Effect of mechanical finishes on secondary electron emission of alumina ceramics

The effect of surface roughness of insulator on the secondary electron emission (SEE) coefficients was investigated with changing the incident angle of primary electrons. The SEE coefficients were measured using a scanning electron microscope with a single-pulse electron beam (100 pA, 1 ms). As a result, the SEE coefficients increased with the incident angle for smooth surface, while those of rough surface almost did not change with the incident angle. The SEE coefficients of commercial alumina ceramics with three different surface finishes, i.e. as-sintered, as-ground and mirror-finished samples, were also measured before and after annealing treatments. This treatment was carried out in air at 1400 degrees C for 1 h. After annealing, the SEE coefficients were higher than those of unannealed samples. This increase is proposed to be due to the defect recoveries as well as neutralizations of charging, which significantly influence the SEE. For relative low purity (95% or less), the SEE coefficients of annealed alumina became lower after mechanical grinding operations and lower again after mirror-finished operations. The SEE coefficients of 99.7% purity alumina were almost unaffected by the mechanical finishes.