Electronic Properties Research Articles

Solid-Solution MXenes: Synthesis, Properties, and Applications.

ConspectusMXenes, among other two-dimensional (2D) materials such as graphene, hexagonal BN, transition metal dichalcogenides (TMDs), 2D metal-organic frameworks (MOFs), and covalent organic frameworks (COFs), are the fastest growing class discovered thus far. The general formula of MXenes is Mn+1XnTx, where M, X, and Tx represent an early transition metal (Ti, V, Nb, Mo, etc.), C and/or N, and the surface functional groups (typically, O, OH, F, Cl), respectively, and n can be between 1 and 4. MXenes as a class of materials have extraordinary properties, such as high electrical conductivity, nonlinear optical properties, solution processability, scalability and ease of synthesis, redox capability, and tunable surface properties, among others; the specific properties, however, depend on their chemistry. Since the initial report of the first MXene in 2011, the research community has primarily focused on Ti3C2Tx, and the amount of research work to investigate its synthesis and properties has increased exponentially over the years. In materials science, alloying is a useful way of synthesizing new materials to improve the properties of a class of materials. Advancement of steel and synthesis of inorganic semiconductors can be regarded as some of the major historical advancements in the concept of alloying. Thus, just one year after the initial report of MXenes, the first solid-solution MXene, (TiNb)2CTx, was reported, which demonstrates the inherent chemical tunability of this class of materials.MXenes have two sites for compositional variation: elemental substitution on both the metal (M) and carbon/nitrogen (X) sites, presenting promising routes for tailoring their properties. X-site solid-solutions include carbonitride MXenes and are the least studied class of MXenes to date. Comparatively, multi-M MXenes have acquired significant attention, leading to the extreme example of high-entropy solid-solution MXenes. By using multiple M elements, a significant expansion of the structural and chemical diversity is possible, giving rise to novel chemical, magnetic, electronic, and optical properties that cannot be accessed by single-M MXenes. Solid-solution MXenes represent the largest and most tunable class of MXenes; solid-solution MXenes are those that have multiple metals that are randomly distributed on their M sites with no distinct chemical ordering. Using multiple M elements in MXenes, it is possible to synthesize novel MXene structures that cannot be produced otherwise, such as M5X4Tx MXenes. Based on their chemistry, it is possible to rationally control the electronic, optical, mechanical, and chemical properties in a way that no other class of MXenes can. In some cases, the resultant property is linearly related to the chemistry, such as the electrical conductivity, while in other cases the properties are nonlinear or emergent: optical properties, enabling these MXenes to fulfill roles that no other MXene, or 2D material, can.In this Account, we discuss the recent progress in the synthesis, properties, applications, and outlook of solid-solution MXenes. Importantly, we demonstrate how multi-M solid-solutions can be used to tailor properties for specific applications easily.

Device simulation study of multilayer MoS2Schottky barrier field-effect transistors.

Molybdenum disulfide (MoS2) is a representative two-dimensional layered transition-metal dichalcogenide semiconductor. Layer-number-dependent electronic properties are attractive in the development of nanomaterial-based electronics for a wide range of applications including sensors, switches, and amplifiers. MoS2field-effect transistors (FETs) have been studied as promising future nanoelectronic devices with desirable features of atomic-level thickness and high electrical properties. When a naturally n-doped MoS2is contacted with metals, a strong Fermi-level pinning effect adjusts a Schottky barrier and influences its electronic characteristics significantly. In this study, we investigate multilayer MoS2Schottky barrier FETs (SBFETs), emphasizing the metal-contact impact on device performance via computational device modeling. We find that p-type MoS2 SBFETs may be built with appropriate metals and gate voltage control. Furthermore, we propose ambipolar multilayer MoS2 SBFETs with asymmetric metal electrodes, which exhibit gate-voltage dependent ambipolar transport behavior through optimizing metal contacts in MoS2 device. Introducing a dual-split gate geometry, the MoS2SBFETs can further operate in four distinct configurations: p - p, n - n, p - n, and n - p. Electrical characteristics are calculated, and improved performance of a high rectification ratio can be feasible as an attractive feature for efficient electrical and photonic devices.

