Band Structure Properties Research Articles

First Principle Study on the Z-Type Characteristic Modulation of GaN/g-C3N4 Heterojunction.

This study investigates the stability, electronic structure, and optical properties of the GaN/g-C3N4 heterojunction using the plane wave super-soft pseudopotential method based on first principles. Additionally, an external electric field is employed to modulate the band structure and optical properties of GaN/g-C3N4. The computational results demonstrate that this heterojunction possesses a direct band gap and is classified as type II heterojunction, where the intrinsic electric field formed at the interface effectively suppresses carrier recombination. When the external electric field intensity (E) falls below -0.1 V/Å and includes -0.1 V/Å, or exceeds 0.2 V/Å, the heterojunction undergoes a transition from a type II structure to the superior Z-scheme, leading to a significant enhancement in the rate of separation of photogenerated carriers and an augmentation in its redox capability. Furthermore, the introduction of a positive electric field induces a redshift in the absorption spectrum, effectively broadening the light absorption range of the heterojunction. The aforementioned findings demonstrate that the optical properties of GaN/g-C3N4 can be precisely tuned by applying an external electric field, thereby facilitating its highly efficient utilization in the field of photocatalysis.

Core‐Shell Colloidal Quantum Dots for Energy Conversion

AbstractColloidal quantum dots (QDs) are promising building blocks in optoelectronic devices, mainly due to their size/shape/composition‐tunable properties. Core–shell QDs, in particular, offer enhanced stability, mitigated photoluminescence blinking, and suppressed non‐radiative recombination compared to plain QDs, making them highly promising for energy conversion applications such as photovoltaic devices, luminescent solar concentrators, solar‐driven hydrogen production, and light‐emitting diodes. Here, a comprehensive analysis of core–shell QDs in energy conversion technologies is provided. Emerging design strategies are explored and various synthetic methods focusing on optimizing band structure, band alignment, and optical properties are critically explored. Insights into the structure‐property relationship are discussed, highlighting recent advancements and the most effective strategies to enhance energy conversion performance. The review is concluded by addressing key challenges and proposing future research directions, emphasizing the need for rational design, precise synthesis, effective surface engineering, and the integration of machine learning to achieve optimized properties for technological applications.

A-Site Cation Chemistry in Halide Perovskites.

Metal halide perovskites are an important class of semiconductors now being implemented as photovoltaic absorbers and explored for light emission, among other device applications. The semiconducting properties of halide perovskites are deeply intertwined with their composition and structure. Specifically the symmetry, tilting, and distortions of the metal halide octahedra impact the band structure and other optoelectronic properties. In this review, we examine the various compositions of monovalent A-site cations in three-dimensional (3D) halide perovskites AMX3 (M = divalent metal; X = halide). We focus on how the A-site cation templates the inorganic metal-halide perovskite framework, resulting in changes in the crystal structure symmetry, as well as M-X bonding parameters, summarized in a comprehensive table of AMX3 structures. The A-site cation motion, effects of alloying, and 2D Ruddlesden-Popper perovskite structures with unique A-site cations are further overviewed. Correlations are shown between these A-site cation dominated structural parameters and the resulting optoelectronic properties such as band gap. This review should serve as a reference for the A-site cation structural chemistry of metal halide perovskites and inspire continued research into less explored metal halide perovskite compositions and structures.

Investigating the Impact of Stress on the Optical Properties of GaN-MX2 (M=Mo, W; X=S, Se) Heterojunctions Using the First Principles

