Time-resolved ion energy and charge state distributions in pulsed cathodic arc plasmas of Nb−Al cathodes in high vacuum

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.

Experimental Chemistry and Structural Stability of AlNb3 Enabled by Antisite Defects Formation

“…However, the plasma properties and hence the thin film growth conditions are largely affected by the presence of the cathode surface, which is in a direct contact with plasma. In particular, in the case of CAD the formation of intermetallic phases on the cathode surface due to the exposure to the plasma affects the plasma properties, such as ion charge states and energies [5,6,7].…”

Influence of Ar gas pressure on ion energy and charge state distributions in pulsed cathodic arc plasmas from Nb–Al cathodes studied with high time resolution

“…The general experimental setup is similar to that of our previous work [23]; a schematic diagram is shown in figure 1. The plasma source used was a 'self-triggering arc miniature gun' described in [24], where a cylindrical cathode with a diameter of 6.35 mm and about 20 mm length was mounted.…”

“…An additional factor for selecting Ar was the fact that the Nb-Al cathode model system does not show overlapping in terms of mass-per-charge ratios for the ions of interest, which would have complicated the evaluation of the recorded data. In combination with our previously published results of the Nb-Al cathode model system in high vacuum [23], time-resolved charge and energy distributions of Nb, Al and especially Ar ions in a relevant pressure range will enable us to further discuss related hypotheses in cathodic arc physics, like the 'velocity rule' [8], and also improve the understanding of effects induced by a noble gas like Ar in cathodic arcs, which are relevant for applications in physical vapor deposition.…”

“…In a previous work, we used an experimental setup providing high time resolution to study how the presence of metal neutrals in the pulsed cathodic arc plasma from composite Nb-Al cathodes alters the plasma properties like ion energy and charge state distributions [23]. Different stages during the arc pulse were identified where the interaction of metal ions with metal neutrals, in particular charge exchange collisions, changes the plasma properties and, hence, confirmed the importance of metal neutrals for cathodic arc plasmas.…”

Determination of the critical temperature of Nb–Al alloys from the plasma parameters of a vacuum arc cathode spot

“…It should be noted that the charge state of plasma ions in the vacuum arc and their velocity can be measured in detail (see [24,25]), while the critical temperatures can be measured only for a few metals, which is associated with a high energy density in such an extreme state of matter.…”