Coulomb Charging Research Articles

Viola-Seaborg relation forα-decay half-lives: Update and microscopic determination of parameters

Considering the emission process of $\ensuremath{\alpha}$ particles in the transition from an isolated quasibound state to a scattering state, a clear expression for the decay width derived in terms of regular Coulomb function, the quasibound state wave function, and the difference of potentials is analyzed. The Schr\odinger equation with the effective potential representing the $\ensuremath{\alpha}$ + nucleus interaction consistent with the potential obtained in the relativistic mean-field approximation is solved exactly for the wave function. Using this exact wave function at resonance and the difference of the above potential from the point charge Coulomb interaction in the expression of decay width stated above, an analytic expression for the decay half-life is derived from the width. By invoking some approximations for different functions in this expression, a closed formula for the logarithm of half-life in terms of characteristic $Q$ value equal to the resonance energy and the mass and charge numbers of the $\ensuremath{\alpha}$ emitter is obtained. The calculated results of half-life obtained by using the analytic expression of half-life or the closed formula for the logarithm of the half-life are shown to explain the corresponding measured data with values ranging from ${10}^{\ensuremath{-}6}$ s to ${10}^{22}$ y in the case of large numbers of $\ensuremath{\alpha}$ emitters that include heavy and superheavy nuclei. The results of the closed formula aligned in a straight line closely explain the rectilinear arrangement of the logarithm values of experimental results for decay half-lives as a function of a quantity that depends on $Q$ values and charge numbers of the emitters. The analytic closed formula with all its terms defined is preferable to the empirical Viola-Seaborg rule of $\ensuremath{\alpha}$-decay rate.

Theory for the Charge Dependence of POPG:POPC Liposome Repulsions in Deionized Water

Previously we analyzed the shear moduli of a series of deionized suspensions of electrostatically interacting 100 nm POPG:POPC liposomes. The liposome charge was varied by altering the POPG content from 0 to 100% in 10 increments. We used the theory of Joanny (1979), which relates the shear modulus of a deionized bcc-ordered suspension of charged particles to an “effective charge” Z∗ on each particle The Joanny treatment employs a Debye-Huckel (DH) screened Coulomb potential with an effective bulk ionic strength equal to the average dissociated [H+]∗ in the sample. The validity of this approximation is questionable. Moreover, static light scattering shows our samples to be a semi-ordered glass (probably due to surface-charge polydispersity) rather than a bcc crystal.Calculated plots of shear modulus vs Z∗ using the Joanny formalism are non-monotonic with pronounced maxima at Z∗ ∼2000. Below this value, direct Coulombic charge repulsions dominate the interaction, and above it, H+ screening dominates.Experimental plots of shear modulus vs. POPG content have similar maxima, at POPG:POPC ∼ 20:80, corresponding to a chemical liposome charge Z ∼10,000. Z∗ and Z differ due to: 1) failure of the DH approximation near the liposome surface where the potentials are large, and 2) partial protonation of PG- headgroups,which reduces Z below its chemical fully-deprotonated value.We refine the Joanny formulation for our experiment by 1) calculating the shear modulus for a glass geometry, and 2) replacing the DH approximations with a counterion-only solution to the Poisson-Boltzmann equation, thereby replacing Z∗ with Z. The calculated value of Z at the shear-modulus maximum, when compared to the experimental Z ∼10,000 at the same maximum, yields the degree of protonation or charge regulation occurring in this strongly interacting system.

