Band Structure Data Research Articles

Machine-Learning-Assisted Materials Discovery from Electronic Band Structure.

Traditional methods of materials discovery, often relying on intuition and trial-and-error experimentation, are time-consuming and limited in their ability to explore the vast design space effectively. The emergence of machine learning (ML) as a powerful tool for pattern recognition has opened exciting opportunities to revolutionize materials discovery. This work explores the application of ML techniques to assist in the discovery of materials using band structure data. The electronic band structure, which describes the energy levels of electrons in a material, holds vital information regarding its electronic and optical properties. The band structure data of 63,588 materials, including metals and insulators, have been retrieved from the Materials Project database. The data were grouped into 85 batches based on the band path in the first Brillouin zone. Three ML clustering algorithms were trained on the band structure data after performing feature selection and engineering, followed by noise reduction. The models were validated by comparing the materials' properties in a cluster.

Deep learning-based inverse design of lattice metamaterials for tuning bandgap

In this paper, deep learning neural networks is used to predict the band structure of metamaterial lattices, and proactive inverse design is employed in bandgap modulation. A parametric design of the metamaterial lattice is proposed to achieve a rich design space. The corresponding band structure data is calculated by finite element method (FEM) to construct the data set. We successfully bypass complex theoretical or numerical methods to establish the mapping relationship between the lattice geometry parameters of metamaterials and the band structure data by constructing and training fully connected neural networks and convolutional neural networks (CNN). By combining the trained neural network model into an inverse design method of bandgap tuning, the geometric parameters of the metamaterial lattice can be obtained directly by inputting the target band structure. Finally, three object band structures are designed and verified by finite element simulation and experiment, which verifies the effectiveness of the inverse design method. This design approach can be extended to design other metamaterial properties.

The Influence of Geometric Parameters for Training an Artificial Neural Network to Predict the Band Structure of 1-D Fishbone Photonic Crystal

With the rising demand for the transmission of large amounts of information over long distances, the development of integrated light circuits is the key to improving this technology, and silicon photonics have been developed with low absorption in the near-infrared range and with sophisticated fabrication techniques. To build devices that work in different functionalities, photonic crystals are one of the most used structures due to their ability to manipulate light. The investigation of photonic crystals requires the calculation of photonic band structures and is usually time-consuming work. To reduce the time spent on calculations, a trained ANN is introduced in this study to directly predict the band structures using only a minimal amount of pre-calculated band structure data. A well-used 1-D fishbone-like photonic crystal in the form of a nanobeam is used as the training target, and the influence of adjusting the geometric parameters is discussed, especially the lattice constant and the thickness of the nanobeam. To train the ANN with very few band structures, each of the mode points in the band structure is considered as a single datapoint to increase the amount of training data. The datasets are composed of various raw band structure data. The optimized ANN is introduced at the end of this manuscript.

Study of Structural and Electronic Properties of TMDC Compounds: A DFT Approach

Abstract: The structural and electronic properties of transition metal dichalcogenides compounds (TMDC) like TiS2 and FeTiS2 are studied in the current paper using density functional theory (DFT). The generalized gradient approximation (GGA) with ultra-soft pseudopotential is used under the Quantum ESPRESSO package. From the theoretical data, it is noted the TiS2 material is a semiconductor in nature with a small indirect band gap. On the other hand, in the doped intercalated compound FeTiS2, which exhibits a metallic nature, the energy bands overlap within the Fermi region. Consequently, FeTiS2 is a ferromagnetic material with spin-up and spin-down characteristics, as also observed from the band structure data. Keywords: Density Functional Theory (DFT), Generalized Gradient Approximation (GGA), Quantum ESPRESSO code, Intercalated compound.

