Optical Absorption Coefficient Research Articles

Effects of hydrostatic pressure, temperature, and position-dependent mass on the nonlinear optical properties of triple delta-doped GaAs quantum well

In this study, we thoroughly investigate the impacts of hydrostatic pressure, temperature, and position-dependent mass (PDM) on the nonlinear optical properties of asymmetric triple δ-doped GaAs quantum wells. Our analysis covers total optical absorption coefficients, relative refractive index changes, nonlinear optical rectification, second harmonic generation, and third harmonic generation. Initially, we employ PDM to solve the time-independent Schrödinger equation using the diagonalization method under effective mass and parabolic band approaches, considering pressure and temperature dependencies. Utilizing the first four energy eigenvalues and eigenfunctions, we apply the compact density matrix method to compute the system’s nonlinear optical properties numerically. The results indicate a shift in optical property peak positions toward lower (higher) energy spectra with increasing hydrostatic pressure (temperature). Furthermore, the influence of PDM shifts the system’s optical properties toward the higher energy spectrum, resembling the effect of temperature. From an experimental and theoretical perspective, one of the topics that researchers work on most is GaAs-based δ-doped systems (δ-doped heterojunction bipolar transistors, δ-doped field effect transistors, δ-multiple independent gate field effect transistors, etc.). We believe these findings will provide valuable insights for the researchers involved in GaAs-based δ-doped optoelectronic device design.

Optical absorption properties in multi-layer InGaN/GaN core-shell quantum dots: The influences of ternary mixed crystal effect and hydrogen-like impurity

Based on the effective mass approximation and the compact density matrix theory, the electronic states and optical absorption properties of intersubband transitions between the conduction-band energy levels in zinc-blende InGaN/GaN/InGaN/GaN core-shell quantum dots (CSQDs) are investigated by using the finite difference method. The effects of hydrogen-like impurity and In component on the wave functions, transition energies, and optical absorption properties are discussed in detail. The results show that hydrogen-like impurity can cause the peak positions of optical absorption coefficients (OACs) and refractive index changes (RICs) to move to high energy area, and the peak values of OACs rise. Increasing In component of InGaN crystal in the core region of a CSQD has the same effect. But an opposite tendency will be found when increasing In component in the shell-well of a CSQD, i.e. optical absorption peaks move to low energy area and their values decrease. Comparing to the shell-well, the core region has more powerful confinement effect on electrons. So the better absorption properties are more likely to be obtained for this type of multi-layer InGaN/GaN CSQDs when In component in the core is larger than that in the shell-well.

First-principles calculations to investigate Structural, Electronic, mechanical and Optical Properties of SrAlO3 Compound

In this study, density functional theory calculations were used to investigate the structural, electronic, mechanical, and optical properties of SrAlO3 perovskites. Calculations were performed using WEIN2K with the Generalized Gradient Approximation (GGA) and modified Becke-Johnson (MBJ) methods. The present compound shows large band gap around 5.67 eV for GGA method and 6.70 eV for MBJ method. The band structure (BS) and partial density of states (PDOS) reveal the predominant involvement of the oxygen-p orbital in the valence band, while the Al and Sr-s, p and d orbital contribute significantly to the conduction band, that play a significant role in determining the electronic and optical properties. Using the GGA and MBJ methods, the optical properties of SrAlO3 have been determined in terms of optical conductivity, dielectric constant, absorption coefficient, energy loss, optical reflectivity, and refractive index. It has been noted that the features present in the optical absorption spectra obtained experimentally match those of the simulated spectra featuring an oxygen vacancy. We use elastic constants to describe a material's mechanical properties. Under normal conditions, these materials' elastic constants demonstrate their mechanical stability. We meticulously determined the elastic constants by graphing the directional variations of compressibility, Young's modulus, and shear modulus. Our findings indicate that these chemicals have high elastic constants. Furthermore, we collect and interpret the phonon spectra. Complete phonon dispersion simulations validate the dynamic stability of the SrAlO3.

