Electronic Structure Transition Research Articles

Unraveling the Impact of Oxygen Vacancy on Electrochemical Valorization of Polyester Over Spinel Oxides.

Electrochemical upcycling of end-of-life polyethylene terephthalate (PET) using renewable electricity offers a route to generate valuable chemicals while processing plastic wastes. However, it remains a huge challenge to design an electrocatalyst with reliable structure-property relationships for PET valorization. Herein, spinel Co3O4 with rich oxygen vacancies for improved activity toward formic acid (FA) production from PET hydrolysate is reported. Experimental investigations combined with theoretical calculations reveal that incorporation of VO into Co3O4 not only promotes the generation of reactive hydroxyl species (OH*) species at adjacent tetrahedral Co2+ (Co2+ Td), but also induces an electronic structure transition from octahedral Co3+ (Co3+ Oh) to octahedral Co2+ (Co2+ Oh), which typically functions as highly-active catalytic sites for ethylene glycol (EG) chemisorption. Moreover, the enlarged Co-O covalency induced by VO facilitates the electron transfer from EG* to OH* via Co2+ Oh-O-Co2+ Td interaction and the following C─C bond cleavage via direct oxidation with a glyoxal intermediate pathway. As a result, the VO-Co3O4 catalyst exhibits a high half-cell activity for EG oxidation, with a Faradaic efficiency (91%) and productivity (1.02mmol cm-2 h-1) of FA. Lastly, it is demonstrated that hundred gram-scale formate crystals can be produced from the real-world PET bottles via two-electrode electroreforming, with a yield of 82%.

Constructing Slip Stacking Diversity in Van der Waals Homobilayers.

The van der Waals (vdW) interface provides two important degrees of freedom-twist and slip-to tune interlayer structures and inspire unique physics. However, constructing diversified high-quality slip stackings (i.e., lattice orientations between layers are parallel with only interlayer sliding) is more challenging than twisted stackings due to angstrom-scale structural discrepancies between different slip stackings, sparsity of thermodynamically stable candidates and insufficient mechanism understanding. Here, using transition metal dichalcogenide (TMD) homobilayers as a model system, this work theoretically elucidates that vdW materials with low lattice symmetry and weak interlayer coupling allow the creation of multifarious thermodynamically advantageous slip stackings, and experimentally achieves13 and 9 slip stackings in 1T″-ReS2 and 1T″-ReSe2 bilayers via direct growth, which are systematically revealed by atomic-resolution scanning transmission electron microscopy (STEM), angle-resolved polarization Raman spectroscopy, and second harmonic generation (SHG) measurements. This work also develops modulation strategies to switch the stacking via grain boundaries (GBs) and to expand the slip stacking library from thermodynamic to kinetically favored structures via in situ thermal treatment. Finally, density functional theory (DFT) calculations suggest a prominent dependence of the pressure-induced electronic band structure transition on stacking configurations. These studies unveil a unique vdW epitaxy and offer a viable means for manipulating interlayer atomic registries.

Electric field-induced electronic structure and intersubband transitions of a hydrogen molecular ion in a gaussian-type quantum ring

In this work, the influence of an external electric field on the electronic structure and intersubband transitions of a singly ionized double-donor system in a GaAs quantum ring defined by Gaussian-type potentials is investigated theoretically. Within the framework of the effective mass approach, the two-dimensional diagonalization method is used for the solution of the Schrödinger equation to obtain the eigen energies and corresponding wave functions. Numerical results reveal that the electronic energy spectrum and the linear optical absorption coefficient of the ring are remarkably affected by the strength of the lateral electric field, internuclear distance and parameters defining the confinement potential. Also, it has been shown that beyond the anti-crossing point, the wave functions exchange their symmetries without mixing, which is a characteristic feature of energy-level anti-crossing.

Kinetics and Mechanism of the Singlet Oxygen Atom Reaction with Dimethyl Ether.

We combine in situ laser spectroscopy, quantum chemistry, and kinetic calculations to study the reaction of a singlet oxygen atom with dimethyl ether. Infrared laser absorption spectroscopy and Faraday rotation spectroscopy are used for the detection and quantification of the reaction products OH, H2O, HO2, and CH2O on submillisecond time scales. Fitting temporal profiles of products with simulations using an in-house reaction mechanism allows product branching to be quantified at 30, 60, and 150 Torr. The experimentally determined product branching agrees well with master equation calculations based on electronic structure data and transition state theory. The calculations demonstrate that the dimethyl peroxide (CH3OOCH3) generated via O-insertion into the C-O bond undergoes subsequent dissociation to CH3O + CH3O through energetically favored reactions without an intrinsic barrier. This O-insertion mechanism can be important for understanding the fate of biofuels leaking into the atmosphere and for plasma-based biofuel processing technologies.

