Georgy Yu. Yushkov

Production of neutrals and their effects on the ion charge states in cathodic vacuum arc plasmas

Cathodic arc plasmas are considered fully ionized and theycontain multiply charged ions, yet, gaseous and metal neutrals can bepresent. It is shown that they can cause a significant reduction of theion charge states as measured far from the cathode spots. Several cathodematerials were used to study the evolution the mean ion charge state as afunction of time after arc ignition. The type of cathode material, arccurrent amplitude, intentionally increased background gas, additionalsurfaces placed near the plasma flow, and other factors influence thedegree of charge state reduction because all of these factors influencethe density of neutrals. In all cases, it was found that the mean ioncharge state follows an exponential decay of first order, Q(t) = A *exp(t/tau) + Qss, where A is a parameter describing the importance of thedecay, tau is the characteristic decay time, and Qss is a steady-statevalue approached for continuous arc operation. The extrapolated valuesQ(t-->0) indicate surprisingly high mean charge states as produced atcathode spots and not skewed by charge exchange collisions withneutrals.

Extractable, elevated ion charge states in the transition regime from vacuum sparks to high current vacuum arcs

Metal ions were extracted from pulsed discharge plasma operating in the transition region between vacuum spark and vacuum arc. At a peak current of about 4kA, and with a pulse duration of 8μs, we observed mean ion charges states of about 6 for several cathode materials. In the case of platinum, the highest average charge state was 6.74 with charge states present as high as 10, and with gold we found traces of charge state 11. At higher currents, nonmetallic contaminants started to dominate the ion beam, preventing further enhancement of the metal charge states.

Plasma “anti-assistance” and “self-assistance” to high power impulse magnetron sputtering

A plasma assistance system was investigated with the goal to operate high power impulse magnetron sputtering (HiPIMS) at lower pressure than usual, thereby to enhance the utilization of the ballistic atoms and ions with high kinetic energy in the film growth process. Gas plasma flow from a constricted plasma source was aimed at the magnetron target. Contrary to initial expectations, such plasma assistance turned out to be contra-productive because it led to the extinction of the magnetron discharge. The effect can be explained by gas rarefaction. A better method of reducing the necessary gas pressure is operation at relatively high pulse repetition rates where the afterglow plasma of one pulse assists in the development of the next pulse. Here we show that this method, known from medium-frequency (MF) pulsed sputtering, is also very important at the much lower pulse repetition rates of HiPIMS. A minimum in the possible operational pressure is found in the frequency region between HiPIMS and MF pulsed sputtering.

Puzzling differences in bismuth and lead plasmas : Evidence for the significant role of neutrals in cathodic vacuum arcs

Time-dependent ion charge state measurements for Pb and Bi cathodic arc plasmas revealed unexpected differences: the mean Bi ion charge state dropped much stronger and with a longer time constant. It is shown that the differences in thermal conductivity and vapor pressure led to much higher neutral density for Bi, which in turn can cause charge exchange collisions. The results have implications beyond Pb and Bi plasmas: most importantly, they imply that the “true” ion charge states, as emitted from the cathode spots, are higher than what is generally measured and published.

Angular Distribution of Ions in a Vacuum Arc Plasma With Single-Element and Composite Cathodes

The angular distribution of the different cathode materials and gaseous ion flow from vacuum arc plasma is investigated. A metal-vapor-vacuum-arc-type ion source and a time-of-flight mass spectrometer were used. The experiments were performed using a range of different cathode materials, including C, Al, Zn, Cu, Ti, Co, Cr, W, Pb, <formula formulatype=inline><tex Notation=TeX>

Some features of vacuum arc plasmas with increasing gas pressure in the discharge gap

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Temporal development of ion beam mean charge state in pulsed vacuum arc ion sources.

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Boron ion beam generation using a self-sputtering planar magnetrona)

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A study of vacuum arc ion velocities using a linear set of probes

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Plasma of Vacuum Discharges: The Pursuit of Elevating Metal Ion Charge States, Including a Recent Record of Producing Bi 13+

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