Role of Ion Bombardment in Field Emission Current Instability

The role of ion bombardment in field emission current instability is clarified experimentally by varying the emission current level and pressure over a wide range. It is found that bombarding ions sputter-off adsorbed gas molecules on the emitter surface and this causes field emission current fluctuation. This current fluctuation caused by ion bombardment is larger than that caused by gas molecule migration when the product of the pressure and the emission current is higher than 7×10 -12 PaA. The relative fluctuations turn out to be the logarithm of the product of the pressure and the emission current. The ions are mainly generated close to the emitter due to electron collisions with residual gas.