Showing papers on "Charge density published in 2017"
TL;DR: In this article, atomically thin Bi2 MoO6 sheets are acquired that exhibit remarkable high-rate cycling performance in Li-ion batteries, which can be attributed to the interlayer coupling effect, as well as the 2D configuration and intrinsic structural stability.
Abstract: Ultrathin 2D materials can offer promising opportunities for exploring advanced energy storage systems, with satisfactory electrochemical performance. Engineering atomic interfaces by stacking 2D crystals holds huge potential for tuning material properties at the atomic level, owing to the strong layer-layer interactions, enabling unprecedented physical properties. In this work, atomically thin Bi2 MoO6 sheets are acquired that exhibit remarkable high-rate cycling performance in Li-ion batteries, which can be ascribed to the interlayer coupling effect, as well as the 2D configuration and intrinsic structural stability. The unbalanced charge distribution occurs within the crystal and induces built-in electric fields, significantly boosting lithium ion transfer dynamics, while the extra charge transport channels generated on the open surfaces further promote charge transport. The in situ synchrotron X-ray powder diffraction results confirm the material's excellent structural stability. This work provides some insights for designing high-performance electrode materials for energy storage by manipulating the interface interaction and electronic structure.
468 citations
TL;DR: In this article, the authors demonstrate that high-harmonic generation in solids is sensitive to interatomic bonding and show that harmonic efficiency is enhanced for semi-classical electron trajectories that connect (avoid) neighbouring atomic sites in the crystal.
Abstract: High-harmonic generation in a solid turns out to be sensitive to the interatomic bonding — a very useful feature that could enable the all-optical imaging of the interatomic potential. The microscopic valence electron density determines the optical, electronic, structural and thermal properties of materials. However, current techniques for measuring this electron charge density are limited: for example, scanning tunnelling microscopy is confined to investigations at the surface, and electron diffraction requires very thin samples to avoid multiple scattering1. Therefore, an optical method is desirable for measuring the valence charge density of bulk materials. Since the discovery of high-harmonic generation (HHG) in solids2, there has been growing interest in using HHG to probe the electronic structure of solids3,4,5,6,7,8,9,10,11. Here, using single-crystal MgO, we demonstrate that high-harmonic generation in solids is sensitive to interatomic bonding. We find that harmonic efficiency is enhanced (diminished) for semi-classical electron trajectories that connect (avoid) neighbouring atomic sites in the crystal. These results indicate the possibility of using materials’ own electrons for retrieving the interatomic potential and thus the valence electron density, and perhaps even wavefunctions, in an all-optical setting.
353 citations
TL;DR: In this article, the β-(Al x Ga 1− x )2O3 barrier was partially doped by Ge to achieve a two-dimensional electron gas (2DEG) in Ga 2O3, which was confirmed by capacitance-voltage measurements.
Abstract: β-(Al x Ga1− x )2O3/β-Ga2O3 heterostructures were grown via plasma-assisted molecular beam epitaxy. The β-(Al x Ga1− x )2O3 barrier was partially doped by Ge to achieve a two-dimensional electron gas (2DEG) in Ga2O3. The formation of the 2DEG was confirmed by capacitance–voltage measurements. The impact of Ga-polishing on both the surface morphology and the reduction of the unintentionally incorporated Si at the growth interface was investigated using atomic force microscopy and secondary-ion mass spectrometry. Modulation doped field-effect transistors were fabricated. A maximum current density of 20 mA/mm with a pinch-off voltage of −6 V was achieved on a sample with a 2DEG sheet charge density of 1.2 × 1013 cm−2.
163 citations
TL;DR: It is shown that thermal treatments effectively tune the interfacial charge distribution in carbon-supported palladium catalysts with consequential changes in hydrogenation performance, providing a strategy to rationally design carbon- supported catalysts.
