Changes In Electronic Structure Research Articles

Operando resonant soft X-ray emission spectroscopy of the LiMn2O4 cathode using an aqueous electrolyte solution.

The Mn 3d electronic-structure change of the LiMn2O4 cathode during Li-ion extraction/insertion in an aqueous electrolyte solution was studied by operando resonant soft X-ray emission spectroscopy (RXES). The Mn L3 RXES spectra for the charged state revealed the Mn4+ state with strong charge-transfer from the O 2p to Mn 3d orbitals dominates, while for the open-circuit-voltage and discharged states it is ascribed to the mixture of sites with Mn3+ and Mn4+ states. The degree of charge transfer is significantly different between the Mn3+ and Mn4+ states, indicating that the redox reaction takes place on the strongly-hybridized Mn 3d-O 2p orbital rather than the localized Mn 3d orbital.

Analysis on Electronic-Structural Change of Carbon Nanotube Exposed to Atomic Oxygen by HAXPES

Analysis on Electronic-Structural Change of Carbon Nanotube Exposed to Atomic Oxygen by HAXPES

Unveiling Center‐Type Topological Defects on Rosettes of Lead Zirconate Titanate Associated to Oxygen Vacancies

AbstractUnderstanding the formation of topological defects in ferroelectric materials can provide access to their unusual physics, invaluable for possible applications of domain engineering in nanoelectronics. The present study shows the spontaneous formation of center‐type topological defects in lead zirconate titanate (PZT) films, characterized by a strong in‐plane radial electromechanical response on rosette‐like structures, as revealed by piezoelectric response force microscopy. Multi‐modal electron and X‐ray based techniques provide a comprehensive set of tools for delving at atomic scale the local chemistry, electronic, and crystalline structures. The elemental surface‐sensitivity of soft X‐ray absorption shows chemical segregation and drastic changes in the titanium electronic structure, which have been associated to oxygen vacancies, leading to a mechanism that describe the polarization symmetry on the rosettes. X‐ray nanofluorescence experiments revealed titanium segregation, corroborating with the absorption and low energy electron microscopy images. Taking advantage of a nanobeam, 2D nanodiffraction maps probed the complex microstructure of the domains, revealing its mosaicity and lattice strain at the nanoscale. This study highlights a complex topological structure and provides, by the simultaneous application of a set of analytical tools, a broad comprehension of the formation of center‐type ferroelectric topological defects in PZT.

X-ray Transient Absorption Studies of Exciton Self-Trapping

We present optical pump/X-ray absorption probe studies to probe changes in electronic distribution and local structure upon formation of a self-trapped exciton. The experiments were carried out on the mixed-valence halide-bridged transition metal linear chain charge density wave material [Pt(en2)][Pt(en2)Cl2]·(ClO4)4. Photoinduced changes in the Pt LIII XANES spectrum were measured on a picosecond time scale following generation of excitons via optical excitation of the intervalence charge transfer transition. Ab initio FEFF9 modeling of the spectra and the associated angular momentum projected density of states was used to interpret the response. We find photoinduced changes reflecting electronic redistribution and local lattice distortions that correspond to strong localization of the self-trapped state.

Materials informatics-guided superior electrocatalyst: A case of pyrolysis-free single-atom coordinated with N-graphene nanomesh

In this work, we apply materials informatics (MI) techniques for property prediction of nanoporous carbon-based electrocatalyst for oxygen reduction reaction (ORR), which is a key, but sluggish reaction in proton exchange membrane fuel cells and metal–air batteries. Nitrogen-doped graphene nanomesh (NGM) was identified as an appropriate ORR catalyst by the MI techniques, which is a useful support to producing designed nitrogen-coordinated single-atom catalysts via pyrolysis-free pathway. Herein, single-atom catalysts (FePc/NGM) with predictable structures were fabricated by anchoring iron phthalocyanine (FePc) on the MI-guided NGM. Compared with the randomly creating Fe-Nx moieties on a carbon matrix via pyrolysis, FePc were riveted onto NGM via axial interactions between Fe-N4 moieties in FePc and nitrogen in NGM graphene matrix. As a result, Fe-N5 with superior catalytic activity for ORR was created. The elaborately designed FePc/NGM possesses an outstanding electrocatalytic activity owing to its low-dimensional structure and the significant change in electronic and geometric structures arising from the rehybridization of Fe 3d orbitals from FePc with the nitrogen orbitals from NGM at the axial direction. This work demonstrates that fusion of experiments with material informatics is indispensable for the practice of the inorganic synthetic chemistry.

