Polyelectrolyte Adsorption

The problem of charged polymer chains (polyelectrolytes) as they adsorb on a planar surface is addressed theoretically. We review the basic mechanisms and theory underlying polyelectrolyte adsorption on a single surface in two situations: adsorption of a single charged chain, and adsorption from a bulk solution in $\theta$ solvent conditions. The behavior of flexible and semi-rigid chains is discussed separately and is expressed as function of the polymer and surface charges, ionic strength of the solution and polymer bulk concentration. We mainly review mean-field results and briefly comment about fluctuation effects. The phenomenon of polyelectrolyte adsorption on a planar surface as presented here is of relevance to the stabilization of colloidal suspensions. In this respect we also mention calculations of the inter-plate force between two planar surfaces in presence of polyelectrolyte. Finally, we comment on the problem of charge overcompensation and its implication to multi-layers formation of alternating positive and negative polyelectrolytes on planar surfaces and colloidal particles.Comment: 11 pages, 4 PS figures (Latex/RevTex), submitted to C.R. Acad. Sci (Paris

Etching of random solids: hardening dynamics and self-organized fractality

When a finite volume of an etching solution comes in contact with a disordered solid, a complex dynamics of the solid-solution interface develops. Since only the weak parts are corroded, the solid surface hardens progressively. If the etchant is consumed in the chemical reaction, the corrosion dynamics slows down and stops spontaneously leaving a fractal solid surface, which reveals the latent percolation criticality hidden in any random system. Here we introduce and study, both analytically and numerically, a simple model for this phenomenon. In this way we obtain a detailed description of the process in terms of percolation theory. In particular we explain the mechanism of hardening of the surface and connect it to Gradient Percolation.Comment: Latex, aipproc, 6 pages, 3 figures, Proceedings of 6th Granada Seminar on Computational Physic

Investigation of a steady-state cylindrical magnetron discharge for plasma immersion treatment

Ion current distribution in a system with crossed magnetic and electrical fields for plasma immersion ion implantation has been investigated. It is found that the ion current to a target has a nonmonotonic behavior with bias voltage when a magnetic field is applied. For instance, the current density has a maximum of about 150 A/m2 at bias voltage of about 1 kV in the case of a magnetic field parallel to the target of about 0.035 T. These results are explained in terms of ionization by magnetized electrons in the E×BE×B system. Our findings suggest that the system with crossed fields can be used for intense plasma immersed processing. © 2003 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71124/2/JAPIAU-94-3-1408-1.pd

Suppression of current fluctuations in a crossed E×BE×B field system for low-voltage plasma immersion treatment

Plasma transport in a hybrid dc vacuum arc plasma source for ion deposition and plasma immersion treatment is considered. It is found that external crossed electric and magnetic fields near the substrate can significantly reduce the relative amplitude of ion current fluctuations fI¯f at the substrate surface. In particular, fI¯f decreases with the applied magnetic field when the bias voltage exceeds 300 V300V, thus allowing one to reduce the deviations from the rated process parameters. This phenomenon can be attributed to an interaction between the metal-plasma jet from the arc source and the discharge plasma in the crossed fields.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87466/2/013301_1.pd

Effects of segmented electrode in Hall current plasma thrusters

Segmented electrodes placed along a ceramic channel in a Hall thruster are shown to influence significantly the plasma potential distribution. Both the radial potential and the axial acceleration region are sensitive to the location of the segmented electrodes. The measured and theoretical potential profiles appear to be affected in detail by the electrode material (graphite) having lower secondary electron emission than the ceramic channel walls. The measured plasma potential profile is shown as well to correlate with the observed and desirable narrowing of the plasma plume emanating from the thruster. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70788/2/JAPIAU-92-9-4906-1.pd

PERIODICAL PLASMA STRUCTURES CONTROLLED BY EXTERNAL MAGNETIC FIELD

The characteristics of 2D periodical structures in propulsion type magnetized plasma are studied in kinetic PIC MCC simulations.With increasing an angle of magnetic field the ridges (maxima) of electron and ion densities form in the plasma volume in cylindrical chamber. These ridges are shifted relative each other that results in the formation of 2D double-layers structure. Depending on Larmor radius and Debye length up to nineteen potential steps appear across the oblique magnetic field40-4

Characterization of carbon nanotubes produced by arc discharge: Effect of the background pressure

Single walled carbon nanotubes (SWNT) produced by the anodic arc discharge over a range of constant background pressures of helium (100–1000 Torr) were examined under a high-resolution transmission electron microscope, and a Raman spectrometer. It was found that the average SWNT diameter is about 2 nm and fairly independent of the background pressure. Analysis of the relative purity of SWNTs samples suggests that highest SWNT relative concentration can be obtained at background pressure of about 200–300 Torr. Measured anode ablation rate increases linearly with background pressure. The model of the anodic arc discharge was developed. It was found that the predicted anode ablation rate agrees well with experiment suggesting that electron temperature in the anodic arc is about 0.5 eV. © 2004 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69876/2/JAPIAU-95-5-2749-1.pd

Particle Simulation of Plume Flows from an Anode-Layer Hall Thruster

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76848/1/AIAA-28384-370.pd

On the conditions of carbon nanotube growth in the arc discharge

The conditions for single wall carbon nanotube formation in the arc discharge method of nanotube production are described. Carbon nanotube seed formation and charging in the interelectrode gap are found to be very important effects that may alter carbon nanotube formation on the cathode surface. The model predicts that the long carbon nanotubes formed in the relatively dense plasma region can be deposited on the cathode surface. The nanotubes in the cathode deposit are primarily oriented in the cathode surface plane and not along the electric field. This prediction is qualitatively confirmed by an SEM analysis of the cathode deposit.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49221/2/nano4_11_034.pd