POINT SOURCES OF ELECTRONS AND IONS USING MICROPROTRUSION ON THE TOP OF A TIP

Two ways of preparing a single microprotrusion on the top of a tungsten-tip (W-tip) are described. This microprotrusion can be used as point source of electrons and ions. The first way consists in growing W-microprotrusion on the top of W-tip with orientation <111>. In this case the biggest difficulty is to diminish more sharp microprotrusions satellites appearing in regions {114}. The removal of the satellites was attained by iteration of some heating of the tip in the presence of an electric field. The voltage was chosen in such a way to sharpen the microprotrusion on the top and to blunt the satellites. The single microprotrusion on the top of a tip can be produced by using the tips with usual orientation <110>. In this case it is necessary to condense 0.8-1 monoatomic layer of Si-atoms on the W-surface and to heat the tip at the temperature T = 1100-1300 K in presence of an electric field F = 0.3-0.5 V/angstrom. Therefore the single microprotrusion grows at the center of the plane {110} on the top of the tip.