Showing papers on "Charge density published in 2021"

Modulating Interfacial Charge Density of NiP2-FeP2 via Coupling with Metallic Cu for Accelerating Alkaline Hydrogen Evolution

Abstract: Exploring earth-abundant electrocatalysts with Pt-like performance toward alkaline hydrogen evolution reaction (HER) is extremely desirable for the hydrogen economy but remains challenging. Herein,...

Complex charge density waves at Van Hove singularity on hexagonal lattices: Haldane-model phase diagram and potential realization in the kagome metals A V 3 Sb 5 ( A =K, Rb, Cs)

Abstract: The recent discovery of topological charge density waves in the superconducting kagome metals $A$V${}_{3}$Sb${}_{5}$ ($A$=K, Rb, Cs) has attracted enormous attention Motivated by the experiments, the authors analyze here the interplay of real and imaginary charge density waves at the Van Hove singularity, but in a broader scope of general hexagonal lattices Phenomenological analysis uncovers a rich Haldane-model phase diagram The theoretical model sheds light on the experimental observations in these kagome metals and future experiments of hexagonal lattice materials

High-Performance Triboelectric Devices via Dielectric Polarization: A Review.

Abstract: Energy harvesting devices based on the triboelectric effect have attracted great attention because of their higher output performance compared to other nanogenerators, which have been utilized in various wearable applications. Based on the working mechanism, the triboelectric performance is mainly proportional to the surface charge density of the triboelectric materials. Various approaches, such as modification of the surface functional group and dielectric composition of the triboelectric materials, have been employed to enhance the surface charge density, leading to improvements in triboelectric performances. Notably, tuning the dielectric properties of triboelectric materials can significantly increase the surface charge density because the surface charge is proportional to the relative permittivity of the triboelectric material. The relative dielectric constant is modified by dielectric polarization, such as electronic, vibrational (or atomic), orientation (or dipolar), ionic, and interfacial polarization. Therefore, such polarization represents a critical factor toward improving the dielectric constant and consequent triboelectric performance. In this review, we summarize the recent insights on the improvement of triboelectric performance via enhanced dielectric polarization.

Evidence for quantum spin liquid behaviour in single-layer 1T-TaSe2 from scanning tunnelling microscopy

Abstract: Two-dimensional triangular-lattice antiferromagnets are predicted under some conditions to exhibit a quantum spin liquid ground state with no energy barrier to create emergent, fractionalized spinon excitations that carry spin but no charge. Materials that realize this kind of spin liquid are expected to have a low-energy behaviour described by a spinon Fermi surface. Directly imaging the resulting spinons, however, is difficult due to their chargeless nature. Here we use scanning tunnelling spectroscopy to image density waves consistent with the predictions of spinon density modulation arising from a spinon Fermi surface instability in single-layer 1T-TaSe2. We confirm the existence of a triangular lattice of localized spins in this material by contacting it with a metallic 1H-TaSe2 substrate and measuring the Kondo effect. Spectroscopic imaging of isolated single-layer 1T-TaSe2 reveals long-wavelength super-modulations at Hubbard band energies, consistent with the predicted behaviour of itinerant spinons. These super-modulations allow the direct experimental measurement of the spinon Fermi wavevector, in good agreement with theoretical predictions for a two-dimensional quantum spin liquid. Some quantum spin liquids are expected to have an effective Fermi surface of fractionalized spinon excitations. The two-dimensional spin liquid candidate 1T-TaSe2 has charge density modulations that may be caused by an unstable spinon Fermi surface.

Real-space imaging of anisotropic charge of σ-hole by means of Kelvin probe force microscopy.

Abstract: An anisotropic charge distribution on individual atoms, such as σ-holes, may strongly affect the material and structural properties of systems. However, the spatial resolution of such anisotropic c...

