Grain structure in cathode spot trail of low vacuum arc discharge

Low vacuum arc discharge treatment in 10 Pa is applied to cleaning of a stainless steel plate, the surface of which is covered with an oxide layer. During the discharge, several luminous cathode spots move continuously in random directions on the surface of the stainless steel plate. They remove the oxide layer owing to their high energy density and leave their trail on the sample surface. Microscopic observation reveals a chain structure of metallic grains along the center of the cathode spot trail. Some chemical agents put on the oxide layer before cleaning affect on the size and the number density of the grain, which leads to the different surface roughness after treatment.