Evolution Of Electronic Structure Research Articles

Effective model and electron correlations in trilayer nickelate superconductor La4Ni3O10.

Recently, signatures of superconductivity with critical temperature from 20 to 30 K have been reported in pressured trilayer nickelate La$_4$Ni$_3$O$_{10}$ through a pressure-induced structure transition. Here we explore the evolution of electronic structures and electronic correlations in different phases of La$_4$Ni$_3$O$_{10}$ under corresponding pressure regions, by using density functional theory (DFT) combined with dynamical mean-field theory (DMFT). Similar to bilayer superconductor La$_3$Ni$_2$O$_{7}$, the electronic bands in superconducting La$_4$Ni$_3$O$_{10}$ are dominated by Ni-3$d_{x^2-y^2}$ and 3$d_{z^2}$ orbits near the Fermi level, in contrast, the inner Ni-O plane in La$_4$Ni$_3$O$_{10}$ generates a doublet hole-pocket Fermi surfaces around the Brillouin-zone corner, meanwhile one branch of the Ni-$3d_{z^2}$ bands is pushed very close above the Fermi level, which can induce an electron pocket through small electron doping. The DFT+DMFT simulations suggest that the electronic correlations only give minor modification to the Fermi surfaces, meanwhile the Ni-$3d_{z^2}$ and 3$d_{x^2-y^2}$ states on outer Ni-O layers have considerable greater mass enhancements than on the inner layer. The sensitiveness of electronic structure under doping and unique layer dependence of correlation suggest a distinct superconducting mechanism with respect to bilayer La$_3$Ni$_2$O$_{7}$. Based on the DFT and DFT+DMFT simulations, we eventually derive a trilayer effective tight-binding model, which can produce rather precise electronic bands and Fermi surfaces, hence can serve as an appropriate model to further study the superconducting mechanism and paring symmetry in trilayer La$_4$Ni$_3$O$_{10}$.

Hybridization State Transition under Working Conditions: Activity Origin of Single-Atom Catalysts.

Single-atom catalysts (SACs) have been widely investigated and have emerged as a transformative approach in electrocatalysis. Despite their clear structure, the origin of their exceptional activity remains elusive. Herein, we elucidate a common phenomenon of the hybridization state transition of metal centers, which is responsible for the activity origin across various SACs for different reactions. Focusing on N-doped carbon-supported Ni SAC (NiN4 SAC) for CO2 reduction reaction (CO2RR), our comprehensive computations successfully clarify the hybridization state transition under working conditions and its relation with the activity. This transition, triggered by the reaction intermediates and applied potential, converts the Ni center from the inert dsp2 hybridization state to the active d2sp3 hybridization state. Importantly, the calculated activity and selectivity of the CO2RR over the d2sp3-hybridized Ni center are consistent with the experimental results, offering strong support for the proposed hypothesis. This work suggests a universal principle of electronic structure evolution in SACs that could revolutionize catalyst design, which also introduces a new paradigm for manipulating electronic states to enhance catalytic performance, with implications for various reactions and catalyst platforms.

Electronic transport evolution across the successive structural transitions in Ni50-x Fe x Ti50 shape memory alloys

Abstract TiNi-based shape memory alloys have been extensively investigated owing to their significant applications, but a comprehensive understanding of the evolution of electronic structure and electrical transport in a system with martensitic transformations (MT) is still lacking. In this work, we focused on the electronic transport behaviors of three phases in Ni50-x Fe x Ti50 across the MT. A phase diagram of Ni50-x Fe x Ti50was established based on the x-ray diffraction, calorimetric, magnetic, and electrical measurements. To reveal the driving force of MT, the phonon softening was revealed by using the first-principles calculations. Notably, the transverse and longitudinal transport behavior changed significantly across the phase transition, which can be attributed to the reconstruction of electronic structures. This work promotes the understanding of phase transitions and demonstrates the sensitivity of electron transport to phase transition.

