Charge-localized States Research Articles

Local Charge Regulation in Selenides via High‐Entropy Engineering to Boost Electromagnetic Wave Absorption

AbstractLocal charge modulation is an effective method to improve the polarization loss and electromagnetic (EM) absorption characteristics. However, the use of conventional means (doping, defects, heterojunction surfaces) remains singular and limited in achieving local charge modulation. Surprisingly, lattice distortions induced by high‐entropy engineering can intrinsically regulate local charge states and improve EM wave absorption performances. Herein, a series of selenides with enhanced configuration entropy are designed and prepared to improve polarization loss capacity. Due to the different radii of the mixed ions and the Jahn‐Teller distortion effect, the local charge of the selenides is effectively modulated by the presence of defects and strong lattice distortions inside the lattice. Uneven distribution of charge at defects and formation of boundaries promotes defect‐induced polarization and interface polarization, respectively. Compared to single NiSe2, high‐entropy (NiFeCuCoMn)Se2 with an entropy value of 1.53R has more severe lattice defects and suitable impedance matching properties, exhibiting good EM absorption properties both in the absorption intensity and respond frequency. Tailoring the local charge density via an entropy strategy paves a new way for the high‐performance EM absorption materials.

Realizing one-dimensional moiré chains with strong electron localization in two-dimensional twisted bilayer WSe2

Two-dimensional (2D) moiré systems based on twisted bilayer graphene and transition metal dichalcogenides provide a promising platform to investigate emergent phenomena driven by strong electron-electron interactions in partially filled flat bands. A natural question arises: Is it possible to expand the 2D correlated moiré physics to one-dimensional (1D) that electron-electron correlation is expected to be further enhanced? This requires selectively doping of 1D moiré chain, which seems to be not within the grasp of today's technology. Therefore, an experimental demonstration of the 1D moiré chain with partially filled electronic states remains absent. Here, we show that we can introduce 1D boundaries, separating two regions with different twist angles, in twisted bilayer WSe2 (tWSe2) by using scanning tunneling microscopy (STM) and demonstrate that the electronic states of 1D moiré sites along the boundaries can be selectively filled. The strong localized charge states of correlated moiré electrons in the 1D moiré chain can be directly imaged and manipulated by combining a back-gate voltage with the STM bias voltage. Our results open the door for realizing new correlated electronic states of the 1D moiré chain in 2D systems.

Exploring the Facet-Dependent Structural Evolution of Pt/CeO2 Catalysts Induced by Typical Pretreatments for CO Oxidation.

Atomic-scale insights into the interactions between metals and supports play a crucial role in optimizing catalyst design, understanding catalytic mechanisms, and enhancing chemical conversion processes. The effects of oxide support on the dynamic behavior of supported metal species during pretreatments or reactions have been attracting a lot of attention; however, very less systematic integrations are carried out experimentally using real catalysts. In this study, we here utilized facet-controlled CeO2 as examples to explore their influence on the supported Pt species (1.0 wt %) during the reducing and oxidizing pretreatments that are typically applied in heterogeneous catalysts. By employing a combination of microscopy, spectroscopy, and first-principles calculations, it is demonstrated that the exposed crystal facets of CeO2 govern the evolution behavior of supported Pt species under different environmental conditions. This leads to distinct local coordinations and charge states of the Pt species, which directly influence the catalytic reactivity and can be leveraged to control the catalytic performance for CO oxidation reactions.

Deflection and control of the mixing region in membraneless vanadium micro redox flow batteries: Modeling and experimental validation

Membraneless micro redox flow batteries operate within the laminar flow regime to mitigate the convective mixing between catholyte and anolyte. The absence of an ion-exchange membrane reduces manufacturing costs and overall cell resistance, thereby enhancing battery performance. However, it also poses a new challenge: the precise control of the thin mixing layer established between the two co-flowing electrolytes. Undesired displacements of the mixing region lead to increased crossover losses and significant liquid transfer between tanks. This work addresses the deflection of the mixing region under varying flow conditions, considering electrolyte viscosity variations due to the changes in the local state of charge arising during battery operation. This is achieved through a combination of mathematical analysis, numerical simulations, and experimental results. The conservation equations and non-dimensional parameters governing the problem are first written and discussed. The model is then integrated numerically incorporating different inlet and outlet boundary conditions to simulate the effect of various flow control strategies. Next, the numerical results are validated against experimental realizations of the flow. Finally, three case studies are presented and discussed. This work highlights the relevance of variable viscosity in the operation of co-laminar membraneless micro redox flow batteries, and proposes for the first time feasible control methods to mitigate undesired disturbances in the hydraulic circuit, thereby minimizing crossover losses.

