Band States Research Articles

Simulation Study for Nb‐Doped MoS2${\rm MoS}_2$ Layer in CZTS‐Based Solar Cells: Assessment of Challenges

AbstractThe unintentional formation of a layer as a reaction product between the copper zinc tin sulfide (CZTS) thin film and the Mo back contact reduces cell efficiency due to high sheet resistance and carrier recombination. To limit the formation of , an intentionally grown p‐type Nb‐doped layer can serve as an effective hole transport layer. This study presents a detailed study and calculations for CZTS/Mo‐based solar cells, providing guidelines for calibration. Optimizing cell efficiency is influenced by various interconnected factors in Nb‐doped . While a high carrier concentration in Nb‐doped is assumed to enhance efficiency, other parameters such as band state, optical absorption, and carrier mobility also play crucial roles and can limit cell performance. This simulation study evaluated the effect of Nb‐doped layers with different carrier concentrations to determine the optimal conditions for this p‐type layer. This work reveals that a very thin layer (13 nm) of Nb‐doped p‐type can achieve a maximum efficiency of 11.34% (with = 1.5 ) and that for an Nb‐doped p‐type 62 nm is 15.82 % (with = 4.03 ).

The Design of a Multifunctional Coding Transmitarray with Independent Manipulation of the Polarization States.

Manipulating orthogonally polarized waves independently in a single metasurface is pivotal. However, independently controlling the phase shifts of orthogonally polarized waves is difficult, especially in the same frequency bands. Here, we propose a receiver-phase shift-transmitter transmitarray with independent control of arbitrary polarization states in the same frequency bands, in which transmission rates reach more than 90% in the frequency bands 4.2~4.9 GHz and 5.3~5.5 GHz. By introducing a phase-regulation structure to each element, phases covering 360° for different polarized incident waves can be independently controlled by different geometric parameters, and two-bit coding phases can be obtained. The design principle based on the two-port network's scattering matrix has been analyzed. To verify the independent tuning abilities of the proposed transmitarray for different polarization incidences in the same frequency bands, a multifunctional receive-phase shift-radiation coding transmitarray (RPRCT), which is composed of 16×16 elements, with functions of anomalous refraction (for example, orbital angular momentum wave) and focusing transmission for different polarized incident waves was simulated and measured. The measured results agree reasonably well with the simulated ones. Our findings provide a simple method for obtaining a multifunctional metasurface with orthogonal polarization in the same frequency bands, which greatly improves the capacity and spectral efficiency of communication channels.

Electronic structures, thermal properties and molecular dynamics of CsGdCl3 and CsNdCl3 perovskite crystals by first-principles calculations

Lanthanide-based perovskite crystals have been characterized for proposing material design guidelines of perovskite solar cell with stability of photovoltaic performance. The purpose of this study is to characterize band structures, phonon dispersions, molecular dynamics, electronic and thermal conductivities of CsGdCl3 and CsNdCl3 perovskite crystals by first-principles calculation analysis. The CsGdCl3 and CsNdCl3 crystals had wide distributions of 5d orbital of Gd3+ ion, 5d and 4f orbitals of Nd2+ ion near conduction band state as n-type semiconductive behavior. The phonon dispersions and thermal conductivities indicate effects of acoustic phonon on carrier scattering. The CsGdCl3 crystal suppressed carrier scattering as elastic behavior, improving electron diffusion and dynamic stability. The CsNdCl3 crystals expected to cause carrier scattering with acoustic phonon and molecular dynamics. The CsGdCl3 crystal have the superior potential of the performance as semiconductor characteristics equivalent to the performance of the CsPbCl3 crystal.