Point defect distributions in ultrafast laser-induced periodic surface structures on β-Ga2O3

β-Ga2O3 has received widespread attention due to its ultrawide bandgap, which potentially permits applications in extreme conditions. Ultrafast laser irradiation of β-Ga2O3 provides a means for exploring the response of the material under such conditions, which could result in the generation of point defects as well as a localized modification of structural features that could yield properties that differ from the pristine surface. However, an understanding of defects generated by femtosecond laser irradiation in the vicinity of laser-induced periodic surface structures (LIPSS) remains to be explored. We correlate topographic features with optical and electronic properties by combining near-nm scale resolution cathodoluminescence with Kelvin probe force microscopy. Defects are found to correlate with crystalline order and near-surface morphology, as well as changes in work function. They are also suggested to be closely related to the formation of high spatial frequency LIPSS. These results suggest a need for precise tuning of laser irradiation conditions as well as possible post-processing to control defects in future Ga2O3 devices.

Chalcogen and halogen surface termination coverage in MXenes—structure, stability, and properties

MXenes are a diverse family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides. They can be synthesized through both top-down approaches, such as selective etching of A-layers from MAX phases using acids or molten salts, and bottom-up approaches, such as direct synthesis using chemical vapor deposition. However, the degree of the surface termination coverage depends on the synthesis route and is one key parameter for controlling its properties. This study focuses on halogen- and chalcogen-terminated MXenes, particularly M2CTx where M = Ti, Zr, V, Nb, Ta, and T = S, Se, Te, Cl, Br, I, and with surface termination coverage ranging from 100% (ideal, x = 2) to 50% (x = 1). The incorporation of oxygen on vacant termination sites was also evaluated. Using density functional theory (DFT) calculations, we investigated the structural, electronic, and mechanical properties of these MXenes. Our findings reveal that non-ideal termination coverage (x < 2) is more favorable for MXenes terminated with a larger size of T, such as Ti2CBrx, Nb2CClx, and Ta2CClx, and leads to mixed termination sites and lower binding energies. A reduced binding energy may facilitate delamination into single sheets, however, too low termination coverage may also cause structural collapse. Electronic properties showed an increased number of states at the Fermi level under non-ideal coverage, potentially enhancing the conductivity. Mechanically, we find the moduli of MXenes to be comparable to other 2D materials, such as transition metal chalcogenides and hexagonal boron nitride, indicating their suitability for applications requiring flexibility and durability. This study underscores the potential of tailoring MXene properties through precise control of termination coverage and composition, paving the way for enhanced application-specific performance.

Exploring penta-ZnS2 monolayer as potential gas sensor for toxic gases based on first principles

To gain a deeper understanding of the application of ZnS2 monolayer in gas sensors, this paper predicts the electronic properties and gas sensing performance of CO, CH4, Cl2, H2S, NO and NH3 gas molecules adsorbed on ZnS2 monolayer based on first principles research. The results show that ZnS2 is sensitive to CO, Cl2, H2S, NO and NH3 by chemisorption and to CH4 by strong physisorption. The adsorption of gases effectively changes the electronic properties and gas sensing properties on ZnS2, and the bandgap of the adsorbed system changes significantly compared with the intrinsic ZnS2, and the characteristics of the work function can effectively distinguish various gases. Our calculations are of great significance for exploring the sensing applications of ZnS2 monolayer as a new member of the gas sensor family, and we expect that this work will provide new perspectives and theoretical foundations for the possible applications of ZnS2 monolayer in the sensing and processing of CO, CH4, Cl2, H2S, NO and NH3 gases.