An Intelligent, User‐Inclusive Pipeline for Organic Semiconductor Design

AbstractData‐guided methodologies for designing new materials are developing apace, yet advances for organic crystals have been infrequent. For the case of organic crystals, data‐guided design platforms involve two problems: the need to construct regression models that can predict solid‐state properties from molecular structures alone and the vast number of molecular structures that satisfy a targeted solid‐state property. In this paper, a new pipeline is presented for designing molecules with targeted solid‐state electronic properties. Here, the first problem is overcome by means of a novel visualization method for band structure data, which allows the user to specify their design preferences and simplify the creation of the required regression models. The second problem is overcome by allowing for user intervention in the selection of the final molecule for subsequent synthesis. The effectiveness of this pipeline is demonstrated by using it to design a simple new molecule with a targeted bandgap and impressive band dispersion. This pipeline is the first data‐guided method that can design new molecules on the basis of genuine solid‐state electronic properties, and with its emphasis on user‐inclusivity, it can easily be applied in collaborative or industry settings.

Structural and Electronic Properties of Intercalated Transition Metal Dichalcogenides Compounds

The structural and electronic properties of Transition Metal Dichalcogenides Compound (TMDC) TiS2 and its intercalated compound like FeTiS2 are reported in the present work using Density Functional Theory (DFT). The Generalized Gradient Approximation (GGA) with ultrasoft pseudopotential are used under Quantum ESPRESSO code. From the theoretical data, it is concluded that, the energy band structure of the TiS2 material has been a small indirect band gap and possess a semiconductor characteristic. While the doped intercalated compound like FeTiS2, the energy bands are overlapped in the Fermi region, which possess metallic characteristics. Also, FeTiS2 is a ferromagnetic material with spin up and spin down nature observed from the band structure data. BIBECHANA 19 (2022) 97-101

Momentum microscopy of Pb-intercalated graphene on SiC: Charge neutrality and electronic structure of interfacial Pb

Intercalation is an established technique for tailoring the electronic structure of epitaxial graphene. Moreover, it enables the synthesis of otherwise unstable two-dimensional (2D) layers of elements with unique physical properties compared to their bulk versions due to interfacial quantum confinement. In this work, we present uniformly Pb-intercalated quasi-freestanding monolayer graphene on SiC, which turns out to be essentially charge neutral with an unprecedented $p$-type carrier density of only $(5.5\pm2.5)\times10^9$ cm$^{-2}$. Probing the low-energy electronic structure throughout the entire first surface Brillouin zone by means of momentum microscopy, we clearly discern additional bands related to metallic 2D-Pb at the interface. Low-energy electron diffraction further reveals a $10\times10$ Moir\'e superperiodicity relative to graphene, counterparts of which cannot be directly identified in the available band structure data. Our experiments demonstrate 2D interlayer confinement and associated band structure formation of a heavy-element superconductor, paving the way towards strong spin-orbit coupling effects or even 2D superconductivity at the graphene/SiC interface.

Correlating chemical and electronic states from quantitative photoemission electron microscopy of transition-metal dichalcogenide heterostructures

Vertical heterostructures of MoS2 and WSe2 layers are studied by spectroscopic photoemission electron microscopy as an effective technique for correlating chemical and electronic states at the micrometer scale. Element-specific, surface-sensitive images recorded at high lateral and energy resolution from core-level photoelectrons using different laboratory excitation sources are postprocessed to obtain laterally resolved maps of elemental composition and energy shifts in the Mo3d spectra of a few hundred meV. For monolayer MoS2, the method reveals substrate-dependent charge transfer properties within the narrow energy range of 360 meV, with MoS2 becoming more n-type after transfer onto WSe2. The band structure data from momentum microscopy taken over the same areas confirm the charge transfer from WSe2 to MoS2 by the shift of the K-bands away from the Fermi level and illustrates the layer-specific contributions to the electronic band structure of the heterostructure. From work function mapping, the reconstructed energy-level diagram reveals a type II heterostructure but with a very small conduction-band offset.

Intercalated Phosphorene for Improved Spintronic Applications

In this work we study the intercalation of monolayer phosphorene with nitrogen, lithium and calcium for exploring prospects of spintronic applications. The electronic and the magnetic properties of the intercalated structure are investigated via density functional theory to obtain the band structure and the spin polarized density of states. Albeit the band structure data show vanishing band gap, a noticeable difference emerges in the densities of the up and the down spin states induced by the intercalants. To evaluate the performance of the intercalated phosphorene, the spintronic order parameter, measuring the asymmetry among the up and the down spin densities of states, is computed which clearly shows evolution of improved spintronic properties at large intercalant densities. Further, larger atomic numbers of the intercalants seem to aid the performance of phosphorene as a spintronic material.

