Field electron microscope study of niobium surfaces

An account is presented of field emission experiments on contaminated and clean niobium surfaces. It is concluded that the equilibrium thermal end‐forms of niobium single crystal emitters consist of small flat regions of low index crystallographic directions smoothly joined by transition planes to give a shape close to spheroidal. Fowler‐Nordheim graphs of the voltage‐current characteristics of the thermally cleaned cathodes gave a work function of (4.1 ± 0.1) eV which agrees with the results of other measurements.