Visualization of the sheath-lens focusing effect to disk and square electrodes

The property of the sheath evolving to one-side biased electrodes to focus in a discrete manner the positive ions to distinct regions on the surface is demonstrated both theoretically and experimentally. Positive ion trajectories to disk and square electrodes are obtained by solving in three dimensions the Poisson equation. The related ion flux is found to be in excellent agreement with the experimental ion flux developed by exposing the electrodes in Ar plasma.