Microscopic Charge Research Articles

Spatial charge configuration regulates nanoparticle transport and binding behavior in vivo.

Detailed Charge arrangements: A new set of zwitterionic quantum dots were synthesized and used to study the influence of microscopic charge arrangements on the in vivo behavior of nanoparticles. Experiments using cultured cells and live mice demonstrate that the microscopic arrangement of surface charges strongly influence nonspecific binding, clearance behavior, and in vivo transport of nanoparticles.

NMR and NQR investigations of local symmetry in the hidden order phase of URu2Si2

In order to study local symmetries at the 4e(Si)- and 4d(Ru)-sites above and below hidden order transition temperature TO = 17.5 K in URu2Si2, we have investigated the nuclear quadrupole interaction by 73Ge-nuclear magnetic resonance (NMR) measurement on a 10% 73Ge-substituted sample URu2(Si0.9Ge0.1)2, and by 101Ru-nuclear quadrupole resonance (NQR) measurement on a pure single crystal sample. The present 73Ge-NMR measurements do not give any evidence for change in the local symmetry at 4e-site within experimental accuracy. On the other hand, the precise measurement of 101Ru-NQR frequency has detected an anomaly just below TO as sensitively as the thermal expansion measurement dose. Its temperature dependence shows a linear relation with that of the in-plane lattice parameter, which may be a clue to clarify a modification in microscopic charge distribution at TO.

Graphene Transforms Wide Band Gap ZnS to a Visible Light Photocatalyst. The New Role of Graphene as a Macromolecular Photosensitizer

We report the assembly of nanosized ZnS particles on the 2D platform of a graphene oxide (GO) sheet by a facile two-step wet chemistry process, during which the reduced graphene oxide (RGO, also called GR) and the intimate interfacial contact between ZnS nanoparticles and the GR sheet are achieved simultaneously. The ZnS-GR nanocomposites exhibit visible light photoactivity toward aerobic selective oxidation of alcohols and epoxidation of alkenes under ambient conditions. In terms of structure-photoactivity correlation analysis, we for the first time propose a new photocatalytic mechanism where the role of GR in the ZnS-GR nanocomposites acts as an organic dye-like macromolecular "photosensitizer" for ZnS instead of an electron reservoir. This novel photocatalytic mechanism is distinctly different from all previous research on GR-semiconductor photocatalysts, for which GR is claimed to behave as an electron reservoir to capture/shuttle the electrons photogenerated from the semiconductor. This new concept of the reaction mechanism in graphene-semiconductor photocatalysts could provide a new train of thought on designing GR-based composite photocatalysts for targeting applications in solar energy conversion, promoting our in-depth thinking on the microscopic charge carrier transfer pathway connected to the interface between the GR and the semiconductor.

Microscopic Effective Charges and the B(E2) Values of Terminating States in Mirror Nuclei 51Mn and 51Fe

The microscopic effective charges in mirror nuclei 51Mn and 51Fe are investigated with the particle-vibration coupling model based on the self-consistent Skyrme-Hartree-Fock and continuum random-phase-approximation approaches. The isovector parts are predicted to be around 0.15, and the proton effective charges are around 1.25 e, which is less than the empirical value of eeffp = 1.5 e. The microscopic effective charges in neutron rich 51Mn are about 10% less than its proton rich mirror. These effective charges are combined with the shell model to calculate the reduced electric quadrupole transition probability B(E2) values in 51Mn and 51Fe. It turns out that the microscopic effective charges have well reproduced the B(E2) values and its ratio in the terminating states.

Cosmic string evolution with a conserved charge

Cosmic strings with degrees of freedom beyond the standard Abrikosov-Nielsen-Olesen or Nambu-Goto strings are ubiquitous in field theory as well as in models with extra dimensions, such as string theoretic brane inflation scenarios. Here we carry out an analytic study of a simplified version of one such cosmic string model. Specifically, we extend the velocity-dependent one-scale (VOS) string evolution model to the case where there is a conserved microscopic charge on the string worldsheet. We find that whether the standard scale-invariant evolution of the network is preserved or destroyed due to the presence of the charge will crucially depend on the amount of damping and energy losses experienced by the network. This suggests, among other things, that results derived in Minkowski space (field theory) simulations may not extend to the case of an expanding universe.