Unveiling the structural and optoelectronic properties of (P, Bi, Sb)-doped GaAs by first- principles calculations

In this work, we investigate the influence of M substitutions (M = P, Bi, and Sb) on the structural, electronic, and optical properties of gallium arsenide, GaM x As1-x for x=0,0.25,0.50,0.75,1.0 using density functional theory (DFT). We have observed that the cubic symmetry of the semiconductors in conserved, and lattice constants show a linear behavior with dopant concentration, according to Vegard’s law. Specifically, the lattice constants increased for Bi and Sb dopants, whilst decreased for P dopants. Furthermore, the bulk modulus decreased with an increase in M-concentration for all M-doped systems. The energy analysis showed that the P-doped system was the most stable system. In terms of the electronic band structure, all M-doped compounds exhibited a direct electronic band gap. The P-doped system showed a wide band gap, while the Sb-doped systems displayed a narrow band gap, both compared to pristine GaAs. The Bi-doped system showed metallic-like behavior. To gain insights into the linear optical properties of the GaM x As1-x compounds, we calculated the real and imaginary parts of the dielectric function, as well as other optical parameters such as the absorption coefficient, refractive index, extinction coefficient, and reflectivity. The results showed that P doping leads to a blue-shift in the optical absorption coefficient, while Bi and Sb doping lead to a red-shift. These findings provide valuable theoretical insights for the potential application of GaM x As1-x semiconductors in photovoltaics and optoelectronic devices.

Effect of morphology modulation and interface engineering of SnS-MoS2 heterojunction on nonlinear optical response

MoS2 base films with different morphologies were prepared by modulating the magnetron sputtering parameters, and the base films were used to induce the growth of SnS with different structures, forming columnar and worm-like SnS-MoS2 heterojunctions, which were found to have excellent nonlinear absorption properties and their properties could be modulated by the morphology of the films by Z-scanning tests. The tunable morphology and crystalline quality of the films were characterized using scanning electron microscopy, atomic force microscopy and X-ray diffraction techniques and explained using the Stranski-Krastanow growth mechanism. The Raman spectrum of the heterojunction shows the A1g vibrational peak at 320 cm−1 and the appearance of Sn4+ in the X-ray photoelectron spectroscopy confirms the existence of S-Sn-S charge transfer channels between the interfaces. The fine spectra of all the elements in the X-ray photoelectron spectroscopy data as well as the characteristic absorption peaks in the absorption spectra confirm the formation of heterojunctions, and the constructed heterojunctions are determined to be type-II heterojunctions using the method of the core energy level. Heterojunction was determined to be a type-II heterojunction by using the core energy level method. The photoluminescence peak quenching of the heterojunction indicates that there is a process of charge transfer between the interfaces, and the type-II heterostructure of SnS-MoS2 makes the nonlinear absorption performance in the 800 nm band regulated by the morphology of the material. The nonlinear optical absorption coefficient is two orders of magnitude higher than that of the pure materials, and the nonlinear absorption performance of the worm-like SnS-MoS2 heterojunction is superior to that of the columnar SnS-MoS2 heterojunction, which is attributed to the larger interfacial contact area, the better crystalline quality, and the more efficient carrier interfacial transport capability. These tunable type-II SnS-MoS2 heterojunctions with ultrafast nonlinear optical absorption have a positive impact on practical applications such as optical limiter devices and all-optical switching devices.

Bilayer Borophenes Exhibit Silicon‐Like Bandgap and Carrier Mobilities

AbstractBorophene, a boron analogue of graphene, is typically metallic, while all bulk boron phases are insulating. Here, we predict by first‐principles calculations that recently synthesized bilayer borophene, being suggested to be composed of two stacked v1/12 sheets, is a semiconductor with a bandgap of 1.13 eV, almost the same as that of silicon. It is shown that the stacking mode between two boron sheets as well as the density and pattern of the interlayer boron‐boron (B─B) bonds are the key factors for opening the bandgap in the otherwise metallic boron sheet. Moreover, the bilayer borophene exhibits electron mobility of 878.6 cm2 V−1 s−1 and a significantly higher optical absorption coefficient in the visible region than silicon. These excellent electronic and optical properties hosted in a two atom‐thick space, together with high thermal and mechanical stability, position the bilayer borophene as a promising nanomaterial for maintaining the miniaturization of electronics.