A study of optical properties and electron energy loss spectra of ZnS by linear response theory

Abstract The linear response theory has been applied to study the optical properties and electron energy loss spectra of ZnS. The ground state is built using the Full-Potential Linearized Augmented Plane Wave method. Thereafter, the electronic properties such as band structure and density of states are calculated. Calculations of electron energy loss spectra and optical properties are performed on the top of these ground state electronic properties. The calculations are performed using three exchange-correlation kernels namely, adiabatic local density approximation, long range contribution, and the bootstrap. The random phase approximation is also considered. An approach proposed by us to find the material dependent parameter α is used in long range contribution kernel to capture more accurate optical properties. Three values of α viz 0.78, 1.09, and 1.22 are considered. It is observed that the α = 0.78 gives very good results. This proposed scheme is found to work very well for ZnS also. The effect of local field and electron-hole interaction on the spectra is examined. For example after incorporating local field effect the high frequency dielectric constant ε∞ [i.e. ε1 (E→0eV)], reduces by 9.19, 12.26, 13.51 and 11.02% for random phase approximation, adiabatic local density approximation, long range contribution and bootstrap kernel respectively. Plasmon peak positions are found using the three kernels and random phase approximation. A good accord with experimental results is noted after incorporating local field effects. It is observed that local field effect causes redshift of prominent peak (i.e. Plasmon peak) in electron energy loss spectra by 0.61 eV.

Roles of defects in perovskite CsPbX3 (X=I, Br, Cl): a first- principles investigation

Inorganic lead halide perovskite CsPbX3 (X=I, Br, Cl) have a promising application in optoelectronic fields due to their excellent photovoltaic properties. The defects, which have a significant impact on the performance of materials, are often introduced during the synthesis process. However, there is still a lack of systematic theoretical investigation of the effects of these defects. In this study, the effects of vacancies and H-atom interstitial point defects on the structural, electronic and optical properties of CsPbX3 are systematically investigated by using first-principles approach based on density-functional theory. The calculated results show that the introduction of different defects have significantly effect on the band gap, effective mass, semiconductor properties, ion migration and optical absorption coefficient of the perovskite materials. It is also found that VCs and VPb defects introduce shallow transition levels that do not negatively impact the optoelectronic properties. However, VX and interstitial H defects generate deep transition levels within the bandgap, which acts as non-radiative recombination centers and reduce the optoelectronic performance of the perovskite material. This study contributes to the understanding of the nature of halide chalcogenides and optimally regulating the performance of optoelectronic devices.

Study of Structural, Magnetic, and Physical Properties in Nano Cobalt Ferrite by Computational Analysis

Abstract Using the DFT+U method, we investigated the structural, magnetic, electronic, mechanical, thermal, optical, thermoelectric, and thermodynamic properties of the CoFe2O4 system. The GGA approximation was employed to calculate the exchange-correlation potential. The CoFe2O4 has a metallic bond and is ductile, as determined by Poisson's and Pugh's ratio mathematical calculations. Transport properties such as the figure of merit, thermal (k/τ) and electrical (σ/τ) conductivities, power factor, and Seebeck coefficient were computed to explain the thermal behavior of this spinel. Additionally, optical parameters like energy loss L(ω), absorption coefficient α(ω), dielectric constants ε(ω), optical conductivity σ(ω), reflectivity R(ω), extinction coefficient k(ω), and refractive index n(ω) are investigated. Lastly, we study how the magnetic phase transitions, magnetization, critical temperature, and specific heat capacity of this material are affected by an external magnetic field at constant pressure. Around the critical temperature, magnetic entropy and relative cooling capacity for various external magnetic fields are obtained.&amp;#xD;

First-principle investigation of stability, magnetic moments, electronic and optical properties of Fe with GGA and GGA+U

First-principle investigation of stability, magnetic moments, electronic and optical properties of Fe with GGA and GGA+U

Structural, electronic, and mechanical properties of transition metal porphyrin-like graphenes, and their application in hydroxylation of methane

Structural, electronic, and mechanical properties of transition metal porphyrin-like graphenes, and their application in hydroxylation of methane

Enchanting optical, electronic, and mechanical properties of the sodium based Na2MgSiZ6 (Z = I, Br, Cl) halides have been explored through DFT.

