Band Electronic Properties Research Articles

Interlinking electronic band properties in catalysts with electrochemical nitrogen reduction performance: a direct influence

Abstract The wordwide energy demands and the surge towards a net-zero sustainable society let the researchers set a goal towards the end of carbon cycle. This has enormously exaggerated the electrocatalytic processes such as water splitting, CO2 capture and reduction and nitrogen reduction reaction (NRR) as a safe and green alternative as these involve the utilization of renewable green power. Interestingly, the NH3 produced from NRR has been realized as a future fuel in terms of safer green H2 storage and transportation. Nevertheless, to scale up the NH3 production electrochemically, a benevolent catalyst needs to be developed. More interestingly, the electronic features of the catalyst that actually contribute to the interaction and binding between the adsorbate and reaction intermediates should be analyzed such that these can be tuned based on our requirements to obtain the desired high-standard goals of NH3 synthesis. The current topical review aims to provide an illustrative understanding on the experimental and theoretical descriptors that are likely to influence the electronic structure of catalysts for NRR. We have widely covered a detailed explanation regarding work function, d-band center and electronic effect on the electronic structures of the catalysts. While summarizing the same, we realized that there are several discrepancies in this field, which have not been discussed and could be misleading for the newcomers in the field. Thus, we have briefed the limitations and diverging explanations and have provided a few directions that could be looked upon to overcome the issues.

Saturable absorption properties and ultrafast photonics applications of HfS3.

In this Letter, we focus on investigating the ultrafast photonics applications of two-layer HfS3 nanosheets. We prepared two-layer HfS3 nanosheets and carried out experiments to study their nonlinear saturable absorption properties. The results showed that the two-layer HfS3-based saturable absorber exhibited a modulation depth of 16.8%. Additionally, we conducted theoretical calculations using first principles to estimate the structural and electronic band properties of the two-layer HfS3 material. Furthermore, we utilized the two-layer HfS3 materials as SAs in an erbium-doped fiber cavity to generate mode-locked laser pulses. We measured a repetition frequency of 8.74 MHz, a pulse duration of 540 fs, and a signal-to-noise ratio of 77 dB. Overall, our findings demonstrate that the two-layer HfS3 material can serve as a reliable saturable absorber, possessing properties comparable to currently used two-dimensional materials. This expands the application fields of HfS3 materials and highlights their potential for advanced optoelectronic devices.

Optical spectroscopy and band structure calculations of the structural phase transition in the vanadium-based kagome metal ScV6Sn6

In condensed matter physics, materials with kagome lattice display a range of exotic quantum states, including charge density wave (CDW), superconductivity, and magnetism. Recently, the intermetallic kagome metal ${\mathrm{ScV}}_{6}{\mathrm{Sn}}_{6}$ was discovered to undergo a first-order structural phase transition with the formation of a $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ifmmode\times\else\texttimes\fi{}3$ CDW at around 92 K. The bulk electronic band properties are crucial to understanding the origin of the structural phase transition. Here, we conducted an optical spectroscopy study in combination with band structure calculations across the structural transition. Our findings showed abrupt changes in the optical reflectivity/conductivity spectra as a result of the structural transition, without any observable gap formation behavior. The optical measurements and band calculations actually reveal a sudden change of the band structure after transition. It is important to note that this phase transition is of the first-order type, which distinguishes it from conventional density-wave type condensations. Our results provide an insight into the origin of the structural phase transition in this new and unique kagome lattice intermetallic material.

Band structure, superconductivity, and polytypism in AuSn4

The orthorhombic compound AuSn4 is compositionally similar to the Dirac node arc semimetal PtSn$_4$. AuSn$_4$ is, contrary to PtSn$_4$, superconducting with a critical temperature of T$_c$ = 2.35 K. Recent measurements present indications for quasi two-dimensional superconducting behavior in AuSn$_4$. Here we present measurements of the superconducting density of states and the band structure of AuSn$_4$ through Scanning Tunneling Microscopy (STM) and Angular Resolved Photoemission Spectroscopy (ARPES). The superconducting gap values in different portions of the Fermi surface are spread around {\Delta}0 = 0.4 meV, which is close to but somewhat larger than $\Delta =$ 1.76kBT$_c$ expected from BCS theory. We observe superconducting features in the tunneling conductance at the surface up to temperatures about 20% larger than bulk Tc. The band structure calculated with Density Functional Theory (DFT) follows well the results of ARPES. The crystal structure presents two possible stackings of Sn layers, giving two nearly degenerate polytypes. This makes AuSn$_4$ a rather unique case with a three dimensional electronic band structure but properties ressembling those of low dimensional layered compounds.

