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

Abstract

For cathodic arcs, the cathode material is one of the most important determinants of plasma properties. Consequently, the cathode material-plasma relationship is of special interest in related fundamental research as well as in applications like the synthesis of thin films and coatings. In the latter, the use of multi-element cathodes in inert as well as reactive gas atmospheres is common practice. To further improve the physical understanding of cathodic arcs in such settings, we analyze ions in pulsed cathodic arc plasmas from Nb, Al and two composite Nb-Al cathodes with high time-resolution using a mass-energy-analyzer. The experiments were conducted in Ar atmosphere at total pressures of 0.04, 0.20 and 0.40 Pa, and are compared to earlier results in high vacuum at 10 −4 Pa. In addition to examining the influence of Ar on ion properties and their cathode material dependence, the results are used to discuss physical concepts in cathodic arcs, like the gas-dynamic expansion of the cathode spot plasma, or the influence of charge exchange collisions of ions with neutrals. While such inelastic collisions e.g. with Ar atoms cause a reduction of charge states to mainly Al + and Nb 2+ at the highest pressure, Ar atoms also seem to take part in near-cathode processes. Ar ions in different time and energy regimes up to 150 eV were observed and compared to Nb and Al ions, showing overlapping velocity distributions for Nb, Al and Ar + ions, but also Ar 2+ ions faster than other ion species.

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 shielding gas on cathode spot behaviours in alternating current tungsten inert gas welding of aluminium

“…However, in the atmospheric arc, the arc voltage approximately agrees with the ionisation potential of the gas as in Figure 3(a). The sheath voltage is suggested to be influenced by the ionisation potential of the gas [12] and especially affected by the first ionisation potential of the gas due to the charge exchange collision [13].…”

“…The helium arc voltage was lower than the ionisation potential of helium, so He + rarely formed inside the cathode sheath. Whereas in the argon arc, Ar + could high likely to be formed [13]. Therefore, the particle flux from the CS is considered to mainly consist of Ar, Ar + , Al, Al + and Al 2+ in the argon arc and He, Al, Al + and Al 2+ in the helium arc.…”

“…As in the above discussion, the ability of argon ion formation is higher than the helium ion formation due to the higher ionisation energy of helium. The argon ions formed mainly from the gas state, so the high-electrical field from Ar + was easily maintained rather than Al 2+ [13]. Therefore, due to the presence of Ar + , the CS was considered to become more mobile (reaching further and slightly high velocity on the solid).…”

Erosion and cathodic arc plasma of Nb–Al cathodes: composite versus intermetallic

“…In previous works, we used a Nb-Al cathode model system including Nb, Al and three composite Nb-Al cathodes with atomic Nb/Al ratios of 75/25, 67/33 and 25/75 to examine average arc voltages, ion energy/velocity and charge state distributions of related pulsed cathodic arc plasmas in high vacuum and Ar atmosphere using high time resolution [21,22]. The determined voltages and ion properties of arcs from composite Nb-Al cathodes did, however, not show a simple linear interpolation between their single-element counterparts like e.g.…”