Electronic Structure Evolution in the Temperature Range of Metal–Insulator Transitions on Sn/Ge(111)

One‐third of monolayer of Sn adatoms on a Ge(111) substrate forms a 2D triangular lattice with one unpaired electron per site. The system presents a metal–insulator transition when decreasing the temperature and it is known to exhibit strong electron–phonon coupling at 120–150 K. Herein, a study of the electronic band structure for α‐Sn/Ge(111) between 150 and 5 K is reported. Both the experimental Fermi surfaces and the energy dispersions along high symmetry directions as a function of the temperature are presented. At 5 K it is observed a weakly or low‐dispersing spectral feature, exhibiting an extended gap in the reciprocal space. This feature is derived from the topmost occupied band, which is metallic at high temperature and which develops a kink associated with the strong electron–phonon coupling. The spectral evolution is partially explained with an increase of the electron–phonon coupling when decreasing the temperature. The increase of the electron–phonon coupling at low temperatures gives light into the new physics of this 2D system. The bandwidth is progressively reduced when reducing the temperature, enhancing the electronic correlation effects, and triggering the Mott transition.

Chemical Vapor Deposition Growth of Atomically Thin SnSb2Te4 Single Crystals Toward Fast Photodetection

AbstractSnSb2Te4 (SST), a ternary van der Waals (vdW) material, has been widely investigated during last decades for potential applications in superconductivity, thermoelectricity, and optoelectronics. Recently, atomically thin SST has been predicted to show abnormal electronic band structure evolutions, high carrier mobility, and strong light–matter interaction. However, controllable synthesis of such SST crystals has been a huge challenge. Herein, atomically thin SST flakes are prepared via a chemical vapor deposition (CVD) method by using SbCl3, SnCl4·5H2O, and Te as the precursors. Multiple structural characterizations reveal that the SST flakes are single crystals with high crystallinity. Due to the narrow bandgap of 0.42 eV, SST‐based photodetectors have a broadband spectrum detection range from visible light through communication bands (480–1550 nm). More importantly, benefiting from a high room‐temperature carrier mobility over 300 cm2 V−1 s−1, the SST photodetectors demonstrate a response/recovery time of tens of tens of microseconds, which exceeds most typical transition metal dichalcogenide (TMDC) flakes. In addition, the photodetector maintains high performance after being exposed to the air for 2 months, suggesting good environmental stability. These excellent performances suggest that the SST flakes are promising for next‐generation optoelectronics.

Designing transition metal-based porous architectures for supercapacitor electrodes: a review.

Over the past decade, transition metal (TM)-based electrodes have shown intriguing physicochemical properties and widespread applications, especially in the field of supercapacitor energy storage owing to their diverse configurations, composition, porosity, and redox reactions. As one of the most intriguing research interests, the design of porous architectures in TM-based electrode materials has been demonstrated to facilitate ion/electron transport, modulate their electronic structure, diminish strain relaxation, and realize synergistic effects of multi-metals. Herein, the recent advances in porous TM-based electrodes are summarized, focusing on their typical synthesis strategies, including template-mediated assembly, thermal decomposition strategy, chemical deposition strategy, and host-guest hybridization strategy. Simultaneously, the corresponding conversion mechanism of each synthesis strategy are reviewed, and the merits and demerits of each strategy in building porous architectures are also discussed. Subsequently, TM-based electrode materials are categorized into TM oxides, TM hydroxides, TM sulfides, TM phosphides, TM carbides, and other TM species with a detailed review of their crystalline phase, electronic structure, and microstructure evolution to tune their electrochemical energy storage capacity. Finally, the challenges and prospects of porous TM-based electrode materials are presented to guide the future development in this field.