Abstract Materials with the perovskite structure are extensively studied because of exhibiting enormous properties and these materials have proven their importance in many ways of our daily life. In the present approach Na2MgSiZ6 (Z = I, Br, Cl) halides were extensively studied and it was realized that all these halides display semiconducting nature having indirect band gaps. The semiconducting nature of the Na2MgSiZ6 (Z = I, Br, Cl) halides were also confirmed from their TDOS results as well. The optimized values of the lattice constants acquired were: 11.70 Å, 10.4 Å, &amp; 10.22 Å for the Na2MgSiI6, Na2MgSiBr6, &amp; Na2MgSiCl6, respectively. Moreover, higher value of volume was observed for the Na2MgSiI6 compound; while smallest value was seen for the Na2MgSiCl6 compound. Na2MgSiCl6 compound elucidated brittle nature; however, Na2MgSiBr6 and Na2MgSiI6 were found to have ductile nature. All the three materials showed attractive values of optical conductivities, which make these investigated materials as befitting candidates for the solar cells, LEDs, detectors, and various other optoelectronic devices. From the negative values of formation energies for all the Na2MgSiZ6 (Z = I, Br, Cl) halides, it was comprehended that these compounds can be synthesized practically.&amp;#xD;

Synthesis, phase composition, electronic and spectroscopic properties of cobalt-doped aluminum oxynitride

The article presents a comprehensive study of the synthesis, phase formation, electronic structure, and optical properties of cobalt-doped aluminum oxynitride Al5O6N (AlON) in the concentration range of 0.01–5 at%. The solubility limit of cobalt in AlON is found to be 0.1–0.2 at% compared to Al. No corundum is detected even at the lowest cobalt content (0.01 at%), but a low amount of AlN and Co or Co4N is observed. Cobalt ions are incorporated into AlON with the typical oxidation state of Co2+ and form Co–O and Co–N bonds in a ratio of 92/8. The bandgap (Eg) and lattice parameters of AlON:Co are found to be in the range of 5.72–5.84 eV and 7.9411–7.9539 Å, respectively, and are influenced by the oxygen content. Pulsed cathodoluminescence spectra show five emission bands, with some attributed to (VAl–ON)-type defects. The luminescence intensity of AlON:Co decreases with higher contents of cobalt ions.

First-Principles Calculations of the Structural, Mechanical, Optical, and Electronic Properties of X2Bi4Ti5O18 (X = Pb, Ba, Ca, and Sr) Bismuth-Layered Materials for Photovoltaic Applications

For the first time, density functional theory (DFT) calculations have been employed for the measurement of the structural, mechanical, optical, and electrical properties of a bismuth-layered structure ferroelectrics (BLSFs) family member possessing an orthorhombic structure with Cmc21 space group. Based on the exchange–correlation approximation, our calculations show that Pb2Bi4Ti5O18 possesses an indirect band gap, while the materials X2Bi4Ti5O18 (X = Ba, Ca, and Sr) demonstrate direct band gap, where the estimated density functional fundamental band gap values lie between 1.84 to 2.33 eV, which are ideal for photovoltaic applications. The optical performance of these materials has been investigated by tuning the band gaps. The materials demonstrated outstanding optical characteristics, such as high absorption coefficients and low reflection. They exhibited impressive absorption coefficient (α = 105 cm−1) throughout a broad energy range, especially in the visible spectrum (105 cm−1 region). The findings show that the compounds demonstrate lower reflectivity in the visible and UV regions, making them suitable for single-junction photovoltaic cells and optoelectronic applications. The Voigt–Reuss–Hill averaging technique has been employed to derive elastic parameters like bulk modulus (B), Young’s modulus, shear modulus (G), the Pugh ratio (B/G) and the Frantesvich ratio (G/B) at 0.1 GPa. The mechanical stability of the compounds was analyzed using the Born stability criteria. Pugh’s ratio and Frantesvich’s ratio show that all the compounds are ductile, making them ideal for flexible optical applications.

