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Ag-doping treatment is a popular method for enhancing the performance of kesterite-structured Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Among the various methods, incorporating a high concentration of Ag+ into an absorber surface has proven to be particularly effective. However, the exact mechanisms behind this improvement are still unclear. This study aims to investigate the key factors that improve device performance through simulation. Specifically, the influence of the change in the carrier density, CuZn antisite defects, interface defect density, and formation of an n-type AZTSSe surface after heavy surface Ag doping have been examined. The simulation results indicate that the formation of an n-type AZTSSe layer on an absorber surface can significantly improve the open circuit voltage (VOC) and overcome the efficiency saturation problem induced by severe interface recombination for CZTSSe devices with a negative conduction band offset (CBO), compared to other affecting factors. This is because the modified conduction band alignment and the realization of interface-type inversion reduce interface recombination and retard the Fermi level pinning. However, the formation of interface-type inversion does not significantly improve CZTSSe devices with a positive CBO, as these devices already have weaker interface recombination. This work implies that the formation of an n-type AZTSSe layer is crucial for further improving the performance of CZTSSe devices with a negative CBO and can pave the way for improving the performance of thin film solar cells with severe interface recombination. [ABSTRACT FROM AUTHOR]

The massive amount of wasted heat energy from industry has pushed the development of thermoelectric (TE) materials that directly convert heat into electricity to a new level of concern. Recently, multicomponent alloys such as GeTe-based and PbSe-based high-entropy (HE) chalcogenides have attracted a great deal of attention due to their potential application as TE materials. The nature of the interatomic bonding, lattice distortion (LD), and the electronic structure in this class of materials is not fully understood. Herein, we report a comprehensive computational investigation of nine GeTe-based HE alloys with eight metallic elements (Ag, Pb, Sb, Bi, Cu, Cd, Mn, and Sn) with large supercells of 1080 atoms each; seven PbSe-based HE solid solutions: Pb0.99−ySb0.012SnySe1−2xTexSx (x = 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, with y = 0) with supercells of 1000 atoms each; and five Pb0.99−ySb0.012SnySe1−2xTexSx (y = 0.05, 0.1, 0.15, 0.2, 0.25 with x = 0.25) solid solutions with supercells of 1000 atoms each. All these HE models are theoretically investigated for the first time. The electronic structure, interatomic bonding, charge transfer, and lattice distortion (LD) are investigated by first-principles calculations based on density functional theory. Multicomponent HE alloys can cause a significant LD, which affects their mechanical, thermal, and TE properties. The calculations for the GeTe-based HE chalcogenides showed that they are semiconductors with a narrow bandgap, except for m8, which has a semi-metallic characteristic, and this makes them good candidates for TE applications. For most of these models, the Fermi level shifts upward and locates deeply in the conduction bands, resulting in the enhancement of the electrical conductivity (σ). The bonding properties showed that most bonds in m5 are more dispersed, indicating highest LD and lower lattice thermal conductivity. For PbSe-based HE solid solutions, the LD calculations showed that the models Pb0.99Sb0.012Se0.5Te0.25S0.25 and Pb0.89Sb0.012Sn0.1Se0.5Te0.25S0.25 have the higher LD, and thus a lower lattice thermal conductivity. Such investigations are in high demand since it enables us to design new HE chalcogenides for TE applications. We use the novel concept of total bond order density as a single quantum mechanical metric to characterize the internal cohesion of these HE alloys and correlate with calculated properties, especially the mechanical properties. This work provides a solid database for HE chalcogenides and a road map for many potential applications. Moreover, the computational procedure we developed can be used to design new HE chalcogenides for specific TE applications. [ABSTRACT FROM AUTHOR]

The characteristic polytype behaviors of SiC and accompanying low stacking fault energies are known to cause engineering issues, including polytype inclusions and bipolar degradation. The dependence of the relative stability of SiC polytypes and stacking fault energies on excess carrier concentration was investigated using first-principles calculations. The relative energy of 2H-, 4H-, and 6H-SiC to 3C-SiC increased with the excess electrons over 2 × 1019 cm−3, while the energy variation with excess holes was small. The stacking fault energies in 4H-SiC also exhibited a significant decrease with excess electrons over 1.0 × 1019 cm−3, whereas this change was minor with excess holes. These excess carrier dependencies were attributed to variations in the bandgap between polytypes. The energy level of the excess electrons was at the conduction band minimum; this was lowest in 3C-SiC, which had the lowest bandgap energy. Consequently, the energy of 3C-SiC with excess electrons was lower than that of other polytypes. Conversely, the valence band maximum lacked electrons when excess holes were present, resulting in a small difference among the Fermi levels of the polytypes. Hence, the energy difference between the SiC polytypes was similar for excess holes. Similarly, the stacking faults in SiC exhibited quantum-well structures by incorporating other polytypes with different bandgaps. With excess electrons, the Fermi level within the stacking faults was lower than that in the bulk crystals. Consequently, the stacking fault energy decreased for the same reason that the energy in 3C-SiC decreased under excess electron conditions. [ABSTRACT FROM AUTHOR]

We apply an Ising-type model to estimate the bandgaps of the polytypes of group IV elements (C, Si, and Ge) and binary compounds of groups: IV–IV (SiC, GeC, and GeSi), and III–V (nitride, phosphide, and arsenide of B, Al, and Ga). The models use reference bandgaps of the simplest polytypes comprising 2–6 bilayers calculated with the hybrid density functional approximation, HSE06. We report four models capable of estimating bandgaps of nine polytypes containing 7 and 8 bilayers with an average error of ≲0.05 eV. We apply the best model with an error of < 0.04 eV to predict the bandgaps of 497 polytypes with up to 15 bilayers in the unit cell, providing a comprehensive view of the variation in the electronic structure with the degree of hexagonality of the crystal structure. Within our enumeration, we identify four rhombohedral polytypes of SiC—9R, 12R, 15R(1), and 15R(2)—and perform detailed stability and band structure analysis. Of these, 15R(1) that has not been experimentally characterized has the widest bandgap (> 3.4 eV); phonon analysis and cohesive energy reveal 15R(1)-SiC to be metastable. Additionally, we model the energies of valence and conduction bands of the rhombohedral SiC phases at the high-symmetry points of the Brillouin zone and predict band structure characteristics around the Fermi level. The models presented in this study may aid in identifying polytypic phases suitable for various applications, such as the design of wide-gap materials, that are relevant to high-voltage applications. In particular, the method holds promise for forecasting electronic properties of long-period and ultra-long-period polytypes for which accurate first-principles modeling is computationally challenging. [ABSTRACT FROM AUTHOR]