Two-dimensional PdPS and PdPSe nanosheets: Novel promising sensing platforms for harmful gas molecules

Motivated by the latest experimental advances in the fabrication of penta-PdPS and penta-PdPSe layered materials, in this work we theoretically explore the PdPS and PdPSe monolayers as novel platforms for the detection of harmful gas molecules, including CO, CO2, NH3, NO, and NO2. We found that PdPS and PdPSe monolayers are stable semiconductors. Next, we systematically assessed the most favorable adsorption configurations and examined the electronic properties of gas-adsorbed PdPS/PdPSemonolayers. It is manifested that CO, CO2, and NH3 gas molecules are physisorbed on the PdPS, and PdPSe monolayers, while upon the adsorption of NO, and NO2, the electronic structure changes significantly. It is moreover realized that after adsorption of NO, and NO2, respectively, over the PdPS monolayers energies of 0.98, 1.01 eV are released, and over PdPSe energies of 1.12, and 1.21 eV are emitted. According to calculated recovery time, the PdPS platform yields a quick recovery after exposure to NO, and NO2 with times of 4.33 and 11.9 s, respectively, at room temperature and under UV light. PdPSe monolayers exhibits a recovery time of 1.74 s at 498 K and under visible light after interaction with NO2. Our study results suggest that PdPS and PdPSe nanosheets are eminently promising for detecting NO2 molecule.

Redox Activity of Iron Diazine-Diimine Carbonyl and Dinitrogen Complexes: A Comparative Study of the Influence of the Heterocyclic Ring.

A detailed investigation of the electronic structure of diazinediimine iron complexes and their comparison with the pyridine analogues reveals subtle but important differences, imparted by the supporting heterocycle. In the case of LFe(CO)2 complexes (L = pyrazine- and pyrimidinediimine), the characterization of three available redox states confirmed that whereas the nature of the electron-transfer processes is similar, the differences in π-acidity of the supporting heterocycle significantly affect the redox potentials. The reduction of LFe(CO)2 can yield either a ligand-centered radical (for L = pyrimidine) or a C-C-bonded dimer (for L = pyrazine), supported by a dearomatized core. In the latter case, the C-C bond can be reversibly cleaved oxidatively. Compared to the carbonyl analogues, employing weak-field N2 ligands triggers changes in electronic structure for the neutral and reduced LFe(N2) complexes (L = pyrimidinediimine). En route to the synthesis of the nitrogen complexes, the square-planar LFeCl (L = pyrimidinediimine) was isolated. The monoradical character of the supporting chelate triggers the asymmetric distribution of electron density around the heterocycle.

Site-Specific Reduction-Induced Hydrogenation of a Helical Bilayer Nanographene with K and Rb Metals: Electron Multiaddition and Selective Rb+ Complexation.

The chemical reduction of π‐conjugated bilayer nanographene 1 (C138H120) with K and Rb in the presence of 18‐crown‐6 affords [K+(18‐crown‐6)(THF)2][{K+(18‐crown‐6)}2(THF)0.5][C138H122 3−] (2) and [Rb+(18‐crown‐6)2][{Rb+(18‐crown‐6)}2(C138H122 3−)] (3). Whereas K+ cations are fully solvent‐separated from the trianionic core thus affording a “naked” 1.3 − anion, Rb+ cations are coordinated to the negatively charged layers of 1.3 −. According to DFT calculations, the localization of the first two electrons in the helicene moiety leads to an unprecedented site‐specific hydrogenation process at the carbon atoms located on the edge of the helicene backbone. This uncommon reduction‐induced site‐specific hydrogenation provokes dramatic changes in the (electronic) structure of 1 as the helicene backbone becomes more compressed and twisted upon chemical reduction, which results in a clear slippage of the bilayers.