Rydberg electron stabilizes the charge localized state of the diamine cation

A previous controversial discussion regarding the interpretation of Rydberg spectra of gaseous dimethylpiperazine (DMP) as showing the co-existence of a localized and delocalized mixed-valent DMP+ radical cation is revisited. Here we show by high-level quantum-chemical calculations that an apparent barrier separating localized and delocalized DMP+ minima in previous multi-reference configuration-interaction (MRCI) calculations and in some other previous computations were due to unphysical curve crossings of the reference wave functions. These discontinuities on the surface are removed in state-averaged MRCI calculations and with some other, orthogonal high-level approaches, which do not provide a barrier and thus no localized minimum. We then proceed to show that in the actually observed Rydberg state of neutral DMP the 3s-type Rydberg electron binds more strongly to a localized positive charge distribution, generating a localized DMP* Rydberg-state minimum, which is absent for the DMP+ cation. This work presents a case where interactions of a Rydberg electron with the underlying cationic core alter molecular structure in a fundamental way.

Local Net Charge State of Collagen Triple Helix Is a Determinant of FKBP22 Binding to Collagen III.

Mutations in the FKBP14 gene encoding the endoplasmic reticulum resident collagen-related proline isomerase FK506 binding protein 22 kDa (FKBP22) result in kyphoscoliotic Ehlers-Danlos Syndrome (EDS), which is characterized by a broad phenotypic outcome. A plausible explanation for this outcome is that FKBP22 participates in the biosynthesis of subsets of collagen types: FKBP22 selectively binds to collagens III, IV, VI, and X, but not to collagens I, II, V, and XI. However, these binding mechanisms have never been explored, and they may underpin EDS subtype heterogeneity. Here, we used collagen Toolkit peptide libraries to investigate binding specificity. We observed that FKBP22 binding was distributed along the collagen helix. Further, it (1) was higher on collagen III than collagen II peptides and it (2) was correlated with a positive peptide charge. These findings begin to elucidate the mechanism by which FKBP22 interacts with collagen.

Rydberg state dynamics and fragmentation mechanism of N,N,N',N'-tetramethylmethylenediamine.

The non-adiabatic relaxation processes and the fragmentation dynamics of Rydberg-excited N,N,N',N'-tetramethylmethylenediamine (TMMDA) are investigated using femtosecond time-resolved photoelectron imaging and time-resolved mass spectroscopy. Excitation at 208nm populates TMMDA in a charge-localized 3p state. Rapid internal conversion (IC) to 3s produces two charge-delocalized conformers with independent time constants and distinct population ratios. As the system explores the 3s potential surface, the structural evolution continues on a 1.55ps timescale, followed by a slower (12.1ps) relaxation to the ground state. A thorough comparison of the time-dependent mass and photoelectron spectra suggests that ionization out of the 3p state ends up with the parent ion, the vibrational energy of which is insufficient for the bond cleavage. On the contrary, by virtue of the additional energy acquired by IC from 3p, the internal energy deposited in 3s is available to break the C-N bond, leading to the fragment ion. The fragmentation is found to occur on the ion surface instead of the Rydberg surface.