Modulating charge density wave states in 1T-TaS[formula omitted] by self-intercalation: A DFT study

Complicated charge density wave (CDW) phases transitions in the transition-metal dichalcogenide (TMDs) 1T-TaS2 have attracted wide research interest owing to the accompanied complex electronic structure transition which has not been fully understood. Inspired by a recent experimental work (Zhao et al. (2020), reported the successful preparation of Ta atom self-intercalated 2H-TaS2), we employed first-principles methods to investigate Ta atom self-intercalated 1T-TaS2, exploring effects of self-intercalation on electronic structure, magnetism, and stability ofthe charge density wave (CDW) phase in 1T-TaS2. Our first-principle calculation shows that the intercalation of Ta atom into the van der Waals gap of 1T-TaS2 induce the phase transition from 1T phase to CDW phase, and the positions of intercalated Ta atom determine the distribution of David-star clusters. Accompanied by the structural phase transition, the Ta intercalated 1T-TaS2 also undergoes an electronic structure phase transition from non-magnetic metal to half-metal which is also different from conventional charge density wave’s insulating state. When appropriate holes are doped to the intercalation system, the CDW David-star cluster is gradually destroyed and eventually returns to its original 1T phase. Our studies enrich the phase diagram of TaS2 and highlight the effective manipulation of the CDW states via self-intercalation. This type of materials may have very promising applications in future electronic devices.

Twist-Angle Tuning of Electronic Structure in Two-Dimensional Dirac Nodal Line Semimetal Au2Ge on Au(111).

Topological semimetals have emerged as quantum materials including Dirac, Weyl, and nodal line semimetals, and so on. Dirac nodal line (DNL) semimetals possess topologically nontrivial bands crossing along a line or a loop and are considered precursor states for other types of semimetals. Here, we combine scanning tunneling microscopy/spectroscopy (STM/S) measurements and density functional theory (DFT) calculations to investigate a twist angle tuning of electronic structure in two-dimensional DNL semimetal Au2Ge. Theoretical calculations show that two bands of Au2Ge touch each other in Γ-M and Γ-K paths, forming a DNL. A significant transition of electronic structure occurs by tuning the twist angle from 30° to 24° between monolayer Au2Ge and Au(111), as confirmed by STS measurements and DFT calculations. The disappearing of DNL state is a direct consequence of symmetry breaking.

Composition-driven Mott transition within SrTi 1−x V x O3

The last few decades has seen the rapid growth of interest in the bulk perovskite-type transition metal oxides SrVO3 and SrTiO3. The electronic configuration of these perovskites differs by one electron associated to the transition metal species which gives rise to the drastically different electronic properties. Therefore, it is natural to look into how the electronic structure transitions between these bulk structures by using doping. Measurements of the substitutional doped SrTi 1−x V x O3 shows an metal–insulator transition (MIT) as a function of doping. By using supercell density functional theory with dynamical mean field theory (DFT+DMFT), we show that the MIT is indeed the result of the combination of local electron correlation effects (Mott physics) within the t2g orbitals and the atomic site configuration of the transition metals which may indicate dependence on site disorder. SrTi 1−x V x O3 may be an ideal candidate for benchmarking cutting-edge Mott–Anderson models of real systems. We show that applying an effective external perturbation on SrTi 1−x V x O3 can switch the system between the insulating and metallic phase, meaning this is a bulk system with the potential use in Mott electronic devices.

Pressure‐Induced Enhancement of Photoluminescence and Photocurrent in Organic Semiconductor Rubrene

AbstractAs a typical organic semiconductor material, rubrene plays a prominent role in the field of optoelectronic devices. Here, a notable photoluminescence (PL) and photocurrent enhancement of rubrene by 8‐ and 2.5‐fold is reported under compression, respectively. The shortening of the π−π stacking distance and the twisting of the lateral phenyl are crucial reasons for the decrease in the bandgap, resulting in the enhancement of PL emission and photocurrent. Pressure can effectively suppress the excitons transition from a free exciton state to a self‐trapped exciton state and improve the emission efficiency. The photocurrent is subject to dual regulation by bandgap and resistance. Interestingly, rubrene undergoes an electronic structure transition at about 4.8 GPa, which is responsible for the weakening of PL emission and photocurrent. This work provides a strategy for optimizing the performance of rubrene‐based optoelectronic devices and designing novel optoelectronic materials.