Progress in MXene‐based catalysts for oxygen evolution reaction

AbstractElectrochemical water splitting for hydrogen generation is considered one of the most promising strategies for reducing the use of fossil fuels and storing renewable electricity in hydrogen fuel. However, the anodic oxygen evolution process remains a bottleneck due to the remarkably high overpotential of about 300 mV to achieve a current density of 10 mA cm−2. The key to solving this dilemma is the development of highly efficient catalysts with minimized overpotential, long‐term stability, and low cost. As a new 2D material, MXene has emerged as an intriguing material for future energy conversion technology due to its benefits, including superior conductivity, excellent hydrophilic properties, high surface area, versatile chemical composition, and ease of processing, which make it a potential constituent of the oxygen evolution catalyst layer. This review aims to summarize and discuss the recent development of oxygen evolution catalysts using MXene as a component, emphasizing the synthesis and synergistic effect of MXene‐based composite catalysts. Based on the discussions summarized in this review, we also provide future research directions regarding electronic interaction, stability, and structural evolution of MXene‐based oxygen evolution catalysts. We believe that a broader and deeper research in this area could accelerate the discovery of efficient catalysts for electrochemical oxygen evolution.

Fabrication of N-doped TiO2 and TiN nanorods by NH3 treatment: Evolution of morphology, structures, composition and optical properties

We investigate the evolution of morphology, electronic and crystalline structures, elemental composition, and optical properties of TiO2 nanorods (NRs) treated in NH3 in the temperature range of 400–1100 °C using both experiments and theoretical calculations. The results show that N-doped TiO2 NRs are obtained in the temperature range of 400–550 °C, in which the formation of the N substitutional defects is more energetically favorable than the N interstitial defects. Our theoretical calculations reveal that the formation of N substitutional defects causes a significant bandgap narrowing, which arises from two different mechanisms: the upward shift of the valence band maximum for a low doping concentration and the downward shift of the conduction band minimum for a high doping concentration. Experimentally, a bandgap in the range of 2.22–2.41 eV can be achieved for N-doped TiO2, which enables the visible-light absorption and activates the visible-light photocatalytic activity of the TiO2 NRs. The nitridation starts from 700 °C and proceeds rapidly in the temperature range of 800–900 °C. However, complete nitridation is achieved when the temperature exceeds 1000 °C. The rutile phase is found to be more prone to nitridation than the anatase phase. During nitridation, the TiO2 NRs experience significant changes in morphology, structure, and optical properties. The latter is strongly affected by the remaining O concentration in the materials.

Facile and Green Synthesis of Well-Defined Nanocrystal Oxygen Evolution Catalysts by Rational Crystallization Regulation.

The development of catalysts for an economical and efficient oxygen evolution reaction (OER) is critical for clean and sustainable energy storage and conversion. Nickel-iron-based (NiFe) nanostructures are widely investigated as active OER catalysts and especially shape-controlled nanocrystals exhibit optimized surface structure and electronic properties. However, the structural control from amorphous to well-defined crystals is usually time-consuming and requires multiple stages. Here, a universal two-step precipitation-hydrothermal approach is reported to prepare a series of NiFe-based nanocrystals (e.g., hydroxides, sulfides, and molybdates) from amorphous precipitates. Their morphology and evolution of atomic and electronic structure during this process are studied using conclusive microscopy and spectroscopy techniques. The short-term, additive-free, and low-cost method allows for the control of the crystallinity of the materials and facilitates the generation of nanosheets, nanorods, or nano-octahedra with excellent water oxidation activity. The NiFe-based crystalline catalysts exhibit slightly compromised initial activity but more robust long-term stability than their amorphous counterparts during electrochemical operation. This facile, reliable, and universal synthesis method is promising in strategies for fabricating NiFe-based nanostructures as efficient and economically valuable OER electrocatalysts.