Abstract: Controlling the charge transfer between a semiconducting catalyst carrier and the supported transition metal active phase represents an elite strategy for fine turning the electronic structure of the catalytic centers, hence their activity and selectivity. These phenomena have been theoretically and experimentally elucidated for oxide supports but remain poorly understood for carbons due to their complex nanoscale structure. Here, we combine advanced spectroscopy and microscopy on model Pd/C samples to decouple the electronic and surface chemistry effects on catalytic performance. Our investigations reveal trends between the charge distribution at the palladium–carbon interface and the metal’s selectivity for hydrogenation of multifunctional chemicals. These electronic effects are strong enough to affect the performance of large (~5 nm) Pd particles. Our results also demonstrate how simple thermal treatments can be used to tune the interfacial charge distribution, hereby providing a strategy to rationally design carbon-supported catalysts. Control over charge transfer in carbon-supported metal nanoparticles is essential for designing new catalysts. Here, the authors show that thermal treatments effectively tune the interfacial charge distribution in carbon-supported palladium catalysts with consequential changes in hydrogenation performance.
135 citations
TL;DR: The real-space imaging of the (projected) atomic electric field distribution inside single Au atoms is demonstrated, using sub-Å spatial resolution STEM combined with a high-speed segmented detector.
Abstract: In scanning transmission electron microscopy (STEM), single atoms can be imaged by detecting electrons scattered through high angles using post-specimen, annular-type detectors. Recently, it has been shown that the atomic-scale electric field of both the positive atomic nuclei and the surrounding negative electrons within crystalline materials can be probed by atomic-resolution differential phase contrast STEM. Here we demonstrate the real-space imaging of the (projected) atomic electric field distribution inside single Au atoms, using sub-A spatial resolution STEM combined with a high-speed segmented detector. We directly visualize that the electric field distribution (blurred by the sub-A size electron probe) drastically changes within the single Au atom in a shape that relates to the spatial variation of total charge density within the atom. Atomic-resolution electric field mapping with single-atom sensitivity enables us to examine their detailed internal and boundary structures.
131 citations
08 Nov 2017
TL;DR: In this article, a structural transformation of the moire pattern inherent to twisted bilayer graphene taking place at twist angles θ below a crossover angle is revealed by a change in the functional form of the twist energy density.
Abstract: Experiments on bilayer graphene unveiled a fascinating realization of stacking disorder where triangular domains with well-defined Bernal stacking are delimited by a hexagonal network of strain solitons. Here we show by means of numerical simulations that this is a consequence of a structural transformation of the moire pattern inherent to twisted bilayer graphene taking place at twist angles θ below a crossover angle . The transformation is governed by the interplay between the interlayer van der Waals interaction and the in-plane strain field, and is revealed by a change in the functional form of the twist energy density. This transformation unveils an electronic regime characteristic of vanishing twist angles in which the charge density converges, though not uniformly, to that of ideal bilayer graphene with Bernal stacking. On the other hand, the stacking domain boundaries form a distinct charge density pattern that provides the STM signature of the hexagonal solitonic network.
126 citations
TL;DR: The potential energy corrugation is found to be determined by the sliding-induced interfacial charge density fluctuation, suggesting a new perspective to understand the physical origin of the atomic scale friction of two-dimensional materials.
Abstract: Graphene and other two-dimensional materials have been proved to be able to offer low friction. Here we assembled van der Waals heterostructures with graphene and molybdenum disulphide monolayers. The Raman spectrum together with a modified linear chain model indicate a two-orders-of-magnitude decrease in the interlayer lateral force constant, as compared with their homogeneous bilayers, indicating a possible routine to achieve superlubricity. The decrease in the interlayer lateral force constant is consistent with the ultrasmall potential energy corrugation during sliding, which is derived from density functional theory calculations. The potential energy corrugation is found to be determined by the sliding-induced interfacial charge density fluctuation, suggesting a new perspective to understand the physical origin of the atomic scale friction of two-dimensional materials.
125 citations
TL;DR: In this paper, a model GIL spacer in 0.1 MPa air under DC voltage was obtained by an advanced measurement method, from which the dominant uniform charging pattern and random charge speckles were separated.
