Electron Interaction Effects Research Articles

Metal-organic framework-derived self-supporting metal boride for efficient electrocatalytic oxygen evolution reaction

Metal boride has been verified as the highly efficient catalyst for oxygen evolution reaction. However, the design and synthesis of self-supporting metal borides remain a big challenge. Herein, metal-organic framework-derived metal boride electrode is in-situ formed on 3D framework via controllable boronation strategy, which is of great significance to the construction of self-supporting metal borides. This strategy not only produces the metal boride materials but also achieves the metal borides based self-supporting electrode with multiple structures. The as-fabricated CoFe-PBA-B exhibits a low overpotential of 255 mV at the current density of 10 mA cm−2 and a low Tafel slope of 51 mV dec-1 due to the enhanced active sites of multiple structures and effective electronic interaction between metal atoms and boron atom. In addition, CoFe-PBA-B shows good stability with negligible weaken in current density for 40 h. This work provides new boulevard for the design and synthesis of self-supporting metal borides for electrochemical OER.

Electrical transport properties of thick and thin Ta-doped SnO2 films

Ta-doped SnO2 films with high conductivity and high optical transparency have been successfully fabricated using the rf-sputtering method, and their electrical transport properties have been investigated. All films reveal degenerate semiconductor (metal) characteristics in electrical transport properties. For the thick films (t∼1μm with t being the thickness) deposited in pure argon, the electron–phonon scattering alone cannot explain the temperature-dependent behaviors of resistivity, the interference effect between electron–phonon and electron–impurity scattering should be considered. For t≲36 nm films, both the conductivity and the Hall coefficient show a linear relation with the logarithm of temperature (ln⁡T) from ∼100 K down to liquid helium temperature. The ln⁡T behaviors of conductivity and Hall coefficient cannot be explained by the Altshuler-Aronov type electron–electron interaction effect but can be quantitatively interpreted by the electron–electron interaction effects in the presence of granularity. Our results not only provide strong support for the theoretical results on the electron–phonon–impurity interference effect, but also confirm the validity of the theoretical predictions of charge transport in granular metals in a strong coupling regime.

π-Facial Stereoselectivity in Acyl Nitroso Cycloadditions to 5,5-Unsymmetrically Substituted Cyclopentadienes: Computational Exploration of Origins of Selectivity and the Role of Substituent Conformations on Selectivity.

The π-facial selectivity of Diels-Alder cycloadditions of 5-monosubstituted cyclopentadienes is known experimentally and has been extensively studied computationally. Previous studies on 5-monosubstituted cyclopentadienes by the Burnell and Houk groups showed that facial selectivity arises principally from hyperconjugative aromaticity or antiaromaticity of polar groups that cause distortion of the cyclopentadiene; steric effects of nonpolar groups can also be important. We have now explored the stereoselective cycloaddition of 5,5-unsymmetrically substituted cyclopentadienes to an acyl nitroso dienophile reported by Kan and co-workers. Computational studies with M06-2X/6-311+G(d,p) indicate that the stereoselectivity in the cycloadditions of 5,5-unsymmetrically substituted cyclopentadienes is not just a simple combination of effects found for monosubstituted counterparts. Substituent conformations and diene-dienophile steric and electronic interaction effects all influence stereoselectivity. Predictions are made about several as-yet-unstudied cyclopentadiene cycloadditions.

Determination of the atomic structure and radiative transition properties of atoms or ions under the dense and solid density magnetized plasmas

Simulating the magnetic field interactions with plasmas plays a paramount role in astrophysics, having significant impacts in several topics. Here, we propose a novel computational method within the framework of relativistic theory to the determination of the atomic structures and radiative properties of atoms or ions in presence of the dense and solid density magnetized plasma environments. In the method, the dense plasma effects on the atomic structure of highly charged ions are described by using the generalized b-potential model within the general framework of the ion sphere theory, which is somewhat simple and flexible and allows adjusting the b-parameter to consider finite temperature and density as well as solid density plasma environments. The weakly magnetic field effects are described using the perturbation term, which perturbs the Hamiltonian of the field-free case. Its special features include handling the effects of both electron correlation and interaction with the weakly magnetic field within the configuration interaction approximation. As a practical application, we present a systematic study of the plasma screening and magnetic field effects, separately and combined, on the structure and radiative properties of highly charged ions subjected to the magnetized plasma, using the atrophysically relevant He-like Mg10+ ion as an example. A comparison of our calculations with other theories, when available, is made. The present work not only originates a better understanding of the fundamentals of structure and radiative properties of ions in the presence of an external field, but also has some important relevance to applications in laboratory and space plasmas, particularly in solar corona, fusion, laser-produced plasmas, ect.