Tight-binding Hamiltonian considering up to the third nearest neighbours for trans polyacetylene

Utilizing the linear combination of atomic orbitals in the Slater–Koster approach in combination with the density functional theory band structure data, a new tight-binding Hamiltonian up to the third nearest neighbours for the dimerized trans polyacetylene is proposed. The effects of strain are also considered in the Hamiltonian by varying the distance between two successive CH groups along the molecular symmetry axis. Using this new Hamiltonian and exploiting the Green’s function method in the framework of the Landauer–Büttiker formalism, the electronic transport properties in a trans polyacetylene chain in the presence and absence of strain are studied. It is shown that at a peculiar value of compression strain, the electron conductance shifts 0.27 eV in energy which is an exploitable magnitude for straintronic applications of the trans polyacetylene specially as strain sensors and strain switches.

Two-Dimensional Binary Honeycomb Layer Formed by Ag and Te on Ag(111).

Inspired by the unique properties of graphene, research efforts have broadened to investigations of various other two-dimensional materials with the aim of exploring their properties for future applications. Our combined experimental and theoretical study confirms the existence of a binary honeycomb structure formed by Ag and Te on Ag(111). Low-energy electron diffraction shows sharp spots which provide evidence of an undistorted AgTe layer. Band structure data obtained by angle-resolved photoelectron spectroscopy are closely reproduced by first-principles calculations, using density functional theory (DFT). This confirms the formation of a honeycomb structure with one Ag and one Te atom in the unit cell. In addition, the theoretical band structure reproduces also the finer details of the experimental bands, such as a split of one of the AgTe bands.

Characteristics and performance of rutile/anatase/brookite TiO2 and TiO2–Ti2O3(H2O)2(C2O4)·H2O multiphase mixed crystal for the catalytic degradation of emerging contaminants

The as-synthesized rutile/anatase TiO2 and rutile/anatase/brookite TiO2–Ti2O3(H2O)2(C2O4)·H2O, particularly rutile/anatase TiO2, showed excellent catalytic oxidation of organic contaminants (MO and HBA).

Simulation within a DFT framework and experimental study of the valence-band electronic structure and optical properties of quaternary selenide Cu2HgSnSe4

We report data of simulation within a density functional theory (DFT) framework, employing different approaches for exchange correlation (XC) potential, of the electronic structure and experimental verification of these band-structure calculations using X-ray photoelectron spectroscopy (XPS) of Cu2HgSnSe4 crystal. The present studies indicate that fair good agreement of total density of states (DOS) with the valence band XPS spectrum of the Cu2HgSnSe4 crystal is derived when DFT simulation is performed within modified Becke-Johnson (mBJ) potential and taking into consideration Hubbard correction parameter U and spin-orbit (SO) coupling (mBJ–U–SO approach). The mBJ–U–SO calculation reveals the best fit of total DOS to the experimental valence band XPS spectrum as well as a fairly good energy gap value for this compound. The present theoretical data indicate that the principal contributors to the Cu2HgSnSe4 valence band are Se 4p states with their main input in upper and central portions of the band, while Sn 5 s and Hg 6 s states make prevailed contributions in its lower portion and the bottom is formed by Hg 5d states. The quaternary Cu2HgSnSe4 selenide is a direct gap semiconductor. Based on the present mBJ–U–SO band-structure data, the main optical constants are calculated indicating that the compound under consideration is a very promising optoelectronic material.

Transport of Charge Carriers along Dislocations in Si and Ge

Experimental observations and quantum mechanical device simulations point to different electronic properties of dislocations in silicon and germanium. The experimental data suggest a supermetallic behavior of the dislocations in Si and thus the high strain in the dislocation core is thought to cause the confinement of the charge carriers, which leads to the formation of a 1D electron gas along a dislocation (quantum wire). The resulting significant increase in the electron concentration corresponds to a marked increase in the drain current of metal–oxide–semiconductor field‐effect transistor (MOSFET). The specific resistance of an individual dislocation in Ge is about nine orders of magnitude higher than for a dislocation in Si. The experimental measurements of the strain in dislocation cores in Ge are still missing. Based on the band structure data, the generation of a strain equivalent to that of the dislocation cores in Si appears to be very challenging because of the transition from an indirect into a direct semiconductor with about tenfold lower strain levels. The lower strain in the dislocation core in germanium may not support the carrier confinement as proposed for the dislocation core of silicon, and consequently 1D electron gases are not expected to form along the dislocations in Ge.

