Details of the ´Ring Collapse´ on Schottky Electron Emitters

To gain better understanding of the shape stability of the Zr/O/W(100) Schottky electron source, the authors investigate the details of the ring collapse. The ring collapse phenomenon has been described and the shrinkage of a stack of the (100) end planes and its eventual disappearance as its W atom and the adsorbed ZrO_x entities migrate away from the apex towards the shanks. The investigation of the changes of the full emission pattern in combination with SEM imaging and field simulations has revealed detailed information on shape changes taking place in the ring collapse and the origin of the associated probe current drops. They show the typical probe current profile and the typical facet current profile during a ring collapse and also a typical emission patterns characterizing each stage. In general, the duration of a ring collapse decreases with increasing temperature and decreasing extraction voltage, while the SYMMETRY increases