Repulsive Coulomb Force Research Articles

Cluster Agglomeration Induced by Dust-Density Waves in Complex Plasmas

Experimental results showing the agglomeration of large carbonaceous particles in a dusty plasma are reported. Experiments were performed in a capacitively coupled rf argon plasma. Acetylene was injected to produce dust particles. When a sufficient amount of nanoparticles is present in the cathodic sheath, self-excited dust-density waves occur. The latter ones induce the motion of larger clusters, which vertically oscillate with the displacement of wave fronts. In some cases, the relative velocity of large particles was high enough to overcome the Coulomb repulsion forces, and agglomeration can be observed. The mechanisms underlying this process are discussed.

Subbarrier Fusion Reactions and Many-Particle Quantum Tunneling

Low energy heavy-ion fusion reactions are governed by quantum tunneling through the Coulomb barrier formed by a strong cancellation of the repulsive Coulomb force with the attractive nuclear interaction between the colliding nuclei. Extensive experimental as well as theoretical studies have revealed that fusion reactions are strongly influenced by couplings of the relative motion of the colliding nuclei to several nuclear intrinsic motions. Heavy-ion subbarrier fusion reactions thus provide a good opportunity to address a general problem on quantum tunneling in the presence of couplings, which has been a popular subject in the past decades in many branches of physics and chemistry. Here we review theoretical aspects of heavy-ion subbarrier fusion reactions from the view point of quantum tunneling in systems with many degrees of freedom. Particular emphases are put on the coupled-channels approach to fusion reactions, and the barrier distribution representation for multi-channel penetrability. We also discuss an application of the barrier distribution method to elucidation of the mechanism of dissociative adsorption of H$_2$ melecules in surface science.

Autocorrelation Measurement of Fast Electron Pulses Emitted through the Interaction of Femtosecond Laser Pulses with a Solid Target

We report the first direct measurement of the emission duration of laser-accelerated fast electrons from the surface of a solid target irradiated by a high-intensity femtosecond laser pulse. The emission duration is determined by autocorrelation measurement using the Coulomb repulsive forces that act on two equivalent electron pulses. The emission duration depends on the laser pulse duration for laser pulses of 200-690 fs. Numerical modeling of three-dimensional charged particle dynamics indicates that the emission duration of fast electrons is almost equal to the duration of the laser pulse.

Sublinear and superlinear dependences of average charge and energy loss per ion on particle number for MeV/atom linear-chained carbon-cluster ions traversing a carbon foil

The cluster effect in the average charge and the energy loss of swift carbon-cluster ions with kinetic energy of MeV per atom in a linear-chain structure with equal separation of 0.127 nm, passing through carbon foil, was theoretically investigated on the basis of the dielectric function formalism together with the wave-packet model. We assume that inside a foil the dissipated and the conservative forces due to electron polarization are acting on constituent partially stripped ions as well as the repulsive Coulomb forces. In addition, the reductive effect of the cluster average charge is incorporated in a self-consistent manner. On the other hand, outside a foil, only a repulsive Coulomb interaction is assumed to be working. The equation of motion for constituent ions is numerically solved using the molecular dynamics method under the action of the above forces. The calculated results are presented as a function of the incident orientation angle $\ensuremath{\theta}$. By taking the average over $\ensuremath{\theta}$, the energy loss per ion of the carbon cluster displays a sublinear dependence on the number of atoms at lower energies, while at higher energies it shows a superlinear dependence in spite of including the average charge reduction. These two trends in the energy loss are in good agreement with existing experimental results, in which not only the spatial correlation but also the reduction of cluster average charge is found to play a significant role.

Friction Reduction Mechanism of Hydrogen- and Fluorine-Terminated Diamond-Like Carbon Films Investigated by Molecular Dynamics and Quantum Chemical Calculation

The friction reduction mechanisms of diamond-like carbon (DLC) and H- or F-terminated DLC films were investigated using molecular dynamics (MD) and tight-binding quantum chemistry (TBQC) calculations. Atomistic-scale friction dynamics of both DLC and the surface-terminated DLC model in which the unsaturated bonds on their surface were terminated with H or F atoms were investigated by MD. The F-terminated DLC model showed lower friction than that of the H-terminated DLC model because of the stronger repulsive Coulombic force between F atoms at the surfaces. On the other hand, strong van der Waals interaction acting on the interface was observed for the H-terminated DLC model compared to that for the F-terminated DLC models. TBQC calculation indicates a bonding interaction between the surfaces of DLC, while the antibonding interaction was observed for the surface-terminated DLC model. Those interactions would make the difference in the friction properties among the studied models.