Bipolar magnetic semiconductor (BMS) has special electronic structures; i.e., its conduction band minimum (CBM) and valence band maximum (VBM) are completely spin-polarized in opposite directions. In this work, the band structures of 2H-VX2 (X = S, Se, and Te) are examined through first-principles calculations, and the results show that both 2H-VS2 and 2H-VSe2 are BMSs, while 2H-VTe2 is a unipolar magnetic semiconductor (UMS); i.e., its CBM and VBM show the same spin direction. Most interestingly, we find that electronic orbitals near the Fermi level of 2H-VX2 are occupied by d z 2 and d x y orbitals, which can be effectively modulated by the biaxial strain. With appropriate strain modulations, 2H-VX2 can be BMS, UMS, or half-metal (HM). Our investigation reveals strain effects on the band structure of 2H-VX2, which greatly enhances their significance in spintronics. [ABSTRACT FROM AUTHOR]

This work explores the characteristics of two-dimensional (2D) titanium carbide (Ti3C2 MXene) and utilizes first-principles study to weigh its potential for supercapacitor applications. Scanning electron microscopy images confirm the layered morphology of the MXene, and energy-dispersive X-ray spectroscopy (EDX) analysis supports the extraction of aluminum from the MAX phase. Fourier-transform infrared (FTIR) spectroscopy confirms the presence of oxygen-based functional groups on the surface of the MXene and X-ray diffraction (XRD) patterns validate its hexagonal crystalline structure. Cyclic voltammetry (CV) analysis reveals the presence of redox peaks, indicating the pseudocapacitive behaviour of the fabricated electrode. Additionally, galvanostatic charge–discharge (GCD) measurements yield a calculated specific capacitance of 370 F g−1. Electrochemical impedance spectroscopy (EIS) substantiates the low impedance resulting from the layered structure via the adequate adsorption/desorption of cations. The utilization of first-principles density functional theory (DFT) calculations reveals the merging of conduction and valence bands, signifying effective conductivity. Both the total and partial density of states cross the Fermi level, indicating a highly efficient charge mobility process. The combination of prominent surface redox reactions and excellent conductivity contributes to the superior specific capacitance of the fabricated electrode. Overall, these results highlight the excellent electrochemical properties of the Ti3C2 MXene electrode, declaring it as a promising candidate for supercapacitor applications. [ABSTRACT FROM AUTHOR]

Density-functional theory calculations on P-rich InP(001):H surfaces are presented. Depending on temperature, pressure and substrate doping, hydrogen desorption or adsorption will occur and influence the surface electronic properties. For p-doped samples, the charge transition levels of the P dangling bond defects resulting from H desorption will lead to Fermi level pinning in the lower half of the band gap. This explains recent experimental data. For n-doped substrates, H-deficient surfaces are the ground-state structure. This will lead to Fermi level pinning below the bulk conduction band minimum. Surface defects resulting from the adsorption of additional hydrogen can be expected as well, but affect the surface electronic properties less than H desorption. [ABSTRACT FROM AUTHOR]

Recently, the MoSi2N4(MoN)4n homologous compounds have been synthesized, extending the MA2Z4 family materials to the superthick MA2Z4(MZ)n form. Herein, a first‐principles study on the double‐transition‐metal W2TiSi2N6 and related group VI–IV M2M′Si2N6 nanosheets is performed. Robust structural stability is affirmed in this W2TiSi2N6 nanosheet from the energetic, mechanical, dynamical, and thermal perspectives. Unlike the WSi2N4 and WSi2N4(WN)n systems, the W2TiSi2N6 nanosheet exhibits a semimetal behavior with the top valence and bottom conduction bands touching each other at the Fermi level. With the inclusion of spin–orbit coupling, a nontrivial band gap is opened in the W2TiSi2N6 nanosheet, which has a sizeable bulk gap of 0.11 eV. The Z2 invariant is 1 and a pair of topologically protected edge states emerges in the gap region, confirming that W2TiSi2N6 nanosheet is a quantum spin Hall (QSH) insulator. Through in‐plane strain engineering, the bulk gap can be further increased to 0.23 eV, which is sufficiently large for the room‐temperature QSH effect. Such a large‐gap QSH state is also present in other group VI–IV M2M′Si2N6 systems with the combinations of MM′ = WZr, MoZr, and MoHf. This study demonstrates that the double‐metal M2M′Si2N6 nanosheets are promising candidates to realize fascinating topological quantum states. [ABSTRACT FROM AUTHOR]

The combination of strongly coupled Cooper pairs and weak superconducting fluctuations is an important prerequisite for achieving high-temperature superconductivity. The review is devoted to the implementation of this condition in multiband superconductors, in which strongly coupled pairs in the shallow conduction band (the Fermi level is close to the band edge) coexist with ordinary, weakly fluctuating Cooper pairs formed in the deep band. As a result of the Josephson coupling between condensates in different bands, such a system is characterized by a high critical coherence temperature due to the presence of strongly coupled pairs and the suppression of superconducting fluctuations. This suppression does not require any special preconditions, and is almost total even if the Josephson coupling between the bands is weak. [ABSTRACT FROM AUTHOR]

To study the vacancy mechanism of In2O3, we apply the first‐principles method to study the influence of vacancy on the structural stability, electronic and optical properties of the rhombohedral In2O3. Two vacancies: In‐vacancy (V‐In) and O‐vacancy (V‐O) are considered here. The calculated results show that the rhombohedral In2O3 with In‐vacancy and O‐vacancy are thermodynamic and dynamical stabilities based on the vacancy formation energy and phonon dispersion. In particular, In‐vacancy has better thermodynamic stability in comparison to the O‐vacancy. Importantly, the rhombohedral In2O3 exhibits ultraviolet properties. However, two vacancies lead to the peak migration from the ultraviolet region to the visible light region. Furthermore, it is found that the calculated band gap of In2O3 with In‐vacancy is 1.07 eV, which is wider than the parent In2O3 (0.841 eV). Naturally, the wide band gap of In‐vacancy is that the removed In atom aggravates the difficulty of the electronic interaction between the conduction band and the valence band near the Fermi level. On the contrary, O‐vacancy shows metallic behavior because O‐vacancy (V‐O) enhances the electronic interaction near the Fermi level. [ABSTRACT FROM AUTHOR]

How and why the reliability of ferroelectric HfO2‐ and HZO (Hf0.5Zr0.5O2)‐based memory devices strongly depends on the choice of electrode materials is currently under intense discussion. Interface conditions such as band alignment, defect formation, and doping are recognized as decisive and interrelated parameters, but a unified picture of the physical mechanisms is still missing. Here, two opposite scenarios of band alignment are found in TiN/HZO/TiN and IrO2/HZO/IrO2 using hard X‐ray photoelectron spectroscopy, revealing on the one hand the conditions for a stable device performance, and the origin of their degradation on the other. As a key difference, TiN electrodes scavenge oxygen from the HZO, while IrO2 electrodes supply it. Considering the electronic doping limit of HfO2, a key condition for the stability of ferroelectric devices can be identified: The alignment of the charge neutrality levelwith respect to the metallic Fermi level, which is pinned by the doping limit. Stable device performance can only be achieved for oxygen‐deficient HfO2‐based interfaces, where the Fermi level of the metal electrode is close to the conduction band of the ferroelectric insulator. This empirical model explains the fatigue behavior of HfO2‐based capacitors using either oxygen‐scavenging TiN or oxygen‐supplying IrO2 electrodes. [ABSTRACT FROM AUTHOR]

