Tribological coatings with a chromium-based composite structure obtained by reactive deposition in vacuum

The peculiarities inherent to the chemical and phase compositions, microstructure, and tribological behavior of Cr-O, Cr-C-O, Cr-C-H and Cr-C-N-H coatings, obtained by plasma-assisted physical vapor deposition in a chemically active gas atmospheres (activated reactive deposition and magnetron sputtering methods), have been studied. It has been demonstrated that all coatings have a micro- and/or nanocomposite structure comprising nanoscale chromium-based domains, as well as chromium oxide, carbide and nitride phases with different stoichiometries. The tribological properties of the coatings investigated in a broad temperature range under unlubricated friction contact conditions, as well as their correlation with microstructures and reactive-deposition technology parameters, are discussed.     

Interlayer interaction in three-layer films obtained by chemical deposition

The results from experimental investigations on the dependences of the displacement field of hysteresis loop H _E and the saturation field of the polar Kerr effect H _S on the thickness of nonmagnetic interlayers in three-layer films obtained by chemical deposition are presented. Possible mechanisms responsible for oscillating variations in H _S at interlayer thicknesses are presented.     

Observation of tungsten particles in vacuum arcs by laser inducedfluorescence

We have clarified the relation between the decay of tungsten ion density in the vicinity of current zero and vacuum arc mode in high current period by using a laser induced fluorescence method in tungsten vacuum arcs of 60 Hz sinusoidal current with the peak value of 3.3, 6.7, and 9.8 kA. In the case of 6.7 kA, the arc mode was the anode spot mode. Because of the generation of the anode spot, the tungsten ion density near the anode was higher than near the cathode and the density near the anode was about ten times as high as the case of 3.3 kA which was the diffuse mode. In the case of 9.8 kA, which was the intense arc mode, the density near the anode was not significantly different from the case of 6.7 kA. The density near the cathode was higher than near the anode and tungsten ions were observed till about 30 μs after current zero while they disappeared at current zero in the other cases     

Photoelectric properties of nInSb-nPbTe-nCdTe isotype structure prepared by vacuum pulsed-laser deposition technique

With use of the vacuum pulsed-laser deposition technique an isotype nInSb-nPbTe-nCdTe structure is fabricated. Spectral dependence of photoresponse of the obtained structure is studied at the temperature 120 K. In the curve of spectral dependence a change in the sign of photoresponse is observed for both zero bias and external voltage. Qualitative explanation of this phenomenon is given.     

Spectral studies of the structure of copper phthalocyanin-polyimide composites produced by vacuum deposition

Visible and IR absorption spectra are studied for copper phthalocyanin (CuPc)-polyyimide composites. The composite films are obtained by vacuum codeposition of CuPc, pyromellitedianhydride, and diaminodiphenyloxide followed by temperature-induced imidization. On the basis of IR spectra it is shown that in the prepared composites imidization occurs over the whole CuPc concentration range (10–90%). From the visible spectra it is found that CuPc is deposited mainly in the form of a-microcrystals, which are destroyed during imidization to produce noncrystalline molecular aggregates. Subsequent heat treatment (320–350°C) gives rise to CuPc β-microscrystals. A. N. Sevchenko Research Institute of Applied Physical Problems, 7, Kurchatov St., 220064, Minsk, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 502–506, July–August, 1997.     

The origin of current constriction in vacuum arcs

The current constriction in a diffuse vacuum arc is shown theoretically and experimentally to be caused by a pressure source, to which the charged particles and neutral particles contribute.     

Experimental observation of high-voltage, low-current vacuum arcs

A poorly explored type of discharge has been investigated in high vacuum (10^-7 to 10^-6 torr), with a DC high voltage across 0.2- to 0.8-mm gaps. The discharge has been found to be quite different from other widely known types of vacuum and gas discharges by the combination of its voltage-current characteristics (hyperbola-type), source and carriers of current (mostly electrons), and spatial potential distribution (a considerable electric field across the gap and a steep potential fall near the cathode)     

Motion of high-current vacuum arcs on spiral-type contacts

Motion of vacuum arcs on spiral-type contacts is not only controlled by self-induced magnetic fields, but also by heating phenomena. An expression is derived which permits the calculation of the speed of the arc from a computation of the time needed to heat the surface up to boiling temperature. The heat flux density of the constricted arc at the anode is required as input for the calculation. Good coincidence is achieved with experimental data. The speed of the arc varies from 5 to 400 m/s, depending on experimental conditions     

Mechanism of ion flow generation in vacuum arcs

The ecton model of the cathode spot is used to analyze the main parameters of ion flow in vacuum arcs (ion erosion, mean charge, and velocity). It is shown that the arc plasma is formed as a result of microexplosions at the cathode surface, induced by the Joule heating by the high-density current of explosive electron emission. Ionization processes are localized in a narrow region of the order of a micrometer near the cathode and the ionization composition of the plasma subsequently remains unchanged. Under the action of the electron pressure gradient, ions acquire directional velocities of the order of 10⁶ cm/s even over small distances of the order of several micrometers.     

