without NEA surface treatment.

(C(NH2)3)2(I2O5F)(IO3)(H2O) and C(NH2)3IO2F2: Two Guanidine Fluorooxoiodates with Wide Band Gap and Large Birefringence.

Enhancing anisotropy through an effective synergistic arrangement of anionic and cationic groups is crucial for improving the birefringence optical properties of materials. In this work, by transforming I-O into I-F through the fluorination strategy, two metal-free guanidine fluorooxoiodates (C(NH2)3)2(I2O5F)(IO3)(H2O) and C(NH2)3IO2F2 and one guanidine iodate C(NH2)3IO3 were successfully synthesized using the hydrothermal method. An unprecedented dimer [I2O5F] formed by [IO3F] and [IO3] in (C(NH2)3)2(I2O5F)(IO3)(H2O) was found, which greatly enriches the structural diversity of fluorooxoiodates. All three compounds feature a relatively large birefringence (Δn = 0.068, 0.110 and 0.075 at 546 nm) and a short ultraviolet cutoff edge. The theoretical calculation was carried out to understand the electronic structures and linear optical properties.

Systematic First-Principles Calculations of Ce3+-Dopant in Garnet-Type Oxide Phosphors

A study of Ce3+-doped oxide phosphors was performed using first-principles calculations based on the relativistic DV-Xα method. In particular, we focused on the Ce3+-doped garnet-type oxides, which have potential applications in solid-state lighting and display devices. The electronic structure and optical properties of the phosphors were analyzed. The energy levels of the Ce3+ ions were affected by the coordination number and the crystal field strength of the surrounding oxygen ions. In addition, the crystal structure of the material had a significant impact on the energy levels of the Ce3+ ions, with different crystal structures leading to different energy levels.The Ce3+ ion is substitutionally incorporated in the garnet lattice, and the 4f electron of Ce3+ plays an important role in the luminescence of the material. The emission wavelengths of the 5d-4f transition energy of Ce3+ can be tailored by varying the crystal structure and the composition. The 5d orbitals of Ce3+ are substantially affected by the crystal field splitting while the amplitude of crystal field splitting (εcfs) is caused by many parameters: coordination number, symmetry of Ce3+ site, and bond lengths between the Ce3+ ion and the oxygen ions (O2-). This study incorporated the following computational conditions: i) lattice relaxation, ii) the choice of the exchange-correlation potential, and iii) Slater’s transition state method. The effects of these conditions were analyzed. In addition, the correlations among physical properties and electronic structure parameters were also investigated in detail.The first-principles calculation results were compared to the experimental data to validate the accuracy of the theoretical models, which showed a good agreement between the experimental and predicted values.

Theoretical study on structural, electronic structure, elastic and optical properties of α-Cu2S

Based on the first-principles method, the electronic structure, mechanical and optical properties of α-Cu2S are studied. The results show that the optimized structural parameters are in good agreement with the experimental value. The energy band structure and density of states of α-Cu2S is obtained by calculation and analysis. The mechanical properties such as bulk modulus, shear modulus, Young's modulus and Poisson's ratio are calculated at different pressures. At last, the dielectric function, refractive index, absorption coefficient and reflectivity of α-Cu2S is analyzed. It was found that α-Cu2S is a direct bandgap with a band gap of 1.2 eV and has good potential for optoelectronic applications.

Theoretical modeling of nonlinear optical properties in spheroidal CdTe/ZnTe core/shell quantum dot embedded in various dielectric matrices

The theoretical investigation of the electronic and nonlinear optical properties in spheroid-shaped CdTe/ZnTe core/shell quantum dots (CSQDs) embedded into two commonly adopted dielectric matrices (PVA, SiO2) is done in the framework of the Effective Mass Approximation (EMA). The discrete intra-band confined energy levels and their matching wave functions were calculated by solving the stationary Schrödinger equation taking into account the Compact Density Matrix (CDM) approach. The effect of the dielectric mismatch between the system and the capped matrix has been studied and discussed. Our numerical results revealed that the third-order nonlinear (TON) optical susceptibility χ3 is strongly influenced by the geometrical parameters and the dielectric environment.