This study used the first-principles-based CASTEP software to calculate the structural, electronic, and optical properties of heterojunctions based on single-layer GaN. GaN-MX2 exhibited minimal lattice mismatches, typically less than 3.5%, thereby ensuring lattice coherence. Notably, GaN-MoSe2 had the lowest binding energy, signifying its superior stability among the variants. When compared to single-layer GaN, which has an indirect band gap, all four heterojunctions displayed a smaller direct band gap. These heterojunctions were classified as type II. GaN-MoS2 and GaN-MoSe2 possessed relatively larger interface potential differences, hinting at stronger built-in electric fields. This resulted in an enhanced electron–hole separation ability. GaN-MoSe2 exhibited the highest value for the real part of the dielectric function. This suggests a superior electronic polarization capability under an electric field, leading to high electron mobility. GaN-MoSe2 possessed the strongest optical absorption capacity. Consequently, GaN-MoSe2 was inferred to possess the strongest photocatalytic capability. The band structure and optical properties of GaN-MoSe2 under applied pressure were further calculated. The findings revealed that stress significantly influenced the band gap width and light absorption capacity of GaN-MoSe2. Specifically, under a pressure of 5 GPa, GaN-MoSe2 demonstrated a significantly narrower band gap and enhanced absorption capacity compared to its intrinsic state. These results imply that the application of stress could potentially boost its photocatalytic performance, making it a promising candidate for various applications.

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 min. 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.

Non-metallic doped GeC monolayer: tuning electronic and photo-electrocatalysis for water splitting.

We conducted a first-principles study on the electronic, magnetic, and optical characteristics of non-metallic atoms (B, C, F, H, N, O, P, S, and Si) doped in single-layer carbon germanium (GeC). The findings indicate that the introduction of various non-metallic atoms into the monolayer GeC leads to modifications in its band structure properties. Different non-metallic atoms doped in single-layer GeC will produce both magnetic and non-magnetic properties. B-, H-, N-, and P-doped GeC systems exhibit magnetic properties, while C-, F-, O-, S-, and Si-doped single-layer GeC systems exhibit non-magnetic properties. Different non-metallic-doped single-layer GeC systems will produce semiconductor, semimetallic, and metallic properties. The C-, N-, O-, P-, S-, and Si-doped GeC systems still exhibit semiconductor properties. The H-doped GeC system exhibits semimetallic properties, while the B- and F-doped GeC systems exhibit metallic properties. Other than that, the doping of B, H, N, and P atoms can modulate the magnetism of single-layer GeC. Subsequently, we studied the influence of the doping behavior on the work function, where the work function of the single-layer GeC system doped with P atoms is very small, indicating that its corresponding doping system (P-doped GeC system) can produce a good field emission effect. In the optical spectrum, the doped systems have a certain influence in the far ultraviolet region. Furthermore, our results showed that S- and Si-doped single-layer GeC systems are conducive to photocatalysis compared to the single-layer GeC system.

Mechanical and optical properties of MgTa2O6 compounds: First principles study

In this study, we have explored the electronic, optical, and mechanical properties of MgTa2O6 compounds in both tetragonal and orthorhombic phases using the first principles based on density functional theory (DFT) methods. Considering that GGA underestimates the band gap of materials, the HSE06 hybrid functional is performed to get a more accurate result for the band structure and optical property calculations. The calculations indicate that the tetragonal and orthorhombic phases exhibit different optical characteristics, showcasing their potential as exceptional materials for UV absorption. In addition, we have thoroughly investigated the elastic properties of MgTa2O6 for these two phases, including the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio. The results indicate that the tetragonal phase has better volume deformation and shear deformation resistance, and the surface contours of Young's modulus for MgTa2O6 display anisotropy. And according to Pugh's criteria, the tetragonal phase has good ductile properties.

Evaporated Copper‐Based Perovskite Dynamic Memristors for Reservoir Computing Systems

AbstractDynamic memristors are considered as the optimal hardware devices for reservoir computing (RC) enabled by their nonlinear conductance variations. This significantly reduces the extensive training workload typically required by traditional neural networks. Lead halide perovskites, with their tunable band structure and active ion migration properties, have emerged as highly promising materials for developing dynamic memristors. However, large‐scale and consistently stable production remains a challenge for perovskite functional films, while lead elements' toxicity and environmental impact also partly restrict their practical device utilization. In this work, lead‐free copper‐based perovskite (i.e., CsCu2I3) films are prepared by thermal evaporation for constructing dynamic memristors. The effective conductivity modulation of CsCu2I3‐based memristor can be utilized in artificial neural networks, achieving a high handwritten digit recognition accuracy of 91.2%. In addition, the RC system is also constructed based on the dynamic behavior of the devices, by which a letter recognition accuracy of 98.2% with simple training is achieved. This technology provides a feasible pathway to construct copper‐based perovskite dynamic memristors for future neural network information processing.