Experimental investigations of the currents collected by metalshields in high-current vacuum arcs

This paper presents experimental results of currents collected on the three-element condensation shield connected to the cathode potential in high-current vacuum arcs. The arc current had 900 Hz, 150 Hz, or 50 Hz half-cycle sinusoidal shapes and was conducted between the CuCr40 contacts with a diameter of 50 mm (cathode) and 30 mm (anode) spaced 10 mm apart. Most of the measurements were made for the current of 900 Hz with peak values up to 9 kA. Arc voltage, floating shield potential, and distribution of shield currents were measured. It was found that the current collected by the shield and also the arc voltage and floating shield potential are greater for higher frequency currents, and that they are affected by the arc mode. Considerable shield current is observed during a high-amplitude (HA) oscillation sequence of arc voltage while its mean value is increased. For 900-Hz arcs at the 9-kA peak value (I_am), the ratio of shield current (i_s) to an instantaneous value of arc current (i_a) reaches even 40% near I_am value. In the initial half-cycle period (before the initiation of high-voltage oscillation), the ratio of i_s/i_a increases with i_a and current frequency. A close relationship was found between arc voltage and current distribution on a three-element shield     

On the theory of TE-polarized waves guided by a nonlinear three-layer structure

TE-polarized electromagnetic waves guided by a three-layer structure consisting of a film surrounded by semi-infinite media (all media are characterized by a Kerrlike dielectric function) are investigated by expressing the solution of the field equations in terms of Weierstrass' elliptic functions. Evaluation leads to a universal dispersion relation and its solutions and a universal expression for the power flow. Numerical results are presented for the effective wave number as a function of the intensity of the electric field at the lower surface of the nonlinear film, for various profiles of the field intensity, and for the power flow as a function of the effective wave number.     

Cathode processes in free burning and stabilized by axial magneticfield vacuum arcs

Collective behavior of the cathode spots (CS) has been investigated in free burning and stabilized by axial magnetic field (AMF) vacuum arcs. Experiments carried out proved previously discovered phenomenon of CS group formation in free burning arc to be a general phenomenon for a short high-current vacuum arc. The dependency of CS group size in the developed are on arc current for different contact materials has been analyzed. Application of AMF with even relatively low intensity strongly affects on cathode processes. In short arcs, it hinders formation of the CS group and consequently reduces thermal stress applied to the electrodes. It has been revealed that high current vacuum arc under the action of AMF can exist only at current densities exceeding certain minimal value that depends on AMF intensity, contact gap, and does not depend on current itself. The dependency of this minimal (or normal) current density on AMF intensity has been studied for short and long vacuum arcs. A qualitative model of the cathode spot dynamics has also been proposed     

Film deposition by laser-induced vacuum arc evaporation

Recent results of a study of the deposition process and the technological development of laser-arc are presented. Studies of the influence of arc current on film deposition were carried out for Ti, TiC, and C. On the basis of these results, specific multilayered structures have been prepared. As an example, a Ti/TiC multilayer system with 25-nm single layers is described. Results of structural and chemical analysis by means of Auger electron spectroscopy (AES) are presented. They show that diamond-like carbon film with a refractive index in the range of between 2.05 and 2.5 can be deposited effectively     

Experimental observations of steady anodic vacuum arcs withthermionic cathodes

Stationary plasma discharges have been investigated in a high vacuum ambient (background gas pressure <10^-2 Pa), with an externally heated cathode and a consumable hot evaporating anode. With various anode materials like chromium or copper, and electrode separations between 0.5 and 3 mm, the nonself-sustained discharge operates with DC arc currents in the range of 220 A. The waveform of the arc voltage is strongly influenced by the magnetic field of the cathode heating current, and arc voltages between a minimum of 3 V and a maximum exceeding 100 V have been observed. The voltage-current characteristics (V_CC) and the influence of the electrode separation have been measured separately for the minimum and the maximum of the arc voltages and show a different behavior. The metal plasma expands into the ambient vacuum toward the walls of the vacuum vessel and offers a macroparticle free deposition source of thin films. The arc voltage can be varied by external manipulations of the arc discharge, and the mean ion energy of the expanding metal plasma shows a linear dependence of the mean arc voltage     