Tunable hydrogen evolution reaction of vacancy-defective MoSe2/WSe2 heterojunctions based on first-principle calculation

Two-dimensional transition metal disulfides (TMDs) heterojunction is a very promising non-precious metal catalyst that has been widely used as a catalyst for hydrogen evolution reactions. In this paper, the effects of different positions of Se vacancies on the electronic structure and hydrogen evolution reaction electrocatalyst of MoSe2/WSe2 heterojunction are investigated by first-principles calculations. After the introduction of vacancy, defect states appear between the conduction band bottom and the Fermi energy level of the heterojunction. This is more favorable for the electron transfer between H and the substrate. The results of the density of states calculations indicate that the defect states appear because the d orbitals of the transition metal atoms containing the Se vacancy layer hybridize with the p orbitals of the Se atoms. The differential charge density indicates that the Se vacancies promote the charge transfer of MoSe2/WSe2. In addition, calculations of the Gibbs free energy for the hydrogen evolution reaction of heterojunctions show that Se vacancies (especially the outer vacancies) enhance the electrocatalytic hydrogen precipitation performance of heterojunctions. The results provide a new way to regulate the hydrogen evolution properties of MoSe2/WSe2 heterojunctions.

Rapid degradation of Omeprazole and highly effective inactivation of E. coli in the UVA-light photocatalytic process with Cu-doped in spinel-structured ɣAl2O3 as a stable catalyst

Herein, a spinel alumina structure photocatalyst was prepared by a one-pot modified sol–gel technique with rational design and unique electronic structure evolution by Cu doping in the γAl2O3 lattice. Based on the obtained results of a full material characterization (incl. NH3-TPD, 27Al solid-state NMR, XPS, HAADF-STEM), the Cu-γAl2O3 xerogel nanomaterial displayed high dispersion of copper, significant quantities of high-density acid sites, an increase of the oxygen vacancies (OVs) on its surface, and high light absorption efficiency. This mesoporous Cu-γAl2O xerogel displayed brilliant photocatalytic performance under UVA-LED, owing to its suitable band gap, degrading around 92 % of 20 mg/L Omeprazole (OMP) in 30 min (pH = 7, catalyst = 50 mg/L). The effect of operating parameters was investigated, such as pH, concentration of Cu-ɣAl2O3/OMP, water matrix, and stability; the synthesized nanomaterial has shown outstanding stability and recyclability for four runs. The reaction mechanism was proposed using scavenging experiments, and EPR spectroscopy, Cu-doping-induced oxygen vacancies to promote charge separation and molecular oxygen activation, generating mainly ∙OH. The OMP degradation pathway was proposed (LC-MS), while the produced Cu-ɣAl2O3 nanomaterial effectively catalyzed the inactivation of >99.99 % E. coli.

Unveiling the charge migration-induced surface reconstruction of Cu2MoS4 catalyst for boosted CO2 reduction into olefiant gas

Understanding the charge dynamic behavior of the catalyst is crucial to unravel the underlying mechanism for photocatalytic CO2 reduction to C2+ products. However, the structure–activity relationships are not intuitive because of the dynamic evolution of electronic and atomic structures for catalysts under the excitation state. Herein, modeling on layered Cu2MoS4 nanosheets, we for the first time observe charge migration-induced evolution of electronic and atomic structure on Cu2MoS4 catalyst during the CO2 reduction process by combining synchronous-illumination X-ray photoelectron spectroscopy (SI-XPS) with X-ray diffraction (SI-XRD). During the dissociation of CO2 molecules as well as the charge migration process under the visible light irradiation condition, the surface S atoms return back to the lattice phase, leading to the valence-state normalization of Cu, Mo and S atoms and the increases of the interlayer lattice spacing. By virtue of the above unique characteristic changes, Cu2MoS4 nanosheets exhibit excellent activity enhancement (8.7 μmol g−1 h−1) for CO2 reduction to C2H4 under the visible light irradiation in comparison with the trace amount of Cu-doped MoS2 and pure MoS2.