Tutton salt (NH4)2Zn(SO4)2(H2O)6: thermostructural, spectroscopic, Hirshfeld surface, and DFT investigations

ContextAmmonium Tutton salts have been widely studied in recent years due to their thermostructural properties, which make them promising compounds for application in thermochemical energy storage devices. In this work, a detailed experimental study of the Tutton salt with the formula (NH4)2Zn(SO4)2(H2O)6 is carried out. Its structural, vibrational, and thermal properties are analyzed and discussed. Powder X-ray diffraction (PXRD) studies confirm that the compound crystallizes in a structure of a Tutton salt, with monoclinic symmetry and P21/a space group. The Hirshfeld surface analysis results indicate that the main contacts stabilizing the material crystal lattice are H···O/O···H, H···H, and O···O. In addition, a typical behavior of an insulating material is confirmed based on the electronic bandgap calculated from the band structure and experimental absorption coefficient. The Raman and infrared spectra calculated using DFT are in a good agreement with the respective experimental spectroscopic results. Thermal analysis in the range from 300 to 773 K reveals one exothermic and several endothermic events that are investigated using PXRD measurements as a function of temperature. With increasing temperature, two new structural phases are identified, one of which is resolved using the Le Bail method. Our findings suggest that the salt (NH4)2Zn(SO4)2(H2O)6 is a promising thermochemical material suitable for the development of heat storage systems, due to its low dehydration temperature (≈ 330 K), high enthalpy of dehydration (122.43 kJ/mol of H2O), and hydration after 24 h.MethodsComputational studies using Hirshfeld surfaces and void analysis are conducted to identify and quantify the intermolecular contacts occurring in the crystal structure. Furthermore, geometry optimization calculations are performed based on density functional theory (DFT) using the PBE functional and norm-conserving pseudopotentials implemented in the Cambridge Serial Total Energy Package (CASTEP). The primitive unit cell optimization was conducted using the Broyden–Fletcher–Goldfarb–Shanno (BFGS) algorithm. The electronic properties of band structure and density of states, and vibrational modes of the optimized crystal lattice are calculated and analyzed.Graphical abstract

DFT and experimental study on photocatalytic degradation of tetracycline by Sulfur-doped monolayer g-C3N4 as a peroxymonosulfate activator

Doping enhances the activation of peroxymonosulfates (PMS) by metal-free carbon materials, addressing their inherent limitations in performance. In this study, experimental and theoretical calculations are combined to carry out the study of efficient activation of PMS for tetracycline degradation based on sulfur-doped g-C3N4 (SCN) as a promising photocatalyst. Calculation of the energy band structure, electronic and optical properties by density-functional theory methods suggests that doping results in a smaller band gap, smaller bond populations, and work function, leading to a redistribution of charges and dipoles at the g-C3N4 interface with a better ability to separate photogenerated h+/e− pairs. Meanwhile, the characterization and catalyst activity measurements indicate that doping improves the photocatalytic activity, which is in agreement with the theoretical calculations. In particular, the SCN synthesized at 1:1 ratio exhibited the best catalytic activity, and the degradation efficiency of TC within 2 h could reach 89.4 %. This study provides a highly effective metal-free carbon activator for the degradation of antibiotics from wastewater by PMS.

