@article {58924, title = {Drifting potential humps in ionization zones: The {\textquotedblleft}propeller blades{\textquotedblright} of high power impulse magnetron sputtering}, journal = {Applied Physics Letters}, volume = {103}, year = {2013}, month = {10/2013}, pages = {144103}, abstract = {

Ion energy distribution functions measured for high power impulse magnetron sputtering show features, such as a broad peak at several 10\ eV with an extended tail, as well as asymmetry with respect to E {\texttimes} B, where E and B are the local electric and magnetic field vectors, respectively. Here it is proposed that those features are due to the formation of a potential hump of several 10\ V in each of the traveling ionization zones. Potential hump formation is associated with a negative-positive-negative space charge that naturally forms in ionization zones driven by energetic drifting electrons.

}, keywords = {Electric fields, ionization, plasma ionization, sputter deposition, sputtering}, issn = {00036951}, doi = {10.1063/1.4823827}, author = {Andr{\'e} Anders and Matjaž Panjan and Robert Franz and Joakim Andersson and Pavel A. Ni} } @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} }