Radial dependence of ionization losses of protons of the Earth's radiation belts

Abstract. Coulomb losses and charge exchange of protons are considered in detail. On the basis of modern models of the plasmasphere and the exosphere, the radial dependences of the rates of ionization losses of protons, with μ from 0.3 to 10 keV nT−1, of the Earth's radiation belts near the equatorial plane are calculated for quiet periods. For calculation of Coulomb losses of protons we used data of ISEE-1 satellite (protons with energy from 24 to 2081 keV) on L from 3 to 9, data of Explorer-45 satellite (protons with energy from 78.6 to 872 keV) on L from 3 to 5 and data of CRRES satellite (protons with energy from 1 to 100 MeV) on L ≤ 3 (L is the McIlwain parameter). It is shown that with decreasing L the rate of ionization losses of protons of the radiation belts is reduced; for protons with μ > 1.2 keV nT−1 in a narrow region (ΔL ∼ 0.5) in the district of plasmapause in this dependence may form a local minimum of the rate. We found that the dependence from μ of the boundary on L between Coulomb losses and charge exchange of the trapped protons with hydrogen atoms is well approximated by the function Lb = 4.71μ0.32, where [μ] = keV nT−1. Coulomb losses dominate at L < Lb(μ), and at L > Lb(μ) dominates charge exchange of protons. We found the effect of subtracting the Coulomb losses from the charge exchange of protons of the radiation belts at low μ and L, which can simulate a local source of particles.

Double unification of particles with fields and electricity with gravity in non-empty space of continuous complex energies

Non-empty space reading of Maxwell equations as local energy identities explains why a Coulomb field is carried rigidly by electrons in experiments. The analytical solution of the Poisson equation defines the sharp radial shape of charged elementary densities which are proportional to continuous densities of electric self-energy. Both Coulomb field and radial charge densities are free from energy divergences. Non-empty space of electrically charged mass-energy can be described by complex analytical densities resulting in real values for volume mass integrals and in imaginary values for volume charge integrals. Imaginary electric charges in the Newton gravitational law comply with real Coulomb forces. Unification of forces through complex charges rids them of radiation self-acceleration. Strong gravitational fields repeal probe bodies that might explainthe accelerated expansion of the dense Metagalaxy. Outward and inward spherical waves form the standing wave process within the radial carrier of complex energy.

Transversal magnetoresistance in Weyl semimetals

We explore theoretically the magnetoresistvity of three-dimensional Weyl and Dirac semimetals in transversal magnetic fields within two alternative models of disorder: (i) short-range impurities and (ii) charged (Coulomb) impurities. Impurity scattering is treated using the self-consistent Born approximation. We find that an unusual broadening of Landau levels leads to a variety of regimes of the resistivity scaling in the temperature-magnetic field plane. In particular, the magnetoresitance is non-monotonous for the white-noise disorder model. For $H\to 0$ the magnetoresistance for short-range impurities vanishes in a non-analytic way as $H^{1/3}$. In the limits of strongest magnetic fields $H$, the magnetoresistivity vanishes as $1/H$ for pointlike impurities, while it is linear and positive in the model with Coulomb impurities.

Physics Essay: The Nature of Charge, Principle of Charge Interaction and Coulomb's Law

<p class="1Body">What is “electronic charge”? Why there are two kinds of charges? Why do the same charges repel, and dissimilar charges attract each other? Why does their behavior agree with Coulomb's Law? These are among the most basic questions of physics. Let us assume the existence of a kind of microparticle in the universe, which we can call an electon for our purposes here. Three situations are possible: if an object contains a surplus of electons, it will be positively charged; if a deficit of electons, it will be negatively charged; if an object contains electons equal to its expected value, in the saturated state, it is neutral. The charged objects, containing these electons, have the ability to exchange charged or uncharged microparticles in order to achieve a neutral state. The acting force between two charged objects comes from the exchange of charged and uncharged microparticles. The same charges repel, and dissimilar charges attract each other. The value of force is consistent with Coulomb's Law. The material homogeneous between two charged objects affects the value of the acting force between them, but does not affect the direction.</p>

Spin and valley dynamics of excitons in transition metal dichalcogenide monolayers

Monolayers of transition metal dichalcogenides, namely, molybdenum and tungsten disulfides and diselenides demonstrate unusual optical properties related to the spin-valley locking effect. Particularly, excitation of monolayers by circularly polarized light selectively creates electron-hole pairs or excitons in non-equivalent valleys in momentum space, depending on the light helicity. This allows studying the inter-valley dynamics of charge carriers and Coulomb complexes by means of optical spectroscopy. Here we present a concise review of the neutral exciton fine structure and its spin and valley dynamics in monolayers of transition metal dichalcogenides. It is demonstrated that the long-range exchange interaction between an electron and a hole in the exciton is an efficient mechanism for rapid mixing between bright excitons made of electron-hole pairs in different valleys. We discuss the physical origin of the long-range exchange interaction and outline its derivation in both the electrodynamical and $\mathbf k \cdot \mathbf p$ approaches. We further present a model of bright exciton spin dynamics driven by an interplay between the long-range exchange interaction and scattering. Finally, we discuss the application of the model to describe recent experimental data obtained by time-resolved photoluminescence and Kerr rotation techniques.