A multi-edge study: investigating Co oxidation states of pristine LiNixMnyCo1-x-yO2 cathode materials by high energy-resolution X-ray spectrometry.

The investigation of Co oxidation states in pristine LiNixMnyCo1-x-yO2 (NMC) cathodes (NMC111, NMC622, NMC811) has been a subject of ongoing debate, with conflicting findings in the literature. In this study, we present a novel and comprehensive approach to address and clarify this issue using a variety of high energy-resolution X-ray spectroscopy techniques. To shed light on the Co oxidation states in NMC cathodes, we employed independent measurements including X-ray absorption spectrometry in both soft and hard X-ray ranges, as well as resonant X-ray emission spectrometry in the soft X-ray range. The investigation centered on the transition metal (TM) K and L edges, providing a thorough exploration of the electronic structure transitions. The study identified minor shifts in Co oxidation states, and theoretical calculations quantified the ratio of Co atoms undergoing oxidation state changes, which were approximately 2.05% (NMC111 to NMC622) and 3.75% (NMC111 to NMC811). Independent measurements that targeted electronic structure transitions using K-edge and L-edge absorption and emission spectrometry were strategically combined to enhance the reliability of the results. The diverse methodological approach aimed to contribute to a comprehensive understanding of Co oxidation states in NMC cathodes. This study highlights the importance of combining complementary techniques to address intricate scientific debates effectively.

Influence of Shell Thickness on the Photophysical Properties of Core—Shell Perovskite Nanocrystals

AbstractCore–shell perovskite nanocrystals (NCs) have emerged as a promising class of materials for optoelectronic applications due to their unique properties and stability. Although much research has been conducted on the shell growth mechanism and properties of the core–shell NCs, little is known about the role of shell thickness in determining their optical properties. Herein, a heteroepitaxial method is employed to prepare a series of core–shell FAPbBr3/CsPbBr3 NCs with different shell thicknesses. Through temperature‐dependent photoluminescence measurement, it is found that the electronic structure of core–shell FAPbBr3/CsPbBr3 NCs evolves from quasi‐type‐II to type‐I with the increase in shell thickness. This abnormal transition can be attributed to the thickened gradient alloy layer FA1‐xCsxPbBr3, which effectively relieves the lattice mismatch and releases strain in the NCs, resulting in variations in the bandgap between the core and the shell. Furthermore, the biexciton Auger lifetimes in these samples exhibit a non‐monotonic dependence on shell thickness, indicating the electronic structure transition. These results provide valuable insights into the relationship between shell thickness, electronic structure, and optical properties in core–shell perovskite NCs, which may offer guidance for the design of high‐performance optoelectronic devices.

Regulating the Spin State Configuration in Bimetallic Phosphorus Trisulfides for Promoting Sulfur Redox Kinetics.

Lithium-sulfur (Li-S) batteries suffer from sluggish kinetics due to the poor conductivity of sulfur cathodes and polysulfide shutting. Current studies on sulfur redox catalysis mainly focus on the adsorption and catalytic conversion of lithium polysulfides but ignore the modulation of the electronic structure of the catalysts which involves spin-related charge transfer and orbital interactions. In this work, bimetallic phosphorus trisulfides embedded in Prussian blue analogue-derived nitrogen-doped hollow carbon nanocubes (FeCoPS3/NCs) were elaborately synthesized as a host to reveal the relationship between the catalytic activity and the spin state configuration for Li-S batteries. Orbital spin splitting in FeCoPS3 drives the electronic structure transition from low-spin to high-spin states, generating more unpaired electrons on the 3d orbit. Specifically, the nondegenerate orbitals involved in the high-spin configuration of FeCoPS3 result in the upshift of energy levels, generating more active electronic states. Such tailored electronic structure increases the charge transfer, influences the d-band center, and further modifies the adsorption energy with lithium polysulfides and the potential reaction pathways. Consequently, the cell with FeCoPS3/NC host exhibits an ultralow capacity decay of 0.037% per cycle over 1000 cycles. This study proposed a general strategy for sculpting geometric configurations to enable spin and orbital topology regulation in Li-S battery catalysts.