Electronic States of the Conduction Band of Ultrathin Furan-Phenylene Co-Oligomer Films on the Surfaces of Oxidized Silicon and Layer-by-Layer Grown Zinc Oxide

Electronic States of the Conduction Band of Ultrathin Furan-Phenylene Co-Oligomer Films on the Surfaces of Oxidized Silicon and Layer-by-Layer Grown Zinc Oxide

Calculation of the Activation Energy of Electrical ε2‐Conductivity of Weakly Compensated Semiconductors

A model of tunneling (jumping) migration of charge carriers near their mobility edge in the upper band of neutral states of majority hydrogen‐like impurities is proposed to calculate the energy of thermal activation of electrical ‐conductivity of weakly compensated semiconductors. The difference from the known Hubbard model consists in the scheme of interimpurity transitions of charge carriers and in the method of calculating the position of their tunnel mobility edge. The drift mobility edge of free charge carriers corresponds to the thermal ionization energy of majority impurities , which is located near the c‐band bottom or the v‐band top in n‐ and p‐type semiconductors, respectively, and is due to the overlap of excited states of electrically neutral majority impurities. The position of the tunnel mobility edge for ‐conductivity is determined by taking into account the Coulomb interaction of the majority impurities in the charge states and . It is assumed that doping and compensating impurities form a single simple nonstoichiometric cubic lattice in a crystal matrix. The calculations of the activation energy on the insulator side of the insulator–metal concentration phase transition for weakly compensated p‐Si:B, n‐Si:P, and n‐Ge:Sb crystals quantitatively agree with known experimental data.

Beyond Cation Disorder: Site Symmetry‐Tuned Optoelectronic Properties of the Ternary Nitride Photoabsorber ZrTaN3

AbstractTernary nitrides are rapidly emerging as promising compounds for optoelectronic and energy conversion applications, yet comparatively little of this vast composition space has been explored. Furthermore, the crystal structures of these compounds can exhibit a significant amount of disorder, the consequences of which are not yet well understood. Here, the deposition of bixbyite‐type ZrTaN3 thin films is demonstrated by reactive magnetron co‐sputtering and observed semiconducting character, with a strong optical absorption onset at 1.8 eV and significant photoactivity, with prospective application as functional photoanodes. It is found that Wyckoff‐site occupancy of cations is a critical factor in determining these beneficial optoelectronic properties. First‐principles calculations show that cation disorder leads to minor deviations in the total energy but modulates the bandgap by 0.5 eV, changing orbital hybridization of valence and conduction band states. In addition to demonstrating that ZrTaN3 is a promising visible light‐absorbing semiconductor and active photoanode material, the findings provide important insights regarding the role of cation ordering on the electronic structure of ternary semiconductors. In particular, it is shown that not only cation order, but also the cationic Wyckoff site occupancy has a substantial impact on key optoelectronic properties, which can guide future design and synthesis of advanced semiconductors.

G-factor symmetry and topology in semiconductor band states

The [Formula: see text] tensor, which determines the reaction of Kramers-degenerate states to an applied magnetic field, is of increasing importance in the current design of spin qubits. It is affected by details of heterostructure composition, disorder, and electric fields, but it inherits much of its structure from the effect of the spin-orbit interaction working at the crystal-lattice level. Here, we uncover interesting symmetry and topological features of [Formula: see text] for important valence and conduction bands in silicon, germanium, and gallium arsenide. For all crystals with high (cubic) symmetry, we show that large departures from the nonrelativistic value [Formula: see text] are guaranteed by symmetry. In particular, considering the spin part [Formula: see text], we prove that the scalar function [Formula: see text] must go to zero on closed surfaces in the Brillouin zone, no matter how weak the spin-orbit coupling is. We also prove that for wave vectors [Formula: see text] on these surfaces, the Bloch states [Formula: see text] have maximal spin-orbital entanglement. Using tight-binding calculations, we observe that the surfaces [Formula: see text] exhibit many interesting topological features, exhibiting Lifshitz critical points as understood in Fermi-surface theory.

Effect of Surface Electron Trapping and Small Polaron Formation on the Photocatalytic Efficiency of Copper(I) and Copper(II) Oxides.