Electronic structure, optical and elastic properties of Si doped Strontium Selenide: A theoretical investigation

The structural, electronic, optical, and elastic properties of Silicon doped Strontium Selenide binary and ternary semiconductor alloys with the general form of Sr(1-x)SixSe, 0 ≤ x ≤ 1 in B1 and B3 phases have been figured adopting augmented plane wave plus local orbital methods within density functional theory, Structural properties summarize the crystal structure, relevant atomic positions, lattice constant, bulk modulus minimum energy E0 and minimum volume V0. Elastic constants conform to the structure stability of the B1 and B3 phases. Band gap is found to shift from indirect to direct and in some materials with initial direct band gap, the gap width increased which increased the range of applicability of these binary and ternary semiconductor compounds. Whereas optical properties which include the study of zero frequency limit of static dielectric constant ε0(ω) with its real and imaginary parts, static refractive index n(0), optical reflectivity (R), optical absorption coefficient (α), and loss function (L) studied comprehensively to get real electrical and optical properties of these materials and give semiconductor market best alternative candidate which shows its effectiveness in the visible, ultraviolet and infrared region of the electromagnetic spectrum. The obtained results were compared together and with the available experimental along with theoretical work on these binary and ternary Silicon doped Alkaline earth chalcogenides.

Modulating Optical Properties of Graphene with the help of Two‐Dimensional Metal‐Organic Networks

AbstractWe utilize density functional theory to explore dicarbonitrile‐polyphenyl networks overlaid on graphene as a method for manipulating the density of Li atoms in a specific assembly pattern. Ab initio molecular dynamics calculations affirm the thermal stability of the introduced systems. We scrutinized the electronic structure and optical properties of the resultant systems, illustrating a systematic modulation of optical characteristics. Our results suggest that the optical excitation frequencies of (Li‐dicarbonitrile‐polyphenyl)/G can be efficiently tuned by systematically adjusting the density of Li atoms on graphene.

First principles study on band gap modulation of TiO2 (112) surface for enhancing optical properties

Anatase TiO2 is widely used in solar photocatalysis. However, the optical properties are limited by its ability to capture visible light and its poor activity. In order to obtain ideal material properties, GGA + U method based on density functional theory is used to study the electronic structure and optical properties of anatase phase TiO2 and its (112) surface and Cr and Co-doped TiO2 (112) surface. The results show that the transition metal Cr-doped system is more stable than the Co-doped system. The four systems exhibit semiconducting properties. The indirect band gap value of intrinsic TiO2 is 3.245 eV, and the impurity bands appear in the spin-up energy bands after Cr, Co doping. The impurity states of the doped system spin split, which transforms the non-magnetic semiconductor into a semiconductor with net magnetic moments of 2 μB and 3 μB, respectively. In addition, the Cr, Co-doped systems show excellent optical properties, and the absorption coefficients are red-shifted in the range of (0–3 eV) with higher optical absorptivities. Through the investigation, it is evident that doping results in different degree of band gap change. As the conduction band moves towards the lower energy level, an impurity band is generated near the Fermi level. The presence of the impurity band fundamentally alters the initial transition mode of the electron, making the transition require less energy, thus enabling enhanced optical properties. The doping system enhances the lepton threshold of electrons and light absorption by changing the mode of inter-band leaps and decreasing the reflectivity, making them candidates in the field of optoelectronics and photocatalysis.