Electron transport within transparent assemblies of tin-doped indium oxide colloidal nanocrystals

Stripe-like compact assemblies of tin-doped indium oxide (ITO) colloidal nanocrystals (NCs) are fabricated by stop-and-go convective self-assembly (CSA). Systematic evaluation of the electron transport mechanisms in these systems is carried out by varying the length of carboxylate ligands protecting the NCs: butanoate (C4), octanoate (C8) and oleate (C18). The interparticle edge-to-edge distance L0, along with a number of carbon atoms in the alkyl chain of the coating ligand, are deduced from small-angle x-ray scattering (SAXS) measurements and exhibit a linear relationship with a slope of 0.11 nm per carbon pair unit. Temperature-dependent resistance characteristics are analyzed using several electron transport models: Efros–Shklovskii variable range hopping (ES-VRH), inelastic cotunneling (IC), regular island array and percolation. The analysis indicated that the first two models (ES-VRH and IC) fail to explain the observed behavior, and that only simple activated transport takes place in these systems under the experimental conditions studied (T = 300 K to 77 K). Related transport parameters were then extracted using the regular island array and percolation models. The effective tunneling decay constant βeff of the ligands and the Coulomb charging energy EC are found to be around 5.5 nm−1 and 25 meV, respectively, irrespective of ligand lengths. The theoretical tunneling decay constant β calculated using the percolation model is in the range 9 nm−1. Electromechanical tests on the ITO nanoparticle assemblies indicate that their sensitivities are as high as ∼30 and remain the same regardless of ligand lengths, which is in agreement with the constant effective βeff extracted from regular island array and percolation models.

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities.

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene's charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene's electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene's electronic properties. Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge and/or molecular states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies. These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

Charge and Nuclear Dynamics Induced by Deep Inner-Shell Multiphoton Ionization of CH3I Molecules by Intense X-ray Free-Electron Laser Pulses.

In recent years, free-electron lasers operating in the true X-ray regime have opened up access to the femtosecond-scale dynamics induced by deep inner-shell ionization. We have investigated charge creation and transfer dynamics in the context of molecular Coulomb explosion of a single molecule, exposed to sequential deep inner-shell ionization within an ultrashort (10 fs) X-ray pulse. The target molecule was CH3I, methane sensitized to X-rays by halogenization with a heavy element, iodine. Time-of-flight ion spectroscopy and coincident ion analysis was employed to investigate, via the properties of the atomic fragments, single-molecule charge states of up to +22. Experimental findings have been compared with a parametric model of simultaneous Coulomb explosion and charge transfer in the molecule. The study demonstrates that including realistic charge dynamics is imperative when molecular Coulomb explosion experiments using short-pulse facilities are performed.

Coulomb blockade and charge transfer in InSb micrograins

Current-voltage characteristics and density-of-state spectra of indium antimonide (InSb) nano- and micrograins with conductivities close to intrinsic and electronic values have been studied using a tunneling microscope in the field-electron emission regime. Interpretation of the obtained data leads to the conclusion that the effect of current limitation, analogous to the Coulomb blockade in quantum dots, takes place in InSb micrograins. The results are explained in the framework of a model of multielectron recharge of the nanocapacitor formed in a near-surface layer of a micrograin where the charge is localized due to the Coulomb interaction between “ultralight” electrons in the bulk and on the uneven surface of the micrograin.

