Discrete focusing effect of positive ions by a plasma-sheath lens.
We demonstrate that the sheath created adjacent to the surface of a negatively biased electrode that interfaces an insulator acts as a lens that focuses the positive ions to distinct regions on the surface. Thus, the positive ion flux is discrete, leading to the formation of a passive surface, of no ion impact, near the edge and an active surface at the center. Trajectories of positive ions within the sheath are obtained by solving in three dimensions the Poisson equation for electrodes of different geometry. Simulations are confirmed by developing the ion flux profile on the electrode surface as the sputtering pattern produced by ion impact. Measurements are performed in a dc plasma produced in Ar gas.
Stamate
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E
Nagoya University, Department of Electrical Engineering and Computer Science, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.
Sugai
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H