Using the pyrolyzing polymer‐salt compositions method yttrium orthochromite (space group Pnma) was synthesized. A value of oxygen nonstoichiometry δ=.056 and a band gap of 1.64 eV were obtained. With the experimentally determined structural parameters as a basis, we performed ab initio simulations to investigate the defect structure of YCrO3±δ. We studied the presence of interstitial oxygen in the YCrO3 at oxygen nonstoichiometry close to the experimental value and vacancies at the same concentration. Formation energies were estimated for interstitial oxygen atoms and compared with those of oxygen vacancies in the cases neutral and charged supercells. The computational results demonstrate that interstitial oxygen is energetically more favorable than the formation of oxygen vacancies. We considered various configurations of the interstitial oxygen atom within the YCrO3 crystal lattice and identified two fundamentally distinct types. An analysis of projected densities of states and charge distributions was performed for these configurations. The results indicate that direct intercalation of oxygen atoms is energetically more favorable than the formation of a peroxide species when the Fermi level is close to the conduction band minimum. [ABSTRACT FROM AUTHOR]

A magnetic field parallel to the layers of a double quantum well with conventional semiconductor constituents leads to a relative shift of the conduction band spectra of the constituent layers along the wave vector perpendicular to the field. If the states of the layers are tunnel-coupled, a tunneling gap is formed at the intersection of the single-layer spectra and is shifted upward with increasing field. This leads to striking features in the magnetoresistance caused by intersections of the Fermi level with the edges of the tunneling gap. Similar studies of transformations of the spectrum of the double quantum well in a HgTe/CdHgTe heterosystem, which has a p-type conductivity and HgTe layers with a gapless inverse energy spectrum, are reported in this work. Our experiments and corresponding calculations in the eight-band kp approach indicate that the evolution of the magnetoresistance with the variation of the in-plane field here has a much more complex and diverse character depending qualitatively on the thickness of the layers. [ABSTRACT FROM AUTHOR]

This work investigates the function of the oxygen partial pressure in photo-induced current measurement of extended defect properties related to the distribution and quantity of defect states in electronic structures. The Fermi level was adjusted by applying a negative gate bias in the TFT structure, and the measurable range of activation energy was extended to < 2.0 eV. Calculations based on density functional theory are used to investigate the changes in defect characteristics and the role of defects at shallow and deep levels as a function of oxygen partial pressure. Device characteristics, such as mobility and threshold voltage shift under a negative gate bias, showed a linear correlation with the ratio of shallow level to deep level defect density. Shallow level and deep level defects are organically related, and both defects must be considered when understanding device characteristics. [ABSTRACT FROM AUTHOR]

Perovskites attract attention as efficient light absorbers for solar cells due to their high-power conversion efficiency (up to 24%). The high photoelectric conversion efficiency is greatly affected by a suitable band structure. Cation substitution can be an effective approach to tune the electronic band structure of lead halide perovskites. In this work, superalkali cations were introduced to replace the Cs+ cation in the CsPbBr3 material. The bimetallic superalkalis (LiMg, NaMg, LiCa, and NaCa) were inserted since they are structurally simple systems and have a strong tendency to lose one electron to achieve a closed-shell cation. The cation substitution in the lead halide perovskite leads to changes in the shape of both valence and conduction bands compared to CsPbBr3. Introducing superalkali cations produces extra electronic states close to the Fermi level, which arise from the formation of alkali earth metal states at the top of the valence band. Our first-principles computations reveal that bimetallic superalkali substitution decreases the bandgap of the perovskite. The bandgaps of MgLi–PbBr3 (1.35 eV) and MgNa–PbBr3 (1.06 eV) are lower than the bandgap of CsPbBr3 (2.48 eV) and within the optimal bandgap (i.e., 1.1–1.4 eV) for single-junction solar cells. Thus, the MgLi–PbBr3 and MgNa–PbBr3 inorganic perovskites are promising candidates for high-efficiency solar cells. [ABSTRACT FROM AUTHOR]

The realization of the spin Hall effect has opened new frontiers for the design of efficient memory storage devices facilitated by the conversion of charge currents to spin currents. Here, using the Kubo formula, we calculate the intrinsic spin Hall conductivity (SHC) of orthorhombic tin selenide (o-SnSe) under the influence of isotropic compressive strain in the ab-plane. As the strain is gradually increased, we obtain a substantial hybridization between the pz orbitals of Sn and Se atoms of an electron pocket from the lowest conduction band and the topmost valence band, respectively. This hybridization process greatly enhances the SHC at the Fermi level and charge-to-spin conversion efficiency, the latter of which is superior to that of popular transition metals such as Ta and Pt. This makes strained o-SnSe an attractive candidate for use in spintronic devices. [ABSTRACT FROM AUTHOR]

Iron impurities are believed to act as deep acceptors that can compensate for the n-type conductivity in as-grown Ga2O3, but several scientific issues, such as the site occupation of the Fe heteroatom and the complexes of Fe-doped β-Ga2O3 with native defects, are still lacking. In this paper, based on first-principle density functional theory calculations with the generalized gradient approximation approach, the controversy regarding the preferential Fe incorporation on the Ga site in the β-Ga2O3 crystal has been addressed, and our result demonstrates that Fe dopant is energetically favored on the octahedrally coordinated Ga site. The structural stabilities are confirmed by the formation energy calculations, the phonon dispersion relationships, and the strain-dependent analyses. The thermodynamic transition level Fe3+/Fe2+ is located at 0.52 eV below the conduction band minimum, which is consistent with Ingebrigtsen's theoretical conclusion, but slightly smaller than some experimental values between 0.78 eV and 1.2 eV. In order to provide direct guidance for material synthesis and property design in Fe-doped β-Ga2O3, the defect formation energies, charge transitional levels, and optical properties of the defective complexes with different kinds of native defects are investigated. Our results show that VGa and Oi can be easily formed for the Fe-doped β-Ga2O3 crystals under O-rich conditions, where the +3 charge state FeGaGai and −2 charge state FeGaOi are energetically favorable when the Fermi level approaches the valence and conduction band edges, respectively. Optical absorption shows that the complexes of FeGaGai and FeGaVGa can significantly enhance the optical absorption in the visible-infrared region, while the energy-loss function in the β-Ga2O3 material is almost negligible after the extra introduction of various intrinsic defects. [ABSTRACT FROM AUTHOR]