The Microscopic Free Energies of Solvation for K<SUP>+</SUP>, Rb<SUP>+</SUP> and Cs<SUP>+</SUP> in Mixed Methanol (MeOH)-Dimethylformamide (DMFA) Solvents at 298.15 K

The microscopic charging (∆ Gt charging), ion-dipole (∆ Gt ion-dipole) and ion-induced dipole (∆ Gt ion- induced dipole) free energies of transfer for some ions from methanol to mixed methanol (MeOH)-dimethylformamide (DMFA) solvents were calculated. These ions are potassium, rubidium and cesium. These theoretical free energies were compared with that of experimental values and the difference excess free energies of solvation were discussed. I t was ob- served that the excess free energies for all ions are positive and follow the following order: ∆ GT (excess) K + > ∆ GT (excess) Rb + > ∆ GT (excess) Cs + . Indicating more solvation behaviour by increasing the percentage of DMFA in the mixed solvents due to more attraction of these ions in the range rich in DMFA

Comparative Study of Microscopic Charge Dynamics in Crystalline Acceptor-Substituted Oligothiophenes

By performing microscopic charge transport simulations for a set of crystalline dicyanovinyl-substituted oligothiophenes, we find that the internal acceptor-donor-acceptor molecular architecture combined with thermal fluctuations of dihedral angles results in large variations of local electric fields, substantial energetic disorder, and pronounced Poole-Frenkel behavior, which is unexpected for crystalline compounds. We show that the presence of static molecular dipoles causes large energetic disorder, which is mostly reduced not by compensation of dipole moments in a unit cell but by molecular polarizabilities. In addition, the presence of a well-defined π-stacking direction with strong electronic couplings and short intermolecular distances turns out to be disadvantageous for efficient charge transport since it inhibits other transport directions and is prone to charge trapping.

Correlation between interdomain carrier hopping and apparent mobility in polycrystalline organic transistors as investigated by electron spin resonance

Microscopic charge dynamics inside microcrystal domains and across domain boundaries in polycrystalline organic thin-film transistors (OTFTs) were resolved by angle- and temperature-dependent field-induced electron spin resonance (FI-ESR) spectroscopy. We utilized small-molecule and polymer-based polycrystalline OTFTs, both of which are composed of planar microdomains oriented uniaxially on the substrates. Two types of motional narrowing effect are observed at magnetic fields perpendicular and parallel to the substrate: In the former, we observed the motional narrowing effect due to intradomain transport, while in the latter, we observed another motional narrowing effect due to the carrier hopping across the domain boundaries, which averaged out the variation in $g$ factors between respective microdomains. The analyses revealed that the activation energies for the intradomain transport are between 5 and 21 meV, while those for the interdomain carrier hopping are between 45 and 90 meV. The latter ones coincide with those for the apparent mobility for the respective OTFTs. These results demonstrate that the charge transport is limited by the domain boundaries, which form rate-determining barrier potential both in small-molecule and polymer-based polycrystalline OTFTs.

The Quantum Oscillatory Modulated Potential Ⅰ- The Hydrogen Atom

In this work we are presenting a modified Coulomb potential function to describe the interaction between two micro-scopic electric charges. In particular, concerning the interaction between the proton and the electron in the hydrogen atom. The modified potential function is the product of the classical Coulomb potential and an oscillatory function dependent on a quantized phase factor. The oscillatory function picks up only selected points along the Coulomb potential, creating potential wells and barriers around the nucleus of the atom. The new potential reveals us new features of the hydrogen atom. Searching for a manner to determine the phase factor, we are using the concept of the de Broglie particle wavelike behavior and the quantum analogue of the virial theorem for describing the bound motion of a particle in a central force field. This procedure is a kind of feedback action, where we are making use of well established concepts of the quantum mechanics aiming to determine the phase factor of the new interaction potential.

