Surface topography of eroded Cu and Si cathodes in a PIG ion source

The surface topography development on a Cu sheet and a Si(111) wafer was studied after being sputtered in a Penning ionization gauge (PIG) ion source using Ar gas. In the case of Cu, a high density of conical structure was developed on the surface. The most striking feature was that the individual cones, relatively large in size, were often coated with impurity layers. Some cones were decorated with concentric ring-like patterns on their surfaces. The overlying coating was thought to be responsible for the initial growth of the cones and subsequent evolution of secondary protuberances on the surfaces of the cones. In the case of Si, though a few impurity-induced conical protrusions were formed, the dominant morphology was in the form of etch pits. In addition to usual single cones, Si surface developed cones of dimeric structure and cluster of cones.