Site‐Specific Reduction‐Induced Hydrogenation of a Helical Bilayer Nanographene with K and Rb Metals: Electron Multiaddition and Selective Rb+ Complexation

AbstractThe chemical reduction of π‐conjugated bilayer nanographene 1 (C138H120) with K and Rb in the presence of 18‐crown‐6 affords [K+(18‐crown‐6)(THF)2][{K+(18‐crown‐6)}2(THF)0.5][C138H1223−] (2) and [Rb+(18‐crown‐6)2][{Rb+(18‐crown‐6)}2(C138H1223−)] (3). Whereas K+ cations are fully solvent‐separated from the trianionic core thus affording a “naked” 1.3− anion, Rb+ cations are coordinated to the negatively charged layers of 1.3−. According to DFT calculations, the localization of the first two electrons in the helicene moiety leads to an unprecedented site‐specific hydrogenation process at the carbon atoms located on the edge of the helicene backbone. This uncommon reduction‐induced site‐specific hydrogenation provokes dramatic changes in the (electronic) structure of 1 as the helicene backbone becomes more compressed and twisted upon chemical reduction, which results in a clear slippage of the bilayers.

Kβ-to-Kα X-ray intensity ratio studies on changes of valance electron structures of nickel in Ni–B/hBN composite coatings

In this study, Kβ/Kα X-ray intensity ratio values of nickel in Ni coating and Ni–B/hBN (hBN: hexagonal Boron Nitride) composite coatings have been determined by the Energy Dispersive X-ray fluorescence spectroscopy (EDXRF) method. The Kβ/Kα X-ray intensity ratios of nickel in the Ni coating and Ni–B/hBN composite coatings have been compared with theoretical, experimental, and fitted data of the pure nickel. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) measurements have been performed to observe how hBN particles with different bath concentrations affected the crystal structure and microstructure, respectively. The valence electronic structure of Ni in the coatings has been determined by comparing the experimental Kβ/Kα X-ray intensity ratios with Multiconfiguration Dirac-Fock (MCDF) predictions for various electron structures of Ni. The results show that while the values of the Kβ/Kα X-ray intensity ratio of the Ni–B/hBN composite coatings over pure Ni coatings increases, the 3d electron populations decreases. The change in the valence electronic structure were interpreted through charge transfer and rearrangement processes.

Arbitrarily accurate quantum alchemy.

Doping compounds can be considered a perturbation to the nuclear charges in a molecular Hamiltonian. Expansions of this perturbation in a Taylor series, i.e., quantum alchemy, have been used in the literature to assess millions of derivative compounds at once rather than enumerating them in costly quantum chemistry calculations. So far, it was unclear whether this series even converges for small molecules, whether it can be used for geometry relaxation, and how strong this perturbation may be to still obtain convergent numbers. This work provides numerical evidence that this expansion converges and recovers the self-consistent energy of Hartree-Fock calculations. The convergence radius of this expansion is quantified for dimer examples and systematically evaluated for different basis sets, allowing for estimates of the chemical space that can be covered by perturbing one reference calculation alone. Besides electronic energy, convergence is shown for density matrix elements, molecular orbital energies, and density profiles, even for large changes in electronic structure, e.g., transforming He3 into H6. Subsequently, mixed alchemical and spatial derivatives are used to relax H2 from the electronic structure of He alone, highlighting a path to spatially relaxed quantum alchemy. Finally, the underlying code that allows for arbitrarily accurate evaluation of restricted Hartree-Fock energies and arbitrary order derivatives is made available to support future method development.

Controlled high-density interface engineering of Fe3O4-FeS nanoarray for efficient hydrogen evolution

The rational design of double active sites system is vital for constructing high-efficiency iron sulfides electrocatalysts towards hydrogen evolution reaction (HER) in alkaline media. However, it remains a challenge to controllably create the high-density interface of double sites for optimal synergistic effect. Herein, we reported a simple chemical oxidation-induced surface reconfiguration strategy to obtain the interface-rich Fe3O4-FeS nanoarray supported on iron foam (Fe3O4-FeS/IF) using FeS nanosheets as precursors. The abundant Fe3O4-FeS interfaces could improve the dispersion of active sites and facilitate the electron transfer, leading to enhanced hydrogen evolution efficiency. And meanwhile, by altering the oxidation temperature, the content of S and O could be effectively controlled, further achieving the ratio optimization of Fe3O4 to FeS. Synchrotron-based X-ray absorption near-edge structure, X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy consistently confirm the changes of electronic structure and d-band center of Fe3O4-FeS after chemical oxidation. Consequently, Fe3O4-FeS/IF exhibits excellent alkaline HER activity with a low overpotential of 120.8 mV to reach 20 mA cm−2, and remains stable ranging from 10, 20 to 50 mA cm−2 for each 20 h, respectively. Therefore, the facile and controllable chemical oxidation may be an effective strategy for designing high-density interfaces of transition metal-based sulfides towards alkaline HER.