Computer simulation of electric field variations due to movements of electric charges

Simulations were carried out for the orbit of electron-induced secondary electrons around a charged microfibril of a sciatic nerve tissue. In order to set the parameters for the simulation, the shape of the microfibril was determined from a transmission electron microscopy image, while the electric potential on the surface of the charged microfibril was evaluated from a reconstructed phase image obtained with electron holography. On the other hand, the passing point and the angle of secondary electrons at the microfibril surface were determined from a reconstructed amplitude image. Eventually, simulation of orbits of secondary electrons was carried out by changing the kinetic energy of the secondary electrons. Under the given conditions, the orbit of secondary electrons with a kinetic energy of 29.6eV fits the observations. If there are thin layers of electrons, the secondary electrons do not reach the surface but they go over it due to the repulsive Coulomb force resulting in successive revolving motion around the charged microfibril. Furthermore, the electric field variation due to the movement of the electric charges resulting from the specimen drift is also discussed briefly comparing it with electron holography data.

Coulomb Dissociation of Nanoparticles Grazing along Organic Surfaces

A Coulomb dissociation model is presented for molecular nanoparticles, e.g. nanoclusters consisting of identical atoms or small molecules. These nanoparticles graze with velocities less than the Bohr velocity (108 cm=s) along an organic surface at atomic distances. The surface molecules contain IR-antennas, which consist of periodically located identical diatomic valence bonds with significant dipole momenta, e.g. hydrocarbon chains like (CH2) n . Here, we analyse the Coulomb interaction of these surface molecules with grazing nanoparticles, which do not contain any IR-antennas, e.g. fullerene molecules. Provided that the grazing velocity is in the range of 105 - 107 cm=s and the minimum distance of the grazing nanoparticles to the surface is approximately 2 Å , the IR-antennas of the interacting surface molecules will collect vibrational energy quanta, the so-called excimols. The number of excimols accumulated during the interaction time of at least 1 ps increases with the number of dipoles in the IR-antennas. Excimol energy can be transmitted back to the grazing nanoparticle by a ps-photon flux, which is estimated intense enough to induce multi-ionization of nanoparticle constituents. The resulting charges inside the nanoparticles cause high Coulomb repulsion forces, which will be able to promptly dissociate them.

Periodical Distribution of Discrete Gold Islands in Electrodeposition

Discrete gold islands formed in electrodeposition have been investigated using an island pair distribution function (IDF) as the analogy of the atomic pair distribution function (PDF) and the Fourier image analysis. An oscillatory plot in the IDF, the two halo and streak patterns in the Fourier-transformed image indicate that the gold islands have a weak periodical structure. The Monte Carlo simulation for the distribution of gold islands with no interplay or the repulsive Coulomb force well explains the origin of the periodical structure.

Reorganization of Langmuir–Blodgett layers of silica nanoparticles induced by the low energy, high fluence ion irradiation

The Langmuir–Blodgett (LB) layers with different selforganization of small, medium, and large size silica nanoparticles, when exposed to the low energy, high fluence ion beam, show reorganization. The reorganization appears as the net effect between the forces caused by charging and by heating of particles, whereas the Coulomb repulsive force between the particles overcomes their adhesion to the Si substrate. The threshold force was estimated for the case of small thermal effects (solid particle on the solid substrate), of higher thermal effects (soft particle on the solid substrate), and of the strong thermal effects (soft particle on the soft substrate), as function of the ion fluence. The increase of fluence causes simultaneous decrease of the Coulomb repulsion and increase of adhesion, so that the mobility of particles decreases affecting the reorganization process. The reorganization depends on the ion fluence, but also on the initial selforganization of the LB layer, being different for the small, medium, and the large size particles. The hydroclusters of small particles become reorganized into “infinite” complex irregular chain-cluster; the small crystal-grains of medium size particles become rhombic and hexagonal clusters, while the 2D hexagonal crystals of large size particles become only slightly disturbed. The reorganization occurs until the increasing ion fluence reaches the reorganization-breakdown-threshold, and overwhelming thermal effects turn the process into particle destruction.

