Arc cathode root initiation on aluminium oxide films

The factors involved in the initiation of electron emission from a new site at arc cathode roots on aluminium with various aluminium oxide films are discussed. Site lifetimes which have been estimated to be in the range from 173 ns to 376 ns for Al 2 O 3 ranging from 20 nm to 88 nm suggest that rapid switching plays a major part in the emission process from these films. This is confirmed by the experimental results which show that sites which were near the track boundaries were found to be left in a high conductivity state. The effect of arc UV radiation on the surface potential difference (SPD) change on Al 2 O 3 films above certain thicknesses produces a large and positive SPD change. Most of this change is found to be within the film during the anodization process. Thus the electron emission process from the aluminium/aluminium-oxide cathode structure is dominated by positive ions landing on the cathode surface.