External Charge Research Articles

Direct electrochemisty and electrocatalysis of anthraquinone-monosulfonate/polyaniline hybrid film synthesized by a novel electrochemical doping-dedoping-redoping method on pre-activated spectroscopically pure graphite surface

Polyaniline (PANI) film in the form of emeraldine salt (ES) doped with anthraquinone-2-sulfonate (AQS) was synthesized by a novel electrochemical doping-dedoping-redoping method on pre-activated spectroscopically pure graphite electrode surface. SEM showed the highly porous microstructure with sponge-like morphology of the AQS/PANI hybrid film, which has more available active sites for facilitating electron transfer and energy efficiency of redox reactions. FTIR and UV-vis spectra demonstrated the incorporation of AQS into the conductive PANI matrix. Cyclic voltammetric (CV), electrochemical impedance spectroscope (EIS), rotating ring-disk electrode (RRDE) and chronoamperometry (CA) techniques indicated that the AQS/PANI composite has high electrocatalytic activity and remarkable stability for the two-electron reduction of oxygen via an electrochemical-chemical mechanism at the base of the porous PANI film. The acid centers of PANI (protonated imine group) played an important role not only in two internal redox transform processes, but also in an external charge transfer reaction during the electrocatalytic reduction of oxygen. The incorporation of anionic AQS groups into PANI matrix to prepare electroactive PANI using the electrochemical doping-dedoping-redoping method is conceptually new, and may be extended to the development of new functional materials from many other conducting polymers and quinonoid compounds for wide applications in catalysis, sensors, molecular electronics, and so on.

Evanescent Wave Based System for Observing Particle-Substrate-Charge Interactions

A system using interaction of evanescent light waves with particles in a liquid allows one to observe accumulation, stability, and adhesion of such particles at and in the vicinity of a surface. Accumulation can be due to electrophoresis, sedimentation, or equilibration of the substrate surface with the bulk solution. The observation is sensitive only to particles within 1 μm of the interface, so it can be made with an arbitrary thickness of fluid. Evanescent wave absorption is monitored adjacent to an indium tin oxide coated glass slide affixed to a high index prism. The test fluid can be either constrained by a secondary metal electrode or left as a free fluid film. In the latter case a free charge can be injected into the system from an external charge generator allowing one to separate field- and charge-induced effects. This system is ideal for investigating device life limiting interactions between colorants and substrates in displays.

High-energy asymptotics of D-brane decay amplitudes from Coulomb gas electrostatics

We study the high-energy limit of tree-level string production amplitudes from decaying D-branes in bosonic string theory, interpreting the vertex operators as external charges interacting with a Coulomb gas corresponding to the rolling tachyon background, and performing an electrostatic analysis. In particular, we consider two open string - one closed string amplitudes and four open string amplitudes, and calculate explicit formulas for the leading exponential behavior.

Photocatalytic Oxidation Mechanism of As(III) on TiO2: Unique Role of As(III) as a Charge Recombinant Species

Using TiO(2) photocatalyst, arsenite, As(III), can be rapidly oxidized to arsenate, As(V), which is less toxic and less mobile in the aquatic environment. Therefore, the TiO(2)/UV process can be employed as an efficient pretreatment method for arsenic contaminated water. Since we first reported in 2002 that the superoxide (or hydroperoxyl radical) plays the role of main oxidant of As(III) in the TiO(2)/UV process, there has been much debate over the true identity of the major photooxidant among superoxides, holes, and OH radicals. The key issue is centered on why the much stronger OH radicals cannot oxidize As(III), and it has been proposed that the unique role of As(III) as an external charge recombination center on the UV-excited TiO(2) particle is responsible for this eccentric mechanism. Although the proposed mechanism has been supported by many experimental evidences, doubts on it were not clearly removed. In this study, we provided direct and undisputed evidence to support the role of As(III) in the charge recombination dynamics using time-resolved transient absorption spectroscopy. The presence of As(III) indeed mediated the charge recombination in TiO(2). Under this condition, the role of the OH radical is suppressed because of the null cycle, and the weaker oxidant, superoxide, should prevail. The role of the superoxide has been previously doubted on the basis of the observation that the addition of excess formic acid (hole scavenger that should enhance the production of superoxides) inhibited the photocatalytic oxidation of As(III). However, this study proved that this was due to the photogeneration of reducing radicals (HCO(2)·) that recycle As(V)/As(IV) back to As(III). It was also demonstrated that the 4-chlorophenol/TiO(2) system under visible light that cannot generate neither OH radicals nor valence band holes converted As(III) to As(V) through the superoxide pathway.

