[en] The flow of plasma and particularly the flow of ions play an important role in dusty plasmas. Here we present some instances in laboratory experiments where the ion flow is essential in establishing dust dynamics in strongly or weakly coupled dust particles. The formation of ion wake potential and its effect on the dynamics of dust crystals, or the ion drag force exerted on micron size dust grains are some of the phenomena observed in the presented experiments.

[en] Dust can be an inconvenient source of impurities in plasma processing reactors and in many cases it can cause damage to the plasma-treated surfaces. A technique for dust expulsion out of the trapping region in plasma is presented here, based on the wind force exerted on dust particles by a pulsed plasma jet. Its applicability is demonstrated by removing floating dust in the sheath of parallel-plate capacitive radio-frequency plasma.

[en] Re-Cr-Ni composite metallic films were prepared using an original plasma deposition method developed at INFLPR, Bucharest, called thermionic vacuum arc (TVA). The method is based on the evaporation of a metal followed by ignition of a plasma in the vapours. These three-component films/alloy films were deposited using three simultaneous TVA plasma sources in the same vacuum chamber. Surface corrosion at temperatures up to 1000 deg. C was found not to take place in these Re-Cr-Ni alloy films as shown by thermogravimetric analysis. The current results demonstrate that the TVA method is a promising candidate tool for the synthesis of multiple compound films. Films of uniform and controlled composition can be simultaneously obtained using this method. Moreover, high melting point metals can be involved in these superalloy films, thus leading to applications in extremely hot conditions such as turbine blades and aircraft parts. (fast track communication)

[en] In order to understand plasma processes and to obtain technological control in thin film deposition, the study of surface-plasma interactions is essential. Apart from the type and flux of the impinging ions/neutral atoms on the surface, the ion energy distribution (IED) is an important parameter in understanding surface modification due to the plasma. In this paper, results of ion energy analysis of the Thermionic Vacuum Arc (TVA) plasma ignited in carbon vapours are presented. An in-house, computer-controlled retarding field analyzer was used for determining experimentally ion energy distributions of the carbon ions arriving at the substrate. The correlation of the carbon IED with the applied arc voltage in the TVA plasma was put in evidence for the first time.

[en] Co-MgO granular films presenting TMR effects were prepared by thermo-ionic vacuum arc (TVA) method with the simultaneous ignition of plasma in Co and MgO vapors, respectively. The processing method is suitable for the simultaneous preparation of films of different relative content of Co in the MgO insulating matrix. Morphologic, structural and magnetic behaviors were analyzed in as prepared and annealed samples. The influence of the Co content on the magnetic properties of the prepared films was analyzed, in correlation with tunneling magneto-resistance effects. The tunneling magneto-resistance effect is maximal for certain Co content. This behavior was interpreted by the contrary effects of decreasing the average size of the magnetic grains, and hence the average inter-grains distance at higher Co relative content, and the enhanced magnetic disorder in very fine grains dispersed in the insulating matrix. This mechanism was suggested by the comportment of as prepared and thermally annealed samples

[en] In the recent years, titanium nitride has been successfully prepared, by reactive magnetron sputtering, electron ion beam sustained Ti arc ion plating or CVD technique. The hardness of the TiN films was reported to be in the range of 18 to 23 GPa. In the present work we report formation of the superhard TiN films on stainless steel substrates having hardness of 24 to 38 GPa, using neon and nitrogen gases and compare the results obtained in other gas combinations. The principal advantage of the neon-nitrogen discharge is the high degree of ionization, which increases the adhesion of the film to the substrate and improves the hardness. Nitrogen gas is highly excited due to charge transfer from metastable neon atoms to nitrogen gas, and emission from N₂⁺ is very intense. Using a nanoindentation technique the deposited films were analyzed and the TiN formation mechanism is discussed on the basis of obtained results. The sharp increase of the N₂⁺ band head at 391.44 nm of the First Negative System (FNS) compared to N₂ band head at 380.49 nm of the Second Positive System (SPS) was observed when in discharge neon gas was present. This increase can be assumed to the Penning reaction between Ne atoms in metastable state and N₂, generating molecular nitrogen ions. (authors)

