Preequilibrium thermofield microprotrusions as effective field point sources of electrons and ions

Abstract

Field emission methods are employed for studying the conditions of formation, crystallographic localization, and emissive properties of preequilibrium thermofield microprotrusions for a number of refractory metals. Individual preequilibrium microprotrusions can be easily obtained using a W emitter of the ordinary 〈110〉 orientation; however, the number of such protrusions on the surface changes with time in the course of ionic emission, as well as their emission parameters (the parameters and the number of microprotrusions do not change in the case of electron emission). Trihedral angles of the rearranged tip, which are formed in the {111} regions, exhibit higher stability to ionic emission. A single trihedral angle stably emitting ions and located on the geometrical axis of the emitter can easily be obtained with the help of a W emitter with the 〈111〉 orientation. Two stable preequilibrium microprotrusions arranged symmetrically about the axis of the emitter in the {111} regions can be obtained using a Ta emitter of the conventional 〈110〉 orientation. Such microprotrusions virtually do not change the emission parameters during long-term extraction of ionic current.