Atomic structure and electrical properties of a supertip gas field-ion source

By using field-ion microscopy the atomic structure of tungsten supertips was revealed. They are small protrusions of only a few nm of height and width. Surface and volume contain some 10 to some 100 atoms respectively, arranged in bcc orientation. The polyhedral shape leads to local emission patterns with overall emission angles of less than 1 degrees. By performing electrical field calculations the virtual source size was quantified to be of atomic size corresponding to a brightness in the range of 10(10)-10(12) A/cm(2) sr. The geometry of the supertip appears not to be influenced by formation temperature or basetip geometry. Modification of supertips by field evaporation or other postformation treatment will be described.