Abstract
Cathodic arcs have been utilized in various applications including the deposition of thin films and coatings, ion implantation, and high current switching. Despite substantial progress in recent decades, the physical mechanisms responsible for the observed plasma properties are still a matter of dispute, particularly for multi-element cathodes, which can play an essential role in applications. The analysis of plasma properties is complicated by the generally occurring neutral background of metal atoms, which perturbs initial ion properties. By using a time-resolved method in combination with pulsed arcs and a comprehensive Nb−Al cathode model system, we investigate the influence of cathode composition on the plasma, while making the influence of neutrals visible for the observed time frame. The results visualize ion detections of 600 μs plasma pulses, extracted 0.27 m from the cathode, resolved in mass-per-charge, energy-per-charge and time. Ion properties are found to be strongly dependent on the cathode material in a way that cannot be deduced by simple linear extrapolation. Subsequently, current hypotheses in cathodic arc physics applying to multi-element cathodes, like the so-called ‘velocity rule’ or the ‘cohesive energy rule’, are tested for early and late stages of the pulse. Apart from their fundamental character, the findings could be useful in optimizing or designing plasma properties for applications, by actively utilizing effects on ion distributions caused by composite cathode materials and charge exchange with neutrals.
Highlights
Cathodic arcs have been investigated for more than 200 years [1, 2], and various physical concepts have been developed in recent decades—being well established for the simplest case: cathodic arcs of single-element cathodes in high vacuum
Ions in cathodic arcs mainly originate from the cathode; the influence of the cathode material on plasma properties is of particular interest
One has to be aware that these voltages are slightly larger than the actual arc voltage, because of the voltage drop inside the cathode and other relevant parts of the circuit
Summary
Cathodic arcs have been investigated for more than 200 years [1, 2], and various physical concepts have been developed in recent decades—being well established for the simplest case: cathodic arcs of single-element cathodes in high vacuum. Arc properties, like the burning voltage and its noise [4]; the relationship of the latter and other arc properties to the cathode material’s cohesive energy [5]; or the so-called ‘freezing’ of ion charge state and energy distributions in the process of plasma expansion [6]. Ions in cathodic arcs mainly originate from the cathode; the influence of the cathode material on plasma properties is of particular interest. Beside the use of process gases or several single-element cathodes, multi-element
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