Abstract: Charge accumulation on a solid insulator surface is one of the critical factors for the development of dc gas-insulated equipment since it will lead to the overstress of polymeric insulation due to local field distortion and enhancement. Therefore, it is important to study the charge accumulation phenomenon on spacer surface under dc field. For decades, researchers have made tremendous progress on this subject by measurement and simulation. However, measurement results are quite different by different researchers due to various electrode configurations and experimental conditions. Further, most researchers use potential to represent charge density, which is not rigorous in that many charge density distribution details are hidden behind the potential. As for pure numerical simulation, reports are rather academic and sometimes cannot accord with the real fact. In this paper, attempts are made to characterize the charge accumulation patterns on spacer surface in HVDC gas-insulated system. Surface charge distributions on a model GIL spacer in 0.1 MPa air under DC voltage are obtained by an advanced measurement method, from which the dominant uniform charging pattern and random charge speckles are separated. Mechanism responsible for the dominant uniform charging pattern is discussed with the aid of a simulation model. Results indicate that, in a well-cleaned system, the electric current through the spacer bulk is the principal factor, but gas conduction is not negligible due to some inevitable ion sources. Highly localized pockets of charge are also observed, which are referred to as speckles. They may originate from micro discharges due to tiny metal particles on the spacer surface or microscopic protrusions on the electrodes.
112 citations
TL;DR: In this article, a new structured triboelectric nanogenerators (TENG) was designed by adding a transition layer between the friction layer and the conduct layer, which could significantly improve the output performance by one order of magnitude.
107 citations
TL;DR: High-temperature charge correlations are unlocked from the wavevector of the spin correlations, signaling analogies to CDW phases in various other cuprates, indicating that stripe order at low temperatures is stabilized by the coupling of otherwise independent charge and spin density waves.
Abstract: Although all superconducting cuprates display charge-ordering tendencies, their low-temperature properties are distinct, impeding efforts to understand the phenomena within a single conceptual framework. While some systems exhibit stripes of charge and spin, with a locked periodicity, others host charge density waves (CDWs) without any obviously related spin order. Here we use resonant inelastic X-ray scattering to follow the evolution of charge correlations in the canonical stripe-ordered cuprate La1.875Ba0.125CuO4 across its ordering transition. We find that high-temperature charge correlations are unlocked from the wavevector of the spin correlations, signaling analogies to CDW phases in various other cuprates. This indicates that stripe order at low temperatures is stabilized by the coupling of otherwise independent charge and spin density waves, with important implications for the relation between charge and spin correlations in the cuprates.
92 citations
TL;DR: The higher binding energy of glucose and more charge transfer from glucose to Pd-doped NiCo 2O4 compared with bare NiCo2O4 infer that Pd -dopedNiCo2 O4 possesses superior charge-transfer kinetics, which supports the higher glucose-sensing performance.
Abstract: Here, we report the facile synthesis of NiCo2O4 (NCO) and NiCo2O4–Pd (NCO–Pd) nanosheets by the electrodeposition method. We observed enhanced glucose-sensing performance of NCO–Pd nanosheets as compared to bare NCO nanosheets. The sensitivity of the pure NCO nanosheets is 27.5 μA μM–1 cm–2, whereas NCO–Pd nanosheets exhibit sensitivity of 40.03 μA μM–1 cm–2. Density functional theory simulations have been performed to qualitatively support our experimental observations by investigating the interactions and charge-transfer mechanism of glucose on NiCo2O4 and Pd-doped NiCo2O4 through demonstration of partial density of states and charge density distributions. The presence of occupied and unoccupied density of states near the Fermi level implies that both Ni and Co ions in NiCo2O4 can act as communicating media to transfer the charge from glucose by participating in the redox reactions. The higher binding energy of glucose and more charge transfer from glucose to Pd-doped NiCo2O4 compared with bare NiCo2O4 ...
TL;DR: In this paper, a gas-flow assisted nano-template (GANT) infiltration was proposed to grow self-poled Nylon-11 nanowires from solution within nanoporous anodised aluminium oxide (AAO) templates.