Fe/LiNO3/TiN co–modified MgO for enhanced thermochemical energy storage performance in MgO/Mg(OH)2 cycles

MgO/Mg(OH)2 thermochemical energy storage can convert solar energy and industrial waste heat into forms that are easier to store and transport by cyclic hydration/dehydration reactions. To achieve excellent energy storage performance, cyclic stability and optical absorption capability of MgO/Mg(OH)2, Fe/LiNO3/TiN co–modified MgO were synthesized for energy storage cycles by wet-mixing method. The energy storage performance, cyclic stability and dehydration kinetics of Fe/LiNO3/TiN co–modified MgO were studied in dual fixed–bed system and simultaneous thermal analyzer. The experimental results show that the Fe and LiNO3 in the composite not only increase the hydration conversion of MgO by 6.3 times at 30 min, but also reduce the dehydration temperature and dehydration activation energy of Mg(OH)2 by 99.4 °C and 64 %, respectively. TiN overcomes aggregation of MgO and sustains the excellent porous structure, which results in only a 9 % decrease in energy storage performance of Fe/LiNO3/TiN co–modified MgO after 15 energy storage cycles. Subsequently, TiN significantly strengthens the optical absorption performance of Mg(OH)2 and photothermal temperature under xenon-lamp simulated sunlight radiation. Furthermore, density functional theory calculation reveals that Fe and Li enhance the adsorption of H2O on MgO model and reduce energy barrier for hydration reactions by 62.76 %, while TiN effectively inhibits MgO clusters migration within the material and enhances the optical absorption coefficient. Hence, Fe/LiNO3/TiN co–modified MgO shows significant research value in MgO/Mg(OH)2 energy storage process.

Electric field-induced modulation of electronic and optical properties in doped CdTe/CdS core/shell quantum dots embedded in an oxide matrix

This work presents a theoretical analysis of a CdTe/CdS core/shell quantum dots embedded in a dielectric oxide matrix under the influence of hydrogenic impurity and the applied electric field intensity. The eigenstates and their corresponding eigenfunctions are computed by solving the Schrodinger equation using the finite element method within the effective mass approximation. The first-order linear and third-order nonlinear optical absorption coefficients as well as the refractive index changes are computed based on the compact density matrix approach. The obtained result shows that the first-order linear and third-order nonlinear optical properties are more pronounced with the electric field, surrounding oxide matrix and the donor impurity effects. However, the first-order linear and third-order nonlinear optical absorption coefficients and refractive index changes can experience a red or blue shift under the influence of electric field, oxide matrix and hydrogenic impurity. In addition, under all conditions, the height peaks of these optical properties can be raised (fall). Our findings demonstrate the critical importance of considering the roles of electric field, the presence of donor impurity, and the capped dielectric oxide matrix in the design and fabrication of core–shell-based optoelectronic devices.

Electric field-induced electronic structure and intersubband transitions of a hydrogen molecular ion in a gaussian-type quantum ring

In this work, the influence of an external electric field on the electronic structure and intersubband transitions of a singly ionized double-donor system in a GaAs quantum ring defined by Gaussian-type potentials is investigated theoretically. Within the framework of the effective mass approach, the two-dimensional diagonalization method is used for the solution of the Schrödinger equation to obtain the eigen energies and corresponding wave functions. Numerical results reveal that the electronic energy spectrum and the linear optical absorption coefficient of the ring are remarkably affected by the strength of the lateral electric field, internuclear distance and parameters defining the confinement potential. Also, it has been shown that beyond the anti-crossing point, the wave functions exchange their symmetries without mixing, which is a characteristic feature of energy-level anti-crossing.