Transfer learning prediction of spin–orbit correction from bond polarizability for electronic properties of group-III monochalcogenides monolayers

Here, it is shown that the spin–orbit correction, Δ SO , for the electronic properties of group-III monochalcogenides is predictable by their corresponding bond polarizabilities. In this regard, the SOC-based correction for the bandgap and Mexican hat have been calculated from the non-relativistic results together with the bond polarizability parameter. The contribution of the spin–orbit interaction in the mentioned parameters of bandgap and Mexican hat is obtained by a normalized root-mean-square error (nRMSE) of 2 . 8 × 1 0 − 4 and 3 . 2 × 1 0 − 4 , respectively. The transfer learning method has been selected to compensate the size of the dataset. The proposed method reduces the high processing cost associated with the SOC correction calculations by the inclusion of the simple parameter of bond polarizability. From the obtained errors, it is found that the case of the deep learning method results in suitable errors. Thus, the underlying elemental characteristics such as the electronegativity of group-III and VI, bond polarizability and the Mexican hat can deliver numerous electronic band properties through the obtained nonlinear deep transfer method. Interestingly, the Mexican hat parameters can solely be described by the corresponding electronegativities in contrast with the SOC bandgap. • It is shown that the spin–orbit correction for the electronic properties of group-III monochalcogenides is predictable by their corresponding bond polarizabilities. • SOC-based correction for the bandgap and Mexican hat have been calculated from the non-relativistic results together with the bond polarizability parameter. • Bandgap and Mexican hat is obtained by a nRMSE of 2.8e−4 and 3.2e−4, respectively. • The transfer learning method has been selected to compensate the size of the dataset. • The proposed method reduces the high processing cost associated with the SOC correction calculations by the inclusion of the simple parameter of bond polarizability. • It is shown that the Mexican hat parameters can solely be described by the corresponding electronegativities in contrast with the SOC bandgap.

Experimental and theoretical investigation of FeCrVAl and related compounds

We have carried out a combined theoretical and experimental investigation of FeCrVAl, and the effect of Mn and Co doping on its structural, magnetic, and electronic band properties. Our first principles calculations indicate that FeCrVAl, FeCr0.5Mn0.5VAl, and FeCr0.5Co0.5VAl exhibit nearly perfect spin polarization, which may be further enhanced by mechanical strain. At the same time, FeCrV0.5Mn0.5Al and FeCrV0.5Co0.5Al exhibit a relatively small value of spin polarization, making them less attractive for practical applications. Using arc melting and high vacuum annealing, we synthesized three compounds FeCrVAl, FeCr0.5Mn0.5VAl, and FeCr0.5Co0.5VAl, which are predicted to exhibit high spin polarization. The room temperature x-ray diffraction patterns of all samples are fitted with full B2 type disorder with a small amount of FeO2 secondary phase. All samples show very small saturation magnetizations at room temperature. The thermomagnetic curves M(T) of FeCrVAl and FeCr0.5Co0.5VAl are similar to that of a paramagnetic material, whereas that of FeCr0.5Mn0.5VAl indicates ferrimagnetic behavior with the Curie temperature of 135 K. Our findings may be of interest for researchers working on Heusler compounds for spin-based electronic applications.

Janus two-dimensional transition metal dichalcogenides

Structural symmetry plays a crucial role in the electronic band structure and properties of two-dimensional materials. In contrast to graphene, monolayer transition metal dichalcogenides exhibit intrinsic in-plane asymmetry with suitable direct bandgaps and distinctive optical properties. Efforts have been devoted to breaking their out-of-plane mirror symmetry by applying external electric fields, vertical stacking, or functionalization. The successful fabrication of Janus transition metal dichalcogenides offers a synthetic strategy to breaking the vertical mirror symmetry, leading to a variety of novel properties, such as vertical piezoelectricity, Rashba spin splitting, and excellent exciton properties. Here, we discuss the universal fabrication approaches and unique properties of Janus transition metal dichalcogenides and further present a brief perspective on their potential applications and challenges.