Single-atom catalysts anchored to oxide or carbonaceous substances are typically tightly coordinated by oxygen or heteroatoms, which certainly impact their electronic structure and coordination environment, thereby affecting their catalytic activity. In this study, we prepared a stable oxygen evolution reaction (OER) catalyst on tungsten carbide using a simple pyrolysis method. The unique structure of tungsten carbide allows the atomic RuNi catalytic site to weakly bond to the surface W and C atoms. XRD patterns and HRTEM images of the WCx-RuNi showed the characteristics of phase-pure WC and W2C, and the absence of nanoparticles. Combined with XPS, the atomic dispersion of Ru/Ni in the catalyst was confirmed. The catalyst exhibits excellent catalytic ability, with a low overpotential of 330 mV at 50 mA/cm2 in 1 m KOH solutions, and demonstrates high long-term stability. This high OER activity is ascribed to the synergistic action of metal Ru/Ni atoms with double monomers. The addition of Ni increases the state density of WCx-RuNi near the Fermi level, promoting the adsorption of oxygen-containing intermediates and enhancing electron exchange. The larger proximity of the d band center to the Fermi level suggests a strong interaction between the d electrons and the valence or conduction band, facilitating charge transfer. Our research offers a promising avenue for reasonable utilization of inexpensive and durable WCx carrier-supported metal single-atom catalysts for electrochemical catalysis. [ABSTRACT FROM AUTHOR]

Altermagnetism can achieve spin-split bands in collinear symmetry-compensated antiferromagnets. Here, we predict altermagnetic order in Janus monolayer Cr2SO with eliminated inversion symmetry, which can realize the combination of piezoelectricity and altermagnetism in a two-dimensional (2D) material, namely, 2D piezoelectric altermagnetism. It is found that Cr2SO is an altermagnetic semiconductor, and the spin-split bands of both valence and conduction bands are near the Fermi level. The Cr2SO has large out-of-plane piezoelectricity ( | d 31 | = 0.97 pm/V), which is highly desirable for ultrathin piezoelectric device application. Due to spin-valley locking, both spin and valley can be polarized by simply breaking the corresponding crystal symmetry with uniaxial strain. Our findings provide a platform to integrate spin, piezoelectricity, and valley in a single material, which is useful for multi-functional device applications. [ABSTRACT FROM AUTHOR]

This work investigates the function of the oxygen partial pressure in photo-induced current measurement of extended defect properties related to the distribution and quantity of defect states in electronic structures. The Fermi level was adjusted by applying a negative gate bias in the TFT structure, and the measurable range of activation energy was extended to < 2.0 eV. Calculations based on density functional theory are used to investigate the changes in defect characteristics and the role of defects at shallow and deep levels as a function of oxygen partial pressure. Device characteristics, such as mobility and threshold voltage shift under a negative gate bias, showed a linear correlation with the ratio of shallow level to deep level defect density. Shallow level and deep level defects are organically related, and both defects must be considered when understanding device characteristics. [ABSTRACT FROM AUTHOR]

The off-stoichiometry i.e., ZrNi 1+δ Sn (0 < δ < 1), and carrier modulation are the two approaches that have separately been found effective mainly to reduce thermal conductivity and improve power factor. This work explores the combined effect of both of these approaches by tuning the carrier density by varying the Sb-concentration in off-stoichiometric ZrNi 1.04 Sn, which shifts the Fermi level towards the conduction band as confirmed by the band structure calculations. The maximum thermoelectric figure-of-merit ZT∼0.95 at ∼873 K was achieved in the optimum composition ZrNi 1.04 Sn 0.975 Sb 0.025. For evaluating the device applicability of the synthesized materials, the cumulative temperature dependence (CTD) model was applied, predicting the single leg maximum efficiency ∼8.6% at ΔT ∼ 546 K. A series of calculations have been performed to predict electronic band structure and electronic transport properties to unearth the underlying physics. The microhardness and fracture toughness were determined to ensure that the enhanced thermoelectric performance is not deteriorating mechanical robustness. [ABSTRACT FROM AUTHOR]

Dirac semimetals are classified into different phases based on the types of Dirac fermions. Tuning the transition among different types of Dirac fermions in one system remains a challenge. Recently, KMgBi was predicted to be located at a critical state in which various types of Dirac fermions can be induced owing to the existence of a flatband. Here, we carried out systematic studies on the electronic structure of KMgBi single crystals by combining angle-resolve photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. The flatband was clearly observed near the Fermi level. We also revealed a small bandgap of ∼20 meV between the flatband and the conduction band. These results demonstrate the critical states of KMgBi that transition among various types of Dirac fermions can be tuned in one system. [ABSTRACT FROM AUTHOR]

The halide perovskites have truly emerged as efficient optoelectronic materials and show the promise of exhibiting nontrivial topological phases. Since the bandgap is the deterministic factor for these quantum phases, here, we present a comprehensive electronic structure study using first-principle methods by considering nine inorganic halide perovskites CsBX3 (B = Ge, Sn, Pb; X = Cl, Br, I) in their three structural polymorphs (cubic, tetragonal, and orthorhombic). A series of exchange–correlation (XC) functionals are examined toward accurate estimation of the bandgap. Furthermore, while 13 orbitals are active in constructing the valence and conduction band spectra, here, we establish that a 4 orbital based minimal basis set is sufficient to build the Slater–Koster tight-binding (SK-TB) model, which is capable of reproducing the bulk and surface electronic structures in the vicinity of the Fermi level. Therefore, like the Wannier based TB model, the presented SK-TB model can also be considered an efficient tool to examine the bulk and surface electronic structures of the halide family of compounds. As estimated by comparing the model study and DFT band structure, the dominant electron coupling strengths are found to be nearly independent of XC functionals, which further establishes the utility of the SK-TB model. [ABSTRACT FROM AUTHOR]

Van der Waals heterostructures (vdWHs) are effective platforms for exploring various attractive topological phases. Here, based on the low-energy effective k · p model, we propose that the type-III vdWHs, which were previously considered as only belonging to trivial metallic phases, can realize the nontrivial quantum spin Hall (QSH) effect. We reveal that the band inversion of such a QSH phase is attributed to the band alignment of momentum space matching, i.e., the conduction band minimum and valence band maximum located at the same point in momentum space near the Fermi level. Moreover, using first-principles calculations, we show that the Mg(OH)2/Ga2O2 heterobilayer, a typical type-III vdWH with high thermodynamic stability, is an ideal candidate for achieving our strategy. We further calculate the helical gapless edge states and quantized spin Hall conductance, which are visible inside the global bandgap, thus facilitating the experimental observation. Our work offers a promising pathway for realizing the QSH phase in natural materials. [ABSTRACT FROM AUTHOR]

This work reports a high‐detectivity solar‐blind deep ultraviolet photodetector with a fast response speed, based on a nitrogen‐doped graphene/βGa2O3/GaN p‐i‐n heterojunction. The i layer of βGa2O3 with a Fermi level lower than the central level of the forbidden band of 0.2 eV is obtained by reversed substitution growth with oxygen replacing nitrogen in the GaN matrix, indicating the majority carrier is hole. X‐ray diffractometershows that the transformation of GaN into βGa2O3 with (−201) preferred orientation at temperature above 900 °C in an oxygen ambient. The heterojunction shows enhanced self‐powered solar blind detection ability with a response time of 3.2 µs (rise)/0.02 ms (delay) and a detectivity exceeding 1012 Jones. Under a reverse bias of −5 V, the photoresponsivity is 8.3 A W−1 with a high Ilight/Idark ratio of over 106 and a detectivity of ≈9 × 1014 Jones. The excellent performance of the device is attributed to 1) the continuous conduction band without a potential energy barrier, 2) the larger built‐in potential in the heterojunction because of the downward shift of Fermi energy level in β‐Ga2O3, and 3) an enhanced built‐in electric field in the βGa2O3 due to introducing p‐type graphene with a high hole concentration of up to ≈1020 cm−3. [ABSTRACT FROM AUTHOR]