Abstract: Triboelectric generators have emerged as potential candidates for mechanical energy harvesting, relying on motion-generated surface charge transfer between materials with different electron affinities. In this regard, synthetic organic materials with strong electron-donating tendencies are far less common than their electron-accepting counterparts. Nylons are notable exceptions, with odd-numbered Nylons such as Nylon-11, exhibiting electric polarisation that could further enhance the surface charge density crucial to triboelectric generator performance. However, the fabrication of Nylon-11 in the required polarised δ′-phase typically requires extremely rapid crystallisation, such as melt-quenching, as well as “poling” via mechanical stretching and/or large electric fields for dipolar alignment. Here, we propose an alternative one-step, near room-temperature fabrication method, namely gas-flow assisted nano-template (GANT) infiltration, by which highly crystalline “self-poled” δ′-phase Nylon-11 nanowires are grown from solution within nanoporous anodised aluminium oxide (AAO) templates. Our gas-flow assisted method allows for controlled crystallisation of the δ′-phase of Nylon-11 through rapid solvent evaporation and an artificially generated extreme temperature gradient within the nanopores of the AAO template, as accurately predicted by finite-element simulations. Furthermore, preferential crystal orientation originating from template-induced nano-confinement effects leads to self-poled δ′-phase Nylon-11 nanowires with higher surface charge distribution than melt-quenched Nylon-11 films, as observed by Kelvin probe force microscopy (KPFM). Correspondingly, a triboelectric nanogenerator (TENG) device based on as-grown templated Nylon-11 nanowires fabricated via GANT infiltration showed a ten-fold increase in output power density as compared to an aluminium-based triboelectric generator, when subjected to identical mechanical excitations.
TL;DR: The present study reveals the presence of profound structural layering of not only the ionic components of reline but also urea near the electrodes, and shows that both hydrogen-bonding and long-range correlations between different constituents of relines play a crucial role to lay out the bulk structure of Reline.
Abstract: We apply all-atom molecular dynamics simulations to describe the bulk morphology and interfacial structure of reline, a deep eutectic solvent comprising choline chloride and urea in 1:2 molar ratio, near neutral and charged graphene electrodes. For the bulk phase structural investigation, we analyze the simulated real-space radial distribution functions, X-ray/neutron scattering structure functions, and their partial components. Our study shows that both hydrogen-bonding and long-range correlations between different constituents of reline play a crucial role to lay out the bulk structure of reline. Further, we examine the variation of number density profiles, orientational order parameters, and electrostatic potentials near the neutral and charged graphene electrodes with varying electrode charge density. The present study reveals the presence of profound structural layering of not only the ionic components of reline but also urea near the electrodes. In addition, depending on the electrode charge density, the choline ions and urea molecules render different orientations near the electrodes. The simulated number density and electrostatic potential profiles for reline clearly show the presence of multilayer structures up to a distance of 1.2 nm from the respective electrodes. The observation of positive values of the surface potential at zero charge indicates the presence of significant nonelectrostatic attraction between the choline cation and graphene electrode. The computed differential capacitance (Cd) for reline exhibits an asymmetric bell-shaped curve, signifying different variation of Cd with positive and negative surface potentials.
09 Jul 2017
TL;DR: The origin of the charge density wave (CDW) is still under debate as discussed by the authors, partly because the origin and origin and evolution of CDW are still open issues in condensed matter physics.
Abstract: Charge density wave (CDW) is an important concept in condensed matter physics, germane to a number of physical phenomena. But the origin of CDW is still under debate, partly because the origin and ...
TL;DR: In this article, the heat transfer surface charge accumulation model of operating DC-GIL was developed, including the nonlinear relationship between volume current in gas and electric field, and the space charge was also considered in the model.
Abstract: With this expected future advance of HVDC, the use of gas insulated transmission lines (GIL) for dc application are getting increasingly interesting. For now, the problem of surface charge accumulation on gas-insulator interface is one of the critical factors for the development of DC-GIL. In many previous works, the model of surface charge accumulation on insulator was investigated. However, the quantitative relationship between temperature and surface charge accumulation on insulator was not exactly obtained since the lack of complicated heat transfer progress in the model. In this paper, the heat transfer surface charge accumulation model of operating DC-GIL was developed, including the nonlinear relationship between volume current in gas and electric field. Moreover, the space charge was also considered in the model. Based on the developed model, temperature distributions in DC-GIL insulator under different current are obtained. Afterwards, the temperature impact on space charge density in the insulator, the saturation time of surface charge accumulation, the surface charge on the insulator surface, and the electric field distribution on the insulator were investigated. It was proven that the tangential component of the electric field reaches to 5.3 kV/mm on lower interface and 5.0 kV/mm on upper interface for Ti=378 K. This value increase 17.8% on lower interface and 17.6% on upper interface along with the conductor temperature from 298 K to 378 K. The data can be referred in the insulation design of DC-GIL.
