SWITCH-ON PHENOMENA IN FIELD-ELECTRON AND FIELD-ION MICROSCOPY

Recent work in high-field microscopy has demonstrated striking similar ities in the behaviour of metal-insulator (M-I) composite microemitter s when tested in field-electron emission and field-ion operation modes . The composite structures consisted of a metallic core, usually tungs ten, covered by thin layers of various dielectric materials (polyethyl ene in the field-ion case). The main features and similarities in the properties of composite emitters using both field-electron emission an d field-ion regimes include: (i) initial switch-on phenomena; (ii) sub sequent electron emission current-voltage (I-V) characteristics that w ere both smooth and reproducible; (iii) emission I-V characteristics w hich exhibit hysteresis upon cycling the applied voltage; and (iv) sat urated electron emission current behaviour and ifs analogy in the fiel d-ion mode has been observed. This behaviour has been interpreted in t erms of an emission mechanism which involves the formation of a conduc ting filament in the insulator. An analysis of the M-I interface forma tion under the presence of high electric field is also given.