First-principles study on the microstructure, band structure, mechanical and optical properties of AB-stacked bilayer graphene under constant neutron irradiation with different electric field magnitudes and directions

Carbon-based devices have superior performance and lower power consumption compared to silicon-based devices. However, graphene and related two-dimensional materials are easily influenced by radiation due to their extremely high surface-to-volume ratio. Under constant neutron irradiation conditions, there have been no studies on the effects of the magnitude and direction of an external electric field on various properties of the AB system. This study systematically investigated the neutron irradiation effects on the AB system and the influence of the different electric fields on the properties of the AB system under constant irradiation conditions using the density functional theory and ab initio molecular dynamics method that assigns energy to the primary knock-on atom. The results indicate that under constant neutron irradiation with different electric fields, the changes in system configuration dominate the influence on band structure, while the impact of surface ripples is relatively limited. Reducing the interlayer spacing of the system can make the configuration more stable, which makes the band structure under the electric field more stable. The primary factors influencing the Young's modulus (Y) of the system are changes in the microstructure and the appearance of surface ripples, while the influence of system configuration is relatively limited. Under the irradiation conditions, the electric field can to some extent accurately modulate the band gap of the system. However, it will also correspondingly reduce the system's Y to a certain extent, causing negative impacts on the electrical and thermal conductivity.

Twist-angle-dependent optical behaviors of excitons in twisted bilayer MoS2 at low temperature

Twisted bilayers of two-dimensional materials provide a powerful and attractive platform to control band structure and tailor optical properties since the twist angle θ between the bilayer has been shown to be a critical parameter in engineering the moiré potential. Here, we demonstrate the θ-driven effects on excitons in twisted bilayer MoS2 (tBLMs) by measuring photoluminescence (PL) spectra. The localized state exciton between 1.70 eV and 1.80 eV is observed at 7 K with properties periodically modulated by θ. The θ is also a crucial factor affecting direct excitons. Furthermore, the phonon around 410 cm−1 has a θ dependence similar to excitons by measuring Raman spectra. The localized stacking patterns, the recombination of excitons, and the phonon-exciton interactions are confirmed in tBLMs. Our work provides the help to investigate the new quantum phenomena of tBLMs by optical methods and provides possibilities to manipulate the emission of excitons in tBLMs.

Strong Vertical Piezoelectricity and Broad-pH-Value Photocatalyst in Ferroelastic Y2Se2BrF Monolayer.

With the development of miniaturized devices, there is an increasing demand for 2D multifunctional materials. Six ferroelastic semiconductors, Y2Se2XX' (X, X' = I, Br, Cl, or F; X ≠ X') monolayers, are theoretically predicted here. Their in-plane anisotropic band structure, elastic and piezoelectric properties can be switched by ferroelastic strain. Moderate energy barriers can prevent the undesired ferroelastic switching that minor interferences produce. These monolayers exhibit high carrier mobilities (up to 104 cm2 V-1 s-1) with strong in-plane anisotropy. Furthermore, their wide bandgaps and high potential differences make them broad-pH-value and high-performance photocatalysts at pH value of 0-14. Strikingly, Y2Se2BrF possesses outstanding d33 (d33 = -405.97 pm/V), greatly outperforming CuInP2S6 by 4.26 times. Overall, the nano Y2Se2BrF is a hopeful candidate for multifunctional devices to generate a direct current and achieve solar-free photocatalysis. This work provides a new paradigm for the design of multifunctional energy materials.

Highly efficient Bi/BiOCl with oxygen vacancies photocatalyst with synergetic effects of oxygen vacancy, surface plasmon resonance, and electron sink effects of metallic Bi

Bi/BiOCl with oxygen vacancies composite was synthesized through a facile and rapid in situ surface reduction of BiOCl, utilizing NaBH4 as the reductant. The reduction process yielded metallic Bi nanoparticles on the surface of BiOCl and meanwhile created the oxygen vacancies within the BiOCl lattice. As a consequence, the as‐synthesized Bi/BiOCl composites exhibited a substantially enhanced visible‐light absorption capacity, whereas pure BiOCl was only responsive to ultraviolet light. Additionally, the Bi/BiOCl composite demonstrated a markedly accelerated photodegradation rate of Rhodamine, exceeding that of pure BiOCl and P25 by a factor of 6.10 and 19.74, respectively. The density functional theory (DFT) calculation was carried out to estimate the band structural and electronic properties of samples. Based on systematic analysis, the underlying mechanism was attributed to the extended responsive light range due to the surface plasma resonance of metallic Bi and the formation of oxygen vacancy energy level. Moreover, the electron sink effect of Bi nanoparticles was found to suppress the recombination of photoinduced charges, further contributing to the enhanced photocatalytic performance of Bi/BiOCl.