[en] Femtosecond laser pulses with λ = 800 nm were focused in air at one atmosphere and in deuterium (D) at low pressure. Submicron periodic structures were observed on surfaces made of Be, W and a mixture of Be-W immersed in these gases and placed nearly parallel with the laser beam, at 300 μm from the focal spot. In air, no structures were observed on Be. For the Be-W mixture, the periodic structures were uniform and parallel when formed in D but irregular in air. In this last case the striations were organized into small patches of 1 to 2 μm in size

[en] The Thermionic Vacuum Arc (TVA) deposition technology proves out to be a very convenient method for high quality pure metal thin layer deposition. The advantages of this technology are presented in many published papers. An intense thermoelectronic emission from an externally heated cathode (a tungsten filament) is focused by a Whenelt (also grounded) on the anode. The anode consists of a refractory metal crucible, filled with the material to be deposited (Cu in our case). Bombarding the Cu metal with the accelerated electrons, it melts, then evaporates and on the liquid surface appears a small spot of green light emitting plasma. Increasing the applied voltage, this spot extends first on the liquid surface and then to the cathode and all the interelectrode space is filled with radiating Cu plasma, other gases being not present (ultimate vacuum is of the order of 10^-5 to 10^-6 mbar). The so formed free atoms are flying to the substrate where they form a strongly adherent fine structured layer with the density very near to the bulk metal. Near the substrate, we mounted in this experiment a quartz oscillator gauge that has furnished simultaneously the deposition rate and the layer thickness. We made deposition rate measurements for different electrical powers applied to the discharge obtaining an unexpected dependence. Normally when increasing the discharge electrical power (by increasing the applied voltage) we discovered an initial deposition rate increase to a maximum value. Then, even if the applied power increases the deposition rate decreases. This behavior is presented in a plot where the obtained experimental data on the measured deposition rate versus discharge power for different cathode (filament) heating currents are given. By the discharge voltage variation, or by the filament current change, we can produce the desired layer deposition. The deposition rate at these low current discharge values is very convenient for nanometric deposited structures. (authors)

[en] Low friction coating materials are new classes of advanced materials, which exhibit a reduced coefficient of friction in dry sliding and raised wear resistance. Due to demand of high power and high-speed automotive engines, the engine moving parts have to be improved in tribological characteristics. Three copper-alloy layers with 15 - 20 μm overlay are widely in use for plain bearing fabrication. The overlay that provides seizure and wear resistance and conformability is usually made by electroplating of 10 - 30 μm thick lead alloy including In, Sn and Cu. The lead matrix is soft and has relatively low fatigue resistance under high-pressure conditions. New materials and new deposition procedures are needed to improve tribological and mechanical characteristics of the overlay. The purpose of this study is to produce low friction coatings to be used as overlays for automobile plain bearings and to realize depositions with high rate by using thermal plasma jet. We previously reported the formation of silver/graphite overlays by plasma sputtering and spray coating of alumina mono-layer with a new type of the reactor based on the forced constricted type plasma jet generator. In this paper, we study further the composite coatings of Ag and graphite by using the new-type spray gun (i.e. the plasma electrode type spray gun). A plot is given showing the reduction of the coefficient of friction of the Ag/graphite overlay at about 20% compared to that of the bronze substrate measured using a CSEM ball-on-disc tribometer in dry sliding (air, 50% humidity). (authors)

[en] Full text: Nuclear Fuel Plant Pitesti in direct cooperation with the National Institute for Laser, Plasma and Radiation Physics, Magurele, Bucharest studied and coated Inconel tiles with 7-9 μm of beryllium for nuclear fusion and fission applications. In order to evaluate the erosion rate of the thick Be wall tiles due to the plasma, the concept of 'marker' tile was developed, where an interlayer of Ni was used between a bulk beryllium tile and a beryllium outer layer of a few micrometers. If the outer layer is eroded at the same rate as the bulk, then the erosion rate can be determined by measuring the separation between the interlayer and the final surface, for an eroded layer of a thickness equaling that of the outer. The principles of manufacturing processes using thermal evaporation and plasma ignited in pure metal vapors by Thermionic Vacuum Arc (TVA) method and the properties of the Ni and Be coatings are presented. The prepared beryllium layers were characterized by scanning electron and transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and atomic force microscopy. (authors)