Coulomb screening in graphene with topological defects

We analyze the screening of an external Coulomb charge in gapless graphene cone, which is taken as a prototype of a topological defect. In the subcritical regime, the induced charge is calculated using both the Green’s function and the Friedel sum rule. The dependence of the polarization charge on the Coulomb strength obtained from the Green’s function clearly shows the effect of the conical defect and indicates that the critical charge itself depends on the sample topology. Similar analysis using the Friedel sum rule indicates that the two results agree for low values of the Coulomb charge but differ for the higher strengths, especially in the presence of the conical defect. For a given subcritical charge, the transport cross-section has a higher value in the presence of the conical defect. In the supercritical regime we show that the coefficient of the power law tail of polarization charge density can be expressed as a summation of functions which vary log periodically with the distance from the Coulomb impurity. The period of variation depends on the conical defect. In the presence of the conical defect, the Fano resonances begin to appear in the transport cross-section for a lower value of the Coulomb charge. For both sub and supercritical regime we derive the dependence of LDOS on the conical defect. The effects of generalized boundary condition on the physical observables are also discussed.

Giant volume magnetostriction in the Y2Fe17 single crystal at room temperature

An investigation of the Y2Fe17 compound belonging to the class of intermetallic alloys of rare-earth and 3d-transition metals is presented. The magnetization, magnetostriction, and thermal expansion of the Y2Fe17 single crystal were studied. The forced magnetostriction and magnetostriction constants were investigated in the temperature range of the magnetic ordering close to the room temperature. The giant field induced volume magnetostriction was discovered in the room temperature region in the magnetic field up to 1.2 T. The contributions of both anisotropic single-ion and isotropic pair exchange interactions to the volume magnetostriction and magnetostriction constants were determined. The experimental results were interpreted within the framework of the Standard Theory of Magnetostriction and the Landau thermodynamic theory. It was found out that the giant values of the volume magnetostriction were caused by the strong dependence of the 3d-electron Coulomb charge repulsion on the deformations and width of the 3d-electron energy band.

Memristive operation mode of a site-controlled quantum dot floating gate transistor

We have realized a floating gate transistor based on a GaAs/AlGaAs heterostructure with site-controlled InAs quantum dots. By short-circuiting the source contact with the lateral gates and performing closed voltage sweep cycles, we observe a memristive operation mode with pinched hysteresis loops and two clearly distinguishable conductive states. The conductance depends on the quantum dot charge which can be altered in a controllable manner by the voltage value and time interval spent in the charging region. The quantum dot memristor has the potential to realize artificial synapses in a state-of-the-art opto-electronic semiconductor platform by charge localization and Coulomb coupling.

Electrochemical Modulation of the Fluorescence of Cyanine Dye Cy5

AbstractOrganic fluorescent dyes are widely used in single molecule localization microscopy, where their performances are determined by the photophysical properties. Herein, we utilized a sensitive method to modulate the fluorescence of organic dyes by external potentials using a combination of electrochemical cell and super‐resolution fluorescent microscopy. Cy5 (cyanine dye) was chosen as a model molecule considering its wide application and commercial availability. We applied different potentials on the Au electrode to change the Coulombic charge microenvironment of Cy5. When the electrode potential was adjusted negatively, Cy5 displayed a better photostability. This method is proved effective in adjusting the fluorescence of organic dyes.

Ejection and Motion Behaviors Simulation for Multi-Jet Electrospinning

Multi-jet ejection is the key factor to promote the industrial application of electrospinning technology. Simulation model based on Maxwell theory was built up to investigate the ejection and motion behaviors of multi charged jets. The charge Coulomb repulsive force among adjacent jet was introduced into the simulation model, which enhanced the instability motion and promoted the stretching process of charged jets. The stretching ratio of charged jet increased with the increasing of injection distance, applied voltage, distance between spinneret and collector. But stretching ratio of charged jet decreased with the increasing of distance between charged jets. Stretching ratio in multi-jet electrospinning was larger than that in single-jet electrospinning. The maximal stretching ratio of charged jet was larger than 9000 in the nine jets electrospinning mode. This work provided a good method to investigate the controlling technology of multi-jet electrospinning.

