S. Goldsmith

The interaction between plasma and macroparticles in a multi‐cathode‐spot vacuum arc

The interaction between the interelectrode plasma and macroparticles (droplets) produced by a multitude of cathode spots in a vacuum arc between Cu electrodes is analyzed, using previous experimental measurements of the macroparticle size distribution and erosion rate and a flowing plasma model. The effect of the plasma on the macroparticles is considered by treating the macroparticles as floating probes and calculating the particle, momentum, and energy fluxes to them. It is found that slow macroparticles are significantly deflected form their original trajectories owing to ion bombardment, and that steady‐state macroparticle temperatures of 2000–2600 K are obtained from the balance of the energy influx (primarily from ion bombardment) with the evaporative outflux. The effect of the macroparticles on the plasma is considered by calculating the production rate of neutral atoms and ions originating from macroparticle evaporation, by examining the possibility of occlusion of the discharge path by macroparti...

Multicomponent Ti–Zr–N and Ti–Nb–N coatings deposited by vacuum arc

Abstract A triple-cathode vacuum arc plasma gun was used to deposit Ti–Zr–N and Ti–Nb–N multicomponent coatings onto cemented carbide (90% WC, 8% Co, 1.8% TaC, and 0.2% NbC) substrates. The coatings were deposited at a bias voltage of −40 V relative to the anode, and a substrate temperature of 400°C. The influence of the nitrogen background pressure, which was in the range of 0.67–2 Pa, on the structure, phase composition, and microhardness was studied. It was shown that a solid solution (Ti,Zr)N was formed in the Ti–Zr–N coatings, in which the elements Ti, Zr, and N were distributed homogeneously. The films had a fine structure. The (Ti,Zr)N grains had an average diameter of 30 nm and were {111} orientated. The nitrogen concentration in the solid solution was not affected by the nitrogen pressure in the range studied. However, increasing the nitrogen pressure to 2 Pa increased the Zr concentration, while that of Ti decreased and a less dense structure is formed. The formation of a (Ti,Nb)N solid solution was observed in the Ti–Nb–N coatings. The (Ti,Nb)N grains were randomly oriented. A maximum microhardness of 51.5 GPa was obtained for the Ti–Nb–N film deposited at a nitrogen pressure of 1.33 Pa. Increasing the nitrogen pressure to 2 Pa decreased the microhardness to 31.5 GPa.

Annealing and Sb-doping of Sn—O films produced by filtered vacuum arc deposition: structure and electro-optical properties

Abstract Tin oxide films were deposited using a filtered vacuum arc at rates up to 10 nm s−1. Optimal results were obtained with a 160 A arc when the deposition pressure was in the range 6–9 mTorr. The structure of the films was amorphous if the deposition temperature, or the post-deposition annealing temperature, was less than 350°C, while films containing orthorhombic, tetragonal, and amorphous phases were obtained at higher temperatures. Annealing or substrate heating with temperatures within the amorphous range improved the conductivity considerably, and was accompanied by increases in the optical gap, carrier density, and carrier mobility. The improvements are attributed to greater short-range ordering. Annealing or substrate heating into the crystalline range yielded higher resistivity films. Sb doping did not decrease the resistivity of the amorphous films. The lowest resistivities obtained, (5–7) × 10−4ωcm, were equal to or less than any reported in the literature for undoped Sn—O films, and were obtained at deposition rates considerably higher than with other techniques.

The hot refractory anode vacuum arc : a new plasma source for metallic film deposition

Abstract A new mode of the vacuum arc, the Hot Refractory Anode Vacuum Arc (HRAVA), was investigated as a plasma source for depositing coatings. Arc currents of 155–340 A were sustained for periods of up to 120 s between a water-cooled Cu source cathode, and a non-consumable refractory anode, which was heated by the arc. Cu coatings were deposited on ground stainless steel and glass substrates. A shutter controlled when and how long the substrate was exposed to the plasma. The coating rates were measured by weighing the substrates, and the macro particles (MPs) presence on the coating surface was examined by optical microscopy. Films that formed in a 30-s exposure at the beginning of a 175-A arc, when it operated in the cathode spot mode, were heavily contaminated with MPs. The density of MPs with diameters of between 3 μm and 50 μm was ∼10 3 mm −2 . However, with a 30-s exposure, which began 30 s after arc initiation, by which time the arc was in the HRAVA mode, the MP density was reduced to ∼1 mm −2 . The HRAVA deposition rate was ∼1–2μm/min onto substrates placed at distances of ∼110–120 mm from the arc axis. The HRAVA deposition rate is comparable to filtered cathode spot vacuum arc deposition, but over a much larger deposition area.