Cu2O, CuO, and mixed phase Cu2O/CuO represent promising candidates for photoelectrochemical H2 evolution due to their strong visible light absorption, earth-abundance, and chemical stability. However, the photoelectrochemical efficiency in these materials remains far below the theoretical limit, largely due to poorly understood surface electron dynamics. These dynamics depend on defect states, such as Cu atom vacancies and phase boundaries, which control electron trapping, charge carrier separation, and recombination. In this work, we study the photoinduced electron and hole dynamics at the surface of various Cu oxides using ultrafast extreme ultraviolet reflection-absorption (XUV-RA) spectroscopy. In Cu2O we find that photoexcitation occurs as electron promotion from primarily Cu 3d valence band to Cu 4s conduction band states compared to O 2p valence band to Cu 4s conduction band states in CuO. In catalysts with a significant concentration of Cu vacancies, we observe fast electron trapping to the Cu 3d defect band occurring in less than 100 fs. In contrast, photoexcited electrons in phase pure CuO do not trap to midgap states; rather these electrons form small polarons within approximately 500 fs. Photoelectrochemical measurements of these catalysts show that Cu vacancy-mediated electron trapping correlates with a significant loss of photocurrent. Together, these results provide a detailed picture of the defect states and associated ultrafast carrier dynamics that govern the photocatalytic efficiency in widely studied Cu2O and CuO photocatalysts.

A Century of Band Contest Literature Lists: From National Origins to the State of Florida

Band repertoire lists for the National Band Contests evolved from a desire to make school bands “more educational” in the 1920s. The national band contest repertoire lists (1924–1943) formed the basis for the wind band canon during the first half of the twentieth century. Many state band organizations developed their own lists when national contests ended after World War II. This study was an analysis of the pieces and composers that were on the Florida band contest lists, how the lists evolved, and who influenced them, especially compared to the national lists. Findings include greater diversity in Florida’s concert music committee membership than National, but likely only since 1991. The percentage of original wind band works on Florida’s lists maintained the final proportions of the National Band Contest lists (approximately 50%–53%). White male composer representation over the 75 years of lists remained extremely high (98.08% of all works), though the proportion of women composers and composers of color on annual additions since 2015 has increased dramatically.

Possible Wigner states in CrI3 heterostructures with graphene: A tight-binding model perspective

In this study, we present an effective tight-binding model for an accurate description of the lowest energy quadruplet of a conduction band in a ferromagnetic CrX3 monolayer, tuned to the complementary density functional theory simulations. This model, based on a minimum number of chromium orbitals, captures a distinctively flat dispersion in those bands but requires taking into account hoppings beyond nearest neighbors, revealing ligand-mediated electron pathways connecting remote chromium sites. Doping of states in the lowest conduction band of CrX3 requires charge transfer, which, according to recent studies [Tenasini , ; Tseng , ; Cardoso , , can occur in graphene(G)/CrX3 heterostructures. Here, we use the detailed description of the lowest conduction band in CrI3 to show that G/CrI3/G and G/CrI3 are type-II heterostructures where light holes in graphene would coexist with heavy electrons in the magnetic layer, where the latter can be characterized by Wigner-Seitz radius rs∼25−35 (as estimated for hBN-encapsulated structures). Published by the American Physical Society 2024

40Ar diffusion in phlogopite: [formula omitted] atomistic calibration and implications for Ar–melt–solid kinetic interactions and ascent dynamics of mantle xenoliths and kimberlites

40Ar/39Ar ages of phlogopite from kimberlite-hosted mantle xenoliths are commonly older than the kimberlite eruption, despite the fact that argon is supposed not to be retained by phlogopite at temperatures above hydrothermally-derived Ar closure temperatures (<500°C). Combining Molecular Dynamics (MD) with Nudged Elastic Band (NEB) and Transition State Theory (TST), we investigate 40Ar−PVT (Pressure−Volume−Temperature) relationships in pristine, defect-free, phlogopite and show that 40Ar diffusivity is several orders of magnitude slower than existing estimates with a strong effect of pressure on diffusion rates and retention of 40Ar at mantle conditions. These results imply to fundamentally revise residence- and transit-time estimates based on Ar kinetics in phlogopite assuming simple diffusive relaxation during upwelling. When accounting for pressure, 40Ar retention trends in phlogopite predict substantially slower kimberlite ascent rates than documented by independent chronometers, indicating that 40Ar resetting during ascent in phlogopite does not result from simple decompression-driven diffusive relaxation. We argue that 40Ar remobilization probably involves secondary structural–textural modifications induced by reaction-driven recrystallization or rim overgrowth. These findings have far-reaching consequences in terms of argon isotopic mobility at mantle depths as well as for dating and tracing metasomatic events during crust−mantle interactions in the evolution of the subcontinental mantle.

