Angular Confinement of Field Electron and Ion Emission

Three methods of confining the angular dispersion of a field electron beam from 〈100〉 oriented tungsten emitters are investigated; they are (1) thermal-field buildup, (2) selective work function reduction by zirconium adsorption, and (3) high-temperature field evaporation. All three methods confine the emission to a beam half-angle of less than 9° in the dc current range 0.1 to 100 μA. Method (1) results in a ∼50% reduction in beam voltage. Provided that the vacuum level is good (∼10−10 Torr), long and short term current instabilities are negligible for dc current levels below 10 μA at 300°K for each of the emitter end forms investigated. The angular dispersion and beam voltage of a field ion beam can also be reduced by method (1) as described briefly in this paper.