Supersonic metal plasma impact on a surface: an optical investigation of the pre-surface region

Abstract

TitleSupersonic metal plasma impact on a surface: An optical investigation of the pre-surface region DISCLAIMERThis document was prepared as an account of work sponsored in part by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, AbstractAluminum plasma, produced in high vacuum by a pulsed, filtered cathodic arc plasma source, was directed onto a wall where if formed a coating. The accompanying "optical flare" known from the literature was visually observed, photographed, and spectroscopically investigated with appropriately high temporal (1 µs) and spatial (100 µm) resolution. Consistent with other observations using different techniques, it was found that the impact of the fully ionized plasma produces metal neutrals as well as desorbed gases, both of which interact with the incoming plasma. Most effectively are charge exchange collisions between doubly charged aluminum and neutral aluminum, which lead to a reduction of the flow of doubly charged before they reach the wall, and a reduction of neutrals as the move away from the surface. Those plasma-wall interactions are relevant for coating processes as well as for interpreting the plasma properties such as ion charge state distributions.

The evolution of ion charge states in cathodic vacuum arc plasmas: a review

“…The latter effect alone is important in the sense that even a fully ionized plasma flow is a source of neutrals! Evidence for the last point can be found in "optical flares" as reported by Tarrant and coworkers [106] and more recently also studied in our laboratory [107]. Such "flares" manifest themselves as clear intensity enhancement of neutral emission lines close to the surface exposed to flowing cathodic vacuum arc plasma (Fig.…”

“…Figure 8. Open-shutter photograph through the vacuum window showing the enhanced optical emission when a surface (left) is hit by cathodic vacuum arc plasma (steaming from the right); for details see [107].…”

Effect of the anode material on the evolution of the vacuum breakdown process

“…On the other hand, the plasma expansion scenario proposed by Anders et al [36,37] is consistent with the present experimental results. According to this, the cathode plasma gradually expands from the cathode, although it glows only in its vicinity.…”

“…This implies that the cathodic flare must reach the anode so that the atoms of the cathode material can be identified near the anode. It has been suggested earlier [36,37] that the anode flare ignites when the expanding cathode plasma reaches the anode and causes the sputtering of atoms from the anodic surface. To verify this hypothesis, we estimate the cathode plasma expansion velocity to be about 20 000 m s −1 according to the delay times of anodic glow and the corresponding gap lengths, as shown in figure 8.…”

Layer formation by resputtering in Ti–Si–C hard coatings during large scale cathodic arc deposition

“…Hence, this is also expected under the conditions used in our study. Furthermore, the formation of neutrals from initially fully ionized arc plasma interacting with surfaces, has most recently been demonstrated by Ni et al through optical techniques [25]. This is further evidence of plasma-surface interactions creating secondary species under regular arc deposition conditions.…”