Strategies to Obtain Reliable Energy Landscapes from Embedded Multireference Correlated Wavefunction Methods for Surface Reactions.

Embedded correlated wavefunction (ECW) theory is a powerful tool for studying ground- and excited-state reaction mechanisms and associated energetics in heterogeneous catalysis. Several factors are important to obtaining reliable ECW energies, critically the construction of consistent active spaces (ASs) along reaction pathways when using a multireference correlated wavefunction (CW) method that relies on a subset of orbital spaces in the configuration interaction expansion to account for static electron correlation, e.g., complete AS self-consistent field theory, in addition to the adequate partitioning of the system into a cluster and environment, as well as the choice of a suitable basis set and number of states included in excited-state simulations. Here, we conducted a series of systematic studies to develop best-practice guidelines for ground- and excited-state ECW theory simulations, utilizing the decomposition of NH3 on Pd(111) as an example. We determine that ECW theory results are relatively insensitive to cluster size, the aug-cc-pVDZ basis set provides an adequate compromise between computational complexity and accuracy, and that a fixed-clean-surface approximation holds well for the derivation of the embedding potential. Additionally, we demonstrate that a merging approach, which involves generating ASs from the molecular fragments at each configuration, is preferable to a creeping approach, which utilizes ASs from adjacent structures as an initial guess, for the generation of consistent potential energy curves involving open-d-shell metal surfaces, and, finally, we show that it is essential to include bands of excited states in their entirety when simulating excited-state reaction pathways.

The coexistence of Dirac cones and flat band in the twisted WSe2/VSe2 moiré superlattice

The transition metal dichalcogenide twisted superlattices have received widespread attention due to their novel physical properties. Here, the electronic properties of twisted WSe2/VSe2 heterostructure at θ = 60°, 21.79° and 13.17° were studied with DFT + U based on the first-principles calculation. The results show that the WSe2/VSe2 heterostructure moiré superlattice at 13.17° angle appears Dirac cones and a flat band near the Fermi level. The Dirac cones with a band gap of approximately 5.93 meV centered at the K and K’ point in the Brillouin zone. Simultaneously, a flat band at about 65 meV below the Fermi level with a bandwidth as small as 2.86 meV is found. The high density of states of this flat band may give rise to a superconducting signal similar to twisted graphene.

Optical properties of CeF3 crystal at high temperature or pressure by first principles and its application in isolators

In this work, CeF3 single crystal was successfully grown by Bridgman method. The XRD diffraction was tested and the data matched well with the standard card. Further trying its optical performance, CeF3 single crystal has very high transmittance of 90 %, the cut-off absorption edge length of the crystal is better than 300 nm. Testing the magneto-optical Verdet constant of CeF3 single crystal and trial-produced optical isolator shows that the Verdet constants of CeF3 single crystals in the magneto-optical field are similar to those of TGG crystals. The band structure, state density, optical properties and elastic constants of CeF3 crystal under different temperature and pressure are calculated by first principles. The results show that CeF3 crystal has excellent thermal stability and mechanical stability. Under high temperature conditions, light absorption and loss are small, and the optical properties are stable. Under high pressure, the crystal exhibits certain stability and impact resistance, and the optical properties are relatively stable. The results show that CeF3 crystal has significant advantages in replacing TGG crystal in laser field, and has a certain application prospect in window materials.