A spectroscopic investigation of the development of a hot-anode vacuum arc

We present a spectroscopic study of the temporal evolution of a new type of hot-anode vacuum arc discharge. This arc begins as a multi-cathode-spot vacuum arc (MCS) operating for 150 - 200 s duration at 175 or 340 A DC current and is eventually sustained by the metal vapour (originating from the cold copper cathode) that is re-evaporated from a non-consumable and thermally isolated hot graphite anode, located 10 mm away from the cathode. The hot anode acts indirectly as the plasma source by evaporating and/or reflecting the cathode material condensed on it. Spectral lines of Cu I, Cu II and Cu III in the visible were investigated as a function of time near the cathode, near the anode and in the middle of the electrode gap. Line intensity measurement was performed with 40 ms time resolution and 0.4 mm spatial resolution. Time-resolved excited-state densities were determined from the calculated radial distribution. The anodic plasma plume was observed to develop and reach the cathode within approximately 30 and 15 s for arc currents of 175 and 340 A, respectively. The calculated near-anode density of the Cu I level increased from approximately to within 30 s for a 175 A arc. The distribution temperature derived from a Boltzmann diagram was found to be 0.6 eV, approximately. The electron temperature derived from saturated Cu I lines was found to be close to 1 eV during steady-state operation.

The numerical calculation of plasma beam propagation in a toroidal duct with magnetized electrons and unmagnetized ions

Electron-magnetized vacuum arc plasma transport in a magnetic toroidal duct is calculated numerically taking in account electron - ion collisions, electron and ion temperatures, and the high conductivity of the duct wall. The longitudinal magnetic field in the duct, the fully ionized plasma density and the electric potential distribution at the torus entrance are given, while the plasma density, electrical field and current, and macroscopic plasma velocity across the magnetic field inside the duct are calculated. Toroidal coordinates are used to describe plasma beam propagation. A Runge - Kutta routine is used for the calculations along the torus while a finite difference method is used across the torus cross section. It is found that plasma loss due to particle flux to the duct wall depends on the electron and ion temperatures and the plasma density distribution at the torus entrance cross section. With an electron temperature of , 30 000 K and 50 000 K, an ion temperature and a Gaussian distribution of plasma density at the torus entrance with a maximum value , we found that the duct efficiency was less than 10% for longitudinal magnetic field strengths of 10 mT and 20 mT. In the case where only the electrons are magnetized, filter efficiency depends only weakly on the magnetic field strength, on , and on .

Effect of air annealing on opto-electrical properties of amorphous tin oxide films

Amorphous tin oxide films, 100?800?nm thick and of resistivity ~6?8?m??cm, were deposited on glass substrates using a filtered vacuum arc with an oxygen background gas pressure of 4.0?mTorr. The films were annealed in air at a temperature of 300?C for 1, 3, 5, 7, and 10?min. Film morphology, structure, composition, roughness, and light transmission were determined before and after the annealing, on cold samples, with atomic force microscopy, x-ray diffraction diagnostics, x-ray photoelectron spectroscopy, and light transmission meter. The roughness depended weakly on the annealing time, and decreased with the thickness of the film. The film transmission in the visible region was practically independent of the annealing time. Film conductivity increased with the annealing time, reaching a maximum value after 3?7?min, larger by a factor of 2.0?2.9 than that measured before annealing. The oxygen to tin density ratio on the film surface decreased relative to its value before annealing and reached a minimum after annealing for 7?min. After annealing for 10?min, the O/Sn ratio increased relative to the minimum value but was lower than the ratio before annealing. The O/Sn ratio in the bulk decreased monotonically for annealing times longer than 1?min. The film conductivity before and after annealing depended linearly on the film thickness. A model is proposed to elucidate the dependence of the conductivity on the annealing time and on the film thickness.

