Electron field emission from large-area cathodes: evidence for the projection model

Field emission from two kinds of emitters has been studied: intentionally introduced particles of controlled geometry; and sites produced by intentional mechanical damage to the cathode surface. The size of particles seems to play no role in their threshold field, but their shapes are a determinant factor, since spherical particles do not emit for fields up to 120 MV m\+-1\-. The method of creation of damage sites, and the similarity of their emission on Nb and Au substrates, suggest the possibility that emission comes from geometrical protrusions. A model of superimposed geometrical protrusions is proposed to explain the enhanced field emission behaviour of this particular type of surface defect. (Original abstract)