Computational Evaluation of Li-doped g-C2N Monolayer as Advanced Hydrogen Storage Media

The emerging 2D g-C2N obtained increasingly more popularity in functional materials design, and its natural porosity can easily accommodate metal atoms, making itself more suitable for energy gases storage. In this study, we employed DFT computational studies to systematically solve the electronic structure of Li-doped g-C2N monolayer, and evaluate its performance in hydrogen storage. In our calculations, we found that each pore of g-C2N can adsorb at most three Li atoms that bind with pyridinic N atoms. We also noticed that considerable amount of charges were transferred from the adsorbed Li to the pristine materials, potentially enhancing its overall conductivity. The change of electronic structure also leads to its improved performance in H2 adsorption, due to the fact that the electrostatic interactions between the adsorbed H2 and Li can be largely enhanced. The optimised configurations of the Li-doped g-C2N with multiple adsorbed H2 molecules were presented, and the fundamental mechanisms of adsorption were also investigated in details. The highest storage capacity of hydrogen by Li-doped g-C2N can reach to 7.8 wt%, much higher than the target value of 5.5 wt %, defined by the U.S department of energy (DOE). Moreover, except Li, we also found that the nitrogen atoms or the N-C bonds can also serve as active adsorption sites. The computational explorations conducted in this study actually indicates a promising prospect of alkali metals decorated 2D materials in the area of hydrogen storage; and we believe the performance of these kinds of novel materials can be further enhanced via more decent modifications.

Electronic structure and spin–orbit coupling in ternary transition metal chalcogenides Cu2TlX 2 (X = Se, Te)

Ternary transition metal chalcogenides provide a rich platform to search and study intriguing electronic properties. Using angle-resolved photoemission spectroscopy and ab initio calculation, we investigate the electronic structure of Cu2TlX 2 (X = Se, Te), ternary transition metal chalcogenides with quasi-two-dimensional crystal structure. The band dispersions near the Fermi level are mainly contributed by the Te/Se p orbitals. According to our ab-initio calculation, the electronic structure changes from a semiconductor with indirect band gap in Cu2TlSe2 to a semimetal in Cu2TlTe2, suggesting a band-gap tunability with the composition of Se and Te. By comparing ARPES experimental data with the calculated results, we identify strong modulation of the band structure by spin–orbit coupling in the compounds. Our results provide a ternary platform to study and engineer the electronic properties of transition metal chalcogenides related to large spin–orbit coupling.

Laser ablation enhancing the electrochemical sensing performance of copper foam toward glucose

In this work, a copper foam with surface oxidation and micro-nano structure was fabricated via a femtosecond laser ablation technique. The change in surface microscopic morphology and electronic structure was investigated by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Based on its rough surface, unique electronic state and oxygen defects, the laser-treated copper foam exhibited excellent electrochemical sensing performance for glucose. The sensitivity and detection limit was determined to be 27.4517 mA cm −2 mM −1 and 1.5 μM, respectively. Furthermore, the good selectivity of the present laser-treated copper foam was also demonstrated by the anti-interference experiment.

Structural and Physical Properties of Ultrathin Bismuth Films

Bismuth films are interesting objects for research because of the many effects occurring when the film thickness is less than 70 nm. The electronic band structure changes significantly depending on the film thickness. Consequently, by changing the film thickness, it is possible to control the physical properties of the material. The purpose of this paper is to give a brief description of the basic structural and physical properties of bismuth films. The structural properties, namely, morphology, roughness, nanoparticle size, and texture, are discussed first, followed by a description of the transport properties and the band structure. The transport properties are described using the semi-metal–semiconductor transition, which is associated with the quantum size effect. In addition, an important characteristic is a two-channel model, which allows describing the change in resistivity with temperature. The band structure of bismuth films is the most interesting part due to the anomalous effects for which there is still no unambiguous explanation. These effects include anomalous spin polarization, nontrivial topology, and zone changes near the edge of the film.