CoNi Alloy Nanoparticles Embedded in Metal–Organic Framework-Derived Carbon for the Highly Efficient Separation of Xenon and Krypton via a Charge-Transfer Effect

Abstract: Separation of Xe and Kr is one of the greatest challenges in the gas industries owing to their close molecular structure and similar properties. Energy-effective adsorption-based separation using chemically stable carbon adsorbents is a promising technology. We propose a strategy for Xe/Kr separation using MOF-derived metallic carbon adsorbents. M-Gallate (M=Ni, Co) were used as precursors to fabricate CoNi alloy nanoparticles embedded carbon adsorbents by one-step auto-reduction pyrolysis. The optimal NiCo@C-700 exhibits record-high IAST selectivity (24.1) and Henry's selectivity (20.1) of Xe/Kr among reported carbon adsorbents. DFT calculations, local density of states calculation, charge density difference, and Bader charge analysis reveal the great affinity with Xe benefits from the presence of Ni or CoNi nanoparticles as a result of more charge transfer from Xe than Kr to metal, thus providing higher binding energy. Breakthrough experiments further verify NiCo@C-700 a promising candidate for Xe/Kr separation.

A DFT study of the adsorption energy and electronic interactions of the SO2 molecule on a CoP hydrotreating catalyst

Abstract: The adsorption energy and electronic properties of sulfur dioxide (SO2) adsorbed on different low-Miller index cobalt phosphide (CoP) surfaces were examined using density functional theory (DFT). Different surface atomic terminations and initial molecular orientations were systematically investigated in detail to determine the most active and stable surface for use as a hydrotreating catalyst. It was found that the surface catalytic reactivity of CoP and its performance were highly sensitive to the crystal plane, where the surface orientation/termination had a remarkable impact on the interfacial chemical bonding and electronic states toward the adsorption of the SO2 molecule. Specifically, analysis of the surface energy adsorption revealed that SO2 on Co-terminated surfaces, especially in (010), (101) and (110) facets, is energetically more favorable compared to other low index surfaces. Charge density difference, density of states (DOS) and Gibbs free energy studies were also carried out to further understand the bonding mechanism and the electronic interactions with the adsorbate. It is anticipated that the current findings will support experimental research towards the design of catalysts for SO2 hydrodesulfurization based on cobalt phosphide nanoparticles.

Quantum Monte Carlo Simulations of the 2D Su-Schrieffer-Heeger Model.

Abstract: Over the past several years, a new generation of quantum simulations has greatly expanded our understanding of charge density wave phase transitions in Hamiltonians with coupling between local phonon modes and the on-site charge density. A quite different, and interesting, case is one in which the phonons live on the bonds, and hence modulate the electron hopping. This situation, described by the Su-Schrieffer-Heeger (SSH) Hamiltonian, has so far only been studied with quantum Monte Carlo in one dimension. Here we present results for the 2D SSH model, show that a bond ordered wave (BOW) insulator is present in the ground state at half filling, and argue that a critical value of the electron-phonon coupling is required for its onset, in contradistinction with the 1D case where BOW exists for any nonzero coupling. We determine the precise nature of the bond ordering pattern, which has hitherto been controversial, and the critical transition temperature, which is associated with a spontaneous breaking of ${\mathcal{Z}}_{4}$ symmetry.

Tuning of a A-A-D-A-A-Type Small Molecule with Benzodithiophene as a Central Core with Efficient Photovoltaic Properties for Organic Solar Cells.

Abstract: With the aim of upgrading the power conversion efficiency of organic solar cells (OSCs), four novel non-fullerene, A1-A2-D-A2-A1-type small molecules were designed that are derivatives of a recently synthesized molecule SBDT-BDD reported for its efficient properties in all-small-molecule OSCs (ASM-OSCs). Optoelectronic properties of the designed molecules were theoretically computed with a selected CAM-B3LYP functional accompanied by the 6-31G(d,p) basis set of density functional theory (DFT), and excited-state calculations were performed through the time-dependent self-consistent field. The parameters of all analyzed molecules describing the charge distribution (frontier molecular orbitals, density of states, molecular electrostatic potential), absorption properties (UV-vis absorption spectra), exciton dynamics (transition density matrix), electron-hole mobilities (reorganization energies), and exciton binding energies were computed and compared. All the designed molecules were found to be superior regarding the aforesaid properties to the reference molecule. Among all molecules, SBDT1 has the smallest band gap (3.88 eV) and the highest absorption maxima with broad absorption in the visible region. SBDT3 has the lowest binding energy (1.51 eV in chloroform solvent) ensuring easier and faster dissociation of excitons to produce free charge-carriers and has the highest open-circuit voltage (2.46 eV) with PC61BM as the acceptor. SBDT1 possesses the highest hole mobility because it has the lowest value of λ+ (0.0148 eV), and SBDT4 exhibits the highest electron mobility because it has the lowest value of λ- (0.0146 eV). All the designed molecules are good candidates for ASM-OSCs owing to their superior and optimized properties.