Transitional regime of electron resonant interaction with whistler-mode waves in inhomogeneous space plasma.

Resonances with electromagnetic whistler-mode waves are the primary driver for the formation and dynamics of energetic electron fluxes in various space plasma systems, including shock waves and planetary radiation belts. The basic and most elaborated theoretical framework for the description of the integral effect of multiple resonant interactions is the quasilinear theory, which operates through electron diffusion in velocity space. The quasilinear diffusion rate scales linearly with the wave intensity, D_{QL}∼B_{w}^{2}, which should be small enough to satisfy the applicability criteria of this theory. Spacecraft measurements, however, often detect whistle-mode waves sufficiently intense to resonate with electrons nonlinearly. Such nonlinear resonant interactions imply effects of phase trapping and phase bunching, which may quickly change the electron fluxes in a nondiffusive manner. Both regimes of electron resonant interactions (diffusive and nonlinear) are well studied, but there is no theory quantifying the transition between these two regimes. In this paper we describe the integral effect of nonlinear electron interactions with whistler-mode waves in terms of the timescale of electron distribution relaxation, ∼1/D_{NL}. We determine the scaling of D_{NL} with wave intensity B_{w}^{2} and other main wave characteristics, such as wave-packet size. The comparison of D_{QL} and D_{NL} provides the range of wave intensity and wave-packet sizes where the electron distribution evolves at the same rates for the diffusive and nonlinear resonant regimes. The obtained results are discussed in the context of energetic electron dynamics in the Earth's radiation belt.

Heterostructured VN/Mo2C Nanoparticles as Highly Efficient pH-Universal Electrocatalysts toward the Hydrogen Evolution Reaction

Development of cost-effective and high-efficiency electrocatalysts for the hydrogen evolution reaction (HER) is still of great significance for industrial clean hydrogen fuel production. Herein, a novel heterostructured VN/Mo2C nanoparticle is synthesized by a facile and one-step pyrolysis protocol. When applied for the HER, the optimized VN/Mo2C catalyst exhibited quite low overpotentials (alkaline medium: 45 mV, acid medium: 140 mV, and neutral medium: 180 mV) for driving the current density of 10 mA cm–2, obviously superior to the isolated vanadium nitride (VN) and Mo2C counterparts, and remarkable catalytic durability for at least 100 h. Such an outstanding electrocatalytic HER performance is primarily ascribed to the increased catalytically active sites, enhanced electronic interaction effects, as well as the improved electrical conductivity over the heterostructured VN/Mo2C nanoparticles. This study provides a new method for the design of HER electrocatalysts with high efficiency and stability.

Effect of electronic interactions and coordination spheres on ionic diffusion in LaxSr1-xGayMg1-yO3-δ

The effect of the partial covalent character of cations on their ionic diffusivity in LaxSr1-xGayMg1-yO3-δ, a perovskite with AxA'x-1ByB'y-1O3-δ general formula, is determined computationally using plane wave, periodic, pseudopotential density functional theory. The diffusion of ions is assumed to take place by a vacancy-mediated transport mechanism. Using Vineyard's transition state theory, diffusion coefficients for each ion are obtained. The results of the calculations show that at temperature of 1000 K the diffusivity of the oxide ion is greater than that of the A-site cations by at least ten orders of magnitude, and the diffusivities of the A-site cations are greater then the diffusivities of B-site cations by at least eight orders of magnitude. Those results are related to local ionic mobilities and are not representative for macroscopic ionic diffusion. The diffusivities of rather covalent, polarizable, cations (La and Ga) were found to be lower than those of more ionic, hard, cations (Sr and Mg) despite the fact that La and Ga have smaller ionic radii than Sr and Mg, respectively. The migration pathway of the B-site cations is curved for different possible locations of the necessary oxygen vacancies and the calculations revealed that the curved pathway is not caused by steric hindrance of an intervening oxide ion but rather the driving force to maximize the electronic interactions of the B cation with surrounding oxide ions along the entire migration pathway.

