HIGHLY MONOCHROMATIC ELECTRON POINT-SOURCE BEAMS

We have evaporated Cs atoms onto ultrasharp W field emitter tips that act as point sources for electrons. Significant current increases associated with individual atomic adsorption events have been observed while using these tips fn the field emission mode. This indicates that only a small number of atoms is involved in the emission process. The decoration of the tip apex with several tens of Cs atoms leads to an emission voltage of only one-fourth of that required for the pure W emitter. The spread of the energy distribution of the emitted electrons is reduced by a factor of 3 compared to the pure W point-source tip. Thus we have devised a fairly monochromatic electron source with a full width at half-maximum energy spread of 100 meV. (C) 1994 American Institute of Physics.