Exploring the influence of cosegregation on mechanical properties of Mg [formula omitted] twin boundaries: A first-principles investigation

This study employs first-principles calculations to investigate the impact of solute segregation on the mechanical properties of the Mg twin boundary (TB). The investigation delves into single-element segregation and multielement cosegregation at the Mg{101¯1} twin boundary. Several parameters, including segregation energy, solubility energy, and strengthening/embrittlement energy, are determined, and Voronoi volume and electronic structure evolution are analyzed. The study discloses the effects of 21 solute single-segregation, as well as the segregation mechanism of Ca, Y, and Zn solute elements in paired combinations. A comparative assessment of the optimal combination for cosegregation of Ca/Y atoms with larger atomic radii and Zn atoms with smaller atomic radii reveals that the solute elements Ca and Y induce more robust energy changes at the interface segregation than Zn. Additionally, electronic structure analysis suggests that charge transfer between solute atoms with large atomic radii and solute atoms with small atomic radii can strengthen the chemical bond at the twin boundary, thereby enhancing the maximum tensile degree, ductility, and formability of the material. The outcomes of this investigation have significant theoretical implications for composition design and the development of novel high-performance multielement magnesium alloys.

Dimensionality-Driven Evolution of Electronic Structure and Transport Properties in Pressure-Induced Phases of Ca2N Electride

Dimensionality-Driven Evolution of Electronic Structure and Transport Properties in Pressure-Induced Phases of Ca2N Electride

Band structures of strained kagome lattices

Materials with kagome lattices have attracted significant research attention due to their nontrivial features in energy bands. We theoretically investigate the evolution of electronic band structures of kagome lattices in response to uniaxial strain using both a tight-binding model and an antidot model based on a periodic muffin-tin potential. It is found that the Dirac points move with applied strain. Furthermore, the flat band of unstrained kagome lattices is found to develop into a highly anisotropic shape under a stretching strain along y direction, forming a partially flat band with a region dispersionless along ky direction while dispersive along kx direction. Our results shed light on the possibility of engineering the electronic band structures of kagome materials by mechanical strain.

Geometry and electronic properties of alkali metal (rubidium) doped boron clusters

AbstractAlkali metal‐doped boron clusters have captured much attention because of their novel electronic properties and structural evolution. In the study of RbBn0/− (n = 2–12) clusters, the minimum global search of the potential energy surface and structure optimization at the level of PBE1PBE by using the CALYPSO method and Gaussian package coupled with DFT calculation; the geometrical structures and electronic properties are systematically investigated. At n = 8, the ground‐state structures are composed of an Rb atom above B atoms, forming a structurally stable pagoda cone. By stability analysis and charge transfer calculation, the RbB8− cluster shows more stability. It found that s‐p hybridization between Rb atom and B atoms as well as s‐p hybridization between B atoms is one of the reasons for the outstanding stability exhibited in the RbB80/− clusters by using DOS and HOMO–LUMO orbital contour maps. The chemical bonding of the RbB80/− groups was analyzed by using the AdNDP method, and B atoms with larger numbers readily form multi‐center chemical bonds with the Rb atom. From the results of the bonding analysis, the interaction between the Rb atom and B atoms strengthens the stability of the RbB80/− clusters. It is hoped that this work provides a direction for experimental manipulation.

Accumulative Delocalized Mo 4d Electrons to Bound the Volume Expansion and Accelerate Kinetics in Mo6S8 Cathode for High-Performance Aqueous Cu2+ Storage.

Electronic structure defines the conductivity and ion absorption characteristics of a functional electrode, significantly affecting the charge transfer capability in batteries, while it is rarely thought to be involved in mesoscopic volume and diffusion kinetics of the host lattice for promoting ion storage. Here, we first correlate the evolution in electronic structure of the Mo6S8 cathode with the ability to bound volume expansion and accelerate diffusion kinetics for high-performance aqueous Cu2+ storage. Operando synchrotron energy-dispersive X-ray absorption spectroscopy reveals that accumulative delocalized Mo 4d electrons enhance the Mo-Mo interaction with distinctly contracting and uniformizing Mo6 clusters during the reduction of Mo6S8, which potently restrain lattice expansion and release space to promote Cu2+ diffusion kinetics. Operando synchrotron X-ray diffraction and comprehensive characterizations further validate the structural and electrochemical properties induced by the Cu2+ intercalation electronic structure, endowing the Mo6S8 cathode a high specific capacity with small volume expansion, fast ions diffusion, and long-term cycling stability.