Creating High Regioselectivity by Electronic Metal-Support Interaction of a Single-Atomic-Site Catalyst.

Ligands are the most commonly used means to control the regioselectivity of organic reactions. It is very important to develop new regioselective control methods for organic synthesis. In this study, we designed and synthesized a single-atomic-site catalyst (SAC), namely, Cu1-TiC, with strong electronic metal-support interaction (EMSI) effects by studying various reaction mechanisms. π cloud back-donation to the alkyne on the metal catalytic intermediate was enhanced during the reaction by using transient electron-rich characteristics. In this way, the reaction achieved highly linear-E-type regioselective conversion of electronically unbiased alkynes and completely avoided the formation of branched isomers (ln:br >100:1, TON up to 612, 3 times higher than previously recorded). The structural elements of the SACs were designed following the requirements of the synthesis mechanism. Every element in the catalyst played an important role in the synthesis mechanism. This demonstrated that the EMSI, which is normally thought to be responsible for the improvement in catalytic efficiency and durability in heterogeneous catalysis, now first shows exciting potential for regulating the regioselectivity in homogeneous catalysis.

Biomimetic design of graphdiyne supported hemin for enhanced peroxidase-like activity

Effective electronic interactions between molecular catalysts and supports are critical for heterogeneous enzyme mimics, yet they are frequently neglected in most catalyst designs. Taking the enzyme mimics of hemin immobilized on graphdiyne (Hemin-GDY) as an example, we explicate for the first time the underlying role of GDY as a co-catalyst. Based on the robust conjugation between GDY and hemin, the delocalized π-electrons in GDY act as a ligand for Fe ions so that the orbital interactions including electron transport from GDY → Fe can induce the formation of an electron-rich Fe center and an electron-deficient π-electron conjugated system. This mechanism was validated by electron paramagnetic resonance (EPR), Raman spectroscopy, and DFT calculations. Moreover, both EPR spetra and Lineweaver-Burk plots revealed that Hemin-GDY could efficiently catalyze the decomposition of hydrogen peroxide (H2O2) to produce hydroxyl radical (•OH) and superoxide anion (O2•–) by a ping-pong type catalytic mechanism, and particularly, the catalytic activity was increased by 2.3-fold comparing to that of hemin immobilized on graphene (Hemin-GR). In addition, Hemin-GDY with the exceptional activity and stability was demonstrated for efficient catalytic degradation of organic pollutants under acidic conditions. Collectively, this work provides a theoretical basis for the design of GDY supported catalysts and renders great promises of the GDY based enzyme mimics.

Web-based methods for X-ray and photoelectron spectroscopies

We present a simplified web-based application for simulating X-ray and photoelectron spectra of transition metals, built around the notion that web-based applications lower the bar for novice users. The application provides a simple interface to simulate X-ray absorption spectroscopy, resonant inelastic X-ray scattering, and angle-resolved photoemission spectroscopy, incorporating the effects of local electronic interactions, which give rise to multiplets, spin–orbit coupling, crystal field effects, and ligand hybridization/charge transfer. Results can be obtained that highlight the key role of photon polarization.

Synergistic effects of CeO2/Cu2O on CO catalytic oxidation: Electronic interaction and oxygen defect

For CO catalytic oxidation, Cu and Ce species are of great importance, between which the synergistic effect is worth investigating. In this work, CeO2/Cu2O with Cu2O {111} and {100} planes were comparatively explored on CO catalytic oxidation to reveal the effects of interfacial electronic interactions and oxygen defects. The activity result demonstrates that CeO2/o-Cu2O {111} has superior performance compared with CeO2/c-Cu2O {100}. Credit to the coordination unsaturated copper atoms (CuCUS) on o-Cu2O {111} surface, the interfacial electronic interactions on CeO2/o-Cu2O {111} are more obvious than those on CeO2/c-Cu2O {100}, leading to richer oxygen defect generation, better redox and activation abilities of CO and O2 reactants. Furthermore, the reaction mechanism of CeO2/o-Cu2O {111} on CO oxidation is revealed, i.e., CO and O2 are adsorbed on the CuCUS on Cu2O {111} and oxygen defect of CeO2, respectively, and then synergistically promote the CO oxidation to CO2. The work sheds light on the designing optimized ceria and copper-based catalysts and the mechanism of CO oxidation.