Eliminating Local Electrolyte Failure Induced by Asynchronous Reaction for High‐Loading and Long‐Lifespan All‐Solid‐State Batteries

AbstractThe design of practical cathodes with high areal capacity in polymer‐based all‐solid‐state batteries remains challenged by the absence of an effective guiding principle that prolongs battery life‐span. Unlike liquid batteries, the notorious interface incompatibility between cathodes and electrolytes limited the cycling life of the all‐solid‐state batteries. Herein, this study proposes a dynamically stable cathode design with a fully covered surface, effectively mitigating interface failure and enabling the cyclic time of batteries with a cathode loading of 12.7 mg cm‒2 over 10 000 h. This study unveils the importance of local state of charge in affecting the interfacial properties of particles through local oxidative‐stability of electrolytes on the interface. This study shows that the phenomena can be strongly influenced by the porosity of the cathode through the perspective of discreteness of ion transport. These insights and approach provide a broader promise for solid batteries for long lifetime.

Target State Optimized Density Functional Theory for Electronic Excited and Diabatic States.

A flexible self-consistent field method, called target state optimization (TSO), is presented for exploring electronic excited configurations and localized diabatic states. The key idea is to partition molecular orbitals into different subspaces according to the excitation or localization pattern for a target state. Because of the orbital-subspace constraint, orbitals belonging to different subspaces do not mix. Furthermore, the determinant wave function for such excited or diabatic configurations can be variationally optimized as a ground state procedure, unlike conventional ΔSCF methods, without the possibility of collapsing back to the ground state or other lower-energy configurations. The TSO method can be applied both in Hartree-Fock theory and in Kohn-Sham density functional theory (DFT). The density projection procedure and the working equations for implementing the TSO method are described along with several illustrative applications. For valence excited states of organic compounds, it was found that the computed excitation energies from TSO-DFT and time-dependent density functional theory (TD-DFT) are of similar quality with average errors of 0.5 and 0.4 eV, respectively. For core excitation, doubly excited states and charge-transfer states, the performance of TSO-DFT is clearly superior to that from conventional TD-DFT calculations. It is shown that variationally optimized charge-localized diabatic states can be defined using TSO-DFT in energy decomposition analysis to gain both qualitative and quantitative insights on intermolecular interactions. Alternatively, the variational diabatic states may be used in molecular dynamics simulation of charge transfer processes. The TSO method can also be used to define basis states in multistate density functional theory for excited states through nonorthogonal state interaction calculations. The software implementing TSO-DFT can be accessed from the authors.

Synchrotron-based operando X-ray diffraction and X-ray absorption spectroscopy study of LiCo0.5Fe0.5PO4 mixed d-metal olivine cathode

Lithium-ion batteries based on high-voltage cathode materials, such as LiCoPO4, despite being promising in terms of specific power, still suffer from poor cycle life due to the lower stability of common non-aqueous electrolytes at higher voltages. One way to overcome this issue might be decreasing the working potential of the battery by doping LiCoPO4 by Fe, thus reducing electrolyte degradation upon cycling. However, such modification requires a deep understanding of the structural behavior of cathode material upon lithiation/delithiation. Here we used a combination of operando synchrotron-based XRD and XAS to investigate the dynamics of d-metal local atomic structure and charge state upon cycling of LiCo0.5Fe0.5PO4 mixed d-metal olivine cathode material. Principal components analysis (PCA) of XAS data allowed the extraction of spectra of individual phases in the material and their concentrations. For both Co and Fe two components were extracted, they correspond to fully lithiated and delithiated phases of LixMPO4 (where M = Fe, Co). Thus, we were able to track the phase transitions in the material upon charge and discharge and quantitatively analyze the M2+/M3+ electrochemical conversion rate for both Fe and Co. Rietveld's refinement of XRD data allowed us to analyze the changes in the lattice of cathode material and their reversibility upon (de)lithiation during cycling. The calculation of DFT and Bader charge analysis expects the oxygen redox procedure combined with d-metals redox, which supplements iron charge variations and dominates at high voltages when x < 0.75 in LixCoFePO4.