Combined depletion and electrostatic forces in polymer-induced membrane adhesion: A theoretical model

We develop a semi-quantitative analytical theory to describe adhesion between two identical planar charged surfaces embedded in a polymer-containing electrolyte solution. Polymer chains are uncharged and differ from the solvent by their lower dielectric permittivity. The solution mimics physiological fluids: It contains 0.1 M of monovalent ions and a small number of divalent cations that form tight bonds with the headgroups of charged lipids. The components have heterogeneous spatial distributions. The model was derived self-consistently by combining: (a) a Poisson-Boltzmann like equation for the charge densities, (b) a continuum mean-field theory for the polymer profile, (c) a solvation energy forcing the ions toward the polymer-poor regions, and (d) surface interactions of polymers and electrolytes. We validated the theory via extensive coarse-grained Molecular Dynamics (MD) simulations. The results confirm our analytical model and reveal interesting details not detected by the theory. At high surface charges, polymer chains are mainly excluded from the gap region, while the concentration of ions increases. The model shows a strong coupling between osmotic forces, surface potential and salting-out effects of the slightly polar polymer chains. It highlights some of the key differences in the behaviour of monomeric and polymeric mixed solvents and their responses to Coulomb interactions. Our main findings are: (a) the onset of long-ranged ion-induced polymer depletion force that increases with surface charge density and (b) a polymer-modified repulsive Coulomb force that increases with surface charge density. Overall, the system exhibits homeostatic behaviour, resulting in robustness against variations in the amount of charges. Applications and extensions of the model are briefly discussed.

Interplay of strong chemical bonds and the repulsive Coulomb force in the metastable states of triply ionized homonuclear molecules: A theoretical study of N23+and O23+

Interplay of strong chemical bonds and the repulsive Coulomb force in the metastable states of triply ionized homonuclear molecules: A theoretical study of N<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msubsup><mml:mrow /><mml:mn>2</mml:mn><mml:mrow><mml:mn>3</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math>and O<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msubsup><mml:mrow /><mml:mn>2</mml:mn><mml:mrow><mml:mn>3</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math>

Velocity Map Imaging and Theoretical Study of the Coulomb Explosion of CH3I under Intense Femtosecond IR Pulses

The Coulomb explosion of CH(3)I in an intense (10-100 TW cm(-2)), ultrashort (50 fs) and nonresonant (804 nm) laser field has been studied experimentally and justified theoretically. Ion images have been recorded using the velocity map imaging (VMI) technique for different singly and multiply charged ion fragments, CH(3)(p+) (p = 1) and I(q+) (q ≤ 3), arising from different Coulomb explosion channels. The fragment kinetic energy distributions obtained from the measured images for these ion fragments show significantly lower energies than those expected considering only Coulomb repulsion forces. The experimental results have been rationalized in terms of one-dimensional wave packet calculations on ab initio potential energy curves of the different multiply charged species. The calculations reveal the existence of a potential energy barrier due to a bound minimum in the potential energy curve of the CH(3)I(2+) species and a strong stabilization with respect to the pure Coulombic repulsion for the higher charged CH(3)I(n+) (n = 3, 4) species.

Electrical properties of water drops inside the dropwise cluster

The Letter shows that inside a dropwise cluster formed over the heated water surface, water drops are electrically charged. The charge of a separate drop reaches 103 units of an elementary charge. The drops are positioned from each other at the distance of double Debye radius length. It is fixed up that drops levitate over the water surface in consequence of the Stokes force acting from the side of gas–vapor flow rising from water surface. The Stokes force thousand times exceeds the Coulomb drop repulsion force from the water surface.