TL;DR: In this paper, a relationship between differences in electric polarization between bands and the ''shift vector'' that controls part of a material's bulk photocurrent was derived, then demonstrated in several models.
Abstract: A relationship is derived between differences in electric polarization between bands and the ``shift vector'' that controls part of a material's bulk photocurrent, then demonstrated in several models. Electric polarization has a quantized gauge ambiguity and is normally observed at surfaces via the surface charge density, while shift current is a bulk property and is described by shift vector gauge invariant at each point in momentum space. They are connected because the same optical transitions that are described in shift currents pick out a relative gauge between valence and conduction bands. We also discuss subtleties arising when there are points at the Brillouin zone where optical transitions are absent. We conclude that two-dimensional materials with significant interband polarization differences should have high bulk photocurrent, meaning that the modern theory of polarization can be used as a straightforward way to search for bulk photovoltaic material candidates.
TL;DR: Using semiclassical Boltzmann transport theory and density functional formalism, the authors in this paper have systematically studied the thermoelectric performance of layered GeAs2 and found that the figure of merit, ZT value, of this layered structure is 2.78 along the out-of-plane direction, with optimal carrier concentration at 800 K.
Abstract: Using semiclassical Boltzmann transport theory and density functional formalism, we have systematically studied the thermoelectric performance of layered GeAs2. The figure of merit, ZT value, of this layered structure is found to be 2.78 along the out-of-plane direction, with optimal carrier concentration at 800 K. Analysis of the charge density difference and phonon transport properties allows us to attribute such exceptional thermoelectric properties to strong interlayer interaction between the adjacent layers where quasicovalent bonding is responsible for the enhanced electrical conductivity, while the layered structure accounts for the suppressed lattice thermal conductivity. This study highlights the potential of layered crystals for highly efficient thermoelectric materials.
TL;DR: In this paper, the reliability of PIN-gate-all-around (GAA)-tunnel field effect transistor (TFET) with N+ source pocket was examined by analyzing: 1) the impact of interface trap charge (ITC) density and polarity and 2) the temperature affectability on analog/RF performance.
Abstract: This paper investigates the reliability of PIN-gate-all-around (GAA)-tunnel field-effect transistor (TFET) with N+ source pocket. The reliability of the PNIN-GAA-TFET is examined by analyzing: 1) the impact of interface trap charge (ITC) density and polarity and 2) the temperature affectability on analog/RF performance of the device. It is realized that the interface traps existing at the Si/SiO2 interface modifies the flatband voltage and, thereby, alters the analog and RF characteristics of the device. The analysis is done at various trap charge densities and polarities. The results, thus, obtained reveal that, at higher trap charge density, the device performance alters significantly. It is obtained that, for a donor trap charge density of $3 \times 10^{{12}}$ cm $^{-2}$ , the off-state current of the device degrades tremendously (increases from an order of $10^{-17}$ – $10^{-9}\text{A}$ ). The temperature affectability over the device reveals that, at lower gate bias, the Shockley–Read–Hall phenomenon dominates and degrades the subthreshold current of the device at elevated temperatures. However, for the superthreshold regime, the band-to-band tunneling (BTBT) mechanism dominates. Furthermore, the results show enormous degradation in the off-state current at elevated temperatures, such that, with an increase in the ambient temperature from 200 K to 400 K, the $I_{ \mathrm{\scriptscriptstyle OFF}}$ degrades by an order of $10^{5}$ , i.e., increases from $10^{-18}$ A to $10^{-13}$ A. The results specify that the PNIN-GAA-TFET is insusceptible to the acceptor traps existing at the Si/SiO2 interface in comparison with the donor traps.