Tailored Cis-Trans Isomeric Metal-Covalent Organic Frameworks for Coordination Configuration-Dependent Electrochemiluminescence.

Precise manipulation of the coordination configuration within substances can modulate the band structure and catalytic properties of the target material. Metal-covalent organic frameworks (MCOFs), a crystal material amalgamating the benefits of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), can integrate a predetermined coordination environment into the frameworks for amplifying the catalytic effect. In this study, we delicately synthesize isomeric MCOFs using bis(glycinato)copper as the aminoligand via kinetically and thermodynamically favorable pathways to yield cis-MCOF and trans-MCOF products, respectively, thereby introducing a cis-trans isomeric coordination field into the framework. Moreover, the twisted skeleton derived from the flexibility of amino acid and β-ketoenamine linkages endows trans-MCOF with surprising water dispersibility. Compared to cis-MCOF, the trans isomerism displays a significant enhancement in cathodic electrochemiluminescence via the catalysis of Cu nodes toward K2S2O8. The density of states analysis shows that the d-band center of trans-MCOF is closer to the Fermi level, leading to more stable adsorption binding to promote the catalysis. This study is the first report on constructing predesign coordination configuration MCOFs via an easy-handling method, which gives the guidelines for the design of amino acid-based MCOF materials.

Exploring the impact of Sm3+ doping on the structural, optical, and photocatalytic properties of ZnAl2O4 spinels

The development of novel nano-photocatalysts to address the ongoing water purification and organic dye degradation issues is a major concern to the research community today. In view of it, in the present study, Sm3+-doped ZnAl2O4, (ZnAl2-2xSm2xO4; x = 0, 0.005, 0.01, 0.02 & 0.03) nano-catalysts were prepared through solution combustion method using Isoleucine as a fuel. Systematic studies were conducted to evaluate their structural, microstructural and band structure properties to ascertain the feasibility of their use as photocatalysts against acid orange 8 dye under visible light irradiation. It was observed that the substitution of Sm3+ at the Al3+ site has a greater impact on the formation of single-phase spherical nanoparticles of the sample crystallized in the cubic crystal structure. With the increase in the concentration of Sm3+, the average crystallite size was found to decrease towards the quantum limit. Additionally, BET analysis reveals an increase in specific surface area and pore size, accompanied by a reduction in pore volume with higher Sm3+ concentrations. SEM micrographs reveal that the prepared samples are highly porous in nature, supporting the XRD and BET analysis. Also, the band gap was found to increase with Sm3+ concentration. It is worth noting that ZnAl2-2xSmxO4 nanoparticles demonstrate significant photocatalytic activity against Acid Orange 8 dye under visible light, although the band gap increases with Sm3+ concentration. Notably, 3 mol% Sm3+-doped ZnAl2O4 achieves 92 % degradation efficiency of Acid Orange 8 under visible light due to its high surface area, increased active sites, and reduced photogenerated charge carrier recombination. The photocatalytic dye degradation mechanism highlights the role of dye sensitization in enabling visible light photocatalytic activity for Sm3+-doped ZnAl2O4, which primarily absorbs in the UV region. The process relies on the efficient transfer of electrons from the excited dye to the photocatalyst, followed by the formation of reactive species that drive the degradation of pollutants. The corresponding mechanism for this is proposed in detail.