Chemical effect of alkaline-earth metals (Be, Mg, Ca) substitution of BFe2XH hydride perovskites for applications as hydrogen storage materials: A DFT perspective

This study investigated the effect of alkaline-earth metals (X = Be, Mg, Ca) substitution of BFe2XH perovskite materials and the potential applications for hydrogen storage utilizing density functional theory (DFT) approach at the GGA-PBE and the HSE06 methods. The mechanical properties of the studied systems demonstrate the mechanical stability of BFe2MgH, making it the most mechanically robust compound. While the Pugh ratio suggests that BFe2BeH was brittle, while BFe2CaH showed greater ductility, anisotropic factors confirm that all compounds are anisotropic, indicating directional dependence in their properties. The electronic band structure analysis using the HSE06 and the GGA-PBE suggests that the studied perovskites are metallic due to a calculated bandgap of zero. In terms of optical/optoelectronic properties, BFe2MgH exhibits the highest optical conductivity, absorption coefficient, and energy loss function, indicating its superior ability to absorb light and transfer electrons. For practical applications, the hydrogen storage capacity is assessed, with BFe2BeH showing the highest gravimetric and volumetric capacities. These promising results suggest the potential use of BFe2BeH as an efficient material for hydrogen storage.

Optoelectronic, thermoelectric and 3D-Elastic properties of lead-free inorganic perovskites CsInZrX6 (I, Cl and Br) for optoelectronic and thermoelectric applications

Halide perovskite materials have recently gained worldwide attention since they offer a new cost-effective way to generate renewable and green energy. In the current work, the structural, electrical, elastic, optical and thermoelectric properties of new perovskites CsInZrX6 (I, Cl and Br) were explored by density-functional theory (DFT). The results indicated that the computed lattice parameters agree really well with the current experimental and theoretical results. Moreover, the band structure profile strongly suggests that the compounds exhibit a semiconducting nature with a direct band gap. The analysis of their optical properties reveals that the perovskites possess a low reflectivity (below 23%) and a high optical absorption coefficient (106 cm−1). This is also supported by the evaluation of their calculated elastic constants and their related parameters in cubic structure which show that these compounds are brittle, mechanically stable and possess covalent bonds. On the other hand, in addition to exhibiting outstanding optoelectronic and mechanical characteristics, CsInZrCl6 also possesses dynamical stability, making it a promising candidate for application in various optoelectronic devices except for solar cells due to its relatively large bandgap. Furthermore, the BoltzTraP software was used to compute the materials’ thermoelectric properties, with the computed values of the figure of merit (ZT) for CsInZrBr6, CsInZrCl6 and CsInZrI6 being 0.76, 0.73 and 0.725, respectively. This is also a strong indication that these materials are potential for thermoelectric applications.

Narrow bandgap two-dimensional Nb2SiTe4 as broadband saturable absorber for optical switch

Nb2SiTe4 is a novel narrow-bandgap (∼0.39 eV) two-dimensional material with a high optical absorption coefficient, high carrier mobility, and outstanding air stability, which shows great application potential in broadband optical switches. In this study, high-quality layered Nb2SiTe4 nanosheets were efficiently fabricated by the mechanical exfoliation method, and the basic characterizations were carried out comprehensively. Nondegenerate pump-probe technology was implemented to systematically explore the photocarrier dynamics in the Nb2SiTe4 nanosheets, which exhibit the ultrafast recovery time of Nb2SiTe4 (∼0.3 ps). Furthermore, broadband passively Q-switched lasers operating at 1.0, 2.0, and 2.8 μm with the shortest pulse width of 380, 549, and 218 ns were achieved based on Nb2SiTe4 saturable absorber. This work demonstrates the significant advantages of an optical switch based on Nb2SiTe4 saturable absorber, including a narrow output pulse width, wide working bandwidth, high damage threshold, excellent oxidation resistance, and a straightforward synthesis method, which underscore the immense potential of Nb2SiTe4 broadband optical switches in applications involving mid-infrared lasers.