TL;DR: In this paper, an experimental study of the rare-earth intermetallic system LuPt2In reveals a strong enhancement of superconductivity near the charge density wave quantum critical point.
Abstract: An experimental study of the rare-earth intermetallic system LuPt2In reveals a strong enhancement of superconductivity near the charge density wave quantum critical point. This represents an unusual counter-example to cuprates, in which superconductivity and charge density waves tend to compete. Quantum critical points (QCPs), at which a second-order phase transition is continuously suppressed to zero temperature, are currently one of the central topics in solid-state physics1,2. The strong interest emerges from observations of very unusual properties at QCPs such as the onset of unconventional superconductivity (SC)3. While QCPs found at the disappearance of magnetic order are quite common and intensively studied, a QCP that results from a structural transition is scarce and poorly investigated. Here, we report on the observation of a charge density wave (CDW) type of structural ordering in LuPt2In with a second-order transition at TCDW = 490 K. Substituting Pd for Pt suppresses TCDW continuously towards T = 0, leading to a QCP at 58% Pd substitution. We find a strong enhancement of bulk SC just at the QCP, pointing to a new type of interaction between CDW and SC.
TL;DR: In this article, the surface potential distribution was scanned in a raster mode using a Kelvin electrostatic probe, from which the relief map of charge density was obtained by an inverse calculation method.
Abstract: Surface charge decay kinetics on corona-charged polymeric insulators were studied. In the experiment, the sample surface exposed to corona was kept open to ambient air whereas the opposite surface was in contact with a grounded plate. The resulting surface potential distribution was scanned in a raster mode using a Kelvin electrostatic probe, from which the relief map of charge density was obtained by an inverse calculation method. The developed procedure allowed for implementation of two study cases: (i) gas neutralization took place under natural conditions, with enhanced concentration of free ions, and with limited gas volume; (ii) surface charge decay occurred only due to bulk neutralization. Three mechanisms were considered responsible for surface charge decay, i.e., bulk neutralization, gas neutralization, and surface conduction. They were discussed separately with the help of numerical models, which quantified the relative importance of each mechanism on the total process of charge decay. The resul...
TL;DR: In this article, a rational design of a photocatalyst assembly composed of n-type semiconducting two-dimensional g-C3N4 nanosheets, carbon nanotubes (CNTs), and plasmonic Ag nanocubes, which exhibits enhanced density of electrons and controlled unidirectional change flow to promote the photocatalytic hydrogen evolution reaction.
Abstract: The effective separation of the electron and hole (e-h) pairs plays a key role in enhancing the photocatalytic performance of the semiconductors. The density of electrons participating in the reduction reaction also determines photocatalytic performance. We report here a rational design of a photocatalyst assembly composed of n-type semiconducting two-dimensional g-C3N4 nanosheets (2D-C3N4), carbon nanotubes (CNTs), and plasmonic Ag nanocubes, which exhibits enhanced density of electrons and controlled unidirectional change flow to promote the photocatalytic hydrogen evolution reaction. Plasmonic Ag nanocubes inject the hot-electrons into conduction band of 2D-C3N4 to increase the density of electrons while the CNTs act as a power pump of the electrons to steer electron flow from the conduction band of 2D-C3N4 to reactants. The photocatalytic performance of Ag/2D-C3N4/CNTs assembly was dramatically enhanced for the H2 evolution from water. The enhanced photocatalytic activity is due to the efficient unidirectional transfer of the electrons with high density and efficient separation of the e-h pairs.
TL;DR: In this article, the temperature dependence of room temperature ionic liquids differential capacitance was studied with both theoretical and computational methods, and it was found that these structures were dismantled with increasing temperature, as predicted by the mean-field theory.
TL;DR: The authors identify the emergence of a unique charge density wave (CDW) order in monolayer TiTe2 that challenges the current understanding of CDW formation.