First-principles calculations to investigate structural, electronic and phonon properties of sodium bromide (NaBr) and sodium iodide (NaI) crystals

In this paper, the first-principles study is performed to calculate the structural, electronic and phonon properties of alkali halides NaBr and NaI. The calculations for structural and electronic properties have been carried out using the full-potential linearized augmented plane-wave (FP-LAPW) method that is employed in the WIEN2k code, whereas the phonon properties are studied using the Quantum Espresso program based on density-functional theory within plane-wave fundamental sets and pseudo-potentials approaches. The calculation of structural, electronic band properties were carried out using generalized gradient approximation (GGA), local-density approximation (LDA) and a combination of modified Becke-Johnson exchange potential with LDA and GGA (TB-mBJ-GGA/LDA) for exchange-correlation potential. The calculated structural parameters are in good agreement with experimental results. In our electronic calculations, the obtained bandgaps are underestimated by LDA and GGA functionals compared to empirically derived results, which is an expected result. However, the calculated bandgaps by the modified Becke-Johnson exchange potential are in perfect agreement with the experiment. Finally, the dynamic properties of NaBr and NaI compounds were investigated. Both phonon dispersion and phonon density of states curves were calculated for compounds along with the high symmetry directions in the Brillouin region. The dynamical properties of NaBr and NaI crystals are analyzed and discussed.

Comprehensive quantum transport analysis of M-superlattice structures for barrier infrared detectors

In pursuit of designing superior type-II superlattice barrier infrared detectors, this study encompasses an exhaustive analysis of utilizing M-structured superlattices for both the absorber and barrier layers through proper band engineering and discusses its potential benefits over other candidates. The electronic band properties of ideally infinite M-structures are calculated using the eight band k.p method that takes into account the effects of both strain and microscopic interface asymmetry to primarily estimate the bandgap and density-of-states effective mass and their variation with respect to the thicknesses of the constituent material layers. In contrast, for practical finite-period structures, the local density-of-states and spectral tunneling transmission and current calculated using the Keldysh non-equilibrium Green’s function approach with the inclusion of non-coherent scattering processes offer deep insights into the qualitative aspects of miniband and localization engineering via structural variation. Our key results demonstrate how to achieve a wide infrared spectral range, reduce tunneling dark currents, induce strong interband wavefunction overlaps at the interfaces for adequate absorption, and excellent band-tunability to facilitate unipolar or bipolar current blocking barriers. This study, therefore, perfectly exemplifies the utilization of 6.1 Å material library to its full potential through the demonstration of band engineering in M-structured superlattices and sets up the right platform to possibly replace other complex superlattice systems for targeted applications.

Silver nanoparticle-embedded titania nanobelts with tunable electronic band structures and plasmonic resonance for photovoltaic application

Metallic silver nanoparticle (NP)-embedded single-crystalline titania (Ag@TiO2) nanobelts have been prepared by a new process with use of sodium titanates sequentially from ion exchange, thermal hydrogenation to post-calcination. The structural transformation involved and their morphology were characterized. This work explored photovoltaic efficiency of these composite nanobelts as anode materials in dye-sensitized solar cells and their electronic and energy band properties, which correlate with the Ag content. Optical absorption and photoluminescence analyses reveal core Ag NP-induced localized surface plasmon resonance (LSPR) and mediated electron transfer within the titania shell. According to Mott-Schottky analysis, the Ag addition causes an increase in the donor density and an upshift in the flat-band potential of the oxide host. The investigated Ag@TiO2 cells produced higher photocurrents and open-circuit voltages than the bare TiO2 one, and the best performance was attained with a marked enhancement by 72% in the photovoltaic efficiency. As indicated by electrochemical impedance analysis, the Ag-added nanobelts are beneficial to rapid electron diffusion and electron lifetime, so that they promote charge collection efficiency. Synergistic combination of plasmonic resonance, electronic conduction and Fermi-level upshift is a plausible strategy to functionalize the one-dimensional core-shell Ag@TiO2 nanostructures for optoelectronic applications.

Density functional theory study on the influence of tension and compression deformation on the electrical and phonon properties of monolayer and bilayer graphene.

Based on first-principles calculations using density functional theory, this paper systematically studies the effects of uniaxial tension-compression deformation on the stability and electrical and thermal properties of monolayer graphene and AA stacked bilayer graphene. The study shows that the original symmetry of graphene is broken by the tensile and compression deformations, catalyzing the interlayer coupling of bilayer graphene. Its electronic energy band, phonon dispersion, and other physical properties have changed. The transition from metalloid to semiconductor has completed since the deformation weakens the stability of the graphene system to varying degrees and opens the band gap of monolayer graphene. The band gap becomes larger with the increase of tensile and compressive deformation, in which way it can be adjusted. Influenced by the tiny tensile deformation, metalloid properties are exhibited by a small band gap of intrinsic AA-stacked bilayer graphene, and then the band gap becomes larger as the deformation increases. A band gap appears in the system phonon dispersion curves when the compression deformation increases to -15%. The phonon mode softens and shows virtual frequency. The value of virtual frequency increases with the increase of compression deformation. At the very moment, the vibration mode is discontinuous, and the system is unstable.