Thermionic emission laws for general electron dispersion relations and band structure data

In this article, a thermionic electron emission theory for general electron dispersion relations E(k) is presented, relating electron energy E to wave-vector magnitude k = |k|. This theory does not require the construction of a model Hamiltonian for the electrode's materials, like Dirac or Weyl Hamiltonians. Instead, use is made of the material's band structure data, e.g., the parabolic E(k) approximation for the Richardson–Dushman equation and linear E(k), as used for graphene and 3D Dirac semimetals. This new theory confirms previous findings on parabolic E(k), e.g., that the emission current is independent of effective electron mass in the material as long as it is larger than real electron mass m0. For effective mass lower than m0, the emission is reduced and tends to zero for vanishing effective mass. For materials with negative electron affinity, additional terms arise in the emission current equation. It turns out that the linear E(k) dispersion, e.g., for Dirac semimetals, does not have the potential to surpass the Richardson emission in materials with the same work function. In addition, a more rigorous electron emission theory is established by utilizing real anisotropic band structure data En(k) for electrode materials. For collimated electron emission normal to the surface, the transverse electron velocities tend to zero, i.e., the transverse derivatives of En(k) have to be comparatively small. If stable electrode materials of this kind can be realized, a considerable increase of electron emission by a factor 100 or more can be achieved, compared to the Richardson–Dushman theory, especially for small lattice constants perpendicular to the emission direction.

Constructing the Electronic Structure of CH3NH3PbI3 and CH3NH3PbBr3 Perovskite Thin Films from Single-Crystal Band Structure Measurements.

Photovoltaic cells based on halide perovskites, possessing remarkably high power conversion efficiencies have been reported. To push the development of such devices further, a comprehensive and reliable understanding of their electronic properties is essential but presently not available. To provide a solid foundation for understanding the electronic properties of polycrystalline thin films, we employ single-crystal band structure data from angle-resolved photoemission measurements. For two prototypical perovskites (CH3NH3PbBr3 and CH3NH3PbI3), we reveal the band dispersion in two high-symmetry directions and identify the global valence band maxima. With these benchmark data, we construct "standard" photoemission spectra from polycrystalline thin film samples and resolve challenges discussed in the literature for determining the valence band onset with high reliability. Within the framework laid out here, the consistency of relating the energy level alignment in perovskite-based photovoltaic and optoelectronic devices with their functional parameters is substantially enhanced.

Lateral scattering potential of the PTCDA/Ag(111) interface state

A modified scheme of scanning tunneling spectroscopy data analysis has been used to reconstruct the band structure of a strongly dispersive two-dimensional unoccupied electronic state located at the commensurate interface between a monolayer of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) and Ag(111) surface up to the fourth band in the reduced Brillouin zone of the molecular monolayer. The two-dimensional scattering potential, evaluated with the help of the measured band structure data, is highly corrugated. This shows that the accepted picture, describing the interface state of PTCDA/Ag(111) as an upshifted Shockley state of Ag(111), is incomplete. Our findings indicate that the hybridization of unoccupied molecular orbitals of PTCDA on one of the two sublattices with the metal states of Ag(111) substantially influences the interface state properties.

Effect of surface dangling bonds on transport properties of phosphorous doped SiC nanowires

Based on the semiconductor transport theory, a computational model for the axial conductivity of one-dimensional nanowires is established. Utilizing the band structure data from the first principles, the conductivity, carrier concentration and mobility of phosphorus doped SiCNWs (P-SiCNWs) before and after passivation were numerically simulated. The results show that hydrogen passivation can greatly improve the conductivity of P-SiCNWs, above room temperature, the conductivity is improved nearly two orders of magnitude, and enhance the thermal stability. The reason is that hydrogen passivation saturates the surface dangling bonds, leading to the disappearance of discrete impurity band of P-SiCNWs. In addition, the surface dangling bonds lead to greater thermal instability of conductivity under room temperature, but this thermal instability decrease rapidly with the increase of temperature. The study will help us to understand the transport properties of low dimensional semiconductors, and provide theoretical support for the research of nano electronic and optoelectronic devices.