A DFT study of the physical properties of novel vanadium-based half-Heusler alloys VYAl (Y = Ni,Pd, and Pt) pertinent to their optoelectronics application

We investigated three novel 18-valence electron count (VEC) vanadium-based half-Heusler alloys, VYAl (Y = Ni, Pd, and Pt), for their structural, mechanical, electronic, and optical properties using density functional theory (DFT). The computation was carried out employing Vienna Ab-initio Simulation Package (VASP) and all three alloys have exhibited structural, chemical, mechanical, and thermodynamic stability. We obtained the lattice constants of 5.520, 5.800, and 5.820 Å for VNiAl, VPdAl, and VPtAl, respectively. The elastic parameters imply a ductile and hard nature of the system and exhibit anisotropic behavior. Electronic band characterization demonstrated that all three alloys are semiconductors with direct narrow gaps at the Γ-point which is crucial for photovoltaic applications. In addition to that, the high density of the band states near the Fermi level indicates a promising candidate for thermoelectric conversion. The influence of SOC interaction in the system generates a small shift in the bands. From the optical response, we infer that the studied compounds have exceptional light absorption and reflection quality, making them suitable for optoelectronics purposes.

An Advanced Framework for Predictive Maintenance Decisions: Integrating the Proportional Hazards Model and Machine Learning Techniques under CBM Multi-Covariate Scenarios

Under Condition-Based Maintenance, the Proportional Hazards Model (PHM) uses Cox’s partial regression and vital signs as covariates to estimate risk for predictive management. However, maintenance faces challenges when dealing with a multi-covariate scenario due to the impact of the conditions’ heterogeneity on the intervention decisions, especially when the combined measurement lacks a physical interpretation. Therefore, we propose an advanced framework based on a PHM-machine learning formulation integrating four key areas: covariate prioritization, covariate weight estimation, state band definition, and the generation of an enhanced predictive intervention policy. The paper validates the framework’s effectiveness through a comparative analysis of reliability metrics in a case study using real condition monitoring data from an energy company. While the traditional log-likelihood minimization may fall short in covariate weight estimation, sensitivity analyses reveal that the proposed policy using IPOPT and a non-scaler transformation results in consistent prediction quality. Given the challenge of interpreting merged covariates, the scheme yields improved results compared to expert criteria. Finally, the advanced framework strengthens the PHM modeling by coherently integrating diverse covariate scenarios for predictive maintenance purposes.

Dual Exciton Polarization in Bipolar CeO2-x Nanocrystals Controlled by Defect-Based Redox Processes.

Discovering alternative means to control electronic states in semiconductor nanostructures is the key to the development of new quantum technologies. Controlling the cyclotron motion of free charge carriers in semiconductor nanocrystals using an external magnetic field generates a tunable angular momentum, as a collective electronic degree of freedom, which can be imparted to the electronic band states to achieve complete exciton polarization. The sign of this polarization is determined by the type of majority charge carriers in a given lattice. Using magnetic circular dichroism spectroscopy, we demonstrate a simultaneous polarization of excitonic states in substoichiometric oxygen-deficient CeO2-x nanocrystals associated with electrons and holes, which can be controlled by the thermal treatment of colloidal nanocrystals in oxidizing or reducing conditions. The presence of both occupied and unoccupied midgap states, due to Ce3+ 4f and Ce4+ 4f orbitals, respectively, allows for selective probing of the effect of holes in the valence band (VB → Ce4+ 4f) and electrons in the conduction band (Ce3+ 4f → CB). The two transitions show the opposite sign at 300 K due to the opposite angular momenta associated with cyclotron electrons and holes. The ability to manipulate Ce 4f-derived midgap states by defect formation during the synthesis or postsynthesis treatment allows for a range of new technological applications of CeO2-x nanocrystals in optoelectronics.

Atomically Thin Kagome-Structured Co9Te16 Achieved through Self-Intercalation and Its Flat Band Visualization.