Pressure-induced evolution of stoichiometries and electronic structures of host–guest Na–B compounds

Superionic and electride behaviors in materials, which induce a variety of exotic physical properties of ions and electrons, are of great importance both in fundamental research and for practical applications. However, their coexistence in hot alkali-metal borides has not been observed. In this work, we apply first-principles structure search calculations to identify eight Na–B compounds with host–guest structures, which exhibit a wide range of building blocks and interesting properties linked to the Na/B composition. Among the known borides, Na-rich Na9B stands out as the composition with the highest alkali-metal content, featuring vertex- and face-sharing BNa16 polyhedra. Notably, it exhibits electride characteristics and transforms into a superionic electride at 200 GPa and 2000 K, displaying unusual Na atomic diffusion behavior attributed to the modulation of the interstitial anion electrons. It demonstrates semiconductor behavior in the solid state, and metallic properties associated with Na 3p/3s states in the superionic and liquid regions. On the other hand, B-rich NaB7, consisting of a unique covalent B framework, is predicted to exhibit low-frequency phonon-mediated superconductivity with a Tc of 16.8 K at 55 GPa. Our work advances the understanding of the structures and properties of alkali-metal borides.

Surface evolution of Pt/MoO3/4H-SiC(0001) investigated by in situ near-ambient pressure X-ray photoelectron spectroscopy

Achieving effective Ohmic contact between SiC and metal electrodes remains a challenge due to the high Schottky barrier resulting from the large mismatch between the deep-lying valence band of SiC and Fermi level of metals. One promising approach to address this issue is to introduce a high-work-function interfacial layer between the metal and semiconductor. However, the interaction mechanisms of the inserted high-work-function interfacial layer between metal electrodes and the SiC substrate have been rarely studied systematically. In this work, layers of high-work-function molybdenum trioxide (MoO3) and platinum (Pt) were successively grown on the 4H-SiC(0001) surface via conventional physical vapour deposition (PVD). We investigated the chemical and electronic structure evolutions upon Pt deposition on MoO3/4H-SiC(0001) using in situ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and ultraviolet photoelectron spectroscopy (UPS). Subsequently, the evolutions of Pt/MoO3/4H-SiC(0001) system during annealing under ultra-high vacuum (UHV) or various gas phase environments (H2 and O2) were studied via in situ NAP-XPS and UPS. Our results reveal that Pt showed its thermal stability during the annealing process, while Mo presented its versatile chemical characteristics. These results depict a detailed chemical feature of the Pt/MoO3/4H-SiC(0001) system and help gain a better understanding about the impact of different environments on Pt/MoO3 interface.

Ultrathin Pt and Mo films on Al1–xScxN: an interface investigation

Aluminum scandium nitride (Al1–xScxN) with attractive ferroelectric and piezoelectric properties is a promising material for next-generation device applications. However, the understanding of interface properties between integrated ultrathin metal electrodes and Al1-xScxN films is still limited, despite their significant impact on device performance. In the study, we investigated the growth mechanism and interfacial chemistry of ultrathin platinum (Pt) and molybdenum (Mo) films deposited on the high-crystalline Al1-xScxN (x = 0.2) surface. The chemical and electronic structure evolutions of the interface during the deposition process were probed by in-situ X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The structural properties of the interface were further characterized by cross-sectional transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and atomic force microscopy (AFM). Our results reveal the formation of ionic Pt2+-N bonds at the Pt/Al1-xScxN interface, while Mo does not bond with the substrate. Furthermore, we identified electron transfer induces upward band-bending like effects on the Al1-xScxN surface upon both Pt and Mo interactions. Our work on the chemical and structural research of ultrathin metal electrodes and Al1–xScxN interfaces provides guidance towards designing high-performance micro-electromechanical (MEMS) devices.