@article {58925, title = {Drifting Ionization Zone in DC Magnetron Sputtering Discharges at Very Low Currents}, journal = {IEEE Transactions on Plasma Science}, volume = {42}, year = {2014}, month = {10/2014}, pages = {2578 - 2579}, abstract = {

Discharges with crossed electric and magnetic fields are known to develop instabilities that are crucial in the transport of charged particles. Sputtering magnetrons are no exception. While most recent studies focused on traveling ionization zones in high power impulse magnetron sputtering, we show here fast camera images of magnetron discharges at very low current. A single drifting ionization zone is always present, even down to the threshold current of about 10 mA.

}, issn = {0093-3813}, doi = {10.1109/TPS.2014.2334601}, author = {Andr{\'e} Anders and Pavel A Ni and Joakim Andersson} } @article {58927, title = {Spectroscopic imaging of self-organization in high power impulse magnetron sputtering plasmas}, journal = {Applied Physics Letters}, volume = {103}, year = {2013}, month = {07/2013}, pages = {054104}, abstract = {

Excitation and ionization conditions in traveling ionization zones of high power impulse magnetron sputtering plasmas were investigated using fast camera imaging through interference filters. The images, taken in end-on and side-on views using light of selected gas and target atom and ion spectral lines, suggest that ionization zones are regions of enhanced densities of electrons, and excited atoms and ions. Excited atoms and ions of the target material (Al) are strongly concentrated near the target surface. Images from the highest excitation energies exhibit the most localized regions, suggesting localized Ohmic heating consistent with double layer formation.

}, keywords = {Aluminium, ionization, Ionizing radiation, plasma ionization, visible spectra}, issn = {00036951}, doi = {10.1063/1.4817257}, author = {Joakim Andersson and Pavel A Ni and Andr{\'e} Anders} } @article {58923, title = {Drifting localization of ionization runaway: Unraveling the nature of anomalous transport in high power impulse magnetron sputtering}, journal = {Journal of Applied Physics}, volume = {111}, year = {2012}, month = {03/2012}, pages = {053304}, abstract = {

The plasma over a magnetron{\textquoteright}s erosion {\textquotedblleft}racetrack{\textquotedblright} is not azimuthally uniform but concentrated in distinct dense ionization zones which move in the E x B direction with about 10\% of the electron E x B/B2 drift velocity. The ionization zones are investigated with a gated camera working in concert with a streak camera for Al, Nb, Cu, and W targets in Ar or Kr background gas. It is found that each ionization zone has a high plasma density edge, which is the origin of a plasma-generating electron jet leaving the target zone. Each region of strong azimuthal plasma density gradient generates an azimuthal electric field, which promotes the escape of magnetized electrons and the formation of electron jets and plasma flares. The phenomena are proposed to be caused by an ionization instability where each dense plasma zone exhibits a high stopping power for drifting high energy electrons, thereby enhancing itself.

}, keywords = {Cameras, ionization, Magnetic fields, Plasma density, plasma ionization}, issn = {00218979}, doi = {10.1063/1.3692978}, author = {Andr{\'e} Anders and Pavel A Ni and Albert Rauch} } @article {1869, title = {Supersonic metal plasma impact on a surface: an optical investigation of the pre-surface region}, journal = {Journal of Physics D: Applied Physics}, volume = {43}, year = {2010}, month = {04/2010}, chapter = {135201}, abstract = {

Aluminum 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.

}, keywords = {cathodic arc plasma, ions, neutrals, optical emission spectroscopy, plasma-wall interaction}, doi = {10.1088/0022-3727/43/13/135201}, author = {Pavel A Ni and Andr{\'e} Anders} }