A Multi-Scale Electrochemical and Thermal Model of a LiFePO4 Battery

Modeling and simulation of lithium batteries is becoming of in-creasing importance both for improving the fundamental under-standing of electrochemical processes and for developing battery management systems for practical applications. We present a 1D+1D+1D multi-scale electrochemical and thermal model of a lithium-ion battery with lithium iron phosphate (LiFePO4, LFP) positive electrode material. The model uses a hierarchical repre-sentation of spatial scales: On the nanoscopic level, diffusive transport takes place in the active material particles. On the micro-scopic level, multi-component mass and charge transport as well as heat production is described in a single repeat unit (anode, separa-tor, cathode, current collectors). On the macroscopic scale, the model describes heat transport in the radial direction of a cylindri-cal cell. Molar enthalpies and entropies are incorporated as func-tion of state of charge (SOC) for reliable simulation of heat pro-duction. The model is validated using experimentally-determined discharge curves over a wide range of discharge currents.

Local Electronic Properties of Graphene on a BN Substrate via Scanning Tunneling Microscopy

The use of boron nitride (BN) as a substrate for graphene nanodevices has attracted much interest since the recent report that BN greatly improves the mobility of charge carriers in graphene compared to standard SiO(2) substrates. We have explored the local microscopic properties of graphene on a BN substrate using scanning tunneling microscopy. We find that BN substrates result in extraordinarily flat graphene layers that display microscopic Moiré patterns arising from the relative orientation of the graphene and BN lattices. Gate-dependent dI/dV spectra of graphene on BN exhibit spectroscopic features that are sharper than those obtained for graphene on SiO(2). We observe a significant reduction in local microscopic charge inhomogeneity for graphene on BN compared to graphene on SiO(2).

Simulation method of Kelvin probe force microscopy at nanometer range and its application

The partitioned-real-space density-functional-based tight-binding (PR-DFTB) method is proposed as a simulation method for calculating the quantum electronic states in Kelvin probe force microscopy (KPFM). This method can be used when a tip is set on a sample surface with a nonorbital-hybridization distance and an applied bias voltage. The PR-DFTB method can perform self-consistent calculations of a system that consists of two subsystems (the tip and the sample). Each subsystem is expressed by a block element of the Fock matrix and thus is characterized by the Fermi level in the block element. Consequently, charge distributions on the two subsystems can be calculated individually. Furthermore, charge redistributions in the subsystems induced by approach of them under an applied bias voltage can also be calculated. Using the proposed PR-DFTB method, we can clarify the mechanism by observing the local contact potential difference (LCPD). Unlike the conventional description of the Kelvin force, the force acting between a biased tip and a sample depends not only on the net charge transferred between the tip and the sample but also on the multipole forces generated by the microscopic charge distribution within the tip and the sample. This is the mechanism responsible for observing the ``apparent'' LCPD. KPFM images generated from the minimum bias voltage in the force-bias curve (i.e., LCPD images) are theoretically simulated using tip models for a Si or hydrogenated Si cluster for simple models of a $\text{Si}(111)\text{-c}(4\ifmmode\times\else\texttimes\fi{}2)$ surface, a monohydride Si(001) surface with/without a defect, and a $\text{Si}(111)\text{\ensuremath{-}}(5\ifmmode\times\else\texttimes\fi{}5)$ dimer-adatom-stacking fault (DAS) surface.

Plasmonic implementation of a quantum eraser for imaging applications

We describe the use of a plasmonic version of a quantum eraser for imaging applications. Two perpendicular surface plasmon polariton (SPP) beams were excited in a glass-metal sample using a leakage radiation microscope. The polarization state of the SPP-coupled radiation leaked to the sample substrate permits to identify the path of photons along the metal-air interface of the sample. Introduction of a linear polarizer after the microscope high numerical aperture lens erases the which-path information. This enabled us to image on the microscope charge coupled device camera the interference pattern formed in the sample surface.