Conductance of molecularly linked gold nanoparticle films across an insulator-to-metal transition: From hopping to strong Coulomb electron-electron interactions and correlations

We study the influence of Coulomb effects on conductance $(g)$ of 1,4-butanedithiol-linked gold nanoparticle (NP) films near a percolation insulator-to-metal transition. On the insulating side, $g\ensuremath{\sim}\mathrm{exp}[\ensuremath{-}{({T}_{\ensuremath{\circ}}/T)}^{1/2}]$, where $T$ is absolute temperature, a behavior predicted by Efros-Shklovskii's theory for charges optimizing pathways that accommodate Coulomb charging barriers. On the metallic side below $\ensuremath{\sim}20$ K, $g$ varies linearly with ${T}^{1/2}$. Such a correction to $g(T=0)$ is predicted by Altshuler-Aronov's theory for Fermi liquid metals when disorder mediates electron-electron $(e\text{\ensuremath{-}}e)$ Coulomb interactions. Remarkably, in the present system, the ${T}^{1/2}$ component of $g$ is significant compared to $g(T=0)$, and fitting to Boltzmann's transport theory yields elastic scattering lengths that are anomalously small---much smaller than the distance between atoms (Ioffe-Regel limit required for metals). Previous studies of materials such as fullerites, layered organic salts, and transition metal compounds have also reported such anomalously small scattering lengths and large ${T}^{1/2}$ components and attributed them to strong Coulomb mediated $e\text{\ensuremath{-}}e$ correlations, which we believe is likely the case in the present system as well. This study highlights a potential opportunity to use molecularly linked nanoparticle films as a platform to study strongly correlated electrons in a controlled fashion.

Coulomb impurity effect on electrically induced Dirac bound states in graphene

Using the massless Dirac–Weyl model for monolayer graphene sheet, we study the low-lying spectra of a single Dirac electron system bound to an on-center positively charged Coulomb impurity, under both electrostatic potential and magnetic field. Numerical results obtained from diagonalization show that, the increase of the electrostatic potential causes the low-lying states to evolve from one Landau-type plateau to the higher ones, and the whole spectra exhibit similar features with slight shifts in eigenenergies when the on-center impurity is considered. Electrostatic-potential dependent optical spectra with their corresponding absorption coefficients as functions of incident photon energies for transitions between low-lying states are presented.

Tuning the pseudo-Zeeman splitting in graphene cones by magnetic field

The effect of a homogeneous magnetic field on the energy spectrum of gapped graphene cones with long range charged Coulomb impurity is investigated within the framework of the perturbation theory. It is found that, besides lifting the degeneracy of angular momentum channels due to topological defects, the size of the corresponding splitting is enhanced by the introduction of a homogeneous magnetic field. This indicates that the level splitting may be controlled by the strength of a magnetic field in topological cones. Therefore, our results show that the magnetic field may be used as a tool to tune the pseudo-Zeeman splitting in graphene cones.

Surface composition and interactions of mobile charges with immobilized molecules on polycrystalline silicon nanowires

The polycrystalline silicon nanowire field-effect transistor (poly-SiNW FET) is one of the most sensitive sensors used in real-time and label-free biosensing applications. Its low power requirement, mass production potential, and integrability with electronic components make it a highly attractive device in the rapidly growing diagnostic research field. From the viewpoint of device physics, the charges in the vicinity of a nanowire (NW) surface modulate the electrical characteristics of the NW device. The charges can originate from surface molecules or an ionic solution, and their role in NW biosensing systems remains to be clarified. Determining their role is crucial for understanding the physical interactions of charges in a biosensing event and for the realization of NW-based biosensors. Therefore, using poly-SiNW FET, we investigated the interactions of the immobilized molecules on the NW surface with the mobile charges in solutions. We also investigated the interactions between the mobile charged polymers and the immobilized molecules on the NW surface, and we observed the effect of charge neutrality, originating from Coulomb charge–charge interactions, on the NW conductance. Finally, the isoelectric points between native and sulfated PSGL-1 peptides on the NW surface were identified. This study provides a physical understanding of the charge–charge interaction of mobile charges with immobilized charged molecules on a nanoscale surface and presents new opportunities for using charge-based detection in biological and chemical sensing applications.