Abstract: Two-dimensional materials constitute a promising platform for developing nanoscale devices and systems. Their physical properties can be very different from those of the corresponding three-dimensional materials because of extreme quantum confinement and dimensional reduction. Here we report a study of TiTe2 from the single-layer to the bulk limit. Using angle-resolved photoemission spectroscopy and scanning tunneling microscopy and spectroscopy, we observed the emergence of a (2 × 2) charge density wave order in single-layer TiTe2 with a transition temperature of 92 ± 3 K. Also observed was a pseudogap of about 28 meV at the Fermi level at 4.2 K. Surprisingly, no charge density wave transitions were observed in two-layer and multi-layer TiTe2, despite the quasi-two-dimensional nature of the material in the bulk. The unique charge density wave phenomenon in the single layer raises intriguing questions that challenge the prevailing thinking about the mechanisms of charge density wave formation. Due to reduced dimensionality, the properties of 2D materials are often different from their 3D counterparts. Here, the authors identify the emergence of a unique charge density wave (CDW) order in monolayer TiTe2 that challenges the current understanding of CDW formation.
TL;DR: In this article, the authors studied the potential bubble structure of 34 Si on the basis of the self-consistent Green's function many-body method and showed a clear correlation between the occurrence of the bubble structure and the weakening of the 1/2 − − 3 / 2 − splitting in the spectrum of 35 Si as compared to 37 S.
Abstract: Background: The possibility that an unconventional depletion (referred to as a “bubble”) occurs in the center of the charge density distribution of certain nuclei due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. Based on a mean-field rationale, a correlation between the occurrence of such a semibubble and an anomalously weak splitting between low angular-momentum spin-orbit partners has been further conjectured. Energy density functional and valence-space shell model calculations have been performed to identify and characterize the best candidates, among which 34 Si appears as a particularly interesting case. While the experimental determination of the charge density distribution of the unstable 34 Si is currently out of reach, ( d , p ) experiments on this nucleus have been performed recently to test the correlation between the presence of a bubble and an anomalously weak 1 / 2 − − 3 / 2 − splitting in the spectrum of 35 Si as compared to 37 S .Purpose: We study the potential bubble structure of 34 Si on the basis of the state-of-the-art ab initio self-consistent Green's function many-body method. Methods: We perform the first ab initio calculations of 34 Si and 36 S . In addition to binding energies, the first observables of interest are the charge density distribution and the charge root-mean-square radius for which experimental data exist in 36 S . The next observable of interest is the low-lying spectroscopy of 35 Si and 37 S obtained from ( d , p ) experiments along with the spectroscopy of 33 Al and 35 P obtained from knock-out experiments. The interpretation in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input internucleon interactions. The convergence of the results with respect to the truncation of the many-body expansion, i.e., with respect to the many-body correlations included in the calculation, is studied in detail. We eventually compare our predictions to state-of-the-art multireference energy density functional and shell model calculations. Results: The prediction regarding the (non)existence of the bubble structure in 34 Si varies significantly with the nuclear Hamiltonian used. However, demanding that the experimental charge density distribution and the root-mean-square radius of 36 S be well reproduced, along with 34 Si and 36 S binding energies, only leaves the NNLO sat Hamiltonian as a serious candidate to perform this prediction. In this context, a bubble structure, whose fingerprint should be visible in an electron scattering experiment of 34 Si , is predicted. Furthermore, a clear correlation is established between the occurrence of the bubble structure and the weakening of the 1 / 2 − − 3 / 2 − splitting in the spectrum of 35 Si as compared to 37 S .Conclusions: The occurrence of a bubble structure in the charge distribution of 34 Si is convincingly established on the basis of state-of-the-art ab initio calculations. This prediction will have to be reexamined in the future when improved chiral nuclear Hamiltonians are constructed. On the experimental side, present results act as a strong motivation to measure the charge density distribution of 34 Si in future electron scattering experiments on unstable nuclei. In the meantime, it is of interest to perform one-neutron removal on 34 Si and 36 S in order to further test our theoretical spectral strength distributions over a wide energy range.
TL;DR: This work presents a simple, physically motivated model for including charge penetration in the AMOEBA (Atomic Multipole Optimized Energetics for Biomolecular Applications) force field with a function derived from the charge distribution of a hydrogen-like atom and a limited number of parameters that dramatically improves the description of electrostatics at short range.