Harnessing high potential benzothiazole chalcones against dengue virus NS5 protein: A multi-faceted theoretical study through molecular docking, ADME, and DFT

Chalcones bearing tetralone, indanone and benzothiazole cores were synthesized successfully using a general Claisen-Schmidt condensation protocol. The prepared compounds were purified and structurally analyzed by 1H, 13C NMR, and FT-IR techniques. A multi-faceted theoretical approach, combining Density Functional Theory (DFT), molecular docking, and ADME predictions, was employed to evaluate their therapeutic potential. DFT calculations at the B3LYP/def2-TZVP level revealed key electronic properties, with TD3 compound demonstrating the highest chemical reactivity. Molecular Electrostatic Potential (MEP) and Reduced Density Gradient (RDG) analyses provided insights into the compounds' non-covalent interactions and charge distributions. Molecular docking studies against the NS5 protein (PDB: 6KR2) showed superior binding affinities for all three compounds compared to the control ligand SAH, with TD3 exhibiting the lowest binding energy (−8.41 kcal/mol) and theoretical inhibition constant (689.31 nM). ADME predictions indicated favorable drug-like properties with concerns regarding aqueous solubility and potential P-glycoprotein interactions. Toxicity evaluations highlighted challenges, particularly in hepatotoxicity and carcinogenicity. The study identified TD3 as a promising lead compound for Dengue Virus NS5 inhibition, while also emphasizing the need for targeted modifications to address toxicity concerns. This research not only contributes to anti-dengue drug discovery efforts but also provides a robust methodological framework for the theoretical evaluation of similar small compounds in future investigations.

The electronic and optical properties of group III-V semiconductors: Arsenides and antimonides

Investigating the structural, electronic, and optical properties of zinc-blende III-V semiconductors, particularly arsenides, and antimonides, which are crucial for optoelectronic devices such as transistors, infrared detectors, and quantum technologies due to their wide range of direct bandgaps. In this work, we have employed a first-principles approach integrating G0W0 with the HSE06 hybrid functional and spin–orbit coupling (SOC) to study their fundamental properties. Traditional Density Functional Theory (DFT) methods, particularly those using Generalized Gradient Approximation (GGA) PBE functionals, tend to underestimate bandgaps, leading to discrepancies with experimental results. To address this, our study corrects the bandgap underestimation and refines the calculation of optical constants, including the dielectric function, refractive index, extinction coefficient, and absorption coefficient. Moreover, the optimized lattice constants and electronic properties derived from our computational model strongly correlate with experimental data, demonstrating the model’s reliability in predicting material properties. The findings suggest that our methods can be applied to arsenides and antimonides, offering a pathway to designing materials with optoelectronic properties involving III-V compounds and their complex heterostructures for advanced device applications.

Ionic conduction and cathodic properties of CaMO3 (M=Fe and Mn) electrode materials via molecular dynamics and first-principles simulations

Calcium-ion(Ca-ion) batteries are gaining ever-increasing attention for next-generation energy storage systems due to affordability, highly abundant, high energy density, high theoretical capacity, and low redox potential close to Li-ion. In this work, we deployed the first-principles and classical molecular dynamics simulations to investigate the electronic and diffusive properties of isostructural ternary perovskite CaMO3 (M= Fe and Mn). The transport properties at various temperatures from ion dynamics and electronic properties of CaMO3 perovskites are examined using classical molecular dynamics and quantum mechanical simulations, respectively. We present the microscopic origin of the diffusion of multivalent ions like Ca2+ within the crystal structure of perovskite material and the effects of two transition metals, manganese and iron. Dynamic studies of Ca-ions were performed using molecular dynamic simulation, which depicts the diffusivity and conductivity of Ca-ion in CaMO3 material. We find that the diffusivity in both the crystals increases with temperature; as a result, conductivity increases. Among both the crystals, CaFeO3 requires less activation energy for diffusion and ionic conduction than CaMnO3. Using density functional theory, we calculated specific capacity, electronic density of states, phase stability and equilibrium cell voltage, and charge transfer process during intercalation-deintercalation from first-principles calculations. The electronic behavior of these materials shows that CaFeO3 has better electronic and transport properties than CaMnO3.