First-principles calculations investigating structural, electronic optical and elastic properties of ABSe3 (A = Rb, Cs) compounds explored for photovoltaic and optoelectronics applications

In few recent years, great and significant efforts are devoted from researcher all over the world to pursue the revolution of photovoltaic’s materials and their uses in various applications. In the present work, a series of ab-initio simulations based on the density functional theory DFT plane wave pseudo-potential (PW-PP) method and hence performed towards the perselenoborate materials ABSe3 (A = Rb,Cs) for the first time along the three main polarizations of the incident wave directions [100], [010] and [001] with the aim of exploring their structural, electronic, optical and elastic properties. The generalized gradient approximation Perdew–Burke–Ernzerhof (GGA-PBE) carried out with CASTEP code is used for the exchange–correlation potential. The computed results showed that the structural properties of investigated compounds are very good agreement to the available experimental data, showing that the current calculations are quite accurate. Moreover, the density of states and electronic band structure calculations reveal that RbBSe3 (CsBSe3) compounds exhibit direct band gap semiconductor nature 1.66 eV (1,82 eV) respectively within the optimal range band gap 1eV–2eV required for photovoltaic’s applications makes them having great potential to obtain efficient Perovskite solar cell PSC. Additionally, our finding optical properties calculations reveal that the two investigated compounds exhibit strong absorption (prominent absorption peaks up 2,4 × 105cm−1) in UV range, while the real part of the refractive index for RbBSe3 (CsBSe3) was 2.62 (2.60) respectively which might be beneficial for photovoltaic application (top cell in solar cell) and optical applications. Also, high optical conductivity (∼1015sec−1) is found to be observed in visible ultraviolet range (1.7 eV to 30 eV). The lower reflectivity seen by RbBSe3 compared to CsBSe3 in the larger energy spectrum of electromagnetic radiation suggests that RbBSe3 compound is more suitable for electronic applications. Further, once the elastic constants are obtained, the calculated mechanical properties, bulk modulus (B), shear modulus (G), the ratio B/G, Young’s modulus (E), Poisson’s ratio (ν), anisotropy universal (AU) are calculated. Our calculated Young’s modulus indicate that the CsBSe3 is less hardness compared to RbBSe3, while Poisson’s ratio calculated leads them to have a character ionic and RbBSe3 is more ductile than CsBSe3. The calculation value of θ D predicted from elastic constants appears low which is closely related to many physical properties such as specific heat and melting temperature. Finally, the finding results reveal another way of investigating mechanical stability, where both compounds are mechanically stable since all elastic constant computed are perfectly satisfied the Born stability criteria, flexible and brittle. Finally, we hope that all these results will be helpful for designing photovoltaic and optoelectronic devices.

Designed complexes combining brazilein and brazilin with betanidin for dye-sensitized solar cell application: DFT and TD-DFT study

Dye-sensitized solar cells (DSSCs) are promising third-generation photovoltaic cell technology owing to their easy fabrication, flexibility and better performance under diffuse light conditions. Natural pigment sensitizers are abundantly available and environmentally friendliness. However, narrow absorption spectra of natural pigments result in low efficiencies of the DSSCs. Therefore, combining two or more pigments with complementary absorption spectra is considered an appropriate method to broaden the absorption band and boost efficiency. This study reports three complex molecules: brazilin-betanidin-oxane (Braz-Bd-oxane), brazilin-betanidin-ether (Braz-Bd-ether) and brazilein-betanidin-ether (Braze-Bd-ether), obtained from the etherification and bi-etherification reactions of brazilin dye and brazilein dye with betanidin dye. The equilibrium geometrical structure properties, frontier molecular orbital, electrostatic surface potential, reorganization energy, chemical reactivities, and non-linear optical properties of the studied dyes were investigated using density functional theory (DFT)/B3LYP methods, with 6-31+G(d,p) basis sets and LANL2DZ for light atom and heavy atoms respectively. The optical-electronic properties were calculated using TD-DFT/B3LYP/6-31+G(d,p) for isolated dye and TD-DFT/CAM-B3LYP/6-31G(d,p)/LANL2DZ for dyes@(TiO2)9H4. The results reveal that spectra for Braz-Bd-oxane and Braze-Bd-ether complexes red-shifted compared to the individually selected dyes. The simulated absorption spectra of the adsorbed dyes on (TiO2)9H4 are red-shifted compared to the free dye. Moreover, Braz-Bd-oxane and Braz-Bd-ether exhibit better charge transfer and photovoltaic properties than the selected natural dyes forming these complexes. Based on the dyes' optoelectronic properties and photovoltaic properties, the designed molecules Braz-Bd-oxane and Braze-Bd-ether are considered better candidates to be used as photosensitizers in dye solar cells.