A model for a uniform steady-state vacuum arc with a hot anode

A model is formulated and evaluated for a Uniform electrical discharge sustained in vapor evaporated from an arc-heated anode. The plasma potential is positive with respect to both the cathode and anode. For a Cu anode, the anodic vapor dominates the plasma for current densities exceeding 8 kA/m/sup 2/. The anode heating potential is approximately 6.5 V, and the dominant cooling mechanism is evaporation for current densities exceeding 20 kA/m/sup 2/. Over the range 10 to 10000 kA/m/sup 2/, the electron density increases from 8*10/sup 17/ to 5*10/sup 23/ m/sup -3/, while the ionization fraction rises from 0.3% to 4%. At the lower end of this current range the electrical resistivity of 4 m Omega -m is determined primarily by electron-neutral collisions, while with increasing current the resistivity decreases to 0.7 m Omega -m, with electron-ion collisions contributing an equal share. This hot-anode vacuum arc may have potential for industrial application as a macroparticle-free high-deposition-rate coating source. >

Plasma distribution in a triple-cathode vacuum arc deposition apparatus

The distribution of plasma beams produced by Ti, Nb and Zr cathodes in a triple-cathode vacuum arc deposition system was studied. The system consisted of a triple-cathode plasma gun, straight plasma duct, sample chamber, vacuum system and computerized control system. Three cathodes were located on a circle centred on the system axis. An arc was ignited between the cathodes and an anode with three apertures, each located opposite one of the cathodes. Each cathode had a separate trigger ignition system and the cathodes could be operated simultaneously or separately. The plasma produced by the cathode spots passed through the anode aperture to a 160 mm diameter straight duct. Four magnetic field coils coaxial with the duct axis produced a magnetic field to collimate the plasma flow, and two beam steering coils whose axes were normal to the duct axis produced a magnetic field that deflected the plasma beam in the x and y directions. The saturated ion current distribution in the plasma was measured by a 13-segment multi-probe which was positioned in the sample chamber at a distance of 560 mm from the cathode plane. The measurements were carried out for each cathode operated separately in vacuum and in a background nitrogen gas at pressures of 0.4-1.33 Pa. The ion currents collected by the individual elements of the multi-probe were fitted to a two-dimensional Gaussian function. It was shown that the beam steering coils displaced the plasma beam centres in a wide range in the substrate plane. Changing the current of the X or Y steering coils displaced the beam centre linearly in the x or y directions respectively, but had only a weak effect in the y or x (i.e. orthogonal) directions respectively. The background nitrogen pressure did not influence the displacements of the plasma beam centres; however increasing nitrogen pressure decreased the distribution width. The results show that the pair of beam steering coils may direct the plasma beams to any position in the substrate plane without affecting the other beam distribution parameters.

X‐ray diagnostics of a plasma‐jet–liquid interaction in electrothermal guns

The penetration of a plasma jet into liquid water was observed at successive time intervals by means of x‐ray shadowgraphy. The plasma jet was generated by producing in a polyethylene capillary tube a high‐current pulsed discharge. The tube inner diameter and length were 0.64 and 22 cm, respectively. A pulse‐forming network delivered 121–182 kJ of electrical energy in 500 μs. The plasma jet emerged from the open end of the tube and interacted with a column of water gel. Jet velocities around 250 m/s were measured by x‐ray shadowgraphy. The water ablation rate, estimated by calculating the radiative energy flux emitted by the plasma and reaching the water surface, is approximately 0.0155 kg/s cm2. This rate is significantly lower than the measured average flux of mass lost by the water: 3.5 kg/s cm2. It is proposed, but not proven conclusively, that the main mechanism for water loss is in the form of droplets pulled apart by shear forces impressed by the plasma‐water direct interaction. These droplets are ...