Unlocking AlN Piezoelectric Performance with Earth‐Abundant Dopants

AbstractThe increasing demand for high‐performance piezoelectric materials and toxicity and thermal stability issues of the widely used lead zirconate titanates (PZT) have spurred a search for better alternatives in electronic devices. In comparison to PZT, group III nitrides such as aluminum nitride (AlN), are only weakly piezoelectric, but doping AlN with scandium (Sc) improves the piezoelectric response by nearly 500%. Relative to PZT, doped‐AlN piezoelectric materials are advantageous because they are far more compatible with complementary metal–oxide–semiconductor (CMOS) materials, and they maintain both piezoelectric and thermodynamic stability up to very high temperatures. Unfortunately, rare‐earth metals are notoriously expensive, and fabricating stable films with rare‐earth dopants is also challenging, limiting their use in industrial applications. In this work, ab initio calculations are combined with targeted fabrication and experimentation to identify alternative earth‐abundant dopants for AlN from the periodic table d‐block. Amongst the 23 elements screened, it is found that group IVB metals, titanium, zirconium, and hafnium induce large piezoelectric enhancements comparable to Sc. This improvement is traced to shifts in the atomic sublattice structure and changes in the local charge states. In demonstrating a highly accessible and affordable path for technological adaptation of AlN‐based piezoelectrics, this work provides the foundation for sustainable, next‐generation electronics.

InP/ZnSeS/ZnS Quantum Dots with High Quantum Yield and Color Purity for Display Devices

To achieve the quantum yield and color purity suitable for applications to the visible emitters in display devices, the optical features of indium phosphide (InP) quantum dots (QDs) are improved. Two types of InP cores are synthesized with two kinds of the phosphorus precursors, tris(trimethylsilyl)phosphine and tris(dimethylamino)phosphine. The prepared cores are fabricated for the gradient-alloyed inner shell (ZnSeS) and outer shell (ZnS) to complete the environmentally benign QDs with the structures of core/inner-shell/outer-shell. The quantum yields in the two types of QDs are 95 and 85% with the bandwidths of 35 and 36 nm, respectively, comparable to the characteristics of state-of-the-art InP QDs. The band-to-band transition of the neutral states in QDs turns out to be more efficient than the band-to-hole transition, whereas the optical transitions of the charged states are not strong. Despite the similar peak shapes with the equivalent Stokes shift, the optical features investigated by temperature-dependent and time-resolved spectroscopy are distinctive in the two types of QDs. In particular, the formation of the charged states and localized states, in addition to the dark states, is influenced by the precursors. These findings suggest strategies to enhance the quantum yield and color purity of InP QDs for applications to display devices with a green chemistry approach.

Probing the effect of Zn2+ on the local structure, dielectric and magnetic properties of La2CuMnO6 by solid state synthesis

The comparable ionic-radius cation substitution provides a route to investigate the origin of the physical properties of ceramics on the local structure and electronic charge state background. In analogy to our previous work [19] of La2CuMnO6 (LCM) prepared via solid-state route, here we are reporting the effect of Zn substitution at the Cu site of LCM. The detailed structural analysis confirmed the Jahn-Teller (JT) distortion in LCM and Zn2+ substituted LCM (i.e., LCZM) ceramics. Raman analysis further confirmed the JT distortion in these oxides. O K-edge and Mn K-edge XANES spectra confirmed the mixed hybridization states for Mn. A frequency-dependent relaxor state was observed in the dielectric study of LCM and LCZM. The dielectric responses of these systems are prominently driven by electron-phonon coupling. Their magnetic studies showed positive-Curie temperature (TC) and non-zero coercivity, indicating the ceramics' canted-antiferromagnetic nature.

Onsite and intersite electronic correlations in the Hubbard model for halide perovskites

Halide perovskites (HPs) are widely viewed as promising photovoltaic and light-emitting materials for their suitable band gaps in the visible spectrum. Density functional theory (DFT) calculations employing (semi)local exchange-correlation functionals usually underestimate the band gaps for these systems. Accurate descriptions of the electronic structures of HPs often demand higher-order levels of theory such as the Heyd-Scuseria-Ernzerhof (HSE) hybrid density functional and GW approximations that are much more computationally expensive than standard DFT. Here, we investigate three representative types of HPs, ABX3 halide perovskites, vacancy-ordered double perovskites (VODPs), and bond disproportionated halide perovskites (BDHPs), using DFT+U+V with onsite U and intersite V Hubbard parameters computed self-consistently without a priori assumption. The inclusion of Hubbard corrections improves the band gap prediction accuracy for all three types of HPs to a similar level of advanced methods. Moreover, the self-consistent Hubbard U is a meaningful indicator of the true local charge state of multivalence metal atoms in HPs. The inclusion of the intersite Hubbard V is crucial to properly capture the hybridization between valence electrons on neighboring atoms in BDHPs that have breathing-mode distortions of halide octahedra. In particular, the simultaneous convergence of both Hubbard parameters and crystal geometry enables a band gap prediction accuracy superior to HSE for BDHPs but at a fraction of the cost. Our work highlights the importance of using self-consistent Huabbard parameters when dealing with HPs that often possess intricate competitions between onsite localization and intersite hybridization.

