PROBE HOLE FIELD ELECTRON FIELD-ION MICROSCOPY AND ENERGY SPECTROSCOPY OF ULTRASHARP [111]-ORIENTED TUNGSTEN TIPS

Tungsten field emitter tips are frequently being used in electron, sca nning tunneling and point projection microscopes. To characterize the electronic properties as well as the electron and ion emission behavio r for ultrasharp tungsten needles, we have carried out energy-resolved measurements. Hemispherical mirror and retarding potential analyses o f field-emitted electrons and ions have been combined with FEM/FIM exa minations of [111]-oriented tungsten emitter prepared in different way s, for example by neon ion sputtering and by a thermo-field treatment, creating a single atomically sharp microprotrusion. In the electron e mission mode the free electron gas approximation gives satisfactory fi ts to the total energy distributions measured to date. Argon ion energ y distributions show a field-dependent high energy secondary structure possibly indicating a field-gradient-enhanced migration of molecules, such as water, to the microprotrusion.