Electronic structure and optical properties of the new [formula omitted]-CdCr2O4 phase

The electronic and optical properties of β-CdCr2O4 were studied through a periodic spin-polarized Density Functional Theory scheme using a hybrid PBE-type functional. Energy bands reveal the spin-selective semiconductor nature of this crystalline phase, which presents two different band gaps for the spin-up and spin-down states, 1.87 eV and 3.25 eV respectively. From the analysis of the density of states (DOS), it is found that the main contributions around the Fermi level arise from Cr and O atoms, but particularly from the triple degenerate t2g spin-up orbitals associated to Cr1 atom. Furthermore, the dielectric function reported here shows that the optical absorption properties of this material are anisotropic, in agreement with the behavior shown by band structure data.

Ab-initio DFT-FP-LAPW/TB-mBJ/LDA-GGA investigation of structural and electronic properties of MgxZn1−xO alloys in Würtzite, Rocksalt and Zinc-Blende phases

We report on ab-initio DFT/FP-LAPW/TB-mBJ/GGA and LDA investigation of structural and electronic properties of MgxZn1−xO alloys in Würtzite (WZ), Rocksalt (RS) and Zinc-Blende (ZB) phases. TB-mBJ corrections of electronic exchange and correlation interactions make it possible to improve considerably the computational results which we have found very close to the experimental data. As expected, our results show that at 0.375 < x < 0.5, MgxZn1−xO undergoes a phase transition from the tetrahedrally coordinated non-centrosymmetric covalent WZ phase to the octahedrally coordinated ionic RS phase, and the ZB phase remains metastable in the whole 0 ≤ x≤1 range. Our structural properties results show that the lattice parameters vary nonlinearly with x in all three phases. In ZB phase, aZB increases with x very slightly (ΔaZB/aZB≤+0.6%) while in RS phase, aRS decreases with x more strongly (ΔaRS/aRS ≈ −1.7%). The strongest lattice parameters variations with x are found in WZ phase where increasing x results in increasing aWZ (ΔaWZ/aWZ≈+1.4%), decreasing cWZ (ΔcWZ/cWZ ≈ −2.9%), decreasing cWZ/aWZ ratio (Δ(cWZ/aWZ)/(cWZ/aWZ)≈-3.31%), and increasing u internal parameter (Δu/u≈+2.8%). Our electronic properties results show that the fundamental energy bandgap EG is Γ-direct in WZ and ZB MgxZn1−xO in the whole 0 ≤ x≤1 range. In RS MgxZn1−xO, EG is indirect throughout 0 ≤ x < 1 range including RS ZnO and excluding RS MgO where EG is Γ-direct. In all three phases, EG increases with x first linearly in the low x range (x < 0.5), then nonlinearly at higher x (x≥0.5). At x < 0.5, EGZB(x) = 2.609 + 2.861× eV, EGWZ(x) = 2.863 + 1.990× eV, and EGRS(x) = 3.190 + 1.508× eV. At x≥0.5, nonlinear EG(x) variations show strong bowing parameters depending on the crystal phase: bZB = 2.709eV, bWZ = 4.079eV, and bRS = 16.83eV. These strong EG(x) variations which are confined to a narrow high x range, are tightly correlated with the addition of Zn to MgO and are the strongest in RS MgxZn1−xO. Densities of states and energy band structure data analysis show dominant influence of strong exchange and correlation interactions between hybridized O:2p-Zn:3d orbitals which take place as soon as Zn is introduced into MgO. Our results confirm early findings that O:2p-Zn:3d interactions do play a leading role in overall MgxZn1−xO physical properties whatever the phase, with strongest effects in RS phase, especially in huge EG bowings and in RS-WZ phase transition.