Integrating chemical dopants into a pure lattice has fueled a novel concept of tuning the physical and chemical properties of existing materials under and beyond ambient conditions. By using density functional theory (DFT) calculations, we report the structural, electronic, elastic, and optical properties of pure and Mg-doped LaAlO3 structure (La1-xMgxAlO3 and LaAl1-xMgxO3), respectively, with the doping concentrations of x = 0%, 20%, 40%, 60%, 80%, and 100%. Our results show that the doping of Mg along La sites introduce new band (s, p) in the valence bands that is moved towards the conduction bands with increase of doping ration (at x = 60% with a reduced bandgap of 0.04 eV), as well as indirect to direct bandgap transition along Al sites. The density of states shows that the valence band shifts towards the Fermi level by inducing a metallicity in La1-xMgxAlO3 format at 60% configuration. Elastically, LaAlO3 experiences brittle to ductile transition for both doping systems except LaAl1-xMgxO3 at 40% configuration. The higher ranges of optical peaks for both systems are identified for 0%‒40% ranges as compared to other configurations. Fortunately, this study reveals the tunability of LaAlO3 structure in structural, electronic, elastic, and optical aspects, and also extends the availability of this material for future optoelectronic and mechanical applications. [ABSTRACT FROM AUTHOR]

Although changes in the electronic structure of Ti2O3 across the insulator‐to‐metal transition (IMT) by thermal excitation are generally investigated, the role of chemical doping in this context deserves attention. To gain insights into that, soft X‐ray photoelectron (XPS) and absorption spectroscopy (XAS) are adopted to investigate the electronic structure of Ti2O3 upon N doping. Core‐level and valence‐band spectra shift consistently to lower binding energies with N doping, indicating a downward movement of the Fermi level (EF) toward the surface. Meanwhile, valence‐band data reveals an increase in the electron population of the conduction band upon doping. The XAS results at the Ti L‐ and O K‐edge indicate that the a1g orbitals are partially occupied in the Ti3+ sites by N doping, with an enhanced Ti 3d–O 2p hybridization. Consistently, the density functional theory (DFT) calculations illustrate the metallic behavior in an N‐substituted system. It is important that N substitution results in a mixing of the a1g and egπ states because of considerable broadening of a1g orbitals across EF. These observations demonstrate the importance of Ti 3d‐a1g occupation relevant for transportation. This may provide significant insights into the IMT behavior after N doping in Ti2O3. [ABSTRACT FROM AUTHOR]

The use of titanium dioxide for tackling environmental pollution has attracted great research interest recently. The potential of a photocatalyst in removing contaminants depends mainly on its conduction and valence-band edges relative to the standard potential of reactive oxygen species. One of the methods used in determining these band-edge positions is via the Mott–Schottky analysis. Thus, the aim of this work was to investigate the influence of the Mott–Schottky frequency and different electrochemical conditions on flat-band potential values and band-edge positions of pure anatase or Degussa P25, calcined or uncalcined in a 0.2 M Na2SO4 solution. The results showed that the shift in the flat-band potential was not so frequency-dependent in the Mott–Schottky analysis, however, other reasons, such as immersion duration leading to thenardite Na2SO4 salt deposition on the surface, irradiation of sources and the change in the pH of the solution (in the range of 1.64–12.11) were also responsible for it. In general, both the calcined anatase and P25 had a less negative value of the flat-band potential compared to the uncalcined. On the other hand, the calcined anatase had a tendency to have a less negative value of the flat-band potential than the calcined P25. From this study, the frequency range for obtaining the flat-band potential within one standard deviation in the Mott–Schottky at a single-frequency analysis was found to be between 200 and 2000 Hz. The energy difference between the Fermi level and the conduction band edge for anatase and P25, either calcined or uncalcined, was 0.097–0.186 and 0.084–0.192 eV, respectively. On the other hand, the band-edge position of anatase or P25 tended to shift upwards when it was repeatedly used in the photoelectrochemical analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ag intercalated Bi 2 Se 3 samples were synthesised by hydrothermal method followed by cold pressing technique. • HRTEM images and IFFT pattern confirms the presence of stacking faults. • The slight fermi energy shift towards conduction band significantly improved the electrical conductivity. • Low lattice thermal conductivity of 0.3 W/mK obtained at 543 K by various scattering mechanism. • The peak zT of 0.3 was attained at 543 K due to the synergy of enhanced power factor and low lattice thermal conductivity. Bismuth Selenide is a Tellurium free topological insulator in V-VI compounds with an excellent thermoelectric performance from room temperature to mid-temperature region. Herein, hydrothermally prepared polycrystalline Bi 2 Ag x Se 3 nanostructures have been reported for thermoelectric application. The crystal structure identification and morphology with the elemental presence were analyzed by XRD (X-ray diffraction), HR-SEM with EDS (High resolution scanning electron microscope with energy dispersive X-ray), and HR-TEM (High-resolution transmission electron microscope) measurements. The reduced lattice thermal conductivity and enhanced electrical transport properties synergistically boost the thermoelectric properties through the highly-dense stacking faults with the presence of dislocations. The IFFT (Inverse Fast Fourier Transform) pattern reveals the existence of stacking faults and dislocations. These highly dense stacking faults and dislocations act as active phonon scattering centers, which can contribute to effective phonon scattering results in extremely low lattice thermal conduction of 0.3 W/mK at 543 K. On the other hand, the involvement of phonon–phonon scattering primarily reduced the lattice thermal conductivity at elevated temperatures. In addition, phonon-carrier scattering was less compared to phonon–phonon scattering at elevated temperature region. Moreover, the enhancement of electrical conductivity and controlled reduction of the Seebeck coefficient plays a vital role in achieving the maximum power factor of 335 μW/mK2 at 543 K due to the energy filtering effect. The synergistic combination of low thermal conduction and the maximum power factor helps to achieve the high peak zT of 0.3 at 543 K. [ABSTRACT FROM AUTHOR]

Using hybrid functional-based density functional theory calculations, we analyze the structure and kinetics of defects formed in two competing synthesis routes to prepare hydrogen-doped In 2 O 3 films, using a hydrogen and oxygen gas mixture vs synthesis in the presence of water vapor. For both of these synthesis routes, we find that H + is the dominant defect species: when the Fermi level is close to the conduction band, H + has a lower formation energy than other intrinsic or extrinsic defects. Our results also suggest that water molecules spontaneously split into H + (which occupies octahedral voids) and OH − interstitials (which occupies vacant oxygen lattice sites or oxygen vacancies). From the analysis of the binding energies between these different defects, we conclude that these defects do not cluster and are most likely to stay spatially distributed throughout the films. In addition, the sum of formation energies of an oxygen (i.e., O i 2 − ) and a H + interstitial is close to the formation energy of a OH − interstitial, meaning that water molecules are completely split into 2H + and O i 2 − at the synthesis conditions. Further, in the presence of H 2 + O 2 gas mixture, oxygen interstitials occupy oxygen vacancies while hydrogen interstitials occupy vacant oxygen lattice sites and form bonds with lattice oxygens. Our analysis of the defect equilibria suggests that the hydrogen content in films synthesized in the presence of water vapor is higher than films synthesized in the presence of a hydrogen gas mixture. At high dopant concentrations, a hydrogen bond network is formed in the system and this leads to large distortions in the lattice. [ABSTRACT FROM AUTHOR]