Theoretical study of the band structure of 2H-SiC and 4H-SiC of silicon carbide polytypes

We have studied the electronic band properties of 2H-SiC and 4H-SiC silicon carbide polytypes. The structures of the electronic bands and density of state (DOS) using ab initio Density Functional Theory (DFT) were calculated for the first Brillouin zone both in the generalized gradient approximation and taking into account quasiparticle effects according to the GW scheme. The calculated bandgaps obtained using the GW approximation Eg2H-SiC = 3.17 eV and Eg4H-SiC = 3.26 eV agree well with experimental values. The shape and values of total DOS are within agreement with calculations performed by other authors. The calculated total energy values for 2H-SiC and 4H-SiC were close, but they satisfy the condition E2H > E4H, which implies that the 4H-SiC structure is more stable than 2H-SiC. Our calculations of the band structure and DOS of 2H-SiC and 4H-SiC by the DFT method showed that the application of the GW approximation is an optimum approach to the study of the electronic structure of 2H-SiC and 4H-SiC polytypes.

Tunable two dimensional ferromagnetic topological half-metal CrO2 by electronic correction and spin direction

Spintronics is one of the most promising information technologies now, especially for nontrivial topological Dirac half-metal, which exhibits extraordinary electronic band and transport properties. In this work, we propose that 1T-CrO2 nanosheet is mechanical stable, large spin-gap, and room temperature ferromagnetic Dirac half metal. It also exhibits a desirable giant magneto band structure effect, and when the spin direction is switched from in-plane to out-of-plane with a spin orbital coupling effect, it will exhibit nontrivial topological phase transition. The topological tunable electronic band property makes it a very promising two-dimensional nanosheet for spintronics.

First-principles identification of the charge-shifting mechanism and ferroelectricity in hybrid halide perovskites

Hybrid halide perovskite solar cells have recently attracted substantial attention, mainly because of their high power conversion efficiency. Among diverse variants, (CH3NH3)PbI3 and HC(NH2)2PbI3 are particularly promising candidates because their bandgap well matches the energy range of visible light. Here, we demonstrate that the large nonlinear photocurrent in β-(CH3NH3)PbI3 and α-HC(NH2)2PbI3 is mostly determined by the intrinsic electronic band properties near the Fermi level, rooted in the inorganic backbone, whereas the ferroelectric polarization of the hybrid halide perovskite is largely dominated by the ionic contribution of the molecular cation. The spatial charge shift upon excitation is attributed to the charge transfer from iodine to lead atoms in the backbone, which is independent of the presence of the cationic molecules. Our findings can serve as a guiding principle for the design of future materials for halide-perovskite solar cells with further enhanced photovoltaic performance.

Robust and Efficient Electrical Injection of Spin-Polarized Carriers from a Zero-Spin-Gap Half-Metal V2NiAl into n-Si at Room Temperature

In recent times, an engrossing and newly discovered class of materials with unique electronic band properties, namely, zero-spin-gap half-metal, has gained acute attraction worldwide because of its...

Structural, electronic, optical and magnetic properties of EuO and DyO compounds: ab initio study

ABSTRACT In this manuscript, we discussed an ab initio analysis of the structural, electronic, optical and magnetic properties of LnO (Ln = Eu, Dy) compounds. Our assessments were performed by the augmented plane wave method FP LAPW founded on the DFT (density functional theory) and introduced in the Wien2k calculation code. This investigation of the electronic band, structural, optical and magnetic properties were performed using a combination of modified Becke–Johnson exchange potential plus GGA + U-mBJ for exchange-correlation potential. In our study, the ferromagnetic behavior of the two compounds is very clear with magnetic moments of around 7 µB for EuO and 5 µB for DyO. The structure transitions for these materials from B1 to B2 are possible at high pressures and the calculation of the band structure shows that DyO has a direct gap (X–X).