Intramolecular Charge‐Transfer Dynamics in Benzodifuran‐Based Triads

AbstractA facile and efficient approach for the synthesis of new conjugated donor‐π‐acceptor (D‐π‐A) chromophores has been developed, in which benzodifuran (BDF) and/or triphenyl amine (TPA) units are the donor moieties, linked by ethylenic bridges to electron‐deficient anthraquinone (AQ) and 11,11,12,12‐tetracyano‐9,10‐anthraquinodimethane (TCAQ) as the acceptor moieties. The resultant triads either with a symmetric A–D–A or an asymmetric D′–D–A structure show intense absorption bands in the visible spectral region due to efficient intramolecular charge transfer (ICT) from the HOMO localized on the BDF core to the LUMO localized on the AQ or the TCAQ unit. Electronic interactions between these redox‐active components were studied by a combination of cyclic voltammetry, spectroelectrochemistry, UV‐visible and ultrafast transient absorption spectroscopy. Analysis of the femtosecond excited‐state dynamics reveal that all triads undergo a rapid charge recombination process which occurs within a few picoseconds, indicating that ethylenic linkers can facilitate electron delocalization among BDF and AQ/TCAQ units and thus impart effective electronic interactions between them.

Spontaneous Production of Ultrastable Reactive Oxygen Species on Titanium Oxide Surfaces Modified with Organic Ligands

AbstractThe spontaneous formation and long‐term surface stabilization of superoxide radicals are observed on specific TiO2 hybrid materials in which titanium is coordinated to an organic ligand. Here the rationale for this uncommon phenomenon is investigated by a synergistic theoretical and experimental approach involving density functional theory (DFT) calculations and spectroscopic techniques. Stoichiometric and reduced anatase (101) surfaces modified with acetylacetone, dibenzoylmethane, and catechol are comparatively examined. These results reveal that the interaction between organic ligands and adsorbed O2 molecules improves when O vacancies are present on the external layer of the surface, promoting O2 reduction. The electronic features of the ligand play a pivotal role for both an effective electronic interaction with the surface and the stabilization of the generated reactive oxygen species. These results agree with experimental data showing that sol–gel‐derived Ti‐diketonate hybrid oxides spontaneously produce very persistent superoxide radicals under ambient conditions, thus holding a high intrinsic oxidative activity.

Schottky-structured 0D/2D composites via electrostatic self-assembly for efficient photocatalytic hydrogen evolution

Semiconductor-metal heterostructure, especially represented by various inorganic semiconductors-platinum (Pt) hybrids, is widely applied in converting solar power to chemical energy. Given the scarcity of Pt and the availability of coupling, the development of a non-Pt regimen and facile assembly strategy is critical. In this study, CdxZn1-xS/Ti3C2 ultrathin MXene composites were availably prepared with a facile electrostatic assembly strategy. The unique 0D/2D assembly demonstrated remarkably enhanced performance toward photocatalytic hydrogen production compared with bare CdxZn1-xS. Spectroscopic characterization analysis and band theory discussion substantiated the effects of electronic interaction and the Schottky barrier arising from intimate contact of CdxZn1-xS and Ti3C2 MXene on the swift separation of photoinduced electron-hole pairs. Successful application of electrostatic self-assembled CdxZn1-xS with ultrathin MXene opens a new area of utilizing electrical difference and band theory to prepare rational semiconductor/MXene Schottky structure towards various photocatalytic reactions.