Computational Studies for Crystal Structures of Helicate Lanthanide Complexes Based on X-ray Analyses

Abstract Computational approaches to elucidate the phase transitions in lanthanide complexes will support understanding their electronic structure changes by weak stimuli such as gas adsorptions. There are no examples as molecular models of Ln complexes for defining parameters, due to various molecular shapes with unexpected coordination numbers resulting in different packings with different Ln ions. Here, we succeeded in determining molecular force field parameters (van der Waals; vdW for Ln = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm; and torsion parameters of the ligand) to apply the structural optimization of a series of Ln complexes taking uniform helicate for ten Ln ions with the same ligand, L, which reported previously as LnL. SmL, ErL, and TmL were newly synthesized for this calculation and the structure and luminescence properties experimentally determined. The coordination distances surrounding Ln are along the lanthanoid contraction. It is the first case to clarify the lanthanoid contraction in a 10-coordination system of a series of Ln ions. The applied optimized structures with these parameters for Eu well exhibit correspondence to observed results for four analogous of EuL. This work will strongly push development of luminescent Ln complexes with soft-crystalline behaviour.

Operando XAFS on Hydrated Calcium Vanadium Bronze Cathode for Aqueous Zn-ion Storage.

Multivalent ion storage and aqueous electrochemical systems continue to build interest for energy application. The Zn-ion system with 2 electron transfer and an ideal metal anode is a strong candidate but is still at the early stage of development. Using both in situ near-edge (XANES) and X-ray absorption fine structure spectroscopy, EXAFS, a nanostructured cathode material, Cax V2 O5 -H2 O (CVO), was probed at the V-K absorption edge. This operando study reveals the local electronic and geometric structure changes for CVO during galvanostatic cycling as the active material in an aqueous Zn-ion cell. The XANES data provides a fine resolution to track the evolution of the vanadium oxidative state and near-neighbor coordination sphere showing subtle shifts and delocalized charge. The Zn-ion influence on the V-K absorption edge is visualized using a difference technique called Δμ. Coupled with theoretical calculations and modelling, the extended region extracted local bonding information further confirms excellent electronic and structural reversibility of this vanadium oxide bronze in an aqueous Zn-ion electrochemical cell.

All are aromatic: A 3D globally aromatic cage containing five types of 2D aromatic macrocycles

All are aromatic: A 3D globally aromatic cage containing five types of 2D aromatic macrocycles

On the Supra-LUMO Interaction: Case Study of a Sudden Change of Electronic Structure as a Functional Emergence.

The synergistic functioning of redox-active components that emerges from prototypical 2,2'-di(N-methylpyrid-4-ylium)-1,1'-biphenyl is described. Interestingly, even if a trans conformation of the native assembly is expected, due to electrostatic repulsion between cationic pyridinium units, we demonstrate that cis conformation is equally energy-stabilized on account of a peculiar LUMO (SupLUMO) that develops through space, encompassing the two pyridiniums in a single, made-in-one-piece, electronic entity (superelectrophoric behavior). This SupLUMO emergence, with the cis species as superelectrophore embodiment, originates in a sudden change of electronic structure. This finding is substantiated by insights from solid state (single-crystal X-ray diffraction) and solution (NOE NMR and UV-vis-NIR spectroelectrochemistry) studies, combined with electronic structure computations. Electrochemistry shows that electron transfers are so strongly correlated that two-electron reduction manifests itself as a single-step process with a large potential inversion consistent with inner creation of a carbon-carbon bond (digital simulation). Besides, absence of reductive formation of dimers is a further indication of a preferential intramolecular reactivity determined by the SupLUMO interaction (cis isomer pre-organization). The redox-gated covalent bond, serving as electron reservoir, was studied via atropisomerism of the reduction product (VT NMR study). The overall picture derived from this in-depth study of 2,2'-di(N-methylpyrid-4-ylium)-1,1'-biphenyl proves that trans and cis species are worth considered as intrinsically sharply different, that is, as doubly-electrophoric and singly-superelectrophoric switchable assemblies, beyond conformational isomerism. Most importantly, the through-space-mediated SupLUMO may come in complement of other weak interactions encountered in Supramolecular Chemistry as a tool for the design of electroactive architectures.