A.O. Serov

Coagulation of dust grains in the plasma of an RF discharge in argon

Results are presented from experimental studies of coagulation of dust grains of different sizes injected into a low-temperature plasma of an RF discharge in argon. A theoretical model describing the formation of dust clusters in a low-temperature plasma is developed and applied to interpret the results of experiments on the coagulation of dust grains having large negative charges. The grain size at which coagulation under the given plasma conditions is possible is estimated using the developed theory. The theoretical results are compared with the experimental data.

Non-self-sustained discharge in nitrogen with a condensed dispersed phase

A non-self-sustained discharge in nitrogen with a condensed dispersed phase is studied experimentally for the first time under atmospheric pressure at room temperature. It is shown that macroparticles strongly affect the current-voltage characteristics as well as the stability of the discharge process. A numerical simulation of dust particle charging in nitrogen is carried out at room temperature and cryogenic temperatures under continuous medium conditions. It is shown that a considerable charge is accumulated at macroparticles in the nitrogen beam plasma. As the gas temperature decreases, the charge of macroparticles in nitrogen increases, while in argon their charge decreases. For this reason, the Coulomb interaction parameter for dust particles in nitrogen increases strongly upon a transition from room to cryogenic temperature, while in argon this parameter decreases. It is also shown that the characteristic time of dust particle charging is shorter than 1 μs for a beam current density of 90 μA/cm2, while the neutralization of the charge takes milliseconds. Possible mechanisms of the influence of the dust component on the characteristics of non-self-sustained discharge are considered.

Effect of a dust component on the rates of elementary processes in low-temperature plasmas

Elementary processes in dusty, beam-driven plasma discharges are studied experimentally and theoretically for the first time. A theoretical model is constructed for a beam-driven plasma containing macroscopic particles. The effect of macroscopic particles on the electron energy distribution function is estimated assuming a Coulomb field for the particles. The resulting rate of electron-ion recombination on the macroscopic particles is compared with the electron loss constant calculated from the electron energy distribution function with an electron absorption constant in the orbital-motion approximation. This approximation, which is valid in the collisionless case, is found to work satisfactorily beyond its range of applicability. The distributions of the charged particles and electric fields created by macroscopic particles in a helium plasma are determined. The experimental data demonstrate the importance of secondary emission by high-energy electrons.

Synthesis and characterization of macrocomposites based on nickel-coated quasi-crystalline Al-Cu-Fe powder

Disperse composite materials consisting of quasi-crystalline Al-Cu-Fe particles covered by nickel nanolayers have been obtained using a dusty plasma trap coating technology. These powders were processed into macrocomposites by cold pressing with subsequent sintering in hydrogen. The macrocomposites were studied by the electron microscopy, electron-probe microanalysis, and X-ray diffraction techniques. It is established that sintering at ∼750°C yields a high-strength macrocomposite that is not fractured under tribological testing conditions. Despite the fact the samples sintered at 750°C contain about 50 wt % of β phase, their friction coefficient is close to that of Al-Cu-Fe quasi-crystals.

Orbital Motion of Dust Particles in an rf Magnetron Discharge. Ion Drag Force or Neutral Atom Wind Force

Microparticles with sizes up to 130 μm have been confined and the velocity and diameter of particles in a plasma trap of an rf magnetron discharge with an arc magnetic field have been simultaneously measured. The motion of the gas induced by electron and ion cyclotron currents has been numerically simulated using the Navier-Stokes equation. The experimental and numerical results confirm the mechanism of the orbital motion of dust particles in the magnetron discharge plasma that is associated with the orbital motion of the neutral gas accelerated by electron and ion drift flows in crossed electric and magnetic fields.

Spectroscopy, actinometry and simulation of a DC discharge in CO/H2 gas mixtures

We have studied the gas heating and dissociation processes in the direct current (DC) discharge CVD reactor with the closed gas circuit where the working gas mixture is used repeatedly by circulation through the discharge area. Experiments were carried out in mixtures of CO with hydrogen at overall gas pressure of 20 kPa and gas flow up to 40 m/s. The discharge plasma was analyzed by actinometry and optical emission spectroscopy. Twodimensional model of DC discharge CVD reactor has been used to study reactive gas flow, electrodynamics and surface processes. The 2D calculations show that the most important radical production reactions are the CO and H2 dissociation due to electron impact. Calculated results are compared with the experimental ones.

Effect of selective coagulation of the like charged particles in a dusty plasma trap

The phenomenon of selective coagulation of the like charged disperse particles in dusty plasma was theoretically predicted and experimentally revealed. The effect lies in sharp acceleration of coagulation processes after injection into a plasma trap particles which sizes appreciably exceed Debye length and the average size of the particles initially forming a dusty plasma cloud. The absorption process of the fine fraction by the larger particles takes place.

Application of dusty plasma for production of disperse composite materials

Objectives and achievements of the production of disperse composite materials (DCMs) which consist of particles with a metal coating are represented. The prospects of the DCM production by the dusty plasma method based on confining a cloud of micron-sized particles in a discharge plasma and on magnetron sputtering are shown. The method was tested in the preparation of catalyst materials, a superhard diamond polycrystalline material, and a polyquasicrystalline material with a low friction coefficient. The results of investigations of the structure and properties of powdered and sintered DCMs are presented.

Equirate magnetron sputtering of mosaic copper-graphite targets

Based on experimental data on sputtering of copper-graphite cathodes, we propose a mechanism of equirate sputtering of elements of mosaic targets prepared from materials the sputtering yields of which differ by almost an order of magnitude. The mechanism takes into account the occurrence of a height discontinuity between the mosaic elements at the initial stage of sputtering, the redistribution of ion fluxes between the elements, and the effects related to the mass transfer in plasma and the implantation of sputtered atoms into the mosaic elements of the different variety.

Dusty Plasma Technology of DCM with Nanostructure Surface Layer Production

The technique of disperse composite material (DCM) production was developed. The technique based on using special dusty plasma trap in RF plasma, in which fine particles levitate and are exposed by the atomic beam. The two types of covering were obtained: “cauliflower” or smooth, depending on process condition.