Dynamic polarization of graphene by moving external charges: Comparison with 2D electron gas

We calculate the stopping and image forces on a point charge moving over a single-layer graphene grown on an SiC substrate, and compare them with forces arising when a charge moves over a two-dimensional electron gas (2DEG) in an Ag monolayer on a Si substrate. Given that both these systems constitute a one-atom thick 2DEG, major differences are found in the velocity and distance dependencies of the two forces owing to different electronic structures of the respective 2DEG. Within the massless Dirac fermion picture of graphene’s π electron bands, the inter-band single particle excitations are found to affect the stopping and image forces at high speeds in a substantial way, whereas such excitations are absent in the 2DEG of the metallic layer described by a single parabolic band.

Electrostatics of Coulomb gas, lattice paths and discrete polynuclear growth

We study the partition function of a two-dimensional Coulomb gas on a circle, in the presence of external pointlike charges, in a double scaling limit where both the external charges and the number of gas particles are large. Our original motivation comes from studying amplitudes for multi-string emission from a decaying D-brane in the high-energy limit. We analyze the scaling limit of the partition function and calculate explicit results. We also consider applications to random matrix theory. The partition functions can be related to random scattering or to weights of lattice paths in certain growth models. In particular, we consider the discrete polynuclear growth model and use our results to compute the cumulative probability density for the height of long level-1 paths. We also obtain an estimate for an almost certain maximum height.

Publisher's Note: Plasmon excitations on a single-wall carbon nanotube by external charges: Two-dimensional two-fluid hydrodynamic model [Phys. Rev. B82, 035405 (2010)

Publisher's Note: Plasmon excitations on a single-wall carbon nanotube by external charges: Two-dimensional two-fluid hydrodynamic model [Phys. Rev. B<b>82</b>, 035405 (2010)

ChemInform Abstract: Colloidal Molybdoantimonic Acids as Ion Exchangers.

Colloidal particles with a c.c.p. structure were obtained from mixtures of antimonic and molybdic acids through a polymerization process. These particles were octahedral and their sizes fits the log-normal distributions. The mean size decreases and the polydispersity increases with increasing Mo content in the particles. The stability of the aqueous dispersions was due to the surface charge density of the particles which was enhanced when increasing the Mo content. Ion exchange reactions can occur with the dispersions. Two different routes lead to Ag+ fixation: substitution of core H+ without flocculation of the dispersion or cancellation of external charges with flocculation. Key words: inorganic exchangers, colloids, antimonic acid, molybdic acid.

EEPROM을 이용한 전하센서

The devices based on electrically erasable programmable read-only memory (EEPROM) structure are proposed for the detection of external electric charges. A large size charge contact window (CCW) extended from the floating gate is employed to immobilize external charges, and a control gate with stacked metal-insulator-metal (MIM) capacitor is adapted for a standard single polysilicon CMOS process. When positive voltage is applied to the capacitor of CCW of an n-channel EEPROM, the drain current increases due to the negative shift of its threshold voltage. Also when a pre-charged external capacitor is directly connected to the floating gate metal of CCW, the positive charges of the external capacitor make the drain current increase for n-channel, whereas the negative charges cause it to decrease. For an p-channel, however, the opposite behaviors are observed by the external voltage and charges. With the attachment of external charges to the CCW of EEPROM inverter, the characteristic inverter voltage behavior shifts from the reference curve dependent on external charge polarity. Therefore, we have demonstrated that the EEPROM inverter is capable of detecting external immobilized charges on the floating gate. and these devices are applicable to sensing the pH's or biomolecular reactions.

Plasmon excitations on a single-wall carbon nanotube by external charges: Two-dimensional two-fluid hydrodynamic model

We present a quantization of the hydrodynamic model to describe the excitation of plasmons in a single-walled carbon nanotube by a fast point charge moving near its surface at an arbitrary angle of incidence. Using a two-dimensional electron gas represented by two interacting fluids, which takes into account the different nature of the $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ electrons, we obtain plasmon energies in near-quantitative agreement with experiment. Further, the implemented quantization procedure allows us to study the probability of exciting various plasmon modes, as well as the stopping force and energy loss spectra of the incident particle.