Theoretical study on hydrogen abstraction reactions from pentane isomers by NO2

The rate constants for the H-abstraction reactions of C5H12 + NO2 are calculated by high-accuracy electronic structure calculations and transition state theory (TST). The investigation includes three pentane isomers, neopentane, n-pentane, and iso-pentane, each of which leads to the formation of three different HONO isomers, namely cis-HONO, trans-HONO, and HNO2. The lowest energy conformers of all relevant species are determined through geometry optimization, frequency analysis, and one-dimensional hindered rotor scanning at the M06-2X/6-311++G(d,p) level of theory, and are further re-optimized using the B2PLYP-D3/cc-pVTZ method. The single point energies of all the reactants, products, and transition states are obtained at the DLPNO-CCSD(T)/CBS level of theory. Traditional transition state theory was employed to derive the rate constants, which were then fitted to obtain the kinetic parameters in the Arrhenius expression. Simulation results show improved performance in ignition delay times and oxidation species prediction, when the calculated reaction rate constants are implemented in the literature n-pentane kinetic models. The results offer enhanced comprehension of the chemistry of C5H12 + NO2, and will aid in the understanding of the mutual reactions of large hydrocarbon fuels and NOx.

Molecular heteroassociation in films of thiochrome and tryptophan

Optical absorption spectra were studied for films of tryptophan, thiochrome and their layer-by-layer composites. It was shown that the absorption spectra were rearranged in the composites. Quantum-chemical modeling of the electronic structure and optical transitions of the specified molecules, and their complexes, indicate that the reason for the rearrangement of the optical spectra is the heteroassociation between the molecules of thiochrome and tryptophan, which is accompanied by significant changes in the electronic states of the formed complexes.

Electronic structure modulation on SnO2 and hexagonal boron nitride with sulfur atom for effective electrochemical sensing of Bendiocarb

Here we demonstrated the sulfur atoms induced an electronic structure modulation of SnO2 and its synergism with hexagonal boron nitride (hBN) by simple one-step vulcanization process. Thus, S-SnO2/S-hBN exhibits extraordinary catalyst material for the electrochemical detection of a toxic insecticide bendiocarb (BDC). The introduction of sulfur atoms to SnO2 and hBN results an in situ dynamic electronic structure transition, further facilitate the interactions of target with the catalyst structure. Detailed investigation of S-SnO2/S-hBN indicates the role of sulfur atoms as an electron acceptor to facilitate electron transfer to SnO2/hBN for the electrochemical process. The remarkable interfacial active site in S-SnO2/S-hBN provides the lowest limit of detection of 0.285 µM and the best sensitivity of 0.023 µA µM−1 cm−2 under the wide range addition of BDC i.e. 0.02–150.02 µM. Meanwhile, it has proven the top-notch selectivity of BDC even at a higher concentration level of interfering molecules present. This work also satisfies the requirements of commercializing by an appreciable recovery in real-time analysis of food samples with accurate reproducibility and considerable stability shown for electrochemical detection of BDC.

Electronic structure and possible phase transition mechanism of different phases for perovskite structured AgNbO3

Electronic structure, crystal structural evolution and elastic properties of AgNbO3 for phases Pmc21, Pbcm, Cmcm, P4/mbm and Pm3m have been investigated by first-principles calculations. The differences of electronic structure among phases are caused by the various intensity of Nb-4d, O-2p and Ag-4d, 5 s orbitals hybridization. The Nb-O bond and the torsion angle of NbO6 octahedron in different phases are investigated, and the lattice distortion can be attributed to the Jahn-teller effect. The crystal structural evolution among different phases is correlated with the phase transition closely. The elastic constant matrix of each phase satisfies the condition of mechanical stability. AgNbO3 is the ductile material and has the largest rigidity and the strongest volumetric strain resistance in the cubic phase.

Possible evidence of Weyl fermion enhanced thermal conductivity under magnetic fields in the antiferromagnetic topological insulator Mn(Bi1−xSbx)2Te4

We report thermal conductivity and Seebeck effect measurements on $\text{Mn}{({\text{Bi}}_{1\ensuremath{-}x}{\text{Sb}}_{x})}_{2}{\text{Te}}_{4}$ (MBST) with $x=0.26$ under applied magnetic fields below $50\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Our data shows clear indications of the electronic structure transition induced by the antiferromagnetic (AFM) to ferromagnetic (FM) transition driven by applied magnetic field as well as significant positive magnetothermal conductivity in the Weyl semimetal state of MBST. Further, by examining the dependence of magnetothermal conductivity on field orientation for MBST and comparison with the magnetothermal conductivity of ${\text{MnBi}}_{2}{\text{Te}}_{4}$, we see possible evidence of a contribution to thermal conductivity due to Weyl fermions in the FM phase of MBST. From the temperature dependence of the Seebeck coefficient under magnetic fields for MBST, we also observed features consistent with the Fermi surface evolution from a hole pocket in the paramagnetic state to a Fermi surface with coexistence of electron and hole pockets in the FM state. These findings provide further evidence for the field-driven topological phase transition from an AFM topological insulator to a FM Weyl semimetal.