Investigation of arc roots of constricted high current vacuum arcs

The anodic and cathodic arc roots of constricted high current vacuum arcs were investigated with a fast framing charge-coupled device camera of 1 μs exposure time. The experiments were performed with cup-shaped contacts, with sinusoidal currents of amplitudes between 20 and 100 kA, and a sine halfwave duration of 10-12 ms. The arcs were drawn by contact separation and accelerated by the Lorentz force between the arc current and the transverse magnetic field generated by the contrate contact. The anode and cathode arc roots behave reproducibility and arc scaleable within the range of currents investigated. Both types of arc roots are elliptical, with a major to minor axis ratio of 1.4. The major axis points are in the direction of arc propagation. Anodic and cathodic arc root cross-sectional areas as a function of current can both be described by a potential law with a common exponent of 0.76. For currents of 20-100 kA, mean current densities of 81-121 and 41-60 kA/cm ² were found in anode and cathode arc roots, respectively. Estimations of their temperature and vapor densities were performed. For the investigated current range T_A≈3300-3600 K, n_A ≈1.6*10¹⁹-2.2*10¹⁹cm^-3 and T _C≈3200-3400 K, n_C≈0.8*10¹⁹-1.2*10 ¹⁹ cm^-3 were found for anode and cathode, respectively     

Fractal structure of gold clusters formed under vacuum deposition on dielectric substrates

The growth of gold island films under vacuum deposition on the surface of dielectric substrates are investigated. Fractal dimensions of the clusters formed under film deposition at different substrate temperatures and evaporation rates are estimated. The correlation between surface morphology and optical properties of the films deposited are discussed.     

Two-dimensional observation of copper vapor in vacuum arcs bylaser-induced fluorescence

The density distribution and the velocity of copper neutral atoms emitted from a single cathode spot in 40 A vacuum arc were measured by the two-dimensional (2-D) laser-induced fluorescence method. The density was calibrated from the two-dimensional fluorescence image observed by a CCD camera. The gap space was almost filled with the copper atoms, and the density reached 5×10¹⁹/m³. We varied the wavelength of the laser light and measured the velocity of the copper atoms emitted from the cathode spot using the effect of Doppler shift. The velocity of the copper atoms was about 10 km/s     

Residence time of metal ions generated from microsecond vacuum arcs

Vacuum gaps of 1 mm with lead or copper cathode are fired by a 13 μs duration sinusoidal arc or a 10 μs duration exponentially-decaying arc, and time-of-flight (TOF) ion measurements are made at variable times after the arc ignition. At the lead cathode, Pb⁺ and Pb⁺⁺ ions are generated and the upper limit on the times for Pb⁺ ion detection are 48 μs and 46 μs from the arc ignition for the sinusoidal and exponential arcs, respectively. At the copper cathode, Cu⁺, Cu⁺⁺, and Cu⁺⁺⁺ ions are generated and detected within 15 μs and 13 μs from the arc ignition for the sinusoidal and exponential arcs, respectively. The residence time of the Pb⁺ ions in the ion acceleration region is approximately 35 μs, regardless of the waveform of the arc current. The residence time of the copper ions, described by the time constant of the time-of-flight ion current delay characteristics, is 3 μs     

X-ray radiography of aluminum cathodes eroded in high-current vacuum arcs

The aim of the study presented in this paper was to characterize quantitatively the erosion of aluminum cathodes in high-current vacuum arcs. The experimental setup comprised two current generators. The first one, capable of generating a current of amplitude up to 350 kA, was used to produce a plasma jet, that is, the object to be investigated. The second generator was used to produce a source of probe radiation for imaging the object under investigation in soft x rays of energy ?ν ≈ 0.5–3 keV. The findings of the study are based on experimental data obtained by electrophysical and radiographic methods. It has been shown that the cathode erosion rate in a high-current vacuum arc is a function of the charge passed through the cathode.     

Experimental analysis of the electrode products emitted byhigh-current vacuum arcs

The mass distribution of particles produced in the high-current vacuum arc was investigated. The experiments were concentrated on evaluating the spatial mass distribution emitted in the radial as well as in the azimuthal directions calculated from the mass deposition profile on collectors surrounding the arc discharge. The experiments were carried out in a vacuum chamber evacuated to an ambient pressure <10^-4 Pa. High-current arcs in the range from 2-7.5 kA were drawn between butt contacts of 31 and 55 mm in diameter (anode and cathode, respectively) both of a copper-chromium alloy (CuCr25). The surface mass deposited along multi-segment collectors was measured by a micro densitometer, and an inductively coupled plasma (ICP) spectrometer. Two angular mass deposit distributions were determined: the azimuthal distribution on the plane parallel to the cathode surface, and the radial distribution as a function of the angle with respect to the cathode plane. Both distributions were anisotropic and the structure of the deposition layer depended on the angle of incidence of the particles onto the substrate, the density of the particle flux and other factors. The mass deposited on the collectors consisted mostly of chromium molecules (approx. 80% of Cr and 20% Cu) for CuCr25 or CuCr40 electrodes