Electron field emission from intentionally introduced particles on extended niobium surfaces

Field emission properties of microscopic particles of graphite, sulfur, and MoS2 deposited on nonemitting Nb surfaces under ultrahigh vacuum conditions are described. Both graphite and MoS2 particles are shown to emit strongly, with field enhancement factors of the order of 100, in contrast to sulfur particles, which emit only weakly. The emission characteristics are measured locally on the individual sites, and emitting particles are further characterized by microfocus Auger spectroscopy and scanning electron microscopy. Their behavior upon heat treatment was studied, with the main result that both for graphite and MoS2 particles the emission disappears after heating to 1200 °C. The properties of the artificially created emitters are compared with those of naturally occurring field emitters.