In the same way that gases interact with oxide semiconductor surfaces from above, point defects interact from below. Previous experiments have described defect–surface reactions for TiO2(110), but an atomistic picture of the mechanism remains unknown. The present work employs computations by density functional theory of the thermodynamic stabilities of metastable states to elucidate possible reaction pathways for oxygen interstitial atoms at TiO2(110). The simulations uncover unexpected metastable states including dumbbell and split configurations in the surface plane that resemble analogous interstitial species in the deep bulk. Comparison of the energy landscapes involving neutral (unionized) and charged intermediates shows that the Fermi energy EF exerts a strong influence on the identity of the most likely pathway. The largest elementary-step thermodynamic barrier for interstitial injection trends mostly downward by 2.1 eV as EF increases between the valence and conduction band edges, while that for annihilation trends upward by 2.1 eV. Several charged intermediates become stabilized for most values of EF upon receiving conduction band electrons from TiO2, and the behavior of these species governs much of the overall energy landscape. [ABSTRACT FROM AUTHOR]

Semiconductor–metal heterojunction nanostructures possess an ability to store electrons upon photoexcitation through Fermi level equilibration. The unique role of capping ligands in modulating the equilibration of Fermi level in CdSe–Au heteronanostructures is explored by taking alkyl thiols and alkyl amines as examples. Alkyl thiol having its highest occupied molecular orbital (HOMO) above the valence band of the heterojunction nanostructure inhibits the exciton recombination by scavenging the photogenerated hole. This leads to the elevation in the Fermi level of Au and equilibration with the conduction band of CdSe. The Fermi level equilibrated electrons are further transferred to an acceptor molecule such as methyl viologen, demonstrating the potential of heterojunction nanostructures capped with hole accepting ligands for charge transport application in photovoltaics. In contrast, alkyl amine being a non-hole acceptor ligand with its HOMO placed below its valence band promotes rapid Au mediated exciton recombination, limiting its usefulness in charge transport application. Thus, the energetics of ligands on heterojunction nanostructures plays a decisive role in Fermi level equilibration. [ABSTRACT FROM AUTHOR]

Hg3 In2 Te6 (MIT for short) is a stable phase corresponding to x =0. 5 in the II-IV/III-IV compound semiconductor Hg(3-3x) In2x Te3. In this paper, the stability and doping efficiency of Au in MIT were systematically investigated using the firstprinciples method. The results show that Au-Te bonds has polar covalent bond characteristics similar to that of Hg-Te bonds in MIT, indicating that Au has certain doping stability in MIT. In addition, it is found that there are amphoteric doping properties of Au in MIT: Au exhibits acceptor properties in AuHg and AuIn systems, and the Au-5d electron orbital resonates with the Te-5p electron orbital at the top of the valence band and - 4 eV position, respectively, forming acceptor defect levels. While Au exhibits donor characteristics in AuTe and AuI systems, Au-5d resonates with Hg-6s and In-5s electron orbitals at the conduction band bottom, forming donor defect levels. It is worth noting that under Hg-rich conditions, there will be a self-compensation effect between AuI, AuTe and AuHg systems, and the Fermi level will be pinned at the top of valence band, while under Te-rich conditions, the self-compensation effect will be effectively eliminated. [ABSTRACT FROM AUTHOR]

Based on density functional theory, the electronic and optical properties of double perovskites Ba2MnWO6 were studied using the generalized gradient approximation. We have looked into four magnetic configurations, such as collinear antiferromagnetic AF-1, AF-2 and noncollinear antiferromagnetic AF-NC1, AF-NC2 structures. The obtained results show that the valence band maximum is mainly dominated by Mn-3d orbitals, while the conduction band minimum is mainly composed of W-5d orbitals. In addition, Ba2MnWO6 is shown as an indirect band gap semiconductor. The gap between two main t2g,↑ and e2g,↑ manifolds of Mn-3d states, located at about 1.9 and 1 eV below Fermi level, is initiated as consequence of splitting in crystal field. From calculated optical results, Ba2MnWO6 indicates excellent light absorption in the ultraviolet range. Consequently, this material promises potential optical applications, such as solar cell functional in ultraviolet light. [ABSTRACT FROM AUTHOR]

Solid-state synthesis has been used to create ZnFe2O4 materials. The physical phases of ZnFe2O4 were characterized using X-ray diffraction (XRD). Above 800 °C. The particle size of pure ZnFe2O4 is between 20 and 50 nm, and a homogeneous particle distribution were achieved. Materials Studio Software was used to simulate the band structure, density of states (DOS), and optical characteristics of ZnFe2O4 using density functional theory (DFT). The results suggest that using the GGA + U functional to compute the energy band of normal spinel ZnFe2O4 is a good method. The direct band gap of ZnFe2O4 crystal is 1.502 eV. Near the Fermi level, the conduction band of ZnFe2O4 contributes to the 3d orbital of Fe and the 2p orbital of O, whereas the valence band contributes primarily to the 2p orbital of O. In the visible light area, ZnFe2O4 possesses outstanding optical characteristics and significant absorption. It may be utilized as a visible light photocatalytic material, and it also contains magnets, which makes recycling easier. [ABSTRACT FROM AUTHOR]

Pyrite (FeS2), an ultra-cheap material, has garnered much interest in photovoltaic applications due to its suitable bandgap and high absorption coefficient. However, low VOC values and high defect density have limited its efficiency. The high carrier density of FeS2, suboptimal conduction band offset, and interface defects are some of the issues limiting its efficiency. We here performed a computation study to discover the various avenues that could enhance the efficiency of such cost-effective and widely abundant pyrite material. The carrier density and conduction band offset optimization have improved efficiency from 0.01 to 2%. The efficiency improved considerably from 2 to 11% after the crucial Fermi level pining optimization at the FeS2/CdS interfaces. We, step by step, increased the efficiency from ~ 0.01 to 11% by diagnosing the FeS2 defect and following the remedial optimization. [ABSTRACT FROM AUTHOR]