Electronic band gap on graphene induced by interaction with hydrogen cyanide. An DFT analysis

The interaction of cyanide (HCN) with graphene (SGL) is studied using the Density Functional Theory in the van der Waals scheme, using an exchange and correlation functional with the Berland and Hyldgaard (BH) parametrization and non-local norm conserving pseudopotentials. 12 geometric configurations of HCN-SGL system are analyzed in detail. Our results show that the bonding HCN-SGL produces a charge redistribution and localized states into the conduction and valence bands of graphene monolayer. Also, the HCN-SGL interaction induces an energy gap in graphene, which is robust under electric fields, whose value depends both on the cyanide orientation respect to monolayer as the cyanide’s atom interacting with the monolayer. This results guide the potential use of graphene as a cyanide sensor, given the changes in resistivity of the monolayer, as well as the development of electronic nano-devices that require strong localized states in the presence of electronic fields.

In Operando Diffraction Radiography and Tomography on Li-Ion Batteries

Diffraction radiography and tomography were used to study different commercial Li-ion batteries. Depending on the data processing either 'direct' parameters, such as phase distributions, or more abstract, derived parameters, like degree of lithiation of the graphite anode or even local state of charge, can be extracted. Especially the lithium distribution is an interesting parameter and is surprisingly inhomogeneous throughout the volume of a commercial battery cell.

The Role of Viscosity Variations: Analyzing and Modelling Microfluidic Membrane-Free Laminar Flow Batteries

Membraneless micro redox flow batteries prevent the advective mixing of catholyte and anolyte by operating at a small Reynolds number with flow rates of order 100µL/min or less [1] [2] [3] [4]. This laminar flow regime allows to remove the ion-exchange membrane used in conventional macro flow batteries. The absence of membrane decreases the internal electric resistance of the reactor, reduces manufacturing costs and potentially increases the performance of the system. However, removing the physical barrier between the electrolytes poses a new challenge: the accurate control of the thin region where both miscible electrolytes enter in contact. Undesired deflections of that mixing region (see Fig. 1) may lead to increased crossover losses and net liquid transfer between the tanks.In this work we propose a numerical CFD model that sheds light on the behaviour of the mixing region at different flow conditions, considering viscosity changes in the electrolytes resulting from variations in the local state of charge during the operation of the cell. Then, a simplified dynamic model that includes electric current, flow rates and electrolyte properties as input parameters is proposed and validated against the CFD simulations. The present work constitutes the first study of membraneless micro redox flow batteries in non-ideal conditions arising from electrolyte heterogeneities. Our computationally efficient model allows to consider qualitative and long-term trends in a matter of minutes to hours, covering broad operation envelopes, which can be used to guide the design process of these emerging systems. Figure 1: Undesired deflection of the mixing region Acknowledgments This work has been partially funded by the Agencia Estatal de Investigación (PID2019-106740RB-I00/AEI/10.13039/501100011033), and by Grant IND2019/AMB-17273 of the Comunidad de Madrid.

Unravelling the ultrafast dynamics of a N-BODIPY compound

Although the photophysics of BODIPY compounds has been widely investigated in the last few years, their analogues N-BODIPY, with nitrogen substitution at the boron center, did not receive comparable attention. In this work we report the synthesis and photochemical characterization of a substituted N-BODIPY compound, by means of a combined theoretical and spectroscopic approach. Compared to a standard BODIPY, the compound under investigation presents a lower fluorescence quantum yield (QY) in the visible region. The excited state relaxation dynamics of the dye was studied in different solvents, showing further fluorescence quenching in polar solvents, and excited state decay rates strongly dependent on the environment polarity. The role of the pendant moieties and the involvement of charge transfer states in the excited state dynamics was experimentally addressed by transient absorption spectroscopy, and further analyzed with TD-DFT calculations, which allowed precise assignment of the transient signals to the correspondent electronic configuration. The complete picture of the N-BODIPY behavior shows the presence of both charge transfer and localized states, influencing the observed photophysics to different amounts, depending on the excitation conditions and the surrounding environment.