Vibrational Energy Relaxation in Liquid HCl and DCl via the Linearized Semiclassical Method: Electrostriction versus Quantum Delocalization

The rate constant for vibrational energy relaxation of the H-Cl stretch in liquid HCl (T = 188K, ρ = 19.671 nm(-3)) is calculated within the framework of the Landau-Teller formula. The force-force correlation function is calculated via the recently introduced force-derivative-free linearized semiclassical method [Vázquez et al. J. Phys. Chem. A2010, 114, 5682]. The calculated vibrational energy relaxation rate constant is found to be in excellent agreement with experiment, and the electrostatic force is found to contribute significantly to the high frequency component of the force-force correlation function. In contrast, the corresponding classical vibrational energy relaxation rate constant is found to be 2 orders of magnitude slower than the experimental value, and the classical force-force correlation function is found to be dominated by the Lennard-Jones forces. These observations suggest that quantum delocalization, enhanced by the light mass of hydrogen, amplifies the contribution of repulsive Coulombic forces to the force-force correlation function, thereby making electrostriction an unlikely mechanism for vibrational energy relaxation in the case of hydrogen stretches. This interpretation is reinforced by the results of a similar calculation in the case of the D-Cl stretch in liquid DCl under the same conditions. In this case, the quantum enhancement of the vibrational energy relaxation rate constant is observed to be greatly diminished in comparison to HCl, thereby giving rise to a reversal of the isotope effect in comparison to that predicted by the corresponding classical treatment (i.e., whereas the classical vibrational energy relaxation rate of DCl is faster than that of HCl, the opposite trend is predicted by the linearized semiclassical treatment). It is also shown that the vibrational energy relaxation of DCl is completely dominated by the Lennard-Jones forces within either classical and semiclassical treatments, thereby suggesting that electrostriction is the underlying mechanism in this case.

Ionization energies, Coulomb explosion, fragmentation, geometric, and electronic structures of multicharged boron clusters Bn(n=2–13)

Based on the ab initio quantum chemical methods, we have determined fragmentation channels, ionization energies, and the Coulomb explosion of multicharged boron clusters B${}_{n}$ ($n$ $=$ 2--13), where $n$ is the cluster size. The electron-deficient boron clusters sustain more stability and hardly fragment when they are negatively charged. Stability of boron clusters decreases with increasing ionization. Only by the first ionization the odd-size clusters are more stable than the even-size clusters. Further ionizations cause the repulsive Coulomb force between the constituent atoms to get stronger, and lead first to metastable states, then to the Coulomb explosion of clusters. None of the cationic boron clusters studied remain stable after six times ionization. The critical charge for metastability is estimated as ${Q}_{\mathrm{m}}\ensuremath{\leqslant}\frac{n}{2}$ for even-size clusters, and ${Q}_{\mathrm{m}}\ensuremath{\leqslant}\frac{1}{2}(n\ensuremath{-}1)$ for odd-size clusters. In addition, the critical charge for the Coulomb explosion is found to be ${Q}_{\mathrm{c}}=\frac{n}{2}+1$ for even-size clusters, and ${Q}_{\mathrm{c}}=\frac{1}{2}(n+1)$ for odd-size clusters. Relative stability of clusters with respect to their nearest neighbors is determined from the analysis of their second energy difference data. Several dissociation channels of B${}_{n}^{+}$ and B${}_{13}^{Q}$ isomers with the lowest fragmentation energies are presented. All of the vibrational frequencies are found positive indicating that no transition state is possible for the clusters studied. Reliability of our data is verified with a good agreement with experimental results.

Dissociative double ionization of 1-bromo-2-chloroethane irradiated by an intense femtosecond laser field

The dissociative double ionization and multi-photon ionization of 1-bromo-2-chloroethane (BCE) irradiated by the 800 nm femtosecond laser field have been investigated by dc-slice imaging technology. The charged parent ion ratio [BCE(2+)]/[BCE(+)] was measured, and the corresponding ionization process including non-sequential double ionization and sequential double ionization was analyzed. The sliced images of different photo-dissociated ions were detected, and the corresponding kinetic energy release (KER) distributions were calculated and extracted. Furthermore, the dissociative double ionization channels, attributed to the cleavage of the C-C, C-Br, and C-Cl bonds by the Coulombic repulsive forces, were discussed, and the revised equilibrium distance R(e)*, the energy ratio E(exp)/E(coul), and the value a=√(R(e)*)/(E(exp)/E(coul)) were calculated.