Theoretical Characterization of the Air-Stable, High-Mobility Dinaphtho[2,3-b:2′3′-f]thieno[3,2-b]-thiophene Organic Semiconductor

Recently, an optimum mobility of 8.3 cm2/(Vs) has been measured for single-crystal organic field-effect transistors based on the dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]-thiophene (DNTT) molecule. Here, on the basis of quantum chemistry calculations and molecular dynamics simulations, we investigate the microscopic charge transport parameters of the DNTT molecule and crystal. Our findings confirm that the moderate anisotropy of the hole mobility in DNTT is highly dependent on the presence of in-plane herringbonelike intermolecular interactions with large electronic coupling (transfer integral) values (ca. 0.1 eV). Also, we demonstrate that the π-extended heteroaromatic structure leads to strong electronic coupling interactions among neighboring molecules and to a decrease of the intramolecular reorganization energy. In DNTT, thermal modulations of the electronic couplings at 300 K remain small when compared to those exhibited by the pentacene single crystal. This theoretical study suggests that heteroacenes are a promising route toward high-mobility organic semiconductor materials. Charge transport is discussed in the framework of both band and hopping models.

The Dielectric Permittivity of Crystals in the Reduced Hartree–Fock Approximation

In a recent article (Canc\`es, Deleurence and Lewin, Commun. Math. Phys., 281 (2008), pp. 129-177), we have rigorously derived, by means of bulk limit arguments, a new variational model to describe the electronic ground state of insulating or semiconducting crystals in the presence of local defects. In this so-called reduced Hartree-Fock model, the ground state electronic density matrix is decomposed as $\gamma = \gamma^0_{\rm per} + Q_{\nu,\epsilon_{\rm F}}$, where $\gamma^0_{\rm per}$ is the ground state density matrix of the host crystal and $Q_{\nu,\epsilon_{\rm F}}$ the modification of the electronic density matrix generated by a modification $\nu$ of the nuclear charge of the host crystal, the Fermi level $\epsilon_{\rm F}$ being kept fixed. The purpose of the present article is twofold. First, we study more in details the mathematical properties of the density matrix $Q_{\nu,\epsilon_{\rm F}}$ (which is known to be a self-adjoint Hilbert-Schmidt operator on $L^2(\R^3)$). We show in particular that if $\int_{\RR^3} \nu \neq 0$, $Q_{\nu,\epsilon_{\rm F}}$ is not trace-class. Moreover, the associated density of charge is not in $L^1(\R^3)$ if the crystal exhibits anisotropic dielectric properties. These results are obtained by analyzing, for a small defect $\nu$, the linear and nonlinear terms of the resolvent expansion of $Q_{\nu,\epsilon_{\rm F}}$. Second, we show that, after an appropriate rescaling, the potential generated by the microscopic total charge (nuclear plus electronic contributions) of the crystal in the presence of the defect, converges to a homogenized electrostatic potential solution to a Poisson equation involving the macroscopic dielectric permittivity of the crystal. This provides an alternative (and rigorous) derivation of the Adler-Wiser formula.

Evaluation of Born and local effective charges in unoriented materials from vibrational spectra

We present an application of the Lorentz model in which fits to vibrational spectra or a Kramers Kronig analysis are employed along with several useful formalisms to quantify microscopic charge in unoriented (powdered) materials. The conditions under which these techniques can be employed are discussed, and we analyze the vibrational response of a layered transition-metal dichalcogenide and its nanoscale analog to illustrate the utility of this approach.

High rate performance of Li[Ni 1/3Co 1/3Mn 1/3]O 2 synthesized via co-precipitation method by different precipitators

In the present study, we investigated the effect of three different precipitators (NaOH, Na 2CO 3 and (NH 4) 2CO 3) on the synthesized layered Li[Ni 1/3Co 1/3Mn 1/3]O 2 cathode materials via co-precipitation method. The obtained compounds were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and galvanostatic charge–discharge measurements. The XRD patterns analysis showed that all the resulted Li[Ni 1/3Co 1/3Mn 1/3]O 2 materials possess a layered hexagonal structure. It was found that at high discharge rate (2 C), the prepared Li[Ni 1/3Co 1/3Mn 1/3]O 2 system using Na 2CO 3 as the precipitator exhibits better cycling performance in the charge–discharge tests compared to others, indicating that Na 2CO 3 is an optimum precipitator. After 100 cycles at 2 C discharge rate in the voltage range from 2.8 to 4.5 vs. Li/Li +, the Li[Ni 1/3Co 1/3Mn 1/3]O 2 system using Na 2CO 3 as the precipitator retains 97% of its initial discharge capacity.