Investigation of effects of interlayer interaction and biaxial strain on the phonon dispersion and dielectric response of hexagonal boron arsenide

In this study, the effects of interlayer interaction and biaxial strain on the electronic structure, phonon dispersion and optical properties of monolayer and bilayer BAs are studied, using first-principles calculations within the framework of density functional theory. The interlayer coupling in bilayer BAs causes the splitting of out-of-plane acoustic (ZA) and optical (ZO) mode. For both structures, positive phonon modes across the Brillouin zone have been observed under biaxial tensile strain from 0 to 8%, which indicate their dynamical stability under tensile strain. Also, the phonon band gap between longitudinal acoustic (LA) and longitudinal optical (LO)/transverse optical (TO) modes for monolayer and bilayer BAs decreases under tensile strain. An appreciable degree of optical anisotropy is noticeable in the materials for parallel and perpendicular polarizations, accompanied by significant absorption in the ultraviolet and visible regions. The absorption edge of bilayer BAs is at a lower energy with respect to the monolayer BAs. The results demonstrate that the phonon dispersion and optoelectronic properties of BAs sheet could as well be tuned with both interlayer interaction and biaxial strain that are promising for optoelectronic and thermoelectric applications.

Electronic structure, optical properties and high thermoelectric figure of merit in iron phthalocyanine polymer: FP-LAPW comparative studies

The comparative study of optoelectronic and thermoelectric properties of Iron phthalocyanine polymer, FePc, has been performed using the full-potential linearized augmented plane wave (FP-LAPW) method. The results show that the band gap of FePc is 2.039 eV with two deep trap bands. Optical spectra such as the real and imaginary parts of the dielectric function, reflectivity, electron energy loss spectroscopy, refractive index, extinction, and absorption coefficients are calculated and the main peaks are compared with the available experimental data. Calculated optical spectra are in good agreement with the experimental data of diethylamine and triethylamine polymers. The maximum values of 2190.2 μVK−1 and 1.02 are obtained for the Seebeck coefficient and the figure of merit ZT at 300 K for the chemical potentials near the Fermi level, respectively. The results show that FePc polymer is a good candidate for optoelectronic device applications.

First-principles modeling of molecular adsorption on an InSe monolayer

In this paper, it is demonstrated that the calculated physical adsorption energies, substrate–adsorbent distances and substrate distortions strongly depend on the size of the employed supercell and particularly on the type of optimization in the case of very flexible two-dimensional monolayers, such as indium (II) selenide (InSe). It has been established that calculations with optimization of only atomic positions and calculations with optimization of atomic positions and lattice parameters can give energies of different signs and values. In-plane (stretching and compression) and out-of-plane (ripple formation) distortions also lead to significant changes in the calculated adsorption energies. The influence of substrate flexibility and adsorption on the electronic structure and optical properties is also discussed.

