Child-Langmuir sheath structure around wedge-shaped cathodes

Abstract

The steady state Child-Langmuir sheath around a wedge-shaped cathode immersed in a plasma is calculated numerically. The ions drawn from the plasma may be employed to sputter material from the cathode, or may implant into the cathode, depending upon the magnitude of the applied negative voltage. The ion impact rate onto the cathode reaches 2.2 times higher near a square edge and 3.6 times higher near a knife edge than the rate for planar surfaces of the cathode. However, for a knife edge the rate falls to zero at the edge. All the ions strike the cathode with the same kinetic energy, but the angle of impact is nonperpendicular near the edge, which could reduce the implantation depth and increase sputtering.