Ion energy distribution functions of vacuum arc plasmas

Abstract

The velocity distribution function of vacuum arc ions can be measured by a time-of-flight technique similar to a method originally proposed by Yushkov. The measuring principle makes use of the welljustified assumption that the ion drift velocity from the cathode spot region to a collector is approximately constant. It is shown that the negative time derivative of the collector current is directly proportional to the ion distribution function provided that the time-averaged source intensity (i.e., emission of ions from cathode spots) is constant until the arc is rapidly switched off. In the experiment, arc termination took about 700 ns, which is much faster than the decay of the ion current measured at the collector placed in more than 2 meters distance from the cathode. The experimental distribution functions for most cathode materials show one large peak with a tail and one or more small peaks at higher ion velocities. The distribution functions for some other materials exhibit several peaks. No conclusive answer can be given about the nature of these peaks. Arguments are presented that the peaks are not caused by different charge states or plasma contamination but rather due to insufficiently averaged source fluctuations and/or acceleration by plasma instabilties.a Author to whom correspondence should be addressed; electronic mail: aanders@lbl.gov 2

Ion velocities in direct current arc plasma generated from compound cathodes

“…This effect can be explained by the "cohesive energy rule," where material and phases of higher cohesive energy generally result in increasing energies (velocities). This is also consistent with the here obtained peak velocities around 1 The high power and plasma density associated with cathodic arc results in elevated ion charge states (Q) and inherent ion energies (E 0 ) ranging up to >150 eV. 1,2 This corresponds to supersonic ion velocities with respect to the ion sound velocity.…”

Transparent and conductive indium doped cadmium oxide thin films prepared by pulsed filtered cathodic arc deposition

“…The average kinetic energy of Cd ions for a vacuum arc is 26 eV with significant amounts of ions in the tail of the energy distribution function up to 1.5 times the average value [40,41]. Collisions of the Cd ions with oxygen will provide excitation, ionization, and kinetic energy to oxygen, which promotes oxidation of the Cd and formation of high quality CdO.…”

Influence of argon and oxygen on charge-state-resolved ion energy distributions of filtered aluminum arcs

“…The average ion energy is material dependent and ranges from 20 to 150 eV, 1 though the ion energy distributions (IEDs) extend up to several hundreds of eV. 2 The ion charge states (Q i ) are important for plasma processing applications that utilize substrate bias, since the kinetic energy gain (∆E i ) across the potential difference between the plasma and the substrate (∆U) is given by ∆E i =Q i ·e·∆U. It is well known that the kinetic ion energy, and therefore also the charge states, affect the microstructure evolution, and hence the film properties.…”