WSe2 2D p‐type semiconductor‐based electronic devices for information technology: Design, preparation, and applications

AbstractThe pioneering exfoliation of monolayer tungsten diselenide has greatly inspired researchers toward semiconducting applications. WSe2 belongs to a family of transition‐metal dichalcogenides. Similar to graphene, WSe2 and analogous dichalcogenides have layered structures with weak van der Waals interactions between two adjacent layers. First, the readers are presented with the fundamentals of WSe2, such as types, morphologies, and properties. Here, we report the characterization principles and practices such as microscopy, spectroscopy, and diffraction. Second, the methods for obtaining high‐quality WSe2, such as exfoliation, hydrothermal and chemical vapor deposition, are briefly listed. With advantages of light weight, flexibility, and high quantum efficiency, 2D materials may have a niche in optoelectronics as building blocks in p‐n junctions. Therefore, we introduce a state‐of‐the‐art demonstration of heterostructure devices employing the p‐type WSe2 semiconductor. The device architectures include field‐effect transistors, photodetectors, gas sensors, and photovoltaic solar cells. Due to its unique electronic, optical, and energy band properties, WSe2 has been increasingly investigated due to the conductivity of the p‐type charge carrier upon palladium contact. Eventually, the dynamic research on WSe2 and van der Waals heterostructures is summarized to arouse the passion of the 2D research community.image

Specific heat, thermal conductivity, electron transport and electronic band properties of CeNi9In2

We report the results of specific heat Cp(T), thermal conductivity κ(T), thermoelectric power S(T), magnetoresistance MR(H) and Hall coefficient RH(H,T) measurements on an intermediate valence (IV) CeNi9In2 compound in the temperature range 2–300 ​K and in magnetic fields up to 9 ​T. In addition, the data of DFT calculations using FP-LMTO ​+ ​LDA and FP-LAPW ​+ ​PBE-GGA methods are presented. The studied sample reveals an enhanced Sommerfeld coefficient, metallic behaviour in κ(T), S(T), MR(H) and RH(T) properties, but does not exhibit clear crossover phenomenon expected for IV compounds. The DFT studies enunciate a weak 4f-3d hybridization and a major input to density of states at the Fermi level coming from the Ni 3d-electrons. These findings indicate that the contribution of the Ni atoms on the physical properties prevails over that of CeNi9In2 and hence the characteristics of IV of the Ce atoms cannot be demonstrable in the measured physical quantities.

Unified Assessment of the Effects of Van der Waals Interactions on the Structural and Electronic Properties of Some Layered Organic Solids κ-(BEDT-TTF)2X

Proper inclusion of van der Waals interactions (vdW) in ab initio calculations based on the density functional theory (DFT) is crucial to describe soft, organic, layered solids such as κ -(BEDT-TTF) 2 X . Since no consensus has been reached on the reliability of available vdW DFT functionals, most of the first principles calculations have been based on experimental crystal structure data without any structural optimization. Here, we explore optimal DFT-based schemes that account for the effects of vdW interactions on the structural and electronic band properties of three paradigmatic charge transfer salts, κ -(BEDT-TTF) 2 Cu 2 (CN) 3 , κ -(BEDT-TTF) 2 Ag 2 (CN) 3 , and κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl, for which a unified optimization of the structure is possible. Detailed examination of the prototype test system κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl shows that the optB88-vdW functional performs slightly better than the PBE-vdW and that the choice of pseudopotentials is critical to obtaining realistic results.

Electronic structure and optical properties of Cd co-doped wurtizte GaN exposed from first principles study

Abstract We have diligently studied the impact of cadmium (Cd) co-doping on electronic structure, the thickness of states and optical properties of wurtzite gallium nitride (GaN) inside the casing work of first rule thickness useful hypothesis (density functional theory (DFT)). From the electronic structure of single and twofold Cd-doped GaN, it is discovered that Cd-doped GaN is a run of the mill coordinate band hole semiconductor. Be that as it may, d orbitals of Cd are powerful hybridized with the p orbitals of N close to the Fermi level, bringing about p and d charge exchange among Cd and N molecules. This offer ascent to the intersection from a semi-metal to whole metal when a solitary and double of Cd dopant actualized. Besides, we likewise ascertained the optical properties of GaN semiconductor, for example, retention coefficient, reflectivity, and refractive list, which are broke down, and contrasted and those of Cd co-doped GaN. The enhanced electronic band and optical properties of Cd co-doped GaN upgraded the future utilization of optoelectronic gadgets for such sort of materials.