The effect of hydrostatic pressure, temperature and impurity factor on linear and nonlinear optical properties of InxGa1-xAs tuned quantum dot with modified Gaussian potential under the action of a vertical magnetic field

This study presents a detailed theoretical analysis of the effects of hydrostatic pressure, temperature, impurity factors, and external electric fields on the optical properties of InxGa1-xAs tuned quantum dot. A uniform magnetic field, directed perpendicular to the quantum dot plane, is applied. The system is excited using a monochromatic electromagnetic field, considering electron intersubband transitions. Energy levels and wave functions are determined using the parabolic band approximation and effective mass approximation. The linear and nonlinear optical absorption coefficients and refractive index changes are computed using the compact-density matrix approach and the iterative method. Numerical results indicate that the peaks of the linear and nonlinear optical absorption coefficients and refractive index changes shift towards lower energies (red shift) and higher energies (blue shift) under varying hydrostatic pressure, temperature, and impurity factor strength. Additionally, the peak values of the absorption coefficients and refractive index changes increase or decrease based on these parameter variations. These results have significant implications for the design and optimization of quantum dot-based optoelectronic devices.

Reduced charge transfer in mixed-spin ferropericlase inferred from its high-pressure refractive index

Abstract Physical properties of mantle minerals are essential for comprehensive geodynamic modeling. High-pressure experiments allow measurements of physical properties but fundamental insights into their evolution with pressure are often experimentally inaccessible. Here we report the first in situ experimental determination of the optical refractive index, its wavelength-dispersion, and optical absorption coefficient of ferropericlase up to ~140 GPa at room temperature. All these properties change gradually in dominantly high-spin (below ~50 GPa) and low-spin (above ~80 GPa) ferropericlase. However, in the mixed-spin state (i.e., significant presence of both high- and low-spin iron), the index dispersion and the absorption coefficient decrease by a factor of three and ~30%, respectively. These anomalies suggest that charge transport by small polaron is reduced in mixed-spin ferropericlase, providing fundamental insights into the factor-of-three lower electrical conductivity of ferropericlase at ~50–70 GPa.

Study on electronic, optical and photocatalytic properties of vdW heterostructures based on SnS2 and Janus PtSSe monolayers

Based on the SnS2 and Janus-PtSSe monolayers, we designed six new vdW heterostructures (HS). By investigating their structural stability, we selected out the structure most likely to be synthesized in the experiment, AA-stacking SnS2/SPtSe HS. Then we further explored its electronic, optical and photocatalytic properties, and found that this HS has a suitable band gap and considerable optical absorption coefficient. In addition, the HS possesses a typical type-II band structure and build-in electric field from SnS2 to SPtSe at the interfaces, which is benefit to separate the carries into different spaces to enhance its catalytic properties. At the end of this work, photocatalytic properties of this HS for water splitting were studied. Appropriate band edges for SnS2/SPtSe HS make it as potential photocatalyst for water splitting in acid environment.

Structural and Optical Characterization of Porous NiV2O6 Films Synthesized by Nebulizer Spray Pyrolysis for Photodetector Applications.

NiV2O6 thin films were grown on glass slides with varying thicknesses using nebulizer spray pyrolysis. The impact of thickness on the thin films' optical, structural, morphological, and electrical characteristics was systematically investigated. X-ray diffraction and micro-Raman analysis confirmed the formation of the triclinic NiV2O6 system. Surface morphology and roughness variations in the as-deposited NiV2O6 films were studied using scanning electron microscopy (SEM) and a profilometer. Optical properties, including optical band gap (Eg), extinction coefficient (k), absorption coefficient (α), and refractive index (n), were determined through optical reflectance and transmittance measurements. The optical energy gap of the as-deposited NiV2O6 films decreased from 2.02 eV to 1.58 eV with increased layer thickness. Furthermore, the photo-detectivity of the films demonstrated an enhancement corresponding to the prolonged spray time. The sensitivity values obtained for visible irradiation were 328, 511, and 433 for samples S1, S2, and S3, respectively. The obtained results can be imputed to the specific porous microstructure.

Binding Energies and Optical Properties of Power-Exponential and Modified Gaussian Quantum Dots.

