Arguments about emitter shape for a liquid-metal field-ion emission source

Field evaporation is assumed to be a principal emission mechanism for a liquid metal ion source, but emitter apex fields calculated on the basis of the conventional shape hypothesis (rounded Taylor cone) do not seem high enough to make field evaporation possible. A numerical estimate is made of the degree of field enhancement provided by the presence of a microprotrusion. Enhancement factors of about 10 or more seem possible, and these values would be sufficient to render field evaporation a plausible emission mechanism. Alternatively, the Taylor cone apex may be drawn out into a cusp. (author)