Abstract: The principal challenge of using classical physics to model biomolecular interactions is capturing the nature of short-range interactions that drive biological processes from nucleic acid base stacking to protein–ligand binding. In particular most classical force fields suffer from an error in their electrostatic models that arises from an ability to account for the overlap between charge distributions occurring when molecules get close to each other, known as charge penetration. In this work we present a simple, physically motivated model for including charge penetration in the AMOEBA (Atomic Multipole Optimized Energetics for Biomolecular Applications) force field. With a function derived from the charge distribution of a hydrogen-like atom and a limited number of parameters, our charge penetration model dramatically improves the description of electrostatics at short range. On a database of 101 biomolecular dimers, the charge penetration model brings the error in the electrostatic interaction energy relative to the ab initio SAPT electrostatic interaction energy from 13.4 kcal mol−1 to 1.3 kcal mol−1. The model is shown not only to be robust and transferable for the AMOEBA model, but also physically meaningful as it universally improves the description of the electrostatic potential around a given molecule.
TL;DR: In this article, the oxygen evolution reaction has been envisaged on a two-dimensional graphyne (GY) nanosheet based on density functional theory framework, where boron doping at edge sites on GY is the ideal candidate for high OER activity, which is efficient as carbon-based electrocatalysts for water splitting and metal air batteries.
TL;DR: A minimal bottom-up extension of the Chern-Simons bulk action for holographic translational symmetry breaking that naturally gives rise to pair density waves is presented that provides a dual description of a superconducting phase intertwined with charge, current, and parity orders.
Abstract: We present a minimal bottom-up extension of the Chern-Simons bulk action for holographic translational symmetry breaking that naturally gives rise to pair density waves. We construct stationary inhomogeneous black hole solutions in which both the U(1) symmetry and spatially translational symmetry are spontaneously broken at a finite temperature and charge density. This novel solution provides a dual description of a superconducting phase intertwined with charge, current, and parity orders.
TL;DR: The work function of few-layer graphene is almost independent of the number of layers with only a difference between monolayer and multilayer graphene of about 60 meV.
Abstract: A theoretical and experimental study of the work function of few-layer graphene is reported. The influence of the number of layers on the work function is investigated in the presence of a substrate, a molecular dipole layer, and combinations of the two. The work function of few-layer graphene is almost independent of the number of layers with only a difference between monolayer and multilayer graphene of about 60 meV. In the presence of a charge-donating substrate the charge distribution is found to decay exponentially away from the substrate and this is directly reflected in the work function of few-layer graphene. A dipole layer changes the work function only when placed in between the substrate and few-layer graphene through a change of the charge transfer between the two.
TL;DR: In this article, a desktop means of estimating the distribution of charge among the ligands in an organometallic complex is developed, based on an iron charge state of cFe = +2.0.
TL;DR: This work finds that the accumulated charge in the cuprate is due to the depletion of oxygen from specific sites in its unit cell, and shows that interfacing correlated oxides with ionic liquids enables a delicate control of oxygen content, paving the way to novel electrochemical concepts in future oxide electronics.
Abstract: Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2):027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer. However, it has been recently reported that the suppression of the metal to insulator transition induced in VO2 by ionic liquid gating is due to oxygen vacancy formation rather than to electrostatic doping [Jeong J, et al. (2013) Science 339(6126):1402–1405]. These results underscore the debate on the true nature, electrostatic vs. electrochemical, of the doping of cuprates with ionic liquids. Here, we address the doping mechanism of the high-temperature superconductor YBa2Cu3O7-X (YBCO) by simultaneous ionic liquid gating and X-ray absorption experiments. Pronounced spectral changes are observed at the Cu K-edge concomitant with the superconductor-to-insulator transition, evidencing modification of the Cu coordination resulting from the deoxygenation of the CuO chains, as confirmed by first-principles density functional theory (DFT) simulations. Beyond providing evidence of the importance of chemical doping in electric double-layer (EDL) gating experiments with superconducting cuprates, our work shows that interfacing correlated oxides with ionic liquids enables a delicate control of oxygen content, paving the way to novel electrochemical concepts in future oxide electronics.