We examine the optical and electronic properties of a GaAs spherical quantum dot with a hydrogenic impurity in its center. We study two different confining potentials: (1) a modified Gaussian potential and (2) a power-exponential potential. Using the finite difference method, we solve the radial Schrodinger equation for the 1s and 1p energy levels and their probability densities and subsequently compute the optical absorption coefficient (OAC) for each confining potential using Fermi's golden rule. We discuss the role of different physical quantities influencing the behavior of the OAC, such as the structural parameters of each potential, the dipole matrix elements, and their energy separation. Our results show that modification of the structural physical parameters of each potential can enable new optoelectronic devices that can leverage inter-sub-band optical transitions.

Composite nanofilms of graphene and nickel: Fabrication, cw linear and nonlinear optical properties

In this study, the preparation of graphene-nickel composite nanofilms and their linear and linear optical properties under cw regime were investigated. The films were fabricated on glass and c-Si substrates in two steps by electron beam evaporation. The surface morphology of the films showed distinctive features with smooth and rough regions related to the formation of pristine and wrinkled graphene. The complex permittivity functions of the films were calculated using Maxwell-Garnett Theory. The nonlinear optical absorption coefficient and refractive index were calculated based on the open and closed aperture z-scan measurements. Enhanced nonlinear optical properties compared to the pure nickel film were obtained. The enhancement is explained in terms of the participation of the graphene’s π-electrons in the d-band plasmonic oscillation.

Efficient visible-light-driven photocatalytic hydrogen evolution in novel type-II SnS2/Al2S2 van der Waals heterostructures

With the exacerbation of environmental pollution and the energy crisis, the development and design of environmentally friendly and efficient photocatalytic catalysts for water splitting with visible light have become particularly imperative. This study delves into the detailed investigation of the novel type-II van der Waals heterostructure of SnS2/Al2S2 utilizing first-principles calculation methods. By leveraging the advantages of indirect type-II band alignment and high carrier mobility, the efficient separation of electron-hole pairs is achieved, thereby facilitating enhanced participation of electrons and holes in photocatalytic reactions. Furthermore, the heterostructure manifests a peak optical absorption coefficient value of approximately 5.34×104 cm−1 in the visible light spectrum, accompanied by the occurrence of red-shifting, which fosters efficient absorption of visible light. It is noteworthy that under conditions of pH = 0–3.7, the heterojunction surpasses the redox potential of water splitting, concurrently displaying a substantial hydrogen evolution reaction (HER) and a high efficiency of converting sunlight to hydrogen (22.31 %). These results underscore the promising potential of the SnS2/Al2S2 heterostructure as a photocatalyst for water splitting, offering crucial theoretical support and practical guidance for the further advancement of hydrogen production via water splitting technology.

Novel bilayer 2D V2O5 as a potential catalyst for fast photodegradation of organic dyes

Two-dimensional (2D) materials have recently drawn interest in various applications due to their superior electronic properties, high specific surface area, and surface activity. However, studies on the catalytic properties of the 2D counterpart of V2O5 are scarce. In the present study, the catalytic properties of 2D V2O5 vis-à-vis bulk V2O5 for the degradation of methylene blue dye are discussed for the first time. The 2D V2O5 catalyst was synthesized using a modified chemical exfoliation technique. A massive increase in the electrochemically active surface area of 2D V2O5 by one order of magnitude greater than that of bulk V2O5 was observed in this study. Simultaneously, ~ 7 times increase in the optical absorption coefficient of 2D V2O5 significantly increases the number of photogenerated electrons involved in the catalytic performance. In addition, the surface activity of the 2D V2O5 catalyst is enhanced by generating surface oxygen vacancy defects. In the current study, we have achieved ~ 99% degradation of 16 ppm dye using the 2D V2O5 nanosheet catalysts under UV light exposure with a remarkable degradation rate constant of 2.31 min−1, which is an increase of the order of 102 from previous studies using V2O5 nanostructures and nanocomposites as catalysts. Since the enhanced photocatalytic activity emerged from the surface and optical properties of the catalyst, the current study shows great promise for the future application of 2D V2O5 in photo- and electrocatalysis.