Optimizing the photocatalytic properties Er-doped bismuth ferrite for the degradation of mixed dyes under sunlight irradiation

In this study, the erbium (Er)-doped bismuth ferrite (BiFeO3/BFO) with the chemical formulation of Bi1-xErxFeO3 (x = 0, 5, 10, and 15 mol%) are synthesized using hydrothermal method. It is found that Er-doping induces structural distortions in BFO, leading to improved electronic and optical properties in BFO as confirmed by XRD, XPS, UV-visible absorption and PL spectral analysis. The particle size of BFO is found to be decreasing in the range of 60-30 nm with Er-doping, observed from their TEM images. Further, the photocatalytic efficiencies of the synthesized Bi1-xErxFeO3 nanoparticles are studied towards the degradation of methylene blue (MB), rhodamine B (RhB) dyes and their mixture under solar irradiation. While all the Er-BFO showed improved efficiency compare to pristine, the 10 mol% Er-doped BFO showed the highest degradation of ∼99 and 94% for MB and RhB dyes, respectively in 180 minutes. More interestingly, while the pristine BFO selectively degraded only the MB dye in the MB-RhB mixture, the Er-BFO greatly degraded both the dyes in the mixture, which attributed to their improved electronic, electric field and optical band structure properties, especially to the 10% Er-BFO degraded around 93 and 78% of MB and RhB dye in the MB-RhB mixture. The cyclical use of 10 mol% Er-BFO is tested toward the degradation dye mixture, which showed a consistent photocatalytic performance up to 5 cycles, suggesting that the Er-doped BFO is photochemically stable and suitable for sustainable photocatalytic applications.

Small compressive strain tuning of α-TeO2 and β-TeO2 polymorphs: Electronic, linear, and nonlinear optical properties from first-principles calculations

This study examines the effects of 2 % compressive strain on the structural, electronic, and optical properties of α-TeO2 and β-TeO2 polymorphs. α-TeO2’s bandgap increases from 3.64 eV to 3.70 eV, while β-TeO2’s decreases to 3.53 eV. Lattice parameters uniformly reduce in α-TeO2, but vary in β-TeO2. PDOS analysis shows O-2p and Te-5p states dominate near the band edges. Optical behavior is anisotropic, with enhanced polarizability and refractive indices under strain. Nonlinear optical properties improve, especially in susceptibility components, relevant for second-harmonic generation. Born Effective Charges show increased Te polarization and reduced oxygen polarization, impacting dielectric responses.

Machine-learning assistant DFT study of half-metallic full-Heusler alloy N2CaNa: Structural, electronic, mechanical, and thermodynamics properties

We studied the structural, electronic, mechanical, and thermodynamic properties of N2CaNa full Heusler alloys using density functional theory (DFT). Results for the structural analysis establish structural stability with a minimum formation energy of 29.9 eV. The compound is brittle and mechanically stable, having checked out with the Pugh criteria. The B/G ratio of bulk modulus B to shear modulus G for N2CaNa is 4.766, hence the material is ductile. N2CaNa alloy is ductile in nature. The Debye model correctly predicts the low-temperature dependence of heat capacity, which is proportional to Debye’s T3 law. Just like the Einstein model, it also recovers the Dulong–Petit law at high temperatures, suggesting the thermodynamic stability of the compounds at moderate temperatures. The results demonstrate potential N2CaNa for applications in spintronics, structural engineering, and other fields requiring materials with tailored properties.

Tailoring polypyrrole morphology and electronic properties through CTAB-SDS self-assembly

Tailoring polypyrrole morphology and electronic properties through CTAB-SDS self-assembly