Concave-convex surface oxide layers over copper nanowires boost electrochemical nitrate-to-ammonia conversion

The room-temperature nitrate electroreduction to ammonia recycles the fixed nitrogen and offers an appealing ammonia-synthesis scenario. Electrocatalyst engineering is of vital importance to accelerate the reaction kinetics and increase the product selectivity during nitrate electroreduction to ammonia. In this work, Cu nanowires with concave-convex surface Cu2+1O layers (Cu@Cu2+1O NWs) were fabricated by a facile surface engineering strategy. Interior metallic Cu components allow for efficient electronic transmission capability along the nanowire structure, while exterior concave-convex Cu2+1O layers endow abundant catalytically active sites. Furthermore, the electronic interaction and interface effect between Cu/Cu2+1O enable tuning of the Cu d-band center and modulating the adsorption energies of intermediates. Consequently, the electroreduction ability of nitrate-to-ammonia over the Cu@Cu2+1O NWs is substantially improved, evident by the high nitrate-N conversion rate (78.57%), ammonia yield rate (576.53 µg h−1 mgcat.−1) and ammonia Faradaic efficiency (87.07%) at the optimal applied potential (-1.2 V vs. saturated calomel electrode) for 2 h. The findings in the study are worth reference to tailor surface/interface properties and atom structure towards highly efficient electrocatalysts.

Magnetotransport and thermal properties of microwave synthesized nanostructured Bi2Te3

Magnetotransport and thermal properties of microwave-synthesized nanostructured Bi2Te3, a well-known material of topological interest, have been studied in detail. Temperature-dependent resistivity shows a disordered metal-like behavior at high temperature with unsaturated ln(T)-dependent upturns at low temperature manifesting localization tendency. The slopes (κ) of the normalized conductivity (Δσ) vs ln(T) curves change sharply with magnetic fields upto 1 T and then saturate at a certain higher field (Bϕ), which is an indication of a combined electron–electron interaction and quantum interference effect (QIE) dominated transport. A noteworthy result is a crossover from positive to negative Coulomb screening factor (F) in Bi2Te3. Low-field (H ≤ 1 T) magnetoconductivity at low temperature follows a 2D Hikami–Larkin–Nagaoka equation, thereby revealing the QIE and associated dephasing nature of the electronic states at high temperatures. High-field (14 T) magnetoresistance (MR) at 2 K shows interesting features like low-field weak antilocalization, possibly a defect-induced negative MR that vanishes after post-annealing treatment, and a high field parabolic character in place. The Seebeck coefficient (S) is negative and varies quasilinearly with a slight but notable slope change at intermediate temperatures. Heat capacity measurements are in line with a narrow gap degenerate semiconductor with a low θD of 140 K. A combined analysis of heat capacity and thermopower reveals the localization of carriers at low temperatures and is in line with transport data.

Extended Hubbard model in undoped and doped monolayer and bilayer graphene: Selection rules and organizing principle among competing orders

Performing a leading-order renormalization group analysis, here we compute the effects of generic local or short-range electronic interactions in monolayer and Bernal bilayer graphene. Respectively in these two systems chiral quasiparticles display linear and biquadratic band touching, leading to linearly vanishing and constant DOS. Consequently, the former system remains stable for weak enough local interactions, and supports a variety of ordered phases only beyond a critical strength of interactions. By contrast, ordered phases can nucleate for sufficiently weak interactions in bilayer graphene. By tuning the strength of all symmetry allowed local interactions, we construct various cuts of the phase diagram at zero and finite temperature and chemical doping. Typically, at zero doping insulating phases (such as charge-density-wave, antiferromagnet, quantum anomalous and spin Hall insulators) prevail at the lowest temperature, while gapless nematic or smectic liquids stabilize at higher temperatures. On the other hand, at finite doping the lowest temperature ordered phase is occupied by a superconductor. Besides anchoring such an organizing principle among the candidate ordered phases, we also establish a selection rule between them and the interaction channel responsible for the breakdown of linear or biquadrtic chiral nodal Fermi liquid. In addition, we also demonstrate the role of the normal state band structure in selecting the pattern of symmetry breaking from a soup of preselected incipient competing orders. As a direct consequence of the selection rule, while an antiferromagnetic phase develops in undoped monolayer and bilayer graphene, the linear (biquadratic) band dispersion favors condensation of a spin-singlet nematic (translational symmetry breaking Kekul\'e) superconductor in doped monolayer (bilayer) graphene, when the on site Hubbard repulsion dominates in these systems.