Lifshitz transition, wherein the Fermi level shifts from the conduction band to the valence band with increasing temperature, offers a promising platform for exploring the interplay between Fermi-surface topology and Berry curvature field. Here, we highlight the discovery of a switching from extrinsic to intrinsic anomalous Hall effect around a Lifshitz transition in the ferromagnetic Kagome-lattice LiMn6Sn6. The temperature-induced Lifshitz transition manifests prominently as a polarity flip of the ordinary Hall resistivity around 100 K, verifying a vital alteration of the Fermi surface topology. Furthermore, LiMn6Sn6 showcases an extrinsic anomalous Hall effect underneath around 100 K, potentially premised on enhanced skew-scattering of spin-cluster with scalar spin chirality that scales quadratically with longitudinal conductivity, which acquires a maximum anomalous Hall conductivity of 1206 Ω − 1 cm − 1 . Whereas above the critical temperature, the anomalous Hall conductivity maintains virtually constant at approximately 396 Ω − 1 cm − 1 with an anomalous Hall ratio reaching 8.5%, which substantiates the dissipationless intrinsic Berry curvature mechanism from electronic bands of the Kagome plane with broken time-reversal symmetry avoiding crossing near the Fermi level. Our work provides different perspective on the extrinsic–intrinsic crossover within the framework of a unified theoretical model and sheds light on exploring the essence of anomalous Hall effect, especially in Kagome-lattice magnets. [ABSTRACT FROM AUTHOR]

First-principles computations of the structural, electronic, optical and mechanical properties of LaRu2P2 compound are reported. The optimised lattice parameters match well with a previous study, which shows the authenticity of our calculations. The electronic properties indicate the metallic nature of material. At the Fermi level, the overlapping of conduction and valence band represents the metallic nature of the compound. The Mulliken population analysis is used to investigate the bonding nature in the compound. The optical properties indicate that in the low-energy region, LaRu2P2 has a strong absorption coefficient and a high refractive index. The mechanical stability is determined with the help of Born stability criteria and the compound is found mechanically stable. The ductile behaviour of the material was confirmed by Pugh's and Poisson's ratios. The mechanical properties show that the material is anisotropic in nature. Due to the superconducting nature of the compound, it may be utilised for superconducting applications. [ABSTRACT FROM AUTHOR]

It is commonly accepted that the increased degree of graphitization leads to a higher electrical conductivity of carbon materials. However, more and more evidence reveals that heteroatom doping on carbon host can also improve the conductivity, owing to the dopant atoms contributing to higher charge delocalization and density of donor states near Fermi level. The reality is, such conductivity improvement from doping is often overwhelmed by graphitized carbon. Although heteroatom‐doped carbon is widely used as active materials in the fields of energy storage and electrocatalysis, which still requires extra carbon‐based conductive additives to enhance the overall conductivity. In this stu, it is demonstrated that the electrical conductivity of finely designed nitrogen‐doped carbon is even beyond the commercialized carbon conductors over 3.5 times, endowing such conductive agent‐free electrode material an excellent performance in an all‐solid‐state flexible supercapacitor. The theoretical simulation further demonstrates that N‐doped sp2/sp3 hybrid carbon can migrate the Fermi level to the conduction band, leading to an n‐type conductivity due to the additional electrons caused by the N dopant. [ABSTRACT FROM AUTHOR]

Ternary selenometallates, Li5MSe4 (M = Al(I) and Ga(II)), have been synthesized for the first time through high temperature solid-state reactions combining elements and Li2Se in stoichiometric compositions. Li5MSe4 crystallizes in the P21/m space group, forming a pseudo-2D layer type structure with edge sharing LiSe4 and MSe4 tetrahedra along the a-axis. These layers are interleaved by octahedrally coordinated Li ions located in the interlayer space. AC impedance spectroscopy measurements yield room temperature ionic conductivities of 0.60 × 10−7 and 0.58 × 10−7 S cm−1 with calculated activation energies of 0.51 and 0.48 eV for I and II, respectively. An aliovalent substitution of Sn4+ in Li5MSe4 yields compositions of Li4.66Al0.82Sn0.22Se4 (III) and Li4.37Ga0.89Sn0.24Se4 (IV), which crystallize in the P21/m and P3¯m1 space groups, respectively. Sn-doped samples show an ∼5-fold increase in ionic conductivity, 3.37 × 10−7 S cm−1 and 2.4 × 10−7 S cm−1 with activation energies of 0.54 and 0.28 eV, respectively, for III and IV. The optical band gap values of the compounds are 3.65 and 3.2 eV for I and II, respectively, as measured by diffuse reflectance spectroscopy. Density functional theory (DFT) calculations predicted a major contribution from the Se 4p-states in forming the top of the valence band and strongly hybridized the Se 4p and ns orbitals of Al and Ga in forming the bottom of the conduction band with almost no contribution from the Li s-states near the Fermi level indicating their ionic interactions with the ligand. [ABSTRACT FROM AUTHOR]

This work investigates the adsorption behavior of lithium (Li) atoms on zigzag stanene nanoribbon (ZSnNR). This work analyzes the adsorption, open circuit voltage and capacity of Li on ZSnNR. When Li atoms are adsorbed on ZSnNR, it shifts the Fermi level towards the conduction band as compared to the ZSnNR. It indicates a strong interaction between Li and Sn. Our calculations show that the maximum storage capacity of Li on ZSnNR is nearly 200 mAhg − 1 and has a low open-circuit voltage of 2.28 V. The reported findings suggest that ZSnNR can be utilized as anode material for Li ion batteries and it establishes the theoretical foundation for future study on ZSnNR and other Li storage architectures. [ABSTRACT FROM AUTHOR]

Using the GW method within many-body perturbation theory, we investigate the quasiparticle structures of defects, including oxygen vacancy, Ti interstitial, and hydroxyl groups, in the anatase TiO2 (101) surface. We find that the deep defect state in this surface observed experimentally, which is 1 eV below the Fermi level, originates from the σ bond formed between 3d orbitals of the two under-coordinated Ti atoms at the surface oxygen vacancy. Different from the density functional theory modified with on-site Coulomb terms (DFT + U), the GW method predicts that the localized polaron in anatase (101) is a shallow defect state close to the conduction band bottom. Polaronic states play the role in pinning the Fermi level of anatase near the conduction band bottom. Our GW calculations can explain satisfactorily the coexistence of shallow and deep defect states in anatase as observed in experiments. We also find that the conduction band edge of anatase is drawn down greatly after the filling of original empty Ti 3d orbitals by excess electrons, making the calculated bandgap of the reduced anatase agree well with the experiments. This significant difference in the bandgap between the intact and the reduced anatase is missed in DFT + U. [ABSTRACT FROM AUTHOR]

Tungsten trioxide (WO3) is mainly studied as an electrochromic material and received attention due to N-type oxide-based semiconductors. The magnetic, structural, and optical behavior of pristine WO3 and gadolinium (Gd)-doped WO3 are being investigated using density functional theory. For exchange-correlation potential energy, generalized gradient approximation (GGA+U) is used in our calculations, where U is the Hubbard potential. The estimated bandgap of pure WO3 is 2.5 eV. After the doping of Gd, some states cross the Fermi level, and WO3 acts as a degenerate semiconductor with a 2 eV bandgap. Spin-polarized calculations show that the system is antiferromagnetic in its ground state. The WO3 material is a semiconductor, as there is a bandgap of 2.5 eV between the valence and conduction bands. The Gd-doped WO3's band structure shows few states across the Fermi level, which means that the material is metal or semimetal. After the doping of Gd, WO3 becomes the degenerate semiconductor with a bandgap of 2 eV. The energy difference between ferromagnetic (FM) and antiferromagnetic (AFM) configurations is negative, so the Gd-doped WO3 system is AFM. The pure WO3 is nonmagnetic, where the magnetic moment in the system after doping Gd is 9.5599575 μB. [ABSTRACT FROM AUTHOR]