Tripling the reverse electrodialysis power generation in conical nanochannels utilizing soft surfaces.

Abstract: We theoretically investigate the feasibility of enhancing the reverse electrodialysis power generation in nanochannels by covering the surface with a polyelectrolyte layer (PEL). Along these lines, two conical nanochannels are considered that differ in the extent of the covering. Each nanochannel connects two large reservoirs filled with KCl electrolytes of different ionic concentrations. Considering the Poisson–Nernst–Planck and Navier–Brinkman equations, finite-element-based numerical simulations are performed under a steady-state. The influences of the PEL properties and the salinity gradient on the reverse electrodialysis characteristics are examined in detail via a thorough parametric study. It is shown that the maximum power generated is an increasing function of the charge density and the thickness of the PEL. This means that the maximum power generated may be theoretically increased to any desired degree by covering the nanochannel surface with a sufficiently dense and thick PEL. Considering a typical PEL with a charge density of 100 mol m−3 and a thickness of 8 nm along with a high-to-low concentration ratio of 1000, we demonstrate that it is possible to extract a power density of 51.5 W m−2, which is nearly three times the maximum achievable value employing bare conical nanochannels at the same salinity gradient.

Understanding the Percolation Effect in Triboelectric Nanogenerator with Conductive Intermediate Layer

Abstract: Introducing the conductive intermediate layer into a triboelectric nanogenerator (TENG) has been proved as an efficient way to enhance the surface charge density that is attributed to the enhancement of the dielectric permittivity. However, far too little attention has been paid to the companion percolation, another key element to affect the output. Here, the TENG with MXene-embedded polyvinylidene fluoride (PVDF) composite film is fabricated, and the dependence of the output capability on the MXene loading is investigated experimentally and theoretically. Specifically, the surface charge density mainly depends on the dielectric permittivity at lower MXene loadings, and in contrast, the percolation becomes the degrading factor with the further increase of the conductive loadings. At the balance between the dielectric and percolation properties, the surface charge density of the MXene-modified TENG obtained 350% enhancement compared to that with the pure PVDF. This work shed new light on understanding the dielectric and percolation effect in TENG, which renders a universal strategy for the high-performance triboelectronics.

A comprehensive DFT based insights into the physical properties of tetragonal superconducting Mo5PB2

Abstract: Tetragonal Mo5PB2, a recently discovered superconductor, is an extension of transition metal binaries with general formula T5M3. A large number of physical properties of Mo5PB2, including elastic properties and their anisotropy, acoustic behavior, electronic (charge density distribution, electron density difference), thermophysical, bonding characteristics, and optical properties have not been carried out at all till date. In this work, all these properties have been studied in details for the first time employing density functional theory based first-principles method. Mo5PB2 is found to be a mechanically stable, elastically anisotropic compound with ductile character. Chemical bonding characteristics are understood from electronic energy density of states, electron density distribution, elastic properties and Mulliken and Hirshfeld bond population analyses. Mo5PB2 has a combination of ionic, metallic, and covalent bondings. Mo5PB2 possesses high level of machinability. Large electronic density of states at the Fermi level, N(EF), reveals its metallic character. High value of N(EF) facilates superconductivity. Calculated values of different thermal parameters of Mo5PB2 are closely related to the elastic moduli and constants. Energy dependent optical parameters show close agreement to the underlying electronic band structure. The optical absorption and reflectivity spectra and the low energy index of refraction of Mo5PB2 disclose its promise to be used in the optoelectronic device sector. Unlike the notable anisotropy found in elastic properties and minimum thermal conductivity, the optical parameters are found to be almost isotropic with respect to the polarization direction of the electric field.