Interacting spin- 32 fermions in a Luttinger semimetal: Competing phases and their selection in the global phase diagram

We compute the effects of electronic interactions on gapless spin-3/2 excitations that in a noninteracting system emerge at a bi-quadratic touching of Kramers degenerate valence and conduction bands, known as Luttinger semimetal. This model can describe the low-energy physics of HgTe, gray-Sn, 227 pyrochlore iridates and half-Heuslers. For the sake of concreteness we only consider the short-range components of the Coulomb interaction. By combining mean-field analysis with a renormalization group (RG) calculation, we construct multiple cuts of the global phase diagram of interacting spin-3/2 fermions at zero and finite temperature and chemical doping. Such phase diagrams display a rich confluence of competing orders, among which rotational symmetry breaking nematic insulators and time reversal symmetry breaking magnetic orders are the prominent excitonic phases. We also show that even repulsive interactions can be conducive for both s-wave and d-wave pairings. The reconstructed band structure inside the ordered phases allows us to organize them according to the energy (entropy) gain in the following (reverse) order: s-wave pairing, nematic phases, magnetic orders and d-wave pairings, at zero chemical doping. But, the paired states are always energetically superior over the excitonic ones for finite doping. The phase diagrams obtained from the RG analysis show that an ordered phase with higher energy (entropy) gain is realized at low (high) temperature. In addition, we establish a "selection rule" between the interaction channels and the resulting ordered phases, suggesting that repulsive interactions in the magnetic (nematic) channels are conducive for the nucleation of d-wave (s-wave) pairing. The proposed methodology can shed light on the global phase diagram of other strongly interacting multi-band systems, such as doped Dirac semimetal, topological insulators and the like.

Emergent chiral symmetry in a three-dimensional interacting Dirac liquid

We compute the effects of strong Hubbardlike local electronic interactions on three-dimensional four-component massless Dirac fermions, which in a noninteracting system possess a microscopic global U(1) ⊗ SU(2) chiral symmetry. A concrete lattice realization of such chiral Dirac excitations is presented, and the role of electron-electron interactions is studied by performing a field theoretic renormalization group (RG) analysis, controlled by a small parameter ϵ with ϵ = d−1, about the lower-critical one spatial dimension. Besides the noninteracting Gaussian fixed point, the system supports four quantum critical and four bicritical points at nonvanishing interaction couplings ∼ ϵ. Even though the chiral symmetry is absent in the interacting model, it gets restored (either partially or fully) at various RG fixed points as emergent phenomena. A representative cut of the global phase diagram displays a confluence of scalar and pseudoscalar excitonic and superconducting (such as the s-wave and p-wave) mass ordered phases, manifesting restoration of (a) chiral U(1) symmetry between two excitonic masses for repulsive interactions and (b) pseudospin SU(2) symmetry between scalar or pseudoscalar excitonic and superconducting masses for attractive interactions. Finally, we perturbatively study the effects of weak rotational symmetry breaking on the stability of various RG fixed points.

Influence of Dopant Uniformity on Electron Transport in CuxBi2Se3 Films

The contribution of topological insulator surface states to their transport properties can be tuned by doping, but the uniformity effect of the dopants has been ignored in previous studies. In this work, we studied the influence of the degree of uniformity on high-quality CuxBi2Se3 films prepared by pulsed laser deposition with a designed sequential deposition process of Bi2Se3 and Cu. It was found that with a greater uniformity of the Cu dopants a two-dimensional electron–electron interaction (2D EEI) effect becomes more evident below ∼25 K in the presence of weak disorder and a weak antilocalization (WAL) effect near zero magnetic field becomes more pronounced at low temperature. Furthermore, the topological surface state conduction of the CuxBi2Se3 films was verified by the Hikami–Larkin–Nagaoka (HLN) model analysis of the WAL effect. This research may open up new aspects for the further study of the transport properties of disordered topological insulators.