GROWTH AND CURRENT CHARACTERISTICS OF STABLE PROTRUSIONS ON TUNGSTEN FIELD-ION EMITTERS

Protrusions on field ion emitters can improve the angular current intensity of a gas field ion source by two orders of magnitude. We undertook some investigations of the growth of protrusions, here called supertips, by cathode bombardment and their field ion current characteristics. The growth is related to surface migration activated by ion bombardment. The current measurements show that a high lateral gas supply to the supertip and hence a low tip temperature is the most important factor in obtaining high currents from a supertip. He+ angular current intensities of 8 μA/sr at a total current of 10 nA have been reached at 18 K tip temperature.