Superlubricity Behavior with Phosphoric Acid–Water Network Induced by Rubbing

In present work, a superlubricity phenomenon of phosphoric acid (H(3)PO(4)) was found under ambient conditions. An ultralow friction coefficient of about 0.004 between glass/Si(3)N(4) and sapphire/sapphire tribopairs was obtained under the lubrication of a phosphoric acid aqueous solution (pH 1.5) at high contact pressure (the maximum pressure can reach about 1.65 GPa) after a running-in period of about 600 s. The experimental results indicate that the superlow friction state was very stable for more than 3 h. In such a state, solidlike films formed on the two sliding surfaces, which are hydrates of phosphoric acid with a hydrogen-bonded network according to the Raman spectrum. The superlubricity mechanism is mainly attributed to the hydrogen bond effect that forms a hydrated water layer with low shearing strength, and the dipole-dipole effects that form an interfacial Coulomb repulsion force also make some contributions to low friction. This work may help us to introduce a new approach to superlubricity and may lead to the wide application of superlubricity in future technological and biomedical areas.

Two-beam interdigital-H-type radio frequency quadrupole linac with direct plasma injection for high intensity heavy ion acceleration

We developed a two-beam interdigital-H-type radio frequency quadrupole (IH-RFQ) linac as a prototype of a multibeam IH-RFQ for high intensity heavy ion acceleration in the low energy region. This linac has two sets of RFQ electrodes within an IH-type resonant frequency cavity that is a power-efficient structure for low energy beam acceleration. The linac can accelerate two beams in parallel in one cavity with a reduction in the coulomb repulsive force (the space charge effect) between the accelerated heavy ion particles. The resonance frequency and the Q factor of the linac were found to be 47 MHz and 5900, respectively. We also developed a two-beam laser ion source with a direct plasma injection scheme as an injection system for the two-beam IH-RFQ linac and built a system to demonstrate the use of the two-beam IH-RFQ linac. Using this linac system, we were able to accelerate carbon ions from 5 to 60 keV/u and generate an output beam current of about 108 mA (2×54 mA/channel). A coherency between the two beams, derived from the imbalance of the beam loading, was observed in the acceleration test with carbon ions.

On the interaction forces between evaporating drops in charged liquid-drop systems

The pairwise hydrodynamic and electrostatic interaction between micrometer-sized water droplets at small distances between them due to their evaporation and the presence of an electric charge on at least one of them is considered. The velocities of the steady-state motion of charged water drops with radii of 1 and 10 µm evaporating in air are calculated. It is shown that at small distances between the drops the joint action of hydrodynamic attraction and polarization interaction, always of attraction type, favor the coalescence of the drops (or drops and solid particles), leading to the displacement of the maximum of the function of drop distribution over size to the region of greater sizes and the gravity sedimentation of large drops. At large distances between the drops, when the short-distance hydrodynamic and polarization attractive forces become smaller than the long-distance Coulomb repulsion forces between likely charged particles, this distance tends to increase. These phenomena give a microphysical explanation to the phenomenon of electrostatic blooming in optically dense smokes and mists.

Fabrication of Monolayer of Polymer/Nanospheres Hybrid at a Water-Air Interface

A new type of polymer-assisted self-assembly of nanospheres at a water-air interface was uncovered. By adding merely 1-3 ppm of polyethylene oxide in the water, the polystyrene nanospheres, applicable to diameters ranging from 100 nm to 1 μm, were found to gradually move closer to each other and eventually form a close-packed structure confirmed from its diffraction pattern. As it turns out, polyethylene oxides are adsorbed onto the surface of polystyrene nanospheres, giving rise to the effective screening of coulomb repulsive force between nanospheres followed by the onset of polymer-bridging effect as demonstrated from the strong suppression of Brownian motion. The resulting monolayer of close-packed polymer/nanospheres hybrid at the water-air interface with area size more than 1 cm(2) are robust and can be transferred to a substrate of any kind without serious breaking due to surface tension tearing. Our finding may provide a further extension to the scope of nanosphere lithography technique.