Electronic structure and topological phase transition in multi-orbital triangular lattice with rotation and mirror symmetry breaking

Triangular lattice is one of the most generic structures in the two-dimensional (2D) limit with numerous exotic properties, such as magnetic frustration and quantum spin liquid. Here, we investigate the electronic properties of a multi-orbital (p x , p y , p z ) triangular lattice while focusing on the role of rotation and mirror symmetry breaking in regulating the topological phase diagram. The tight-binding modeling reveals that rotation symmetry () breaking splits the Dirac point and preserves the nodal loop. A further inclusion of broken horizontal mirror symmetry () destroys the nodal loop. Consequently, with spin–orbit coupling (SOC), the (p x , p y , p z )-orbital triangular lattice is topologically non-trivial with only or symmetry breaking. With both symmetries breaking, it becomes trivial, except when the SOC is large enough to initiate band inversion. For real materials, we propose that the recently grown AgSe/AgTe monolayer in a binary honeycomb structure is an ideal system to realize the multi-orbital triangular lattice. The first-principles calculations demonstrate that free-standing AgSe and AgTe are Z 2 non-trivial. On the Ag(111) substrate, AgSe becomes trivial because of the breaking of both and symmetries, whereas AgTe remains non-trivial because of the strong SOC of Te. Our work not only provides physical insights into the experimentally synthesized 2D binary honeycomb structures but also highlights the manipulation of electronic and topological properties through symmetry/orbital physics, which are valuable for designing new quantum materials and devices.

Zeolite-Encaged Luminescent Silver Nanoclusters.

Silver nanoclusters (Ag NCs) are nanoscale aggregates that possess molecular-like discrete energy levels, resulting in electronic configuration-dependent tunable luminescence spanning the entire visible range. Benefiting from the efficient ion exchange capacity, nanometer dimensional cages, and high thermal and chemical stabilities, zeolites have been employed as desirable inorganic matrices to disperse and stabilize Ag NCs. This paper reviewed the recent research progresses on the luminescence properties, spectral manipulation, as well as the theoretical modelling of electronic structure and optical transition of Ag NCs confined inside various zeolites with different topology structures. Furthermore, potential applications of the zeolite-encaged luminescent Ag NCs in lighting, gas monitoring and sensing were presented. This review concludes with a brief comment on the possible future directions in the study of zeolite-encaged luminescent Ag NCs.

Anti-ohmic nanoconductors: myth, reality and promise.

The recent accomplishment in the design of molecular nanowires characterized by increasing conductance with length has led to the origin of an extraordinary new family of molecular junctions referred to as "anti-ohmic" wires. Herein, this highly desirable, non-classical behavior, has been examined for molecules long-enough to exhibit pronounced diradical character in their ground state within the unrestricted DFT formalism with spin symmetry breaking. We demonstrate that highly conjugated acenes signal higher resistance in an open-shell singlet (OSS) configuration as compared to their closed-shell counterparts. This anomaly has been further proven for experimentally certified cumulene wires, which reveals phenomenal modulation in the transport characteristics such that an increasing conductance is observed in the closed-shell limit, while higher cumulenes in the OSS ground state yield regular decay of conductance.

A Copper Iodide Cluster-Based Coordination Polymer as an Unconventional Zero-Thermal-Quenching Phosphor.

Phosphor-converted white light-emitting diodes (pc-wLEDs) are promising candidates for next-generation solid-state lighting and display technologies. However, most of the conventional phosphors in pc-wLED devices suffer from serious thermal quenching (TQ) at high temperatures. Herein, we investigate an unconventional high-efficiency metal-halide cluster-based phosphor with dynamic Cu-Cu interactions that can resist the TQ effect of photoluminescence. The temperature-dependent structure and solid-state and in situ NMR spectroscopy reveal that the weakening of the Cu-Cu interaction in such a phosphor system enables the electronic structural transition from a bonding to a nonbonding state and hence sustains the PL efficiency at high temperatures (up to 100 °C). The pc-wLEDs incorporating the zero-TQ phosphor show a rapid brightness rise even at a high bias current (1000 mA) with a color rendering index as high as 90, comparable to the commercial phosphor-based prototype LEDs (e.g., YAG:Ce3+). This work establishes a novel prototype of a cluster-based phosphor featuring dynamic intermetallic interactions, which paves the way for the exploration of pc-wLEDs against thermal quenching.