In this study, we synthesize V5+-doped LiNi 0.5 Mn 1.5 O 4 (LNMO) and subject it to SiO 2 surface modification using a coprecipitation method. The synergistic effect of ion doping and interfacial engineering improves the electrochemical properties of LNMO by accelerating its redox kinetics and prolonging its cycling life. The experimental results and density functional theory simulation data indicate that V5+-ion doping caused the Fermi level of LNMO to shift toward the conduction band, thereby narrowing the bandgap of LNMO because of the n-type doping effect. However, the introduction of V5+ ions prevents Li + -ion migration in LNMO, which hinders the ion intercalation–deintercalation process of LNMO cathodes. Therefore, the V5+-doped LNMO compound with optimal V5+-ion doping concentration was expected to present the highest rate capability. In addition, SiO2 surface modification provides a protective layer that inhibits metal dissolutions and significantly improves cathode cycling stability. Owing to the synergistic effect of doping and interfacial modification, the fabricated LNMO cathode presented remarkable energy storage capacity with discharge capacities of 133/118.8 mAh/g at 0.2/10 C and a capacity retention of 87.9% after 200 cycles at 4 C. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] The O-vacancy Bi 2 WO 6 /SrTiO 3 heterojunction photocatalyst with Z scheme photogenerated electron transfer mechanism was loaded on cellulose fibers to construct a visible light-responsive photocatalytic composite paper for efficient and recyclable degradation of organic dyes in water. The introduction of O vacancies in Bi 2 WO 6 by alkali etching increased the utilization rate of Bi 2 WO 6 for visible light and achieved effective regulation of the energy band structure and Fermi level, which transformed Bi 2 WO 6 /SrTiO 3 type-II heterojunction into Z scheme heterojunction. The light-excited electrons in the conduction band of O-vacancy Bi 2 WO 6 directly migrated to the valence band of SrTiO 3 , which improved the separation efficiency of photogenerated carriers and maximized the redox capability of semiconductors. Compared with other control papers, O-vacancy Bi 2 WO 6 /SrTiO 3 paper exhibited the best photocatalytic performance, and its degradation rate for rhodamine B could reach 71.1% under 100 min of Xe lamp irradiation. The O-vacancy Bi 2 WO 6 /SrTiO 3 paper also showed good photocatalytic cycle stability. Loading heterojunction on the cellulose fibers solved the problem of poor reusability and difficult in recovery for powder semiconductor photocatalyst in practical applications. This study provides a novel strategy for constructing Z scheme heterogeneity on cellulose fibers to prepare composite paper with high photocatalytic activity and good reusability. [ABSTRACT FROM AUTHOR]

Hybrid superconductor–semiconductor heterostructures are a promising platform for quantum devices based on mesoscopic and topological superconductivity. In these structures, a semiconductor must be in close proximity to a superconductor and form an Ohmic contact. This can be accommodated in narrow bandgap semiconductors, such as InAs, where the surface Fermi level is positioned close to the conduction band. In this work, we study the structural properties of near-surface InAs quantum wells and find that surface morphology is closely connected to low-temperature transport, where electron mobility is highly sensitive to the growth temperature of the underlying graded buffer layer. By introducing an In0.81Al0.19As capping layer, we show that we change the surface Fermi level pinning of the In0.81Al0.19As thin film as compared to the In0.81Ga0.19As, giving rise to a tuning of the Fermi level in the InAs layer. Experimental measurements show a strong agreement with Schrödinger–Poisson calculations of the electron density, suggesting the conduction band energy of the In0.81Ga0.19As and In0.81Al0.19As surface is pinned to 40 and 309 meV above the Fermi level, respectively. [ABSTRACT FROM AUTHOR]

This study investigates a high-performance Ag 2 O/β-Ga 2 O 3 self-powered photodiode through experimental and modeling approaches. Initially, a p-type Ag 2 O film, with a bandgap close to 4 eV and a hole density of approximately 6.35×1018 cm−3, was fabricated using faced two-target sputtering. The conduction and valence band offsets between Ag 2 O and β-Ga 2 O 3 were determined via X-ray photoelectron spectroscopy, confirming a type II heterojunction. The device had a low on-voltage of 1.50 V and a low on-resistance of 5.40 mΩ.cm² in the dark. Subsequent illumination at 254 nm resulted in a notably high photocurrent, responsivity, and detectivity. To confirm the role of trap-assisted tunneling in the type II Ag 2 O/β-Ga 2 O 3 heterojunction, Silvaco simulations were employed to model both the dark current and photocurrent. These simulations confirmed the prevalence of the trap-assisted tunneling mechanism, particularly through energy levels situated above the equilibrium Fermi level at the Ag 2 O/β-Ga 2 O 3 interface, as described by the Danielsson model. Understanding the transport mechanism is paramount for the development of high-performance photodetectors. By comprehending how charge carriers navigate through the device and the influence of traps on their behavior, researchers can optimize device design and fabrication processes to enhance performance. [Display omitted] • Demonstration of ultra-high bandgap (4 eV) P-type Ag 2 O deposited on β-Ga 2 O 3 • Type II Ag 2 O/β-Ga 2 O 3 heterojunction was demonstrated using X-ray photoelectron spectroscopy analysis. • High performance Ag 2 O/β-Ga 2 O 3 heterojunction and self-powered photodetector was validated. • Silvaco TCAD was utilized to confirm the role of trap-assisted tunneling mechanisms in carrier injection. [ABSTRACT FROM AUTHOR]

Substitutional doping to engineer the electronic structure of materials has received high prominence in developing high performance thermoelectric materials. Herein, we study the effect of molybdenum doping on the electronic structure of GeTe and provide insights into the observed enhancement of thermoelectric performance. We discover that Mo doping has a huge impact on the band structure of both rhombohedral and cubic phase of GeTe. In addition to increasing the band gap, Mo doping causes huge increase in the density of states near the Fermi level. We also notice convergence of valence sub-bands and hyperconvergence of conduction sub-bands besides introduction of multiple carrier valleys promoting transport in both p and n-type materials. These features undoubtedly make Mo doping a beneficial approach in the development of lead free GeTe thermoelectrics. [Display omitted] • First principles study on electronic structure engineering of GeTe by doping Mo. • Large increase in band gap caused by Mo doping in both rhombohedral and cubic phases. • Valence band convergence and generation of multiple valleys leading to increase in Nv. • First report on hyperconvergence of conduction band induced by Mo doping in GeTe. • Study reveals the potential to be developed into high performing p-type as well as n-type TE material. [ABSTRACT FROM AUTHOR]