Effect of fluorine–fluorine repulsive coupling on charge transport in cyclopentadithiophene-based donor–acceptor-type conjugated copolymer films

This study elucidates the effect of fluorine–fluorine interactions on the charge transport properties of semiconductor channels in polymer-based field effect transistors (PFETs) in which both a donor–acceptor (D–A)-type conjugated polymer and a polymer dielectric material contain fluorinated units. The fluorinated units on the benzothiadiazole (BTZ) block of cyclopentadithiophene- alt -benzothiadiazole (CDT-BTZ) allow conformation locking via F⋯S nonbonding interactions, which increases the planarity of cyclopentadithiophene- alt -fluoro-2,1,3-benzothiadiazole (CDT-FBTZ). Thus, the CDT-FBTZ copolymer films are highly crystalline and adopt the edge-on orientation, resulting in an eight-fold increase in the field-effect mobility for CDT-FBTZ-based PFETs coated with a poly(methyl methacrylate) (PMMA) dielectric layer compared with PMMA-coated CDT-BTZ-based PFETs. Meanwhile, the field-effect mobility of CDT-BTZ-based PFETs containing a fluorinated dielectric polymer (CYTOP) is double that of PMMA-coated CDT-BTZ-based PFETs. These enhanced electrical properties are attributed to surface polarization doping at the interface between the conjugated polymer and the fluorinated polymer dielectric. However, despite the effect of surface polarization doping, the electrical properties of CDT-FBTZ-based PFETs deteriorate when combined with the fluorinated CYTOP dielectric. Charge transport analyses based on the Gaussian disorder model reveal that, for CDT-based D–A-type conjugated copolymer PFETs, very few localized states in the semiconducting channel of PFET devices in which fluorine–fluorine interaction effects occur at the interface switch to delocalized states as the gate-bias increases. In contrast, the localized charge states in PFET channels without fluorine–fluorine interactions depend strongly on the applied gate-bias and become delocalized upon applying a gate-bias. Thus, it is inferred that the fluorine–fluorine repulsive coupling in D–A-type conjugated copolymers containing fluorinated functional moieties that interface with fluorinated polymer dielectric layers hinders the delocalization of charges induced by the gate-bias, thereby degrading the device performance. • Effect of fluorine–fluorine interactions on charge transport in polymer transistors investigated. • High-performance polymer field effect transistor obtained using fluorinated polymer. • Temperature-variable current-voltage analyses of the devices conducted. • Electrical degradation of polymer transistor caused by the fluorine–fluorine interactions.

Battery Energy Storage Participation in Automatic Generation Control of Island Systems, Coordinated with State of Charge Regulation

Efficient storage participation in the secondary frequency regulation of island systems is a prerequisite towards their complete decarbonization. However, energy reserve limitations of storage resources pose challenges to their integration in centralized automatic generation control (AGC). This paper presents a frequency control method, in which battery energy storage systems (BESSs) participate in automatic frequency restoration reserve (aFRR) provision, through their integration in the AGC of an island system. A local state of charge (SOC) controller ensures safe operation of the BESS in case of disturbances, without jeopardizing system security when available energy reserves are diminishing. The aFRR participation factors of regulating units are altered when the storage systems approach their SOC limits, re-allocating their reserves to other load-following units. Restoration of BESS energy reserves is achieved by integrating SOC regulation in the real-time economic dispatch of the system, formulated as a mixed-integer linear programming problem and solved every few minutes to determine the base points of the AGC units. A small autonomous power system, comprising conventional units, renewable energy sources and a BESS, is used as a study case to evaluate the performance of the proposed method, which is compared with alternative approaches to secondary regulation with BESS participation.