Kagome materials have recently garnered substantial attention due to the intrinsic flat band feature and the stimulated magnetic and spin-related many-body physics. In contrast to their bulk counterparts, two-dimensional (2D) kagome materials feature more distinct kagome bands, beneficial for exploring novel quantum phenomena. Herein, we report the direct synthesis of an ultrathin kagome-structured Co-telluride (Co9Te16) via a molecular beam epitaxy (MBE) route and clarify its formation mechanism from the Co-intercalation in the 1T-CoTe2 layers. More significantly, we unveil the flat band states in the ultrathin Co9Te16 and identify the real-space localization of the flat band states by in situ scanning tunneling microscopy/spectroscopy (STM/STS) combined with first-principles calculations. A ferrimagnetic order is also predicted in kagome-Co9Te16. This work should provide a novel route for the direct synthesis of ultrathin kagome materials via a metal self-intercalation route, which should shed light on the exploration of the intriguing flat band physics in the related systems.

Advancing Predictive Maintenance with PHM-ML Modeling: Optimal Covariate Weight Estimation and State Band Definition under Multi-Condition Scenarios

The proportional hazards model (PHM) is a vital statistical procedure for condition-based maintenance that integrates age and covariates monitoring to estimate asset health and predict failure risks. However, when dealing with multi-covariate scenarios, the PHM faces interpretability challenges when it lacks coherent criteria for defining each covariate’s influence degree on the hazard rate. Hence, we proposed a comprehensive machine learning (ML) formulation with Interior Point Optimizer and gradient boosting to maximize and converge the logarithmic likelihood for estimating covariate weights, and a K-means and Gaussian mixture model (GMM) for condition state bands. Using real industrial data, this paper evaluates both clustering techniques to determine their suitability regarding reliability, remaining useful life, and asset intervention decision rules. By developing models differing in the selected covariates, the results show that although K-means and GMM produce comparable policies, GMM stands out for its robustness in cluster definition and intuitive interpretation in generating the state bands. Ultimately, as the evaluated models suggest similar policies, the novel PHM-ML demonstrates the robustness of its covariate weight estimation process, thereby strengthening the guidance for predictive maintenance decisions.

Assembly of S-Scheme heterojunctions In2S3/Zr-bcu-22bipy44dc and In2S3/PCN-224: Polishing band states to boost highly efficient photochemical scavenging of X-, K- and KN-types reactive dyes and Cr(VI)

Remarkable capability in utilizing visible light and the low CB potential makes In2S3 appealing in assembling MOFs-based heterojunctions. To achieve dual-functional photocatalytic decontamination of Cr(VI) and dyes via low-energy light, the focus remains on assembly of advanced heterostructures based on water-stable Zr-MOFs and In2S3. Herein, Zr-bcu-22bipy44dc and PCN-224 were deployed to fabricate two novel heterojunctions In2S3/Zr-bcu-22bipy44dc (IS/2244) and In2S3/PCN-224 (IS/P224), respectively. Indeed, IS/2244–2 and IS/P224–2 (with 50 % mass ratio of Zr-MOFs) exhibit the optimized optical-electronic properties. The new findings confirm that IS/P224–2, assembled from visible light-sensitive PCN-224, displays higher photocatalytic REDOX abilities than IS/2244–2 in degrading X-, K- and KN-types reactive dyes (RR2, RB13 and RB21) and reducing Cr2O72- ions. The elimination efficiencies of IS/P224–2 towards RR2, RB13, RB21 and Cr(VI) have reached 93.9 %, 95.8 %, 89.4 % and 98.0 % under 500 W xenon lamp, providing accelerated kinetic rates of 7.32, 14.04, 40.2 and 23.67 times of PCN-224, 112.8, 19.95, 10.58 and 3.38 times of In2S3, 5.04, 1.02, 1.39 and 1.78 times of IS/2244–2, respectively, which have been well maintained even after four photocatalytic cycles. More prominently, its performance has surpassed that of some reported MOFs-based materials and other photocatalysts. Mechanism studies have confirmed the potential active radical species, carriers transfer path and S-Scheme talents of two heterojunction materials. This study offers a feasible avenue to design low-energy light-driven bifunctional photocatalysts for water environment remediation.