Electronic Structure and Optical Properties of the Adducts of Er3+ and Yb3+ Thenoyltrifluoracetonate with TPPO

Electronic Structure and Optical Properties of the Adducts of Er3+ and Yb3+ Thenoyltrifluoracetonate with TPPO

X-ray Photoelectron Spectroscopy and Optical Studies of Assembled Gold Clusters

The electronic structures and optical properties of assembled gold nanoclusters prepared through wet chemical method have been investigated. The scanning electron microscopic analysis revealed gold clusters growing into beaded nanowires. The core level electronic states of the samples analyzed using X-ray Photoelectron spectroscopy, confirm the presence of gold. Further, the shift of core 4f orbitals towards higher energy indicates the interaction between Au and ligand in comparison with the bulk counterpart. The appearance of a sharp peak at 371 nm in the optical absorption spectrum refers to the excitonic transition between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) states. The luminescence peak observed at 403 nm and 615 nm may be due to the transitions between HOMO-LUMO gaps and the surface states and/or states originating from cluster-ligand interactions, respectively.

Unveiling the electronic structure and optical properties of two-dimensional TMDCs: first-principles study

Transition metal dichalcogenide (TMDC) materials are considered extremely efficient materials with significant applications in photovoltaics and optoelectronics. Here, the electronic structure and optoelectronic features of new transition metal-containing dichalcogenides are studied using state-of-the-art density functional theoretical calculations. For the analysis of the electronic band structures, we employed a modified Becke-Johnson potential. According to the band structure analysis, Platinum-based dichalcogenides possess an indirect band profile, having the valence band maximum and the conduction band minimum situated at discrete symmetry regions. At the same time, the zirconium-based materials have a direct type band structure at the same Γ-point. We calculated cohesive energies and formation energies to assess the stability of these materials. The substantial optical parameters such as the two parts of the dielectric constant, absorption coefficients, energy loss functions, reflectivity spectra, refractive index, real optical conductivity spectra, spectra, and the extinction coefficients, are calculated. These findings provide insight into potential applications in optoelectronic devices. The calculated band gaps and refractive index revealed an inverse relationship. This research aims to make a significant contribution to the advancement of various and possibly gainful semiconducting technologies, as well as their practical applications.

Ti3C2-MXene/NiO Nanocomposites-Decorated CsPbI3 Perovskite Active Materials under UV-Light Irradiation for the Enhancement of Crystal-Violet Dye Photodegradation

Ti3C2-MXene material, known for its strong electronic conductivity and optical properties, has emerged as a promising alternative to noble metals as a cocatalyst for the development of efficient photocatalysts used in environmental cleanup. In this study, we investigated the photodegradation of crystal-violet (CV) dye when exposed to UV light using a newly developed photocatalyst known as Ti3C2-MXene/NiO nanocomposite-decorated CsPbI3 perovskite, which was synthesized through a hydrothermal method. Our research investigation into the structural, morphological, and optical characteristics of the Ti3C2-MXene/NiO/CsPbI3 composite using techniques such as FTIR, XRD, TEM, SEM–EDS mapping, XPS, UV–Vis, and PL spectroscopy. The photocatalytic efficacy of the Ti3C2-MXene/NiO/CsPbI3 composite was assessed by evaluating its ability to degrade CV dye in an aqueous solution under UV-light irradiation. Remarkably, the Ti3C2-MXene/NiO/CsPbI3 composite displayed a significant improvement in both the degradation rate and stability of CV dye when compared to the Ti3C2-MXene/NiO nanocomposite and CsPbI3 perovskite materials. Furthermore, the UV–visible absorption spectrum of the Ti3C2-MXene/NiO/CsPbI3 composite demonstrated a reduced band gap of 2.41 eV, which is lower than that of Ti3C2-MXene/NiO (3.10 eV) and Ti3C2-MXene (1.60 eV). In practical terms, the Ti3C2-MXene/NiO/CsPbI3 composite achieved an impressive 92.8% degradation of CV dye within 90 min of UV light exposure. We also confirmed the significant role of photogenerated holes and radicals in the CV dye removal process through radical scavenger trapping experiments. Based on our findings, we proposed a plausible photocatalytic mechanism for the Ti3C2-MXene/NiO/CsPbI3 composite. This research may open up new avenues for the development of cost-effective and high-performance MXene-based perovskite photocatalysts, utilizing abundant and sustainable materials for environmental remediation.