Stress-induced fluorescence in diamond at ultrahigh pressures and low temperatures

Diamond is widely used as an anvil material in high pressure experiments, such as diamond anvil cell (DAC). The study of the fluorescence emission behaviour of the diamond at high pressure is of great significance for understanding its band structure and optical properties. Here, by combining low-temperature photoluminescence experiments, and fluorescence spectroscopy at controlled pressure (181 GPa–122 GPa) and temperature (296 K–77 K) reveals the relationship between stress-induced diamond fluorescence as a function of temperature and pressure. We also demonstrate that the electron-phonon interaction has an effect on the diamond energy gap, and the temperature and pressure jointly affect the band structure. The electron band gap decreases rapidly under low temperature and high-pressure conditions.

Tailoring structural and optical properties of ZnO system through elemental Mn Doping through First-principles calculations

In this study, band structure and optical properties of Manganese (Mn) doped ZnO are investigated adopting first-principles study calculations. It is observed that, by addition of Mn in ZnO crystal, the electrical properties like conductivity and dielectric function of material have been improved. The elastic constants for the elements are also calculated which shows that the element is stable after addition of dopant. The computational study is done on CASTEP and Material Studio. The ZnO system is simulated and atoms of Mn has been added replacing Zn atoms. The properties that studied are band structure and optics including conductivity, reflectivity, dielectric function, absorption and refractive index. Furthermore, this study also includes calculation of Elastic constants, XRD Spectra, Phonon dispersion and Temperature profile of doped ZnO systems. The computational study produced promising results and experimental approach can be adopted to reinforce the outcomes of this study.

Enhanced synergistic removal of tetracycline and uranium in wastewater using Defective-Enriched S-scheme hollow dodecahedron K3PW12O40@WS2 heterojunction

In aquatic environments, the coexistence and interaction of multiple the pollutants complicate remediation process. This study focuses on developing a defective-enriched S-scheme heterojunction of K3PW12O40@WS2 (KPW@WS2) with hollow structure for the simultaneous removal of tetracycline (TC) and hexavalent uranium (U(VI)) in wastewater. The internal electric field (IEF) within this heterojunction plays a crucial role in efficiently separating photo-generated carriers, creating high reduction and oxidation active sites. The band structure and optical properties suggest that WS2-Vs have a narrower band gap energy compared to conventional WS2, leading to improved charge carrier separation and transfer rates. Density functional theory (DFT) calculations support the reduced recombination of electron-hole pairs in WS2-Vs due to the presence of S vacancies. Experimental results reveal a synergistic effect between the removal of TC and U(VI), with a significant increase in the reaction rate constant for the reduction of U(VI) to 0.0426 min−1, 1.6 times higher than in a single U(VI) reduction system. Additionally, the reaction rate constant for the oxidation of TC also rises from 0.0573 to 0.0729 min−1. The study also delves into the photocatalytic mechanism, degradation pathways, and intermediate products. Overall, this research offers an innovative strategy for simultaneous pollutant removal and optimizing photocatalytic redox reactions to enhance solar energy utilization.

Exploring Anisotropic Carrier Transport in WSe2-WTe2 Superlattices: A Computational Study.

Superlattice structures offer distinct benefits in modern semiconductor technology, enabling the development of a deeper understanding of their sublayer arising from the interfaces. However, the advancement of large-scale applications encounters additional concerns, such as the stability and performance of the superlattice. In this study, we employ density functional theory calculations combined with the Boltzmann transport theory to comprehensively analyze the electronic structural and transport properties of the hexagonal phase of WSe2 and the WSe2-WTe2 superlattice for their applications in carrier transport fields. Previous studies showed that longitudinal acoustics phonon limited carrier mobility determined by deformation potential theory (DPT) often compromises the accuracy and overestimates the relaxation time by 2 orders. Herein, we conduct an in-depth analysis of band structural and transport properties, addressing the aforementioned inconsistency by exclusively incorporating scattering from longitudinal optical phonons to accurately compute mobility using the Fröhlich interaction. Our findings reveal a significant enhancement in mobility for both electrons and holes in the WSe2-WTe2 superlattice, reaching 545 and 476 cm2 V-1 s-1, respectively, compared to 104 and 132 cm2 V-1 s-1 for WSe2, which suggests that this superlattice is a promising material for electronics and transport applications.