Acid–base behavior of a colloidal clays fraction extracted from natural quartz sand: Effect of permanent surface charge

The electrical double-layer model (EDLM), generally used in order to describe the behaviour of the solids bearing only amphoteric groups at the surface (i.e. oxides), can be extended to solid based dispersion presenting simultaneously amphoteric sites (pH-dependent charge) and permanent structural charges (pH-independent charge) at the surface (i.e. clays). In this study, the acid–base behaviours of a fraction of colloidal clays extracted from a natural quartz sand have been modelled within the EDLM frameworks. These colloidal clays also exhibit heterogeneous macroscopic surface charge distribution. We have considered the case where the colloidal fraction presents only amphoteric sites at the surface (case 1) and the case where both pH-depending and pH-independent charges are present simultaneously at the surface (case 2). The modelling results show a great difference between the theory and the experimental data for case 1 but a good corroboration for case 2. Therefore, in order to describe correctly the physical-chemistry properties of the colloidal fraction it is necessary to take into account the permanent charges (microscopic surface charge heterogeneity) to explain the increase in the zero protonic charge (ZPC) and in the protonation amount with decreasing ionic strength. In case 1, the double-layer model leads to a constant ZPC and to an increase in the protonation amount as a function of ionic strength, which is in disagreement with the experimental results.

Refraction Indices of Non-Uniform Systems from the First Principles

ABSTRACTA novel, first-principle theoretical approach and synergetic computational methods designed to predict electronic and magnetic transport properties of strongly spatially inhomogeneous systems, including small quantum dots and wires (QDs and QWs, respectively), and molecules, have been developed recently. This approach is based on a many-body quantum theoretical formalism - a projection operator method due to Zubarev and Tserkovnikov (ZT) - formulated in terms of the equilibrium, two-time temperature Green functions (or TTGFs). There are several significant advantages of this approach, as compared to traditional non-equilibrium two-time thermodynamic and field-theoretical Green's function (NGF) methods that are currently used to study electronic and magnetic transport properties of strongly spatially inhomogeneous systems. In particular, the TTGFs are directly related to experimentally assessable microscopic charge, spin and microcurrent densities.In the work reported here the TTGF-based approach has been used to derive a fundamental, yet tractable expression for the space-time Fourier transform of the tensor of quasi-local refraction indices (TRI) from the first principles. The TTGFs necessary to predict TRI can be calculated using quantum statistical mechanical means, modeling and simulations, and experimental data. Applications of the theoretical predictions for TRI open new prospects in materials design. In particular, the derived theoretical expression for TRI can be used to guide experimental synthesis of structured materials and systems with both direction- and position-dependent indices of refraction in desirable frequency ranges.

Charge transport studies in electroluminescent biphenylyl substituted PPV derivatives using time‐of‐flight photoconductivity method

AbstractThe charge transport properties in a series of electroluminescent biphenylyl substituted PPV derivatives, poly[(2‐(3′‐(p‐2″‐ethylhexyloxyphenyl)phenyl)‐1,4‐phenylenevinylene) (MP‐PPV), poly[2‐(2′‐phenyl‐4′,5′‐bis(3″‐methylbutoxy))phenyl‐1,4‐phenylene vinylene] (BP‐PPV) and poly{[2‐(4′,5′‐bis(3″‐methylbutoxy)‐2′‐phenyl)phenyl‐1,4‐phenylene‐vinylene]‐co‐(9,9‐dioctyl‐2,7‐fluorenylene‐vinylene)} (BPPPV‐PF), have been studied using a time of flight (TOF) photoconductivity technique. The TOF transients for holes in these polymers were weakly dispersive in nature with a mobility of the order of ∼10−5cm2/V s at room temperature. The temperature and field dependence of charge mobility has been studied and analyzed using the disorder formalisms (Bässler's Gaussian disorder model (GDM) and correlated disorder model (CDM)). The charge transport parameters, such as mobility prefactor, energetic disorder, positional disorder, and the average intersite distance, were estimated from the fit and correlated to the molecular structure of the polymer. The microscopic charge transport parameters derived for these polymers indicate that these biphenylyl substituted PPV derivatives have very good chemical purity and structural regularity, which is similar to the reported values for structurally related fully conjugated polymers with high chemical purity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1159–1166, 2008