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- ItemTime-resolved ion energy and charge state distributions in pulsed cathodic arc plasmas of Nb−Al cathodes in high vacuum(Bristol : IOP Publ., 2018-5-15) Zöhrer, Siegfried; Anders, André; Franz, RobertCathodic 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.
- ItemInsights into surface modification and erosion of multi-element arc cathodes using a novel multilayer cathode design(Melville, NY : American Inst. of Physics, 2020) Golizadeh, Mehran; Anders, André; Martin, Francisca Mendez; Kolozsvári, Szilard; Franz, RobertNowadays, multi-element cathodes are frequently employed to grow multi-element thin films and coatings using cathodic arc deposition processes. During cathode erosion, the cathode spot sequentially ignites on the cathode surface and imposes melting-solidification cycles that lead to material intermixing and the formation of a modified layer on the cathode surface. To allow us to study these surface modifications, a 10 µm thick Mo/Al multilayer coating was sputter-deposited onto a standard Ti arc cathode. This cathode was eroded by a dc steered arc discharge for a short duration enabling the observation of single craters formed by type 1 and 2 cathode spots. Furthermore, separated clusters of overlapping craters and a fully eroded surface caused by different stages of erosion were differentiated when scanning the erosion track in the lateral direction. Cross sections of single craters were prepared by focused ion beam techniques while metallographic methods were applied to obtain cross sections of overlapping craters and the modified layer. The layers of the multilayer coating acted as trace markers providing new insights into the material intermixing within craters, the material displacements during crater formation, the plasma pressure acting on the craters, and the temperature gradient (heat-affected zone) below the craters. The observations are discussed within the framework of established arc crater formation models. © 2020 Author(s).
- ItemInfluence 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(Bristol : IOP Publ., 2019) Zöhrer, Siegfried; Anders, André; Franz, RobertFor 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. 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 Nb2+ 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 Ar2+ ions faster than other ion species. © 2018 IOP Publishing Ltd.