CONFORMAL BLOCKS AS DOTSENKO–FATEEV INTEGRAL DISCRIMINANTS

As anticipated in Ref. 1, elaborated in Refs. 2–4, and explicitly formulated in Ref. 5, the Dotsenko–Fateev integral discriminant coincides with conformal blocks, thus providing an elegant approach to the AGT conjecture, without any reference to an auxiliary subject of Nekrasov functions. Internal dimensions of conformal blocks in this identification are associated with the choice of contours: parameters of the Dijkgraaf–Vafa phase of the corresponding matrix models. In this paper, we provide further evidence in support of this identity for the 6-parametric family of the 4-point spherical conformal blocks, up to level 3 and for arbitrary values of external dimensions and central charges. We also extend this result to multipoint spherical functions and comment on a similar description of the 1-point function on a torus.

Phase transitions in a 3 dimensional lattice loop gas

We investigate, via Monte Carlo simulations, the phase structure of a system of closed, nonintersecting but otherwise non-interacting, loops in 3 Euclidean dimensions. The loops correspond to closed trajectories of massive particles and we find a phase transition as a function of their mass. We identify the order parameter as the average length of the loops at equilibrium. This order parameter exhibits a sharp increase as the mass is decreased through a critical value, the behaviour seems to be a cross-over transition. We believe that the model represents an effective description of the broken-symmetry sector of the 2+1 dimensional abelian Higgs model, in the extreme strong coupling limit. The massive gauge bosons and the neutral scalars are decoupled, and the relevant low-lying excitations correspond to vortices and anti-vortices. The functional integral can be approximated by a sum over simple, closed vortex loop configurations. We present a novel fashion to generate non-intersecting closed loops, starting from a tetrahedral tessellation of three space. The two phases that we find admit the following interpretation: the usual Higgs phase and a novel phase which is heralded by the appearance of effectively infinitely long loops. We compute the expectation value of the Wilson loop operator and that of the Polyakov loop operator. The Wilson loop exhibits perimeter law behaviour in both phases implying that the transition corresponds neither to the restoration of symmetry nor to confinement. The effective interaction between external charges is screened in both phases, however there is a dramatic increase in the polarization cloud in the novel phase as shown by the energy shift introduced by the Wilson loop.

Theory of surface polaritons and image potentials in polar crystals

A quantum-mechanical derivation is presented for the dispersion of surface polaritons on polar materials. We do not assume a local dielectric function exists at the surface of the solid. We introduce quantum operators for the phonons (or excitons) and photons, and couple them in the Coulomb gauge. We derive and solve the equations of motion of these coupled oscillators. We find two solutions. One is the surface polariton that agrees with the classical result of Fuchs and Kliewer. The other is a new surface polariton that exists at the frequency of the bulk longitudinal phonon. We also prove that these are the only two solutions. We also find exactly the polarization in the solid from a static external charge, and show that it is not given by surface polaritons.

Phenomenological stochastic theory of macroscopic charge states on charged surface

A description of the properties of a charged dielectric surface is proposed in terms of the concept of stochastic charge distribution on the surface and the corresponding character of fields that govern the motion of external charges near such a surface. The applicability of the approach is shown on the basis of an analytical expression derived for secondary-electron emission current from the charged dielectric surface (depending on the current of primary electrons that excite the emission, the electric parameters of the dielectric, and its geometric dimensions).

Development of an exhaust gas recirculation strategy for an acetylene-fuelled homogeneous charge compression ignition engine

This paper deals with experimental investigations carried out to develop an exhaust gas recirculation (EGR) strategy for an acetylene-fuelled homogeneous charge compression ignition (HCCI) engine. This study involves an analysis of the external inlet charge heating, the use of a mix of hot EGR and cool EGR to extend the load range, and the performance of the engine in the acetylene HCCI mode. First, experiments are conducted on a single-cylinder engine in the acetylene HCCI mode with external electrical heating at different load conditions, and the best inlet charge temperatures at each load condition are obtained. Second, hot EGR or a mix of hot EGR and cool EGR (i.e. the EGR strategy) is used to reduce or eliminate external charge heating and to extend the upper load limit, or to improve the brake thermal efficiency. In both cases, the engine performance is compared with that of the conventional diesel compression ignition (CI) mode. It is found that with EGR, above 25 per cent of load, the upper load limit at different inlet charge temperatures increases by about 16 28 per cent without any external charge heating. Below 25 per cent of load, the electrical heating at different inlet charge conditions is reduced by about 67–87 per cent. The brake thermal efficiency increases by 5–24 per cent under all the load conditions and it is comparable with that in the conventional CI mode. In the HCCI mode, nitrogen oxide levels are less than 20ppm. Smoke levels are always lower than 0.1 Bosch smoke unit. Hydrocarbon and carbon monoxide emissions are relatively higher than for the conventional CI mode.

