The grain agglomeration in the decay of secondary electron yield induced by electrons

In this work, the box-and-grid electron multiplier (EM) operating under specific conditions for 120 h was disassembled. The secondary electron yield (SEY) and the surface morphology of the decayed film from dynodes of EM were tested. It was demonstrated that the SEY decay was linked to the change of grain size in the film. The more severe the film's decay, the larger the grain size in the decayed film. The results of the Energy Dispersive Spectrometer (EDS) indicated that the increase in grain size was not the introduction of impurities but the grain agglomeration. The grain agglomeration will increase the incident depth of the primary electrons and decrease the range of escapable angles for emitted electrons, which is the mechanism of SEY reduction caused by grain agglomeration. Furthermore, the cause of grain agglomeration was explained by the thermal effect on the surface and the electrostatic attraction between grains.