Analysis of charge sensitivity and low frequency noise limitation in silicon nanowire sensors

This paper discusses the limit of the sensitivity that can be given to the design of nanowire sensors when the low frequency (LF) noise, due to trapping-detrapping at the nanowire surface, is taken into account. The sensitivity is calculated as the relative conductance variation per unit of external charge density. The LF noise is shown to limit the minimum detectable charge density. Our modeling approach shows how the performance can be optimized by tuning the channel length and the width, and the doping concentration. The implications of these developments are outlined as useful features for the design and the optimization of silicon nanowire sensors.

Nonlinear screening of external charge by doped graphene

We solve a nonlinear integral equation for the electrostatic potential in doped graphene due to an external charge, arising from a Thomas-Fermi (TF) model for screening by graphene's $\pi$ electron bands. In particular, we study the effects of a finite equilibrium charge carrier density in graphene, non-zero temperature, non-zero gap between graphene and a dielectric substrate, as well as the nonlinearity in the band density of states. Effects of the exchange and correlation interactions are also briefly discussed for undoped graphene at zero temperature. Nonlinear results are compared with both the linearized TF model and the dielectric screening model within random phase approximation (RPA). In addition, image potential of the external charge is evaluated from the solution of the nonlinear integral equation and compared to the results of linear models. We have found generally good agreement between the results of the nonlinear TF model and the RPA model in doped graphene, apart from Friedel oscillations in the latter model. However, relatively strong nonlinear effects are found in the TF model to persist even at high doping densities and large distances of the external charge.

Model Systems for the Investigation of the Opsin Shift in Bacteriorhodopsin

Donor-acceptor substituted styrenes and phenylbutadienes with substituents varying in donor and acceptor strength and as reconstituted chromophore-protein complexes were investigated as model compounds for the protonated Schiff base chromophore in bacteriorhodopsin (bR) both experimentally and theoretically. Charge distribution, donor-acceptor strength, and the shift of the absorption energy are correlated. The effect of the external electrostatic field was tested with a compound carrying an additional nonconjugated charge. The concept of overpolarization by the external charge, that is, the reversal of the relative importance of the two main resonance structures in S(0) and S(1), has been emphasized and related to a simple qualitative 2 x 2 interaction model. The variable donor approach is a new way for a better understanding of the Opsin shift in Bacteriorhodopsin.

Water transportation across narrow channel of nanometer dimension

Since the discovery of the carbon nanotube and aquaporin, the study of the transportation of water across nanochannels has become one of the hot subjects. When the radius of a nanochannel is only about one nanometer or a little larger, water confined in those nanoscale channels usually exhibits dynamics different from those in bulk system, such as the wet–dry transition due to the confinement, concerted hydrogen-bond orientations and flipping, concerted motion of water molecules, and strong interactions with external charges. Those dynamics correlate with the unique behavior of the water transportation across the channels, such as the extra-high permeability, excellent on–off gating behavior with response to the external mechanical and electrical signals and noises, enhancement by structure outside the channel, directional transportation driven by charges close to a channel or electric field. In this article, we review some of the recent progress on the study of the water molecules inside those narrow nanochannels.

Mechanism of photocatalytic degradation of dye MG by TiO2-film electrode with cathodic bias potential

Photoelectrocatalytic degradation of malachite green (MG) under visible light irradiation with TiO2-film electrode has been investigated to reveal the mechanism for TiO2 photocatalytic degradation of dyes. The supported TiO2 electrode was prepared in laboratory and detected by scanning electron micros-copy and X-ray diffractometry. We have examined the degradation kinetics, change in degradation rate of MG and photocurrent change with the bias potential, voltage-induced adsorption of dyes, accumu-lation of electrons in the TiO2 electrode, effect of various additives such as benzoquinone (BQ), and formation of active oxygen species by UV-visible spectroscopy, TOC and spin-trap ESR spectrometry. It was found that the dyes could controllably interact with TiO2 surface by external bias and charge of dyes. The cationic dye MG underwent efficient mineralization at negative bias under visible light irradiation, but N-dealkylation process predominated at positive bias under visible light irradiation. At negative bias of −0.4 V vs SCE, the O2·− and dye·+ were formed simultaneously at the electrode/electrolyte interface during degradation of cationic MG. Experimental results imply both the superoxide radical and the dye cationic